# CHEMISTRY: The Molecular Nature of Matter and Change 2016

## Educators

ML

Problem 1

What two factors cause water to be polar?

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Problem 2

What types of substances are most likely to be soluble in water?

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Problem 3

What must be present in an aqueous solution for it to conduct an electric current? What general classes of compounds form solutions that conduct?

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Problem 4

What occurs on the molecular level when an ionic compound dissolves in water?

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Problem 5

Which of the following scenes best represents how the ions occur in an aqueous solution of: $(\mathrm{a}) \mathrm{CaCl}_{2} ;(\mathrm{b}) \mathrm{Li}_{2} \mathrm{SO}_{4} ;(\mathrm{c}) \mathrm{NH}_{4} \mathrm{Br}?$

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Problem 6

Which of the following scenes best represents a volume from a solution of magnesium nitrate?

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Problem 7

Why are some ionic compounds soluble in water and others are not?

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Problem 8

Why are some covalent compounds soluble in water and others are not?

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Problem 9

Some covalent compounds dissociate into ions in water. What atom do these compounds have in their structures? What type of solution do they form? Name three examples of such a solution.

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Problem 10

Box A represents one unit volume of solution A. Which box—B, C, or D—represents one unit volume after adding enough solvent to solution A to (a) triple its volume; (b) double its volume; (c) quadruple its volume?

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Problem 11

A mathematical equation useful for dilution calculations is $M_{\mathrm{dil}} \times V_{\mathrm{dil}}=M_{\mathrm{conc}} \times V_{\mathrm{conc}}.$ (a) What does each symbol mean, and why does the equation work? (b) Given the volume and molarity of a $\mathrm{CaCl}_{2}$ solution, how do you determine the amount (mol) and the mass (g) of solute?

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Problem 12

Six different aqueous solutions (with solvent molecules omitted for clarity) are represented in the beakers below, and their total volumes are noted.

(a) Which solution has the highest molarity? (b) Which solutions have the same molarity? (c) If you mix solutions $A$ and $C,$ does the resulting solution have a higher, a lower, or the same molarity as solution $B?$ (d) After 50. mL of water is added to solution $D,$ is its molarity higher, lower, or the same as the molarity of solution $F$ after 75 mL is added to it? (e) How much solvent must be evaporated from solution $E$ for it to have the same molarity as solution $A?$

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Problem 13

Are the following instructions for diluting a 10.0$M$ solution to a 1.00$M$ solution correct: "Take 100.0 $\mathrm{mL}$ of the 10.0 $\mathrm{M}$ solution and add 900.0 $\mathrm{mL}$ water'? Explain.

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Problem 14

Is each of the following very soluble in water? Explain.

$\begin{array}{ll}{\text { (a) Benzene, } \mathrm{C}_{6} \mathrm{H}_{6}} & {\text { (b) Sodium hydroxide }} \\ {\text { (c) Ethanol, } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}} & {\text { (d) Potassium acetate }}\end{array}$

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Problem 15

Is each of the following very soluble in water? Explain.

$\begin{array}{ll}{\text { (a) Lithium nitrate }} & {\text { (b) Glycine, } \mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{COOH}} \\ {\text { (c) Pentane }} & {\text { (d) Ethylene glycol, } \mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}}\end{array}$

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Problem 16

Does an aqueous solution of each of the following conduct an electric current? Explain.

(a) Cesium bromide $\quad$ (b) Hydrogen iodide

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Problem 17

Does an aqueous solution of each of the following conduct an electric current? Explain.

(a) Potassium sulfate $\quad$ (b) Sucrose, $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}$

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Problem 18

How many total moles of ions are released when each of the following dissolves in water?

(a) 0.32 $\mathrm{mol}$ of $\mathrm{NH}_{4} \mathrm{Cl} \quad$ (b) 25.4 $\mathrm{g}$ of $\mathrm{Ba}(\mathrm{OH})_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O}$
(c) $3.55 \times 10^{19}$ formula units of $\mathrm{LiCl}$

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Problem 19

How many total moles of ions are released when each of the following dissolves in water?

(a) 0.805 mol of $\mathrm{Rb}_{2} \mathrm{SO}_{4} \quad$ (b) $3.85 \times 10^{-3} \mathrm{g}$ of $\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}$
(c) $4.03 \times 10^{19}$ formula units of $\mathrm{Sr}\left(\mathrm{HCO}_{3}\right)_{2}$

ML
Mona L.

Problem 20

How many total moles of ions are released when each of the following dissolves in water?

(a) 0.75 mol of $\mathrm{K}_{3} \mathrm{PO}_{4} \quad$ (b) $6.88 \times 10^{-3} \mathrm{g}$ of $\mathrm{NiBr}_{2} \cdot 3 \mathrm{H}_{2} \mathrm{O}$
(c) $2.23 \times 10^{22}$ formula units of $\mathrm{FeCl}_{3}$

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Problem 21

How many total moles of ions are released when each of the following dissolves in water?

(a) 0.734 $\mathrm{mol}$ of $\mathrm{Na}_{2} \mathrm{HPO}_{4} \quad$ (b) 3.86 $\mathrm{g}$ of $\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}$
(c) $8.66 \times 10^{20}$ formula units of $\mathrm{NiCl}_{2}$

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Problem 22

Calculate each of the following quantities:
(a) Mass (g) of solute in 185.8 mL of 0.267 $M$ calcium acetate
(b) Molarity of 500 . mL of solution containing 21.1 $\mathrm{g}$ of potassium iodide

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Problem 23

Calculate each of the following quantities:
(a) Volume $\mathrm{mL}$ of 2.26$M$ potassium hydroxide that contains 8.42 g of solute
(b) Number of $\mathrm{Cu}^{2+}$ ions in 52 $\mathrm{L}$ of 2.3$M$ copper(II) chloride
(c) Molarity of 275 $\mathrm{mL}$ of solution containing 135 $\mathrm{mmol}$ of glucose

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Problem 24

Calculate each of the following quantities:
(a) Mass (g) of solute needed to make 475 $\mathrm{mL}$ of $5.62 \times 10^{-2} M$ potassium sulfate
(b) Molarity of a solution that contains 7.25 mg of calcium chloride in each milliliter
(c) Number of $Mg^{2+}$ ions in each milliliter of 0.184 $M$ magnesium bromide

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Problem 25

Calculate each of the following quantities:
(a) Molarity of the solution resulting from dissolving 46.0 g of silver nitrate in enough water to give a final volume of 335 mL
(b) Volume (L) of 0.385 $M$ manganese(Il) sulfate that contains 63.0 g of solute
(c) Volume $(\mathrm{mL})$ of $6.44 \times 10^{-2} M$ adenosine triphosphate (ATP)
that contains 1.68 mmol of ATP

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Problem 26

How many moles and how many ions of each type are present in each of the following?
(a) 130. mL of 0.45 $M$ aluminum chloride
(b) 9.80 mL of a solution containing 2.59 g lithium sulfate/L
(c) 245 mL of a solution containing $3.68 \times 10^{22}$ formula units of potassium bromide per liter

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Problem 27

How many moles and how many ions of each type are present in each of the following?
(a) 88 mL of 1.75 $M$ magnesium chloride
(b) 321 mL of a solution containing 0.22 g aluminum sulfate/L
(c) 1.65 L of a solution containing $8.83 \times 10^{21}$ formula units of cesium nitrate per liter

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Problem 28

Calculate each of the following quantities:
(a) Molarity of a solution prepared by diluting 37.00 mL of 0.250 $M$ potassium chloride to 150.00 mL
(b) Molarity of a solution prepared by diluting 25.71 mL of 0.0706 $M$ ammonium sulfate to 500.00 mL
(c) Molarity of sodium ion in a solution made by mixing 3.58 mL of 0.348 $M$ sodium chloride with 500. mL of $6.81 \times 10^{-2} M$ sodium sulfate (assume volumes are additive)

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Problem 29

Calculate each of the following quantities:
(a) Volume $(L)$ of 2.050$M$ copper $(II)$ nitrate that must be diluted with water to prepare 750.0 mL of a 0.8543 $M$ solution
(b) Volume (L) of 1.63$M$ calcium chloride that must be diluted with water to prepare $350 . \mathrm{mL}$ of a $2.86 \times 10^{-2} M$ chloride ion solution
(c) Final volume (L) of a 0.700$M$ solution prepared by diluting 18.0 mL of 0.155$M$ lithium carbonate with water

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Problem 30

A sample of concentrated nitric acid has a density of 1.41 g/mL and contains 70.0$\% \mathrm{HNO}_{3}$ by mass.
(a) What mass $(\mathrm{g})$ of $\mathrm{HNO}_{3}$ is present per liter of solution?
(b) What is the molarity of the solution?

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Problem 31

Concentrated sulfuric acid $(18.3 M)$ has a density of 1.84 $\mathrm{g} / \mathrm{mL}$ .
(a) How many moles of $\mathrm{H}_{2} \mathrm{SO}_{4}$ are in each milliter of solution?
(b) What is the mass $\%$ of $\mathrm{H}_{2} \mathrm{SO}_{4}$ in the solution?

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Problem 32

Ordinary household bleach is an aqueous solution of sodium hypochlorite. What is the molarity of a bleach solution that contains 20.5 g of sodium hypochlorite in 375 mL?

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Problem 33

Muriatic acid, an industrial grade of concentrated $\mathrm{HCl},$ is used to clean masonry and cement. Its concentration is 11.7 $\mathrm{M}$ . (a) Write instructions for diluting the concentrated acid to make 3.0 gallons of 3.5$M$ acid for routine use $(1 \text { gal }=4 \text { qt; } 1 \text { qt }=$ 0.946 $\mathrm{L}$ ). (b) How many milliliters of the muriatic acid solution contain 9.66 $\mathrm{g}$ of $\mathrm{HCl} ?$

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Problem 34

To study a marine organism, a biologist prepares a 1.00-kg sample to simulate the ion concentrations in seawater. She mixes 26.5 $\mathrm{g}$ of $\mathrm{NaCl}, 2.40 \mathrm{g}$ of $\mathrm{MgCl}_{2}, 3.35 \mathrm{g}$ of $\mathrm{MgSO}_{4}, 1.20 \mathrm{g}$ of $\mathrm{CaCl}_{2}, 1.05 \mathrm{g}$ of $\mathrm{KCl}, 0.315 \mathrm{g}$ of $\mathrm{NaHCO}_{3},$ and $0.098 \mathrm{g}$ of $\mathrm{NaBr}$ in distilled water. (a) If the density of the solution is $1.025 \mathrm{g} / \mathrm{cm}^{3},$ what is the molarity of each ion? (b) What is the total molarity of alkali metal ions? (c) What is the total molarity of alkaline earth metal ions? (d) What is the total molarity of anions?

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Problem 35

Water "softeners" remove metal ions such as $\mathrm{Ca}^{2+}$ and $\mathrm{Fe}^{3+}$ by replacing them with enough Na^{+} ions to maintain the same number of positive charges in the solution. If $1.0 \times 10^{3} \mathrm{L}$ of "hard" water is 0.015$M \mathrm{Ca}^{2+}$ and $0.0010 M \mathrm{Fe}^{3+},$ how many moles of $\mathrm{Na}^{+}$ are needed to replace these ions?

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Problem 36

Which ions do not appear in a net ionic equation? Why?

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Problem 37

Write two sets of equations (both molecular and total ionic) with different reactants that have the same net ionic equation as the following equation:
$$\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{Na}_{2} \mathrm{CO}_{3}(a q) \longrightarrow \mathrm{BaCO}_{3}(s)+2 \mathrm{NaNO}_{3}(a q)$$

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Problem 38

Why do some pairs of ions precipitate and others do not?

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Problem 39

Use Table 4.1 to determine which of the following combinations leads to a precipitation reaction. How can you identify the spectator ions in the reaction?

(a) Calcium nitrate $(a q)+$ sodium chloride $(a q) \longrightarrow$
(b) Potassium chloride $(a q)+$ lead(Il) nitrate $(a q) \longrightarrow$

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Problem 40

The beakers represent the aqueous reaction of $\mathrm{AgNO}_{3}$ NaCl. Silver ions are gray. What colors are used to represent $\mathrm{NO}_{3}^{-}, \mathrm{Na}^{+},$ and $\mathrm{Cl}^{-} ?$ Write molecular, total ionic, and net ionic equations for the reaction.

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Problem 41

Complete the following precipitation reactions with balanced molecular, total ionic, and net ionic equations:

(a) $\mathrm{Hg}_{2}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{KI}(a q) \longrightarrow$
(b) $\mathrm{FeSO}_{4}(a q)+\mathrm{Sr}(\mathrm{OH})_{2}(a q) \longrightarrow$

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Problem 42

Complete the following precipitation reactions with balanced molecular, total ionic, and net ionic equations:

(a) $\mathrm{CaCl}_{2}(a q)+\mathrm{Cs}_{3} \mathrm{PO}_{4}(a q) \longrightarrow$
(b) $\mathrm{Na}_{2} \mathrm{S}(a q)+\mathrm{ZnSO}_{4}(a q) \longrightarrow$

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Problem 43

When each of the following pairs of aqueous solutions is mixed, does a precipitation reaction occur? If so, write balanced molecular, total ionic, and net ionic equations:
(a) Sodium nitrate $+$ copper (II) sulfate
(b) Ammonium bromide + silver nitrate

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Problem 44

When each of the following pairs of aqueous solutions is mixed, does a precipitation reaction occur? If so, write balanced molecular, total ionic, and net ionic equations:
(a) Potassium carbonate $+$ barium hydroxide
(b) Aluminum nitrate $+$ sodium phosphate

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Problem 45

When each of the following pairs of aqueous solutions is mixed, does a precipitation reaction occur? If so, write balanced molecular, total ionic, and net ionic equations.
(a) Potassium chloride $+$ iron(III) nitrate
(b) Ammonium sulfate $+$ barium chloride

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Problem 46

When each of the following pairs of aqueous solutions is mixed, does a precipitation reaction occur? If so, write balanced molecular, total ionic, and net ionic equations:
(a) Sodium sulfide $+$ nickel(II) sulfate
(b) Lead(II) nitrate $+$ potassium bromide

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Problem 47

If 38.5 mL of lead(II) nitrate solution reacts completely with excess sodium iodide solution to yield 0.628 g of precipitate, what is the molarity of lead(II) ion in the original solution?

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Problem 48

If 25.0 mL of silver nitrate solution reacts with excess potassium chloride solution to yield 0.842 g of precipitate, what is the molarity of silver ion in the original solution?

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Problem 49

How many grams of barium sulfate form when 35.0 mL of 0.160 $M$ barium chloride reacts with 58.0 mL of 0.065 $M$ sodium sulfate?

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Problem 50

How many grams of iron(III) sulfide form when 62.0 mL of 0.135 $M$ iron(III) chloride reacts with 45.0 mL of 0.285 $M$ calcium sulfide?

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Problem 51

With ions shown as spheres and solvent molecules omitted for clarity, the circle (right) illustrates the solid formed when a solution containing $\mathrm{K}^{+}, \mathrm{Mg}^{2+}$ $\mathrm{Ag}^{+},$ or $\mathrm{Pb}^{2+}$ (blue) is mixed with one containing $\mathrm{ClO}_{4}^{-}, \mathrm{NO}_{3}^{-},$ or $\mathrm{SO}_{4}^{2-}(\text { yellow) }$ (a) Identify the solid. (b) Write a balanced net ionic equation for the reaction. (c) If each sphere represents $5.0 \times 10^{-4}$ mol of ion, what mass of product forms?

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Problem 52

The precipitation reaction between 25.0 mL of a solution containing a cation (purple) and 35.0 mL of a solution containing an anion (green) is depicted below (with ions shown as spheres and solvent molecules omitted for clarity).
(a) Given the following choices of reactants, write balanced total ionic and net ionic equations that best represent the reaction:
(1) $\mathrm{KNO}_{3}(a q)+\mathrm{CuCl}_{2}(a q) \longrightarrow$
(2) $\mathrm{NaClO}_{4}(a q)+\mathrm{CaCl}_{2}(a q) \longrightarrow$
(3) $\mathrm{Li}_{2} \mathrm{SO}_{4}(a q)+\mathrm{AgNO}_{3}(a q) \longrightarrow$
(4) $\mathrm{NH}_{4} \mathrm{Br}(a q)+\mathrm{Pb}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2}(a q) \longrightarrow$
(b) If each sphere represents $2.5 \times 10^{-3}$ mol of ion, find the total number of ions present.
(c) What is the mass of solid formed?

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Problem 53

A 1.50-g sample of an unknown alkali-metal carbonate was dissolved in water, and 31.10 $\mathrm{mL}$ of 0.350 $\mathrm{M} \mathrm{CaCl}_{2}$ was required to precipitate all the carbonate ions as $\mathrm{CaCO}_{3}$ . Give the name and formula of the unknown compound.

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Problem 54

A 0.750-g sample of a compound that might be iron(II) chloride, nickel(II) chloride, or zinc chloride is dissolved in water, and 22.40 $\mathrm{mL}$ of 0.515 $\mathrm{M} \mathrm{AgNO}_{3}$ is required to completely precipitate all the chloride ion as AgCl. Name the compound, and write its formula.

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Problem 55

The mass percent of $\mathrm{Cl}^{-}$ in a seawater sample is determined by titrating 25.00 mL of seawater with $\mathrm{AgNO}_{3}$ solution, causing a precipitation reaction. An indicator is used to detect the end point, which occurs when free $\mathrm{Ag}^{+}$ ion is present in solution after all the
$\mathrm{Cl}^{-}$ has reacted. If 53.63 $\mathrm{mL}$ of 0.2970 $\mathrm{M} \mathrm{AgNO}_{3}$ is required to reach the end point, what is the mass percent of $\mathrm{Cl}^{-}$ in the seawater $(d \text { of seawater }=1.024 \mathrm{g} / \mathrm{mL}) ?$

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Problem 56

Aluminum sulfate, known as cake alum, has a wide range of uses, from dyeing leather and cloth to purifying sewage. In aqueous solution, it reacts with base to form a white precipitate. (a) Write balanced total and net ionic equations for its reaction with aqueous NaOH. (b) What mass of precipitate forms when 185.5 mL of 0.533 $M$ NaOH is added to 627 mL of a solution that contains 15.8 g of aluminum sulfate per liter?

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Problem 57

Is the total ionic equation the same as the net ionic equation when $\mathrm{Sr}(\mathrm{OH})_{2}(a q)$ and $\mathrm{H}_{2} \mathrm{SO}_{4}(a q)$ react? Explain.

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Problem 58

Write a general equation for a neutralization reaction.

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Problem 59

(a) Name three common strong acids. (b) Name three common strong bases. (c) What is a characteristic behavior of a strong acid or a strong base?

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Problem 60

(a) Name three common weak acids. (b) Name one common weak base. (c) What is the major difference between a weak acid and a strong acid or between a weak base and a strong base, and what experiment would you perform to observe it?

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Problem 61

Do either of the following reactions go to completion? If so, what factor(s) cause(s) each to do so?

(a) $\mathrm{MgSO}_{3}(s)+2 \mathrm{HCl}(a q) \longrightarrow \mathrm{MgCl}_{2}(a q)+\mathrm{SO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l)$
(b) $3 \mathrm{Ba}(\mathrm{OH})_{2}(a q)+2 \mathrm{H}_{3} \mathrm{PO}_{4}(a q) \longrightarrow \mathrm{Ba}_{3}\left(\mathrm{PO}_{4}\right)_{2}(s)+6 \mathrm{H}_{2} \mathrm{O}(l)$

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Problem 62

(a) The net ionic equation for the aqueous neutralization reaction between acetic acid and sodium hydroxide is different from that for the reaction between hydrochloric acid and sodium hydroxide. Explain by writing balanced net ionic equations. (b) For a solution of acetic acid in water, list the major species in decreasing order of concentration.

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Problem 63

How many moles of $\mathrm{H}^{+}$ ions are present in the following aqueous solutions?

(a) 1.40 $\mathrm{L}$ of 0.25$M$ perchloric acid
(b) 6.8 $\mathrm{mL}$ of 0.92$M$ nitric acid
(c) 2.6 $\mathrm{L}$ of 0.085 M hydrochloric acid

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Problem 64

How many moles of $\mathrm{H}^{+}$ ions are present in the following aqueous solutions?

(a) 1.4 mL of 0.75 $M$ hydrobromic acid
(b) 2.47 mL of 1.98 $M$ hydriodic acid
(c) 395 mL of 0.270 $M$ nitric acid

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Problem 65

Complete the following acid-base reactions with balanced molecular, total ionic, and net ionic equations:

(a) Potassium hydroxide $(a q)+$ hydrobromic acid $(a q) \longrightarrow$
(b) Ammonia $(a q)+$ hydrochloric acid $(a q) \longrightarrow$

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Problem 66

Complete the following acid-base reactions with balanced molecular, total ionic, and net ionic equations:

(a) Cesium hydroxide(aq) + nitric acid(aq) $\rightarrow$
(b) Calcium hydroxide(aq) $+$ acetic acid $(a q) \longrightarrow$

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Problem 67

Limestone (calcium carbonate) is insoluble in water but dissolves when a hydrochloric acid solution is added. Write balanced total ionic and net ionic equations, showing hydrochloric acid as it actually exists in water and the reaction as a proton-transfer process.

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Problem 68

Zinc hydroxide is insoluble in water but dissolves when a nitric acid solution is added. Why? Write balanced total ionic and net ionic equations, showing nitric acid as it actually exists in water and the reaction as a proton-transfer process.

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Problem 69

How many milliliters of 0.383$M \mathrm{HCl}$ are needed to react with 16.2 $\mathrm{g}$ of $\mathrm{CaCO}_{3} ?$
$$2 \mathrm{HCl}(a q)+\mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaCl}_{2}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l)$$

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Problem 70

How many grams of $\mathrm{NaH}_{2} \mathrm{PO}_{4}$ are needed to react with 43.74 $\mathrm{mL}$ of 0.285 $\mathrm{M} \mathrm{NaOH} ?$

$$\mathrm{NaH}_{2} \mathrm{PO}_{4}(s)+2 \mathrm{NaOH}(a q) \longrightarrow \mathrm{Na}_{3} \mathrm{PO}_{4}(a q)+2 \mathrm{H}_{2} \mathrm{O}(l)$$

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Problem 71

If 25.98 $\mathrm{mL}$ of 0.1180 $\mathrm{M} \mathrm{KOH}$ solution reacts with 52.50 $\mathrm{mL}$ of $\mathrm{CH}_{3} \mathrm{COOH}$ solution, what is the molarity of the acid solution?

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Problem 72

If 26.25 $\mathrm{mL}$ of 0.1850 $\mathrm{M}$ $\mathrm{NaOH}$ solution reacts with 25.00 $\mathrm{mL}$ of $\mathrm{H}_{2} \mathrm{SO}_{4},$ what is the molarity of the acid solution?

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Problem 73

An auto mechanic spills 88 $\mathrm{mL}$ of 2.6 $\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}$ solution from an auto battery. How many milliters of 1.6 $\mathrm{M} \mathrm{NaHCO}_{3}$ must be poured on the spill to react completely with the sulfuric acid?

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Problem 74

Sodium hydroxide is used extensively in acid-base titrations because it is a strong, inexpensive base. A sodium hydroxide solution was standardized by titrating 25.00 mL of 0.1528 $M$ standard hydrochloric acid. The initial buret reading of the sodium hydroxide was 2.24 mL, and the final reading was 39.21 mL. What was the molarity of the base solution?

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Problem 75

An unknown amount of acid can often be determined by adding an excess of base and then “back-titrating” the excess. A 0.3471-g sample of a mixture of oxalic acid, which has two ionizable protons, and benzoic acid, which has one, is treated with 100.0 mL of 0.1000 M NaOH. The excess NaOH is titrated with 20.00 mL of 0.2000 M HCl. Find the mass % of benzoic acid.

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Problem 76

One of the first steps in the enrichment of uranium for use in nuclear power plants involves a displacement reaction between $\mathrm{UO}_{2}$ and aqueous $\mathrm{HF}:$

$$\mathrm{UO}_{2}(s)+\mathrm{HF}(a q) \longrightarrow \mathrm{UF}_{4}(s)+\mathrm{H}_{2} \mathrm{O}(l)[\text { unbalanced }]$$

How many liters of 2.40$M$ $\mathrm{HF}$ will react with 2.15 $\mathrm{kg}$ of $\mathrm{UO}_{2}?$

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Problem 77

A mixture of bases can sometimes be the active ingredient in antacid tablets. If 0.4826 g of a mixture of $\mathrm{Al}(\mathrm{OH})_{3}$ and $\mathrm{Mg}(\mathrm{OH})_{2}$ is neutralized with 17.30 mL of $1.000 M \mathrm{HNO}_{3},$ what is the mass $\%$ of $\mathrm{Al}(\mathrm{OH})_{3}$ in the mixture?

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Problem 78

Describe how to determine the oxidation number of sulfur in
(a) $\mathrm{H}_{2} \mathrm{S}$ and (b) $\mathrm{SO}_{3}^{2-}$

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Problem 79

Is the following a redox reaction? Explain.

$$\mathrm{NH}_{3}(a q)+\mathrm{HCl}(a q) \longrightarrow \mathrm{NH}_{4} \mathrm{Cl}(a q)$$

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Problem 80

Explain why an oxidizing agent undergoes reduction.

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Problem 81

Why must every redox reaction involve an oxidizing agent and a reducing agent?

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Problem 82

In which of the following equations does sulfuric acid act as an oxidizing agent? In which does it act as an acid? Explain.

(a) $4 \mathrm{H}^{+}(a q)+\mathrm{SO}_{4}^{2-}(a q)+2 \mathrm{NaI}(s) \longrightarrow 2 \mathrm{Na}^{+}(a q)+\mathrm{I}_{2}(s)+\mathrm{SO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l)$
(b) $\mathrm{BaF}_{2}(s)+2 \mathrm{H}^{+}(a q)+\mathrm{SO}_{4}^{2-}(a q) \longrightarrow 2 \mathrm{HF}(a q)+\mathrm{BaSO}_{4}(s)$

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Problem 83

Identify the oxidizing agent and the reducing agent in the following reaction, and explain your answer:

$$8 \mathrm{NH}_{3}(g)+6 \mathrm{NO}_{2}(g) \longrightarrow 7 \mathrm{N}_{2}(g)+12 \mathrm{H}_{2} \mathrm{O}(l)$$

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Problem 84

Give the oxidation number of carbon in the following:
(a) $\mathrm{CF}_{2} \mathrm{Cl}_{2} \quad$ (b) $\mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \quad$ (c) $\mathrm{HCO}_{3}^{-} \quad$ (d) $\mathrm{C}_{2} \mathrm{H}_{6}$

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Problem 85

Give the oxidation number of bromine in the following:

(a) $\mathrm{KBr} \quad$ (b) $\mathrm{BrF}_{3} \quad$ (c) $\mathrm{HBrO}_{3} \quad$ (d) $\mathrm{CBr}_{4}$

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Problem 86

Give the oxidation number of nitrogen in the following:
(a) $\mathrm{NH}_{2} \mathrm{OH} \quad$ (b) $\mathrm{N}_{2} \mathrm{F}_{4} \quad$ (c) $\mathrm{NH}_{4}^{+} \quad$ (d) $\mathrm{HNO}_{2}$

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Problem 87

Give the oxidation number of sulfur in the following:
(a) $\mathrm{SOCl}_{2} \quad$ (b) $\mathrm{H}_{2} \mathrm{S}_{2} \quad$ (c) $\mathrm{H}_{2} \mathrm{SO}_{3} \quad$ (d) $\mathrm{Na}_{2} \mathrm{S}$

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Problem 88

Give the oxidation number of arsenic in the following:
(a) $\mathrm{AsH}_{3} \quad$ (b) $\mathrm{H}_{2} \mathrm{AsO}_{4}^{-} \quad$ (c) $\mathrm{AsCl}_{3}$

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Problem 89

Give the oxidation number of phosphorus in the following:
(a) $\mathrm{H}_{2} \mathrm{P}_{2} \mathrm{O}_{7}^{2-} \quad$ (b) $\mathrm{PH}_{4}^{+} \quad$ (c) $\mathrm{PCl}_{5}$

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Problem 90

Give the oxidation number of manganese in the following:
(a) $\mathrm{MnO}_{4}^{2-} \quad$ (b) $\mathrm{Mn}_{2} \mathrm{O}_{3} \quad$ (c) $\mathrm{KMnO}_{4}$

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Problem 91

Give the oxidation number of chromium in the following:
(a) $\mathrm{Cr} \mathrm{O}_{3} \quad$ (b) $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-} \quad$ (c) $\mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3}$

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Problem 92

Identify the oxidizing and reducing agents in the following:
(a) $5 \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(a q)+2 \mathrm{MnO}_{4}^{-}(a q)+6 \mathrm{H}^{+}(a q) \longrightarrow 2 \mathrm{Mn}^{2+}(a q)+10 \mathrm{CO}_{2}(g)+8 \mathrm{H}_{2} \mathrm{O}(l)$
(b) $3 \mathrm{Cu}(s)+8 \mathrm{H}^{+}(a q)+2 \mathrm{NO}_{3}^{-}(a q) \longrightarrow 3 \mathrm{Cu}^{2+}(a q)+2 \mathrm{NO}(g)+4 \mathrm{H}_{2} \mathrm{O}(l)$

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Problem 93

Identify the oxidizing and reducing agents in the following:
(a) $\mathrm{Sn}(s)+2 \mathrm{H}^{+}(a q) \longrightarrow \mathrm{Sn}^{2+}(a q)+\mathrm{H}_{2}(g)$
(b) $2 \mathrm{H}^{+}(a q)+\mathrm{H}_{2} \mathrm{O}_{2}(a q)+2 \mathrm{Fe}^{2+}(a q) \longrightarrow 2 \mathrm{Fe}^{3+}(a q)+2 \mathrm{H}_{2} \mathrm{O}(l)$

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Problem 94

Identify the oxidizing and reducing agents in the following:
(a) $8 \mathrm{H}^{+}(a q)+6 \mathrm{Cl}^{-}(a q)+\mathrm{Sn}(s)+4 \mathrm{NO}_{3}^{-}(a q) \longrightarrow \mathrm{SnCl}_{6}^{2-}(a q)+4 \mathrm{NO}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(l)$
(b) $2 \mathrm{MnO}_{4}^{-}(a q)+10 \mathrm{Cl}^{-}(a q)+16 \mathrm{H}^{+}(a q) \longrightarrow 5 \mathrm{Cl}_{2}(g)+2 \mathrm{Mn}^{2+}(a q)+8 \mathrm{H}_{2} \mathrm{O}(l)$

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Problem 95

Identify the oxidizing and reducing agents in the following:
(a) $8 \mathrm{H}^{+}(a q)+\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+3 \mathrm{SO}_{3}^{2-}(a q) \longrightarrow 2 \mathrm{Cr}^{3+}(a q)+3 \mathrm{SO}_{4}^{2-}(a q)+4 \mathrm{H}_{2} \mathrm{O}(l)$
(b) $\mathrm{NO}_{3}^{-}(a q)+4 \mathrm{Zn}(s)+7 \mathrm{OH}^{-}(a q)+6 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow 4 \mathrm{Zn}(\mathrm{OH})_{4}^{2-}(a q)+\mathrm{NH}_{3}(a q)$

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Problem 96

The active agent in many hair bleaches is hydrogen peroxide. The amount of $\mathrm{H}_{2} \mathrm{O}_{2}$ in 14.8 $\mathrm{g}$ of hair bleach was determined by titration with a standard potassium permanganate solution:
\begin{aligned} 2 \mathrm{MnO}_{4}^{-}(a q)+5 \mathrm{H}_{2} \mathrm{O}_{2}(a q)+& 6 \mathrm{H}^{+}(a q) \longrightarrow \\ & 5 \mathrm{O}_{2}(g)+2 \mathrm{Mn}^{2+}(a q)+8 \mathrm{H}_{2} \mathrm{O}(l) \end{aligned}
(a) How many moles of $\mathrm{MnO}_{4}^{-}$ were required for the titration if 43.2 $\mathrm{mL}$ of 0.105 $\mathrm{M} \mathrm{KMnO}_{4}$ was needed to reach the end point?
(b) How many moles of $\mathrm{H}_{2} \mathrm{O}_{2}$ were present in the 14.8 -g sample of bleach?
(c) How many grams of $\mathrm{H}_{2} \mathrm{O}_{2}$ were in the sample?
(d) What is the mass percent of $\mathrm{H}_{2} \mathrm{O}_{2}$ in the sample?
(e) What is the reducing agent in the redox reaction?

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Problem 97

A person's blood alcohol $\left(\mathrm{C}_{2} \mathrm{H}_{3}, \mathrm{OH}\right)$ level can be determined by titrating a sample of blood plasma with a potassium dichromate solution. The balanced equation is
\begin{aligned} 16 \mathrm{H}^{+}(a q)+2 \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+& \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(a q) \longrightarrow \\ & 4 \mathrm{Cr}^{3+}(a q)+2 \mathrm{CO}_{2}(g)+11 \mathrm{H}_{2} \mathrm{O}(l) \end{aligned}
If 35.46 $\mathrm{mL}$ of 0.05961$M \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ is required to titrate 28.00 $\mathrm{g}$ of plasma, what is the mass percent of alcohol in the blood?

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Problem 98

Which type of redox reaction leads to each of the following?
(a) An increase in the number of substances
(b) A decrease in the number of substances
(c) No change in the number of substances

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Problem 99

Why do decomposition redox reactions typically have compounds as reactants, whereas combination redox and displacement redox reactions have one or more elements?

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Problem 100

Which of the types of reactions discussed in Section 4.6 commonly produce more than one compound?

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Problem 101

Are all combustion reactions redox reactions? Explain.

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Problem 102

Give one example of a combination reaction that is a redox reaction and another that is not a redox reaction.

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Problem 103

Balance each of the following redox reactions and classify it as a combination, decomposition, or displacement reaction:
(a) $\mathrm{Ca}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(a q)+\mathrm{H}_{2}(g)$
(b) $\mathrm{NaNO}_{3}(s) \longrightarrow \mathrm{NaNO}_{2}(s)+\mathrm{O}_{2}(g)$
(c) $\mathrm{C}_{2} \mathrm{H}_{2}(g)+\mathrm{H}_{2}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)$

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Problem 104

Balance each of the following redox reactions and classify it as a combination, decomposition, or displacement reaction:
(a) HI(g) $\longrightarrow \mathrm{H}_{2}(g)+\mathrm{I}_{2}(g)$
(b) $\mathrm{Zn}(s)+\mathrm{AgNO}_{3}(a q) \longrightarrow \mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{Ag}(s)$
(c) $\mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{N}_{2} \mathrm{O}_{4}(l)$

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Problem 105

Balance each of the following redox reactions and classify it as a combination, decomposition, or displacement reaction:
(a) $\mathrm{Sb}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \operatorname{SbCl}_{3}(s)$
(b) AsH $_{3}(g) \longrightarrow \mathrm{As}(s)+\mathrm{H}_{2}(g)$
(c) $\mathrm{Zn}(s)+\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(a q) \longrightarrow \mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{Fe}(s)$

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Problem 106

Balance each of the following redox reactions and classify it as a combination, decomposition, or displacement reaction:
(a) $\mathrm{Mg}(s)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{Mg}(\mathrm{OH})_{2}(s)+\mathrm{H}_{2}(g)$
(b) $\mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3}(a q)+\mathrm{Al}(s) \longrightarrow \mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}(a q)+\mathrm{Cr}(s)$
(c) $\mathrm{PF}_{3}(g)+\mathrm{F}_{2}(g) \longrightarrow \mathrm{PF}_{5}(g)$

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Problem 107

Predict the product(s) and write a balanced equation for each of the following redox reactions:
(a) $\operatorname{Sr}(s)+\operatorname{Br}_{2}(l) \longrightarrow$
(b) $\mathrm{Ag}_{2} \mathrm{O}(s) \stackrel{\Delta}{\longrightarrow}$
(c) $\mathrm{Mn}(s)+\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(a q) \longrightarrow$

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Problem 108

Predict the product(s) and write a balanced equation for each of the following redox reactions:
(a) $\operatorname{Mg}(s)+\mathrm{HCl}(a q) \longrightarrow$
(b) $\operatorname{LiCl}(l) \stackrel{\text {electricity}}{\longrightarrow}$
(c) $\operatorname{Sn} \mathrm{Cl}_{2}(a q)+\mathrm{Co}(s) \longrightarrow$

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Problem 109

Predict the product(s) and write a balanced equation for each of the following redox reactions:
(a) $\mathrm{N}_{2}(g)+\mathrm{H}_{2}(g) \longrightarrow$
(b) $\mathrm{NaClO}_{3}(s) \stackrel{\Delta}{\longrightarrow}$
(c) $\mathrm{Ba}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow$

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Problem 110

Predict the product(s) and write a balanced equation for each of the following redox reactions:
(a) Fe(s) $+\mathrm{HClO}_{4}(a q) \longrightarrow$
(b) $\mathrm{S}_{8}(s)+\mathrm{O}_{2}(g) \longrightarrow$
(c) $\mathrm{BaCl}_{2}(l) \stackrel{\text { electricity }}{\longrightarrow}$

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Problem 111

Predict the product(s) and write a balanced equation for each of the following redox reactions:
(a) Cesium $+$ iodine $\longrightarrow$
(b) Aluminum $+$ aqueous manganese (II) sulfate $\longrightarrow$
(c) Sulfur dioxide $+$ oxygen $\longrightarrow$
(d) Butane $+$ oxygen $\longrightarrow$
(e) Write a balanced net ionic equation for (b).

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Problem 112

Predict the product(s) and write a balanced equation for each of the following redox reactions:
(a) Pentane $\left(\mathrm{C}_{5} \mathrm{H}_{12}\right)+$ oxygen $\longrightarrow$
(b) Phosphorus trichloride + chlorine $\longrightarrow$
(c) Zinc + hydrobromic acid $\longrightarrow$
(d) Aqueous potassium iodide + bromine $\longrightarrow$
(e) Write a balanced net ionic equation for (d).

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Problem 113

How many grams of $\mathrm{O}_{2}$ can be prepared from the thermal decomposition of 4.27 kg of $\mathrm{HgO} ?$ Name and calculate the mass (in kg) of the other product.

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Problem 114

How many grams of chlorine gas can be produced from the electrolytic decomposition of 874 g of calcium chloride? Name and calculate the mass (in g) of the other product.

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Problem 115

In a combination reaction, 1.62 g of lithium is mixed with 6.50 g of oxygen.
(a) Which reactant is present in excess?
(b) How many moles of product are formed?
(c) After reaction, how many grams of each reactant and product are present?

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Problem 116

In a combination reaction, 2.22 g of magnesium is heated with 3.75 g of nitrogen.
(a) Which reactant is present in excess?
(b) How many moles of product are formed?
(c) After reaction, how many grams of each reactant and product are present?

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Problem 117

A mixture of $\mathrm{KClO}_{3}$ and $\mathrm{KCl}$ with a mass of 0.950 $\mathrm{g}$ was
heated to produce $\mathrm{O}_{2} .$ After heating, the mass of residue was 0.700 $\mathrm{g} .$ Assuming all the $\mathrm{KClO}_{3}$ decomposed to $\mathrm{KCl}$ and $\mathrm{O}_{2},$ calculate the mass percent of $\mathrm{KClO}_{3}$ in the original mixture.

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Problem 118

A mixture of $\mathrm{CaCO}_{3}$ and CaO weighing 0.693 g was heated to produce gaseous $\mathrm{CO}_{2} .$ After heating, the remaining solid weighed 0.508 g. Assuming all the $\mathrm{CaCO}_{3}$ broke down to $\mathrm{CaO}$ and $\mathrm{CO}_{2},$ calculate the mass percent of $\mathrm{CaCO}_{3}$ in the original mixture.

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Problem 119

Before arc welding was developed, a displacement reaction involving aluminum and iron(III) oxide was commonly used to produce molten iron (the thermite process). This reaction was used, for example, to connect sections of iron rails for train tracks. Calculate the mass of molten iron produced when 1.50 kg of aluminum reacts with 25.0 mol of iron(III) oxide

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Problem 120

Iron reacts rapidly with chlorine gas to form a reddish brown, ionic compound (A), which contains iron in the higher of its two common oxidation states. Strong heating decomposes compound A to compound B, another ionic compound, which contains iron in the lower of its two oxidation states. When com pound A is formed by the reaction of 50.6 $\mathrm{g}$ of $\mathrm{Fe}$ and 83.8 $\mathrm{g}$ of $\mathrm{Cl}_{2}$ and then heated, how much compound B forms?

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Problem 121

A sample of impure magnesium was analyzed by allowing it to react with excess $\mathrm{HCl}$ solution. After 1.32 $\mathrm{g}$ of the impure metal was treated with 0.100 $\mathrm{L}$ of $0.750 \mathrm{M}$ $\mathrm{HCl}, 0.0125 \mathrm{mol}$ of $\mathrm{HCl}$ remained. Assuming the impurities do not react, what is the mass $\%$ of $\mathrm{Mg}$ in the sample?

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Problem 122

Why is the equilibrium state called “dynamic”?

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Problem 123

In a decomposition reaction involving a gaseous product, what must be done for the reaction to reach equilibrium?

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Problem 124

Describe what happens on the molecular level when acetic acid dissolves in water.

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Problem 125

When either a mixture of NO and Br_ or pure nitrosyl bromide (NOBr) is placed in a reaction vessel, the product mixture contains $\mathrm{NO}, \mathrm{Br}_{2},$ and $\mathrm{NOBr}$ . Explain.

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Problem 126

Ammonia is produced by the millions of tons annually for use as a fertilizer. It is commonly made from $\mathrm{N}_{2}$ and $\mathrm{H}_{2}$ by the Haber process. Because the reaction reaches equilibrium before going completely to product, the stoichiometric amount of ammonia is not obtained. At a particular temperature and pressure, 10.0 $\mathrm{g}$ of $\mathrm{H}_{2}$ reacts with 20.0 $\mathrm{g}$ of $\mathrm{N}_{2}$ to form ammonia. When equilibrium is reached, 15.0 $\mathrm{g}$ of $\mathrm{NH}_{3}$ has formed. (a) Calculate the percent yield. (b) How many moles of $\mathrm{N}_{2}$ and $\mathrm{H}_{2}$ are present at equilibrium?

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Problem 127

Nutritional biochemists have known for decades that acidic foods cooked in cast-iron cookware can supply significant amounts of dietary iron (ferrous ion). (a) Write a balanced net ionic equation, with oxidation numbers, that supports this fact. (b) Measurements show an increase from 3.3 mg of iron to 49 mg of iron per $\frac{1}{2}-\operatorname{cup}$ (125-g) serving during the slow preparation of tomato sauce in a cast-iron pot. How many ferrous ions are present in a 26-oz (737-g) jar of the tomato sauce?

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Problem 128

Limestone $\left(\mathrm{CaCO}_{3}\right)$ is used to remove acidic pollutants from smokestack flue gases. It is heated to form lime $(\mathrm{CaO})$, which reacts with sulfur dioxide to form calcium sulfite. Assuming a $70 . \%$ yield in the overall reaction, what mass of limestone is required to remove all the sulfur dioxide formed by the combustion of $8.5 \times 10^{4} \mathrm{kg}$ of coal that is 0.33 mass $\%$ sulfur?

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Problem 129

The brewing industry uses yeast to convert glucose to ethanol. The baking industry uses the carbon dioxide produced in the same reaction to make bread rise:

$$\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s) \stackrel{\text { yeast }}{\longrightarrow} 2 \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l)+2 \mathrm{CO}_{2}(g)$$

How many grams of ethanol can be produced from $100 .$ g of glucose? What volume of $\mathrm{CO}_{2}$ is produced? (Assume 1 $\mathrm{mol}$ of gas occupies 22.4 $\mathrm{L}$ at the conditions used.)

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Problem 130

A chemical engineer determines the mass percent of iron in an ore sample by converting the Fe to $\mathrm{Fe}^{2+}$ in acid and then titrating the $\mathrm{Fe}^{2+}$ with $\mathrm{MnO}_{4}^{-} \cdot \mathrm{A} 1.081-\mathrm{g}$ sample was dissolved in acid and then titrated with 39.32 $\mathrm{mL}$ of 0.03190 $\mathrm{M}$ $\mathrm{KMnO}_{4}$ . The balanced equation is

$$8 \mathrm{H}^{+}(a q)+5 \mathrm{Fe}^{2+}(a q)+\mathrm{MnO}_{4}^{-}(a q) \longrightarrow \mathrm{Fe}^{3+}(a q)+\mathrm{Mn}^{2+}(a q)+4 \mathrm{H}_{2} \mathrm{O}(l)$$

Calculate the mass percent of iron in the ore.

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Problem 131

Mixtures of $\mathrm{CaCl}_{2}$ and $\mathrm{NaCl}$ are used to melt ice on roads. A dissolved 1.9348 -g sample of such a mixture was analyzed by using excess $\mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4}$ to precipitate the Ca't as $\mathrm{CaC}_{2} \mathrm{O}_{4}$ The $\mathrm{CaC}_{2} \mathrm{O}_{4}$ was dissolved in sulfuric acid, and the resulting $\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}$ was titrated with 37.68 $\mathrm{mL}$ of 0.1019 $\mathrm{M} \mathrm{KMnO}_{4}$ solution.

(a) Write the balanced net ionic equation for the precipitation reaction.
(b) Write the balanced net ionic equation for the titration reaction. (See Sample Problem 4.19.)
(c) What is the oxidizing agent?
(d) What is the reducing agent?
(e) Calculate the mass percent of $\mathrm{CaCl}_{2}$ in the original sample.

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Problem 132

You are given solutions of $\mathrm{HCl}$ and $\mathrm{NaOH}$ and must determine their concentrations. You use 27.5 $\mathrm{mL}$ of $\mathrm{NaOH}$ to titrate $100 . \mathrm{mL}$ of $\mathrm{HCl}$ and 18.4 $\mathrm{mL}$ of $\mathrm{NaOH}$ to titrate 50.0 $\mathrm{mL}$ of 0.0782 $\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}$ . Find the unknown concentrations.

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Problem 133

The flask (right) represents the products of the titration of 25 mL of sulfuric acid with 25 mL of sodium hydroxide.
(a) Write balanced molecular, total ionic, and net ionic equations for the reaction.
(b) If each orange sphere represents 0.010 mol of sulfate ion, how many moles of acid and of base reacted?
(c) What are the molarities of the acid and the base?

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Problem 134

To find the mass percent of dolomite $\left[\mathrm{CaMg}\left(\mathrm{CO}_{3}\right)_{2}\right]$ in a soil sample, a geochemist titrates 13.86 $\mathrm{g}$ of soil with 33.56 $\mathrm{mL}$ of 0.2516 $\mathrm{HCl}$ . What is the mass percent of dolomite in the soil?

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Problem 135

On a lab exam, you have to find the concentrations of the monoprotic (one proton per molecule) acids $\mathrm{HA}$ and $\mathrm{HB}$. You are given 43.5 $\mathrm{mL}$ of $\mathrm{HA}$ solution in one flask. A second flask contains 37.2 $\mathrm{mL}$ of $\mathrm{HA}$, and you add enough $\mathrm{HB}$ solution to it to reach a final volume of 50.0 $\mathrm{mL}$ . You titrate the first $\mathrm{HA}$ solution with 87.3 $\mathrm{mL}$ of 0.0906 $\mathrm{M}$ $\mathrm{NaOH}$ and the mixture of HA and HB in the second flask with 96.4 $\mathrm{mL}$ of the $\mathrm{NaOH}$ solution. Calculate the molarity of the $\mathrm{HA}$ and $\mathrm{HB}$ solutions.

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Problem 136

Nitric acid, a major industrial and laboratory acid, is produced commercially by the multi step Ostwald process, which begins with the oxidation of ammonia:

Step $1 . \quad 4 \mathrm{NH}_{3}(g)+5 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(l)$
Step $2 . \quad 2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g)$
Step $3 . \quad 3 \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow 2 \mathrm{HNO}_{3}(l)+\mathrm{NO}(g)$
(a) What are the oxidizing and reducing agents in each step?
(b) Assuming 100% yield in each step, what mass (in kg) of ammonia must be used to produce $3.0 \times 10^{4} \mathrm{kg}$ of $\mathrm{HNO}_{3} ?$

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Problem 137

Various data can be used to find the composition of an alloy (a metallic mixture). Show that calculating the mass $\%$ of Mg in a magnesium-aluminum alloy $\left(d=2.40 \mathrm{g} / \mathrm{cm}^{3}\right)$ using each of the following pieces of data gives the same answer (within rounding): (a) a sample of the alloy has a mass of $0.263 \mathrm{g}(d \text { of Mg }=$ $1.74 \mathrm{g} / \mathrm{cm}^{3} ; d$ of $\mathrm{Al}=2.70 \mathrm{g} / \mathrm{cm}^{3} ) ;(\mathrm{b})$ an identical sample reacting with excess aqueous HCl forms $1.38 \times 10^{-2} \mathrm{mol}$ of $\mathrm{H}_{2} ;(\mathrm{c})$ an identical sample reacting with excess $\mathrm{O}_{2}$ forms 0.483 $\mathrm{g}$ of oxide.

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Problem 138

In 1995, Mario Molina, Paul Crutzen, and F. Sherwood Rowland shared the Nobel Prize in chemistry for their work on atmospheric chemistry. One reaction sequence they proposed for the role of chlorine in the decomposition of stratospheric ozone (we’ll see another sequence in Chapter 16) is
(1) $\mathrm{Cl}(g)+\mathrm{O}_{3}(g) \longrightarrow \mathrm{ClO}(g)+\mathrm{O}_{2}(g)$
(2) $\mathrm{ClO}(g)+\mathrm{ClO}(g) \longrightarrow \mathrm{Cl}_{2} \mathrm{O}_{2}(g)$
(3) $\mathrm{Cl}_{2} \mathrm{O}_{2}(g) \stackrel{\text { light }}{\longrightarrow} 2 \mathrm{Cl}(g)+\mathrm{O}_{2}(g)$
Over the tropics, O atoms are more common in the stratosphere:
(4) $\mathrm{ClO}(g)+\mathrm{O}(g) \longrightarrow \mathrm{Cl}(g)+\mathrm{O}_{2}(g)$
(a) Which, if any, of these are oxidation-reduction reactions?
(b) Write an overall equation combining reactions 1–3.

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Problem 139

Sodium peroxide $\left(\mathrm{Na}_{2} \mathrm{O}_{2}\right)$ is often used in self-contained breathing devices, such as those used in fire emergencies, because it reacts with exhaled $\mathrm{CO}_{2}$ to form $\mathrm{Na}_{2} \mathrm{CO}_{3}$ and $\mathrm{O}_{2}$ . How many
liters of respired air can react with 80.0 $\mathrm{g}$ of $\mathrm{Na}_{2} \mathrm{O}_{2}$ if each liter of respired air contains 0.0720 $\mathrm{g}$ of $\mathrm{CO}_{2} ?$

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Problem 140

A student forgets to weigh a mixture of sodium bromide dihydrate and magnesium bromide hexahydrate. Upon strong heating, the sample loses 252.1 mg of water. The mixture of anhydrous salts reacts with excess $\mathrm{AgNO}_{3}$ solution to form $6.00 \times 10^{-3} \mathrm{mol}$ of solid AgBr. Find the mass $\%$ of each compound in the original mixture.

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Problem 141

A typical formulation for window glass is $75 \% \mathrm{SiO}_{2}, 15 \%$ $\mathrm{Na}_{2} \mathrm{O},$ and $10 . \%$ $\mathrm{CaO}$ by mass. What masses of sand $\left(\mathrm{SiO}_{2}\right),$ sodium carbonate, and calcium carbonate must be combined to produce 1.00 kg of glass after carbon dioxide is driven off by thermal decomposition of the carbonates?

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Problem 142

The quantity of dissolved oxygen (DO) in natural waters is an essential parameter for monitoring survival of most aquatic life. DO is affected by temperature and the amount of organic waste. An earlier method for determining DO involved a two-step process:
1. The water sample is treated with $\mathrm{KI}$,
$$\mathrm{O}_{2}(a q)+4 \mathrm{KI}(a q)+2 \mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow 2 \mathrm{I}_{2}(a q)+2 \mathrm{H}_{2} \mathrm{O}(l)+2 \mathrm{K}_{2} \mathrm{SO}_{4}(a q)$$
2. The $\mathrm{I}_{2}$ is titrated with sodium thiosulfate,
$$\mathrm{I}_{2}(a q)+2 \mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3}(a q) \longrightarrow \mathrm{Na}_{2} \mathrm{S}_{4} \mathrm{O}_{6}(a q)+2 \mathrm{NaI}(a q)$$
A 50.0 -mL water sample is treated with KI, and then 15.75 $\mathrm{mL}$ of 0.0105 $\mathrm{M} \mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3}$ is required to reach the end point.
(a) Which substance is oxidized in step 1, and which is reduced in step 2?
(b) What mass $(g)$ of $\mathrm{O}_{2}$ is dissolved in the water sample?

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Problem 143

Physicians who specialize in sports medicine routinely treat athletes and dancers. Ethyl chloride, a local anesthetic commonly used for simple injuries, is the product of the combination of ethylene with hydrogen chloride:
$$\mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{HCl}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(g)$$
If 0.100 $\mathrm{kg}$ of $\mathrm{C}_{2} \mathrm{H}_{4}$ and 0.100 $\mathrm{kg}$ of $\mathrm{HCl}$ react: (a) How many molecules of gas (reactants plus products) are present when the reaction is complete? (b) How many moles of gas are present when half the product forms?

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Problem 144

Thyroxine $\left(\mathrm{C}_{15} \mathrm{H}_{11} \mathrm{I}_{4} \mathrm{NO}_{4}\right)$ is a hormone synthesized by the thyroid gland and used to control many metabolic functions in the body. A physiologist determines the mass percent of thyroxine in a thyroid extract by igniting 0.4332 g of extract with sodium carbonate, which converts the iodine to iodide. The iodide is dissolved in water, and bromine and hydrochloric acid are added, which convert the iodide to iodate.
(a) How many moles of iodate form per mole of thyroxine?
(b) Excess bromine is boiled off and more iodide is added, which reacts as shown in the following equation:
$$\mathrm{IO}_{3}^{-}(a q)+6 \mathrm{H}^{+}(a q)+5 \mathrm{I}^{-}(a q) \longrightarrow 3 \mathrm{I}_{2}(a q)+3 \mathrm{H}_{2} \mathrm{O}(l)$$
How many moles of iodine are produced per mole of thyroxine? (Hint: Be sure to balance the charges as well as the atoms.) What are the oxidizing and reducing agents in the reaction?
(c) The iodine reacts completely with 17.23 mL of 0.1000 $M$ thiosulfate as shown in the following unbalanced equation:
$$\mathrm{I}_{2}(a q)+\mathrm{S}_{2} \mathrm{O}_{3}^{2-}(a q) \longrightarrow \mathrm{I}^{-}(a q)+\mathrm{S}_{4} \mathrm{O}_{6}^{2-}(a q)$$
What is the mass percent of thyroxine in the thyroid extract?

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Problem 145

Over time, as their free fatty acid $(\mathrm{FFA})$ content increases, edible fats and oils become rancid. To measure rancidity, the fat or oil is dissolved in ethanol, and any $\mathrm{FFA}$ present is titrated with $\mathrm{KOH}$ dissolved in ethanol. In a series of tests on olive oil, a stock solution of 0.050$M$ ethanolic $\mathrm{KOH}$ was prepared at $25^{\circ} \mathrm{C},$ stored at $0^{\circ} \mathrm{C},$ and then placed in a $100-\mathrm{mL}$ buret to titrate oleic acid [an $\mathrm{FFA}$with formula $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{7} \mathrm{CH}=\mathrm{CH}\left(\mathrm{CH}_{2}\right)_{7} \mathrm{COOH} ]$ in the oil. Each of four $10.00-$ g samples of oil took several minutes to titrate: the first required 19.60 $\mathrm{mL}$ , the second 19.80 $\mathrm{mL}$ , and the third and fourth 20.00 $\mathrm{mL}$ of the ethanolic $\mathrm{KOH}$.
(a) What is the apparent acidity of each sample, in terms of mass $\%$ of oleic acid? (Note: As the ethanolic KOH warms in the buret, its volume increases by a factor of 0.00104$/^{\circ} \mathrm{C} .$ )
(b) Is the variation in acidity a random or systematic error? Explain.
(c) What is the actual acidity? How would you demonstrate this?

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Problem 146

A chemist mixes solid AgCl, $\mathrm{CuCl}_{2},$ and $\mathrm{MgCl}_{2}$ in enough water to give a final volume of 50.0 $\mathrm{mL}$ .
(a) With ions shown as spheres and solvent molecules omitted for clarity, which scene best represents the resulting mixture?
(b) If each sphere represents $5.0 \times 10^{-3}$ mol of ions, what is the total concentration of dissolved (separated) ions?
(c) What is the total mass of solid?

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Problem 147

Calcium dihydrogen phosphate, $\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2},$ and sodium hydrogen carbonate, $\mathrm{NaHCO}_{3},$ are ingredients of baking powder that react to produce $\mathrm{CO}_{2},$ which causes dough or batter to rise:

\begin{aligned} \mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2}(s)+& \mathrm{NaHCO}_{3}(s) \longrightarrow \\ & \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)+\mathrm{CaHPO}_{4}(s)+\mathrm{Na}_{2} \mathrm{HPO}_{4}(s) \end{aligned}

If the baking powder contains 31$\% \mathrm{NaHCO}_{3}$ and 35$\% \mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2}$ by mass:

(a) How many moles of $\mathrm{CO}_{2}$ are produced from 1.00 $\mathrm{g}$ of baking powder?
(b) If 1 $\mathrm{mol}$ of $\mathrm{CO}_{2}$ occupies 37.0 $\mathrm{L}$ at $350^{\circ} \mathrm{F}$ (a typical baking temperature), what volume of $\mathrm{CO}_{2}$ is produced from 1.00 $\mathrm{g}$ of baking powder?

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Problem 148

In a titration of $\mathrm{HNO}_{3},$ you add a few drops of phenolphthalein indicator to 50.00 $\mathrm{mL}$ of acid in a flask. You quickly add 20.00 $\mathrm{mL}$ of 0.0502 $M$ $\mathrm{NaOH}$ but overshoot the end point, and the solution turns deep pink. Instead of starting over, you add 30.00 mL of the acid, and the solution turns colorless. Then, it takes 3.22 mL of the NaOH to reach the end point.
(a) What is the concentration of the $\mathrm{HNO}_{3}$ solution?
(b) How many moles of $\mathrm{NaOH}$ were in excess after the first addition?

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Problem 149

The active compound in Pepto-Bismol contains $\mathrm{C}, \mathrm{H}, \mathrm{O},$ and
$\mathrm{Bi}$
(a) When 0.22105 g of it was burned in excess $\mathrm{O}_{2}, 0.1422$ g of bismuth(III) oxide, 0.1880 g of carbon dioxide, and 0.02750 $\mathrm{g}$ of water were formed. What is the empirical formula of this compound?
(b) Given a molar mass of 1086 $\mathrm{g} / \mathrm{mol}$ , determine the molecular formula.
(c) Complete and balance the acid-base reaction between bismuth $(\mathrm{IIl})$ hydroxide and salicylic acid $\left(\mathrm{HC}_{7} \mathrm{H}_{5} \mathrm{O}_{3}\right),$ which is used to form this compound.
(d) A dose of Pepto-Bismol contains 0.600 mg of active ingredient. If the yield of the reaction in part (c) is 88.0%, what mass (in mg) of bismuth(III) hydroxide is required to prepare one dose?

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Problem 150

Two aqueous solutions contain the ions indicated below.
(a) Write balanced molecular, total ionic, and net ionic equations for the reaction that occurs when the solutions are mixed.
(b) If each sphere represents 0.050 mol of ion, what mass (in g) of precipitate forms, assuming 100% yield?
(c) What is the concentration of each ion in solution after reaction?

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Problem 151

In 1997 and 2009, at United Nations conferences on climate change, many nations agreed to expand their research efforts to develop renewable sources of carbon-based fuels. For more than a quarter century, Brazil has been engaged in a program to replace gasoline with ethanol derived from the root crop manioc (cassava).

(a) Write separate balanced equations for the complete combustion of ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ and of gasoline (represented by the formula $\mathrm{C}_{8} \mathrm{H}_{18} .$
(b) What mass of oxygen is required to burn completely 1.00 $\mathrm{L}$ of a mixture that is 90.0$\%$ gasoline $(d=0.742 \mathrm{g} / \mathrm{mL})$ and 10.0$\%$ ethanol $(d=0.789 \mathrm{g} / \mathrm{mL})$ by volume?
(c) If 1.00 mol of $\mathrm{O}_{2}$ occupies $22.4 \mathrm{L},$ what volume of $\mathrm{O}_{2}$ is needed to burn 1.00 $\mathrm{L}$ of the mixture?
(d) Air is 20.9$\% \mathrm{O}_{2}$ by volume. What volume of air is needed to burn 1.00 $\mathrm{L}$ of the mixture?

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Problem 152

In a car engine, gasoline (represented by $\mathrm{C}_{8} \mathrm{H}_{18} )$ does not burn completely, and some $\mathrm{CO},$ a toxic pollutant, forms along with $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ . If 5.0$\%$ of the gasoline forms $\mathrm{CO} :$
(a) What is the ratio of $\mathrm{CO}_{2}$ to CO molecules in the exhaust?
(b) What is the mass ratio of $\mathrm{CO}_{2}$ to $\mathrm{CO} ?$
(c) What percentage of the gasoline must form $\mathrm{CO}$ for the mass ratio of $\mathrm{CO}_{2}$ to $\mathrm{CO}$ to be exactly $1/1 ?$

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Problem 153

The amount of ascorbic acid (vitamin $\mathrm{C} ; \mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6} )$ in tablets is determined by reaction with bromine and then titration of the hydrobromic acid with standard base:

$$\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6}(a q)+\mathrm{Br}_{2}(a q) \longrightarrow \mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}_{6}(a q)+2 \mathrm{HBr}(a q)$$
$$\mathrm{HBr}(a q)+\mathrm{NaOH}(a q) \longrightarrow \operatorname{NaBr}(a q)+\mathrm{H}_{2} \mathrm{O}(l)$$

A certain tablet is advertised as containing 500 $\mathrm{mg}$ of vitamin $\mathrm{C}$ . One tablet was dissolved in water and reacted with Br. The solution was then titrated with 43.20 $\mathrm{mL}$ of 0.1350 $M$ $\mathrm{NaOH}$ . Did the tablet contain the advertised guantity of yitamin $\mathrm{C}$ ?

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Problem 154

In the process of salting-in, protein solubility in a dilute salt solution is increased by adding more salt. Because the protein solubility depends on the total ion concentration as well as the ion charge, salts containing doubly charged ions are often more effective than those containing singly charged ions.
(a) How many grams of $\mathrm{MgCl}_{2}$ must dissolve to equal the ion concentration of 12.4 $\mathrm{g}$ of $\mathrm{NaCl} ?$
(b) How many grams of CaS must dissolve?
(c) Which of the three salt solutions would dissolve the most protein?

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Problem 155

At liftoff, a space shuttle uses a solid mixture of ammonium perchlorate and aluminum powder to great thrust from the volume change of solid to gas. In the presence of a catalyst, the mixture forms solid aluminum oxide and aluminum trichloride and gaseous water and nitrogen monoxide.
(a) Write a balanced equation for the reaction, and identify the reducing and oxidizing agents.
(b) How many total moles of gas (water vapor and nitrogen monoxide) are produced when 50.0 kg of ammonium perchlorate reacts with a stoichiometric amount of Al?
(c) What is the change in volume from this reaction? $(d \text { of }$ $\mathrm{NH}_{4} \mathrm{ClO}_{4}=1.95 \mathrm{g} / \mathrm{cc}, \mathrm{Al}=2.70 \mathrm{g} / \mathrm{cc}, \mathrm{Al}_{2} \mathrm{O}_{3}=3.97 \mathrm{g} / \mathrm{cc},$ and $\mathrm{AlCl}_{3}=2.44 \mathrm{g} / \mathrm{cc} ;$ assume 1 $\mathrm{mol}$ of gas occupies 22.4 $\mathrm{L.}$ )

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Problem 156

A reaction cycle for an element is a series of reactions beginning and ending with that element. In the following copper reaction cycle, copper has either a 0 or a $+2$ oxidation state. Write balanced molecular and net ionic equations for each step.
(1) Copper metal reacts with aqueous bromine to produce a green blue solution.
(2) Adding aqueous sodium hydroxide forms a blue precipitate.
(3) The precipitate is heated and turns black (water is released).
(4) The black solid dissolves in nitric acid to give a blue solution.
(5) Adding aqueous sodium phosphate forms a green precipitate.
(6) The precipitate forms a blue solution in sulfuric acid.
(7) Copper metal is recovered from the blue solution when zinc metal is added.

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Problem 157

Two 25.0-mL aqueous solutions, labeled A and B, contain the ions indicated:
(a) If each sphere represents $1.0 \times 10^{-3}$ mol of ion, will the equivalence point have been reached when all of $B$ has been added to A?
(b) What is the molarity of B?
(c) What additional volume (mL) of B must be added to reach the equivalence point?

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