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# CHEMISTRY: The Molecular Nature of Matter and Change 2016

## Educators

LP

### Problem 1

The atomic mass of $\mathrm{Cl}$ is 35.45 amu, and the atomic mass of Al is 26.98 amu. What are the masses in grams of 3 $\mathrm{mol}$ of $\mathrm{Al}$ atoms and of 2 $\mathrm{mol}$ of $\mathrm{Cl}$ atoms?

Stephen H.

Stephen H.

### Problem 3

Why might the expression "1 mol of chlorine" be confusing? What change would remove any uncertainty? For what other elements might a similar confusion exist? Why?

Stephen H.

### Problem 3

Why might the expression "1 mol of chlorine" be confusing? What change would remove any uncertainty? For what other elements might a similar confusion exist? Why?

Katherine M.

### Problem 4

How is the molecular mass of a compound the same as the molar mass, and how is it different?

Stephen H.

Stephen H.

### Problem 6

You need to calculate the number of $\mathrm{P}_{4}$ molecules that can form from 2.5 $\mathrm{g}$ of $\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2} .$ Draw a road map for solving this and write a Plan, without doing any calculations.

Katherine M.

Katherine M.

### Problem 8

Calculate the molar mass of each of the following:
$$\begin{array}{llll}{\text { (a) } \operatorname{Sr}(\mathrm{OH})_{2}} & {\text { (b) } \mathrm{N}_{2} \mathrm{O}_{3}} & {\text { (c) } \mathrm{NaClO}_{3}} & {\text { (d) } \mathrm{Cr}_{2} \mathrm{O}_{3}}\end{array}$$

Stephen H.

### Problem 9

Calculate the molar mass of each of the following:
(a) $\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4} \quad(\mathrm{b}) \mathrm{CH}_{2} \mathrm{Cl}_{2} \quad$ (c) $\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O} \quad(\mathrm{d}) \mathrm{BrF}_{3}$

Stephen H.

### Problem 10

Calculate the molar mass of each of the following:
$$\begin{array}{llll}{\text { (a) } \mathrm{SnO}} & {\text { (b) } \mathrm{BaF}_{2}} & {\text { (c) } \mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}} & {\text { (d) } \mathrm{MnCl}_{2}}\end{array}$$

Stephen H.

### Problem 11

Calculate the molar mass of each of the following:
$$\begin{array}{llll}{\text { (a) } \mathrm{N}_{2} \mathrm{O}_{4}} & {\text { (b) } \mathrm{C}_{4} \mathrm{H}_{9} \mathrm{OH}} & {\text { (c) } \mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}} & {\text { (d) } \mathrm{Ca}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}}\end{array}$$

Stephen H.

### Problem 12

Calculate each of the following quantities:
(a) Mass (g) of 0.346 mol of Zn
(b) Number of $\mathrm{F}$ atoms in 2.62 $\mathrm{mol}$ of $\mathrm{F}_{2}$
(c) Number of $\mathrm{Ca}$ atoms in 28.5 $\mathrm{g}$ of $\mathrm{Ca}$

Stephen H.

### Problem 13

Calculate each of the following quantities:
(a) Amount (mol) of Mn atoms in 62.0 $\mathrm{mg}$ of Mn
(b) Amount (mol) for $1.36 \times 10^{22}$ atoms of $\mathrm{Cu}$
(c) Mass ( g) of $8.05 \times 10^{24}$ Li atoms

Stephen H.

Stephen H.

Stephen H.

### Problem 16

Calculate each of the following quantities:
(a) Mass (g) of $6.44 \times 10^{-2} \mathrm{mol}$ of $\mathrm{MnSO}_{4}$
(b) Amount (mol) of compound in 15.8 $\mathrm{kg}$ of $\mathrm{Fe}\left(\mathrm{ClO}_{4}\right)_{3}$
(c) Number of $\mathrm{N}$ atoms in 92.6 $\mathrm{mg}$ of $\mathrm{NH}_{4} \mathrm{NO}_{2}$

Katherine M.

### Problem 17

Calculate each of the following quantities:
(a) Total number of ions in 38.1 $\mathrm{g}$ of $\mathrm{SrF}_{2}$
(b) Mass $(\mathrm{kg})$ of 3.58 $\mathrm{mol}$ of $\mathrm{CuCl}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}$
(c) Mass $(\mathrm{mg})$ of $2.88 \times 10^{22}$ formula units of $\mathrm{Bi}\left(\mathrm{NO}_{3}\right)_{3} \cdot 5 \mathrm{H}_{2} \mathrm{O}$

Katherine M.

### Problem 18

Calculate each of the following quantities:
(a) Mass (g) of 8.35 mol of copper(I) carbonate
(b) Mass (g) of $4.04 \times 10^{20}$ molecules of dinitrogen pentoxide
(c) Amount (mol) and number of formula units in 78.9 $\mathrm{g}$ of sodium perchlorate
(d) Number of sodium ions, perchlorate ions, chlorine atoms, and oxygen atoms in the mass of compound in part (c)

Katherine M.

Katherine M.

### Problem 20

Calculate each of the following:
(a) Mass $\%$ of $\mathrm{H}$ in ammonium bicarbonate
(b) Mass $\%$ of $\mathrm{O}$ in sodium dihydrogen phosphate heptahydrate

Stephen H.

### Problem 21

Calculate each of the following:
(a) Mass $\%$ of I in strontium periodate
(b) Mass $\%$ of $\mathrm{Mn}$ in potassium permanganate

Stephen H.

### Problem 22

Calculate each of the following:
(a) Mass fraction of $\mathrm{C}$ in cesium acetate
(b) Mass fraction of $\mathrm{O}$ in uranyl sulfate trihydrate (the uranyl ion is $\mathrm{UO}_{2}^{2+} )$

Stephen H.

Stephen H.

Stephen H.

Stephen H.

Stephen H.

### Problem 27

Iron reacts slowly with oxygen and water to form a compound commonly called rust $\left(\mathrm{Fe}_{2} \mathrm{O}_{3} \cdot 4 \mathrm{H}_{2} \mathrm{O}\right) .$ For 45.2 $\mathrm{kg}$ of rust, calculate (a) moles of compound; (b) moles of $\mathrm{Fe}_{2} \mathrm{O}_{3} ;(\mathrm{c})$ grams of $\mathrm{Fe} .$

Stephen H.

### Problem 28

Propane is widely used in liquid form as a fuel for barbecue grills and camp stoves. For 85.5 $\mathrm{g}$ of propane, calculate (a) moles of compound; (b) grams of carbon.

Stephen H.

### Problem 29

The effectiveness of a nitrogen fertilizer is determined mainly by its mass $\%$ N. Rank the following fertilizers, most effective first: potassium nitrate; ammonium nitrate; ammonium sulfate; urea, $\mathrm{CO}\left(\mathrm{NH}_{2}\right)_{2}$

Katherine M.

### Problem 30

The mineral galena is composed of lead(II) sulfide and has an average density of 7.46 $\mathrm{g} / \mathrm{cm}^{3} .$ (a) How many moles of lead(II) sulfide are in 1.00 $\mathrm{ft}^{3}$ of galena? (b) How many lead atoms are in 1.00 $\mathrm{dm}^{3}$ of galena?

Katherine M.

### Problem 31

Hemoglobin, a protein in red blood cells, carries $\mathrm{O}_{2}$ from the lungs to the body's cells. Iron (as ferrous ion, Fe $^{2+} )$ makes up 0.33 mass $\%$ of hemoglobin. If the molar mass of hemoglobin is $6.8 \times 10^{4} \mathrm{g} / \mathrm{mol},$ how many $\mathrm{Fe}^{2+}$ ions are in one molecule?

Stephen H.

### Problem 32

What is the difference between an empirical formula and a molecular formula? Can they ever be the same?

Stephen H.

### Problem 33

List three ways compositional data may be given in a problem that involves finding an empirical formula.

Katherine M.

### Problem 34

Which of the following sets of information allows you to obtain the molecular formula of a covalent compound? In each case that allows it, explain how you would proceed (draw a road map and write a Plan for a solution).
(a) Number of moles of each type of atom in a given sample of the compound
(b) Mass $\%$ of each element and the total number of atoms in a molecule of the compound
(c) Mass $\%$ of each element and the number of atoms of one element in a molecule of the compound
(d) Empirical formula and mass $\%$ of each element
(e) Structural formula

Katherine M.

### Problem 35

Is $\mathrm{MgCl}_{2}$ an empirical or a molecular formula for magnesium chloride? Explain.

Stephen H.

### Problem 36

What is the empirical formula and empirical formula mass for each of the following compounds?
$\begin{array}{ll}{\text { (a) } \mathrm{C}_{2} \mathrm{H}_{4}} & {\text { (b) } \mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}_{2}} & {\text { (c) } \mathrm{N}_{2} \mathrm{O}_{5}} \\ {\text { (d) } \mathrm{Ba}_{3}\left(\mathrm{PO}_{4}\right)_{2}} & {\text { (e) } \mathrm{Te}_{4} \mathrm{I}_{16}}\end{array}$

Stephen H.

### Problem 37

What is the empirical formula and empirical formula mass for each of the following compounds?
$\begin{array}{ll}{\text { (a) } \mathrm{C}_{4} \mathrm{H}_{8}} & {\text { (b) } \mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{3}} & {\text { (c) } \mathrm{P}_{4} \mathrm{O}_{10}}\end{array}$
(d) $\mathrm{Ga}_{2}\left(\mathrm{SO}_{4}\right)_{3} \quad$ (e) $\mathrm{Al}_{2} \mathrm{Br}_{6}$

Stephen H.

### Problem 38

Give the name, empirical formula, and molar mass of the compound depicted in Figure P3.38.

Stephen H.

### Problem 39

Give the name, empirical formula, and molar mass of the compound depicted in Figure P3.39.

Stephen H.

### Problem 40

What is the molecular formula of each compound?
(a) Empirical formula $\mathrm{CH}_{2}(M=42.08 \mathrm{g} / \mathrm{mol})$
(b) Empirical formula $\mathrm{NH}_{2}(\mathscr{M}=32.05 \mathrm{g} / \mathrm{mol})$
(c) Empirical formula $\mathrm{NO}_{2}(\mathscr{M}=92.02 \mathrm{g} / \mathrm{mol})$
(d) Empirical formula CHN $(M=135.14 \mathrm{g} / \mathrm{mol})$

Stephen H.

### Problem 41

What is the molecular formula of each compound?
(a) Empirical formula $\mathrm{CH}(\mathscr{M}=78.11 \mathrm{g} / \mathrm{mol})$
(b) Empirical formula $\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{2}(\mathscr{M}=74.08 \mathrm{g} / \mathrm{mol})$
(c) Empirical formula $\mathrm{HgCl}(\mathscr{M}=472.1 \mathrm{g} / \mathrm{mol})$
(d) Empirical formula $\mathrm{C}_{7} \mathrm{H}_{4} \mathrm{O}_{2}(\mathscr{M}=240.20 \mathrm{g} / \mathrm{mol})$

Stephen H.

### Problem 42

Find the empirical formula of the following compounds:
(a) 0.063 mol of chlorine atoms combined with 0.22 mol oxy-
gen atoms; (b) 2.45 g of silicon combined with 12.4 g of chlorine;
(c) 27.3 mass $\%$ carbon and 72.7 mass $\%$ oxygen

Stephen H.

### Problem 43

Find the empirical formula of the following compounds:
(a) 0.039 mol of iron atoms combined with 0.052 mol of oxygen
atoms; (b) 0.903 g of phosphorus combined with 6.99 g of bro-
mine; (c) A hydrocarbon with 79.9 mass $\%$ carbon

Stephen H.

### Problem 44

An oxide of nitrogen contains 30.45 mass $\% \mathrm{N}$ . (a) What is the empirical formula of the oxide? (b) If the molar mass is $90 \pm 5 \mathrm{g} / \mathrm{mol},$ what is the molecular formula?

Stephen H.

### Problem 45

A chloride of silicon contains 79.1 mass $\% \mathrm{Cl.}$ (a) What is the empirical formula of the chloride? If the molar mass is $269 \mathrm{g} / \mathrm{mol},$ what is the molecular formula?

Stephen H.

Stephen H.

Stephen H.

Stephen H.

### Problem 49

Cortisol $(M=362.47 \mathrm{g} / \mathrm{mol})$ is a steroid hormone involved in protein synthesis. Medically, it has a major use in reducing inflammation from rheumatoid arthritis. Cortisol is $69.6 \% \mathrm{C},$ $8.34 \% \mathrm{H},$ and 22.1$\% \mathrm{O}$ by mass. What is its molecular formula?

Stephen H.

### Problem 50

Acetaminophen (below) is a popular nonaspirin pain reliever. What is the mass $\%$ of each element in acetaminophen?

Katherine M.

### Problem 51

Menthol $(\mathscr{M}=156.3 \mathrm{g} / \mathrm{mol})$ , the strong-smelling substance in many cough drops, is a compound of carbon, hydrogen, and oxygen. When 0.1595 $\mathrm{g}$ of menthol was burned in a combustion apparatus, 0.449 $\mathrm{g}$ of $\mathrm{CO}_{2}$ and 0.184 $\mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}$ formed. What is menthol's molecular formula?

Stephen H.

### Problem 52

What three types of information does a balanced chemical equation provide? How?

Katherine M.

### Problem 53

How does a balanced chemical equation apply the law of conservation of mass?

Katherine M.

### Problem 54

In the process of balancing the equation
$$\mathrm{Al}+\mathrm{Cl}_{2} \longrightarrow \mathrm{AlCl}_{3}$$
Student I writes: Al $+\mathrm{Cl}_{2} \longrightarrow \mathrm{AlCl}_{2}$
Student II writes: $\mathrm{Al}+\mathrm{Cl}_{2}+\mathrm{Cl} \longrightarrow 2 \mathrm{AlCl}_{3}$
Student III writes: $2 \mathrm{Al}+3 \mathrm{Cl}_{2} \longrightarrow 2 \mathrm{AlCl}_{3}$
Is the approach of Student I valid? Student II? Student III?
Explain.

Katherine M.

### Problem 55

The scenes below represent a chemical reaction between elements A (red) and B (green):
Which best represents the balanced equation for the reaction?
$\begin{array}{ll}{\text { (a) } 2 \mathrm{A}+2 \mathrm{B} \longrightarrow \mathrm{A}_{2}+\mathrm{B}_{2}} & {\text { (b) } \mathrm{A}_{2}+\mathrm{B}_{2} \longrightarrow 2 \mathrm{AB}} \\ {\text { (c) } \mathrm{B}_{2}+2 \mathrm{AB} \longrightarrow 2 \mathrm{B}_{2}+\mathrm{A}_{2}} & {\text { (d) } 4 \mathrm{A}_{2}+4 \mathrm{B}_{2} \longrightarrow 8 \mathrm{AB}}\end{array}$

Katherine M.

### Problem 56

Write balanced equations for each of the following by inserting the correct coefficients in the blanks:
(a) $_{-}\mathrm{Cu}(s)+_{-}\mathrm{S}_{8}(s) \longrightarrow_{-}\mathrm{Cu}_{2} \mathrm{S}(s)$
(b) $_{-}\mathrm{\mathrm{P}}_{4} \mathrm{O}_{10}(s)+_{-}\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow_{-}\mathrm{H}_{3} \mathrm{PO}_{4}(\mathrm{l})$
(c) $_{-}\mathrm{B}_{2} \mathrm{O}_{3}(s)+_{-}\mathrm{NaOH}(a q) \longrightarrow_{-}\mathrm{Na}_{3} \mathrm{BO}_{3}(a q)+_{-}\mathrm{H}_{2} \mathrm{O}(l)$
(d) $_{-}\mathrm{CH}_{3} \mathrm{NH}_{2}(g)+_{-}\mathrm{O}_{2}(g) \longrightarrow_{-}\mathrm{CO}_{2}(g)+_{-}\mathrm{H}_{2} \mathrm{O}(g)+_{-}\mathrm{N}_{2}(g)$

Stephen H.

### Problem 57

Write balanced equations for each of the following by inserting the correct coefficients in the blanks:
(a) $_{-}\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(a q)+_{-}\mathrm{KOH}(a q) \longrightarrow _{-}\mathrm{Cu}(\mathrm{OH}_{2}(s)+_{-}\mathrm{KNO}_{3}(a q)$
(b) $_{-}\mathrm {BCl}_{3}(g)+_{-}\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow_{-}\mathrm{H}_{3} \mathrm{BO}_{3}(s)+_{-}\mathrm{HCl}(g)$
(c) $_{-} \mathrm{CaSiO}_{3}(s)+_{-} \mathrm{HF}(g) \longrightarrow$
$_{-}\mathrm{SiF}_{4}(g)+_{-}\mathrm{CaF}_{2}(s)+_{-}\mathrm{H}_{2} \mathrm{O}(l)$
(d) $_{-}(\mathrm{CN})_{2}(g)+_{-} \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow_{-}\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(a q)+_{-} \mathrm{NH}_{3}(g)$

Stephen H.

### Problem 58

Write balanced equations for each of the following by inserting the correct coefficients in the blanks:
(a) $_{-}\mathrm{SO}_{2}(g)+_{-} \mathrm{O}_{2}(g) \longrightarrow_{-}\mathrm{SO}_{3}(g)$
(b) $_{-}\mathrm{Sc}_{2} \mathrm{O}_{3}(s)+_{-}\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow_{-}\mathrm{Sc}(\mathrm{OH})_{3}(s)$
(c) $_{-}\mathrm{H}_{3} \mathrm{PO}_{4}(a q)+_{-}\mathrm{NaOH}(a q) \longrightarrow{_{-}\mathrm{Na}_{2} \mathrm{HPO}_{4}(a q)+}_{-}\mathrm{H}_{2} \mathrm{O}(l)$
(d) $_{-} \mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{5}(s)+_{-} \mathrm{O}_{2}(g) \longrightarrow_{-} \mathrm{CO}_{2}(g)+_{-} \mathrm{H}_{2} \mathrm{O}(g)$

Stephen H.

### Problem 59

Write balanced equations for each of the following by inserting the correct coefficients in the blanks:
(a) $_{-}\mathrm{As}_{4} \mathrm{S}_{6}(s)+{_{-}\mathrm{O}_{2}(g)} \longrightarrow_{-}\mathrm{As}_{4} \mathrm{O}_{6}(s)+_{-}\mathrm{SO}_{2}(g)$
(b) $_{-}\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}(s)+_{-}\mathrm{SiO}_{2}(s)+_{-}\mathrm{C}(s) \longrightarrow _{-}\mathrm{P}_{4}(g)+_{-}\mathrm{CaSiO}_{3}(l)+_{-}\mathrm{CO}(g)$
(c) $_{-}\mathrm{Fe}(s)+_{-}\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow-_{-}\mathrm{Fe}_{3} \mathrm{O}_{4}(s)+_{-}\mathrm{H}_{2}(g)$
(d) $_{-}\mathrm S_{2} \mathrm{Cl}_{2}(l)+_{-}\mathrm{NH}_{3}(g) \longrightarrow_{-} \mathrm{S}_{4} \mathrm{N}_{4}(s)+_{-}\mathrm{S}_{8}(s)+_{-}\mathrm{NH}_{4} \mathrm{Cl}(s)$

Stephen H.

### Problem 60

Convert the following into balanced equations:
(a) When gallium metal is heated in oxygen gas, it melts and forms solid gallium (III) oxide.
(b) Liquid hexane burns in oxygen gas to form carbon dioxide gas and water vapor.
(c) When solutions of calcium chloride and sodium phosphate are mixed, solid calcium phosphate forms and sodium chloride remains in solution.

Katherine M.

### Problem 61

Convert the following into balanced equations:
(a) When lead(II) nitrate solution is added to potassium iodide solution, solid lead(Il) iodide forms and potassium nitrate solution remains.
(b) Liquid disilicon hexachloride reacts with water to form solid silicon dioxide, hydrogen chloride gas, and hydrogen gas.
(c) When nitrogen dioxide is bubbled into water, a solution of nitric acid forms and gaseous nitrogen monoxide is released.

Katherine M.

Katherine M.

### Problem 63

What does the term stoichiometrically equivalent molar ratio mean, and how is it applied in solving problems?

Katherine M.

### Problem 64

The scene below represents a mixture of A2 and B2 before they react to form $\mathrm{AB}_{3}$
(a) What is the limiting reactant?
(b) How many molecules of product can form?

Katherine M.

### Problem 65

Percent yields are generally calculated from masses. Would the result be the same if amounts (mol) were used instead? Why?

Katherine M.

### Problem 66

Reactants $A$ and $B$ form product $C .$ Draw a road map and write a Plan to find the mass (g) of $C$ when 25 g of A reacts with excess $B$

Katherine M.

### Problem 67

Reactants D and E form product F. Draw a road map and write a Plan to find the mass (g) of F when 27 g of D reacts with 31 g of E.

Katherine M.

### Problem 68

Chlorine gas can be made in the laboratory by the reaction of hydrochloric acid and manganese(IV) oxide:
$$4 \mathrm{HCl}(a q)+\mathrm{MnO}_{2}(s) \longrightarrow \mathrm{MnCl}_{2}(a q)+2 \mathrm{H}_{2} \mathrm{O}(g)+\mathrm{Cl}_{2}(g)$$
When 1.82 mol of $\mathrm{HCl}$ reacts with excess $\mathrm{MnO}_{2},$ how many (a) moles of $\mathrm{Cl}_{2}$ and (b) grams of $\mathrm{Cl}_{2}$ form?

Stephen H.

### Problem 69

Bismuth oxide reacts with carbon to form bismuth metal:
$$\mathrm{Bi}_{2} \mathrm{O}_{3}(s)+3 \mathrm{C}(s) \longrightarrow 2 \mathrm{Bi}(s)+3 \mathrm{CO}(g)$$
When 283 g of $\mathrm{Bi}_{2} \mathrm{O}_{3}$ reacts with excess carbon, how many
(a) moles of $\mathrm{Bi}_{2} \mathrm{O}_{3}$ react and (b) moles of Bi form?

Stephen H.

### Problem 70

Potassium nitrate decomposes on heating, producing potassium oxide and gaseous nitrogen and oxygen:
$$4 \mathrm{KNO}_{3}(s) \longrightarrow 2 \mathrm{K}_{2} \mathrm{O}(s)+2 \mathrm{N}_{2}(g)+5 \mathrm{O}_{2}(g)$$
To produce 56.6 $\mathrm{kg}$ of oxygen, how many (a) moles of $\mathrm{KNO}_{3}$
and (b) grams of $\mathrm{KNO}_{3}$ must be heated?

Stephen H.

### Problem 71

Chromium(III) oxide reacts with hydrogen sulfide (H2S) gas to form chromium(III) sulfide and water:
$$\mathrm{Cr}_{2} \mathrm{O}_{3}(s)+3 \mathrm{H}_{2} \mathrm{S}(g) \longrightarrow \mathrm{Cr}_{2} \mathrm{S}_{3}(s)+3 \mathrm{H}_{2} \mathrm{O}(l)$$
To produce 421 $\mathrm{g}$ of $\mathrm{Cr}_{2} \mathrm{S}_{3},$ how many (a) moles of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ and (b) grams of $\mathrm{Cr}_{2} \mathrm{O}_{3}$ are required?

Stephen H.

### Problem 72

Calculate the mass (g) of each product formed when 43.82 $\mathrm{g}$ of diborane $\left(\mathrm{B}_{2} \mathrm{H}_{6}\right)$ reacts with excess water:
$$\mathrm{B}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{H}_{3} \mathrm{BO}_{3}(s)+\mathrm{H}_{2}(g)[\text { unbalanced }]$$

Stephen H.

### Problem 73

Calculate the mass (g) of each product formed when 174 $\mathrm{g}$ of silver sulfide reacts with excess hydrochloric acid:
$$\mathrm{Ag}_{2} \mathrm{S}(s)+\mathrm{HCl}(a q) \longrightarrow \mathrm{AgCl}(s)+\mathrm{H}_{2} \mathrm{S}(g)[\text { unbalanced }]$$

Stephen H.

### Problem 74

Elemental phosphorus occurs as tetratomic molecules, $\mathrm{P}_{4}$ .
What mass (g) of chlorine gas is needed to react completely with
455 $\mathrm{g}$ of phosphorus to form phosphorus pentachloride?

Stephen H.

### Problem 75

Elemental sulfur occurs as octatomic molecules, S. $\mathrm{S}_{8}$ . What mass $(\mathrm{g})$ of fluorine gas is needed to react completely with 17.8 $\mathrm{g}$ of sulfur to form sulfur hexafluoride?

Stephen H.

### Problem 76

Solid iodine trichloride is prepared in two steps: first, a reaction between solid iodine and gaseous chlorine to form solid iodine monochloride; then, treatment with more chlorine.
(a) Write a balanced equation for each step.
(b) Write a balanced equation for the overall reaction.
(c) How many grams of iodine are needed to prepare 2.45 $\mathrm{kg}$ of
final product?

Stephen H.

### Problem 77

Lead can be prepared from galena [lead(II) sulfide] by first roasting the galena in oxygen gas to form lead(II) oxide and sulfur dioxide. Heating the metal oxide with more galena forms the molten metal and more sulfur dioxide.
(a) Write a balanced equation for each step.
(b) Write an overall balanced equation for the process.
(c) How many metric tons of sulfur dioxide form for every metric

LP
Laura P.

### Problem 78

Many metals react with oxygen gas to form the metal oxide. For example, calcium reacts as follows:
$$2 \mathrm{Ca}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{CaO}(s)$$
You wish to calculate the mass (g) of calcium oxide that can be prepared from 4.20 $\mathrm{g}$ of $\mathrm{Ca}$ and 2.80 $\mathrm{g}$ of $\mathrm{O}_{2} .$
(a) What amount (mol) of $\mathrm{CaO}$ can be produced from the given mass of Ca?
(b) What amount (mol) of CaO can be produced from the given mass of $\mathrm{O}_{2} ?$
(c) Which is the limiting reactant?
(d) How many grams of CaO can be produced?

Stephen H.

### Problem 79

Metal hydrides react with water to form hydrogen gas and the metal hydroxide. For example,
$$\mathrm{SrH}_{2}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Sr}(\mathrm{OH})_{2}(s)+2 \mathrm{H}_{2}(g)$$
You wish to calculate the mass (g) of hydrogen gas that can be prepared from 5.70 $\mathrm{g}$ of $\mathrm{SrH}_{2}$ and 4.75 $\mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}$ .
(a) What amount (mol) of $\mathrm{H}_{2}$ can be produced from the given
mass of $\mathrm{SrH}_{2} ?$
(b) What amount (mol) of $\mathrm{H}_{2}$ can be produced from the given
mass of $\mathrm{H}_{2} \mathrm{O}$ ?
(c) Which is the limiting reactant?
(d) How many grams of $\mathrm{H}_{2}$ can be produced?

Katherine M.

### Problem 80

Calculate the maximum numbers of moles and grams of iodic acid (HIO $_{3}$ that can form when 635 $\mathrm{g}$ of iodine trichloride reacts with 118.5 $\mathrm{g}$ of water:
$$\mathrm{ICl}_{3}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{ICl}+\mathrm{HIO}_{3}+\mathrm{HCl}[\text { unbalanced }]$$
How many grams of the excess reactant remains?

Stephen H.

### Problem 81

Calculate the maximum numbers of moles and grams of H2S that can form when 158 g of aluminum sulfide reacts with 131 g of water:
$$\mathrm{Al}_{2} \mathrm{S}_{3}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{Al}(\mathrm{OH})_{3}+\mathrm{H}_{2} \mathrm{S}[\text { unbalanced }]$$
How many grams of the excess reactant remain?

Stephen H.

### Problem 82

When 0.100 mol of carbon is burned in a closed vessel with 8.00 $\mathrm{g}$ of oxygen, how many grams of carbon dioxide can form? Which reactant is in excess, and how many grams of it remain
after the reaction?

Stephen H.

### Problem 83

A mixture of 0.0375 g of hydrogen and 0.0185 mol oxygen in a closed container is sparked to initiate a reaction. How many grams of water can form? Which reactant is in excess, and how many grams of it remain after the reaction?

Stephen H.

### Problem 84

Aluminum nitrite and ammonium chloride react to form aluminum chloride, nitrogen, and water. How many grams of each substance are present after 72.5 $\mathrm{g}$ of aluminum nitrite and 58.6 $\mathrm{g}$ of ammonium chloride react completely?

Katherine M.

### Problem 85

Calcium nitrate and ammonium fluoride react to form calcium fluoride, dinitrogen monoxide, and water vapor. How many grams of each substance are present after 16.8 $\mathrm{g}$ of calcium nitrate
and 17.50 $\mathrm{g}$ of ammonium fluoride react completely?

Stephen H.

### Problem 86

Two successive reactions, $\mathrm{A} \longrightarrow \mathrm{B}$ and $\mathrm{B} \longrightarrow \mathrm{C},$ have yields of 73$\%$ and 68$\%$ , respectively. What is the overall percent yield for conversion of $\mathrm{A}$ to $\mathrm{C} ?$

Stephen H.

### Problem 87

Two successive reactions, D $\longrightarrow \mathrm{E}$ and $\mathrm{E} \longrightarrow \mathrm{F}$ , have yields of 48$\%$ and $73 \%,$ respectively. What is the overall percent yield for conversion of $\mathrm{D}$ to $\mathrm{F} ?$

Stephen H.

### Problem 88

What is the percent yield of a reaction in which 45.5 $\mathrm{g}$ of $\operatorname{tungsten}(\mathrm{VI})$ oxide $\left(\mathrm{WO}_{3}\right)$ reacts with excess hydrogen gas to produce metallic tungsten and 9.60 $\mathrm{mL}$ of water $(d=1.00 \mathrm{g} / \mathrm{mL}) ?$

Stephen H.

### Problem 89

What is the percent yield of a reaction in which $200 .$ g of phosphorus trichloride reacts with excess water to form 128 $\mathrm{g}$ of $\mathrm{HCl}$ and aqueous phosphorous acid $\left(\mathrm{H}_{3} \mathrm{PO}_{3}\right) ?$

Katherine M.

### Problem 90

When 20.5 g of methane and 45.0 g of chlorine gas undergo a reaction that has a 75.0$\%$ yield, what mass (g) of chloromethane $\left(\mathrm{CH}_{3} \mathrm{Cl}\right)$ forms? Hydrogen chloride also forms.

Stephen H.

### Problem 91

When 56.6 $\mathrm{g}$ of calcium and 30.5 $\mathrm{g}$ of nitrogen gas undergo a reaction that has a 93.0$\%$ yield, what mass (g) of calcium nitride forms?

Stephen H.

### Problem 92

Cyanogen, (CN)_, has been observed in the atmosphere of Titan, Saturn's largest moon, and in the gases of interstellar nebulas. On Earth, it is used as a welding gas and a fumigant. In its reaction with fluorine gas, carbon tetrafluoride and nitrogen trifluoride gases are produced. What mass $(\mathrm{g})$ of carbon tetrafluoride forms when 60.0 $\mathrm{g}$ of each reactant is used?

Stephen H.

### Problem 93

Gaseous dichlorine monoxide decomposes readily to chlorine $(\text {green})$ and oxygen (red) gases.
(a) Which scene best depicts the product mixture after the decomposition?
(b) Write the balanced equation for the decomposition.
(c) If each oxygen atom represents 0.050 mol, how many molecules of dichlorine monoxide were present before the decomposition?

Katherine M.

Stephen H.

Stephen H.

### Problem 96

Sodium borohydride (NaBH_ ) is used industrially in many organic syntheses. One way to prepare it is by reacting sodium hydride with gaseous diborane $\left(\mathrm{B}_{2} \mathrm{H}_{6}\right) .$ Assuming an 88.5$\%$ yield, how many grams of $\mathrm{NaBH}_{4}$ can be prepared by reacting 7.98 $\mathrm{g}$ of sodium hydride and 8.16 $\mathrm{g}$ of diborane?

Stephen H.

### Problem 97

The mole is defined in terms of the carbon-12 atom. Use the definition to find (a) the mass in grams equal to 1 atomic mass unit; (b) the ratio of the gram to the atomic mass unit.

Katherine M.

### Problem 98

The first sulfur-nitrogen compound was prepared in 1835 and has been used to synthesize many others. In the early 1980 $\mathrm{s}$ researchers made another such compound that conducts electricity
like a metal. Mass spectrometry of the compound shows a molar mass of 184.27 $\mathrm{g} / \mathrm{mol}$ , and analysis shows it to contain 2.288 $\mathrm{g}$ of S for every 1.000 $\mathrm{g}$ of $\mathrm{N}$ . What is its molecular formula?

Katherine M.

### Problem 99

Hydroxyapatite, $\mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3}(\mathrm{OH}),$ is the main mineral component of dental enamel, dentin, and bone. Coating the compound on metallic implants (such as titanium alloys and stainless steels) helps the body accept the implant. When placed in bone voids, the
powder encourages natural bone to grow into the void. Hydroxyapatite is prepared by adding aqueous phosphoric acid to a dilute slurry of calcium hydroxide. (a) Write a balanced equation for this
preparation. (b) What mass $(\mathrm{g})$ of hydroxyapatite could form from $100 . \mathrm{g}$ of 85$\%$ phosphoric acid and $100 . \mathrm{g}$ of calcium hydroxide?

Katherine M.

Stephen H.

Katherine M.

### Problem 102

Serotonin $(M=176 \mathrm{g} / \mathrm{mol})$ transmits nerve impulses between neurons. It contains $68.2 \% \mathrm{C}, 6.86 \% \mathrm{H}, 15.9 \% \mathrm{N},$ and 9.08$\% \mathrm{O}$ by mass. What is its molecular formula?

Stephen H.

Katherine M.

### Problem 105

Isobutylene is a hydrocarbon used in the manufacture of synthetic rubber. When 0.847 g of isobutylene was subjected to combustion analysis, the gain in mass of the $\mathrm{CO}_{2}$ absorber was
2.657 $\mathrm{g}$ and that of the $\mathrm{H}_{2} \mathrm{O}$ absorber was 1.089 $\mathrm{g} .$ What is the empirical formula of isobutylene?

Stephen H.

### Problem 106

The multistep smelting of ferric oxide to form elemental iron occurs at high temperatures in a blast furnace. In the first step, ferric oxide reacts with carbon monoxide to form $\mathrm{Fe}_{3} \mathrm{O}_{4}$ . This substance reacts with more carbon monoxide to form iron(II) oxide, which reacts with still more carbon monoxide to form molten iron. Carbon dioxide is also produced in each step. (a) Write an overall balanced equation for the iron-smelting process. (b) How many grams of carbon monoxide are required to form 45.0 metric tons of iron from ferric oxide?

Katherine M.

### Problem 107

One of the compounds used to increase the octane rating of gasoline is toluene (right). Suppose 20.0 $\mathrm{mL}$ of toluene $(d=$ 0.867 $\mathrm{g} / \mathrm{mL}$ ) is consumed when a sample of gasoline burns in air.
(a) How many grams of oxygen are needed for complete combustion of the toluene? (b) How many total moles of gaseous products form? (c) How many molecules of water vapor form?

Stephen H.

### Problem 108

During studies of the reaction in Sample Problem 3.20
$$2 \mathrm{N}_{2} \mathrm{H}_{4}(l)+\mathrm{N}_{2} \mathrm{O}_{4}(l) \longrightarrow 3 \mathrm{N}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)$$
a chemical engineer measured a less-than-expected yield of $\mathrm{N}_{2}$ and discovered that the following side reaction occurs:
$$\mathrm{N}_{2} \mathrm{H}_{4}(l)+2 \mathrm{N}_{2} \mathrm{O}_{4}(l) \longrightarrow 6 \mathrm{NO}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$$
In one experiment, 10.0 g of NO formed when 100.0 g of each
reactant was used. What is the highest percent yield of $\mathrm{N}_{2}$ that can
be expected?

Katherine M.

### Problem 109

A 0.652 -g sample of a pure strontium halide reacts with excess sulfuric acid. The solid strontium sulfate formed is separated, dried, and found to weigh 0.755 $\mathrm{g}$ . What is the formula of
the original halide?

Stephen H.

### Problem 110

The following scenes represent a chemical reaction between $\mathrm{AB}_{2}$ and $\mathrm{B}_{2}$ :
(a) Write a balanced equation for the reaction. (b) What is the limiting reactant? (c) How many moles of product can be made from 3.0 $\mathrm{mol}$ of $\mathrm{B}_{2}$ and 5.0 $\mathrm{mol}$ of $\mathrm{AB}_{2} ?(\mathrm{d})$ How many moles of excess reactant remain after the reaction in part (c)?

Katherine M.

### Problem 111

Which of the following models represent compounds having the same empirical formula? What is the empirical formula mass of this common formula?

Katherine M.

### Problem 112

The zirconium oxalate $\mathrm{K}_{2} \mathrm{Zr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\left(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\right) \cdot \mathrm{H}_{2} \mathrm{O}$ was
synthesized by mixing $1.68 \mathrm{~g}$ of $\mathrm{ZrOCl}_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O}$ with $5.20 \mathrm{~g}$ of $\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}$ and an excess of aqueous $\mathrm{KOH}$. After $2 \mathrm{months}$ $1.25 \mathrm{~g}$ of crystalline product was obtained, along with aqueous $\mathrm{KCl}$ and water. Calculate the percent yield.

Katherine M.

### Problem 113

Seawater is approximately 4.0$\%$ by mass dissolved ions, 85$\%$ of which are from NaCl. (a) Find the mass $\%$ of $\mathrm{NaCl}$ in seawater. (b) Find the mass $\%$ of Na' ions and of $\mathrm{Cl}^{-}$ ions in seawater.

Stephen H.

### Problem 114

Is each of the following statements true or false? Correct any that are false.
(a) A mole of one substance has the same number of atoms as a mole of any other substance.
(b) The theoretical yield for a reaction is based on the balanced chemical equation.
(c) A limiting-reactant problem is being stated when the available quantity of one of the reactants is given in moles.
(d) The empirical and molecular formulas of a compound are always different.

Katherine M.

### Problem 115

In each pair, choose the larger of the indicated quantities or state that the samples are equal:
(a) Entities: 0.4 mol of $\mathrm{O}_{3}$ molecules or 0.4 $\mathrm{mol}$ of $\mathrm{O}$ atoms
(b) Grams: 0.4 $\mathrm{mol}$ of $\mathrm{O}_{3}$ molecules or 0.4 $\mathrm{mol}$ of $\mathrm{O}$ atoms
(c) Moles: 4.0 $\mathrm{g}$ of $\mathrm{N}_{2} \mathrm{O}_{4}$ or 3.3 $\mathrm{g}$ of $\mathrm{SO}_{2}$
(d) Grams: 0.6 $\mathrm{mol}$ of $\mathrm{C}_{2} \mathrm{H}_{4}$ or 0.6 $\mathrm{mol}$ of $\mathrm{F}_{2}$
(e) Total ions: 2.3 $\mathrm{mol}$ of sodium chlorate or 2.2 $\mathrm{mol}$ of magnesium
chloride
(f) Molecules: 1.0 $\mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}$ or 1.0 $\mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}_{2}$
(g) Grams: $6.02 \times 10^{23}$ atoms of $^{235} \mathrm{U}$ or $6.02 \times 10^{23}$ atoms of $^{238} \mathrm{U}$

Katherine M.

### Problem 116

3.116 For the reaction between solid tetraphosphorus trisulfide and oxygen gas to form solid tetraphosphorus decoxide and sulfur dioxide gas, write a balanced equation. Show the equation (see
Table 3.4 ) in terms of (a) molecules, (b) moles, and (c) grams.

Katherine M.

### Problem 117

Hydrogen gas is considered a clean fuel because it produces only water vapor when it burns. If the reaction has a 98.8$\%$ yield, what mass ( g of hydrogen forms 105 $\mathrm{kg}$ of water?

Stephen H.

### Problem 118

Solar winds composed of free protons, electrons, and $\alpha$ particles bombard Earth constantly, knocking gas molecules out of the atmosphere. In this way, Earth loses about 3.0 $\mathrm{kg}$ of matter per second. It is estimated that the atmosphere will be gone in about 50 billion years. Use this estimate to calculate (a) the mass (kg) of Earth's atmosphere and (b) the amount (mol) of nitrogen,
which makes up 75.5 mass $\%$ of the atmosphere.

Katherine M.

### Problem 119

Calculate each of the following quantities:
(a) Amount (mol) of 0.588 g of ammonium bromide
(b) Number of potassium ions in 88.5 $\mathrm{g}$ of potassium nitrate
(c) Mass (g) of 5.85 mol of glycerol $\left(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}_{3}\right)$
(d) Volume (L) of 2.85 $\mathrm{mol}$ of chloroform $\left(\mathrm{CHCl}_{3} ; d=1.48 \mathrm{g} / \mathrm{mL}\right)$
(e) Number of sodium ions in 2.11 mol of sodium caa
(f) Number of atoms in 25.0$\mu \mathrm{g}$ of cadmium
(g) Number of atoms in 0.0015 mol of fluorine gas

Katherine M.

### Problem 120

Elements $X(\text {green})$ and $\mathrm{Y}$ (purple) react according to the following equation: $\mathrm{X}_{2}+3 \mathrm{Y}_{2} \longrightarrow 2 \mathrm{XY}_{3} .$ Which molecular
scene represents the product of the reaction?

Katherine M.

### Problem 121

Hydrocarbon mixtures are used as fuels. (a) How many grams of $\mathrm{CO}_{2}(g)$ are produced by the combustion of $200 . \mathrm{g}$ of a mixture that is 25.0$\% \mathrm{CH}_{4}$ and 75.0$\% \mathrm{C}_{3} \mathrm{H}_{8}$ by mass? (b) $\mathrm{A} 252-\mathrm{g}$
gaseous mixture of $\mathrm{CH}_{4}$ and $\mathrm{C}_{3} \mathrm{H}_{8}$ burns in excess $\mathrm{O}_{2},$ and 748 $\mathrm{g}$ of $\mathrm{CO}_{2}$ gas is collected. What is the mass $\%$ of $\mathrm{CH}_{4}$ in the mixture?

Stephen H.

### Problem 122

nutrients in plant fertilizers. By industry convention, the numbers on a label refer to the mass percents of $\mathrm{N}, \mathrm{P}_{2} \mathrm{O}_{5},$ and $\mathrm{K}_{2} \mathrm{O}$ , in that order.
Calculate the N/P/K ratio of a 30$/ 10 / 10$ fertilizer in terms of moles of each element, and express it as $x / y / 1.0 .$

Katherine M.

### Problem 123

What mass percents of ammonium sulfate, ammonium hydrogen phosphate, and potassium chloride would you use to prepare 10$/ 10 / 10$ plant fertilizer (see Problem 3.122$) ?$

Check back soon!

Stephen H.

### Problem 125

When carbon-containing compounds are burned in a limited amount of air, some $\mathrm{CO}(g)$ as well as $\mathrm{CO}_{2}(g)$ is produced. A gaseous product mixture is 35.0 mass $\% \mathrm{CO}$ and 65.0 mass $\% \mathrm{CO}_{2} .$ What is the mass $\%$ of $\mathrm{C}$ in the mixture?

Katherine M.

Katherine M.

### Problem 127

Citric acid (right) is concentrated in citrus fruits and plays a central metabolic role in nearly every animal and plant cell. (a) What are the molar mass and formula of citric acid? (b) How many moles of citric acid are in 1.50 qt of lemon juice $(d=1.09 \mathrm{g} / \mathrm{mL})$ that is 6.82$\%$ citric acid by mass?

Katherine M.

### Problem 128

Various nitrogen oxides, as well as sulfur oxides, contribute to acidic rainfall through complex reaction sequences. Nitrogen and oxygen combine during the high-temperature combustion of fuels in air to form nitrogen monoxide gas, which reacts with more oxygen to form nitrogen dioxide gas. In contact with water vapor, nitrogen dioxide forms aqueous nitric acid and more nitrogen monoxide. (a) Write balanced equations for these reactions.
(b) Use the equations to write one overall balanced equation that does not include nitrogen monoxide and nitrogen dioxide. ( $(\text { ) How }$many metric tons (t) of nitric acid form when 1350 t of atmospheric nitrogen is consumed $(1 \mathrm{t}=1000 \mathrm{kg}) ?$

Katherine M.

### Problem 129

Nitrogen monoxide reacts with elemental oxygen to form nitrogen dioxide. The scene at right represents an initial mixture of reactants. If the reaction has a 66$\%$ yield, which of the scenes below $(\mathrm{A},$ $\mathrm{B},$ or $\mathrm{C}$ ) best represents the final product mixture?

Katherine M.

### Problem 130

Fluorine is so reactive that it forms compounds with several of the noble gases.
(a) When 0.327 g of platinum is heated in fluorine, 0.519 g of a dark red, volatile solid forms. What is its empirical formula?
(b) When 0.265 g of this red solid reacts with excess xenon gas, 0.378 of an orange-yellow solid forms. What is the empirical formula of this compound, the first to contain a noble gas?
(c) Fluorides of xenon can be formed by direct reaction of the elements at high pressure and temperature. Under conditions that produce only the tetra- and hexafluorides, $1.85 \times 10^{-4}$ mol of xenon reacted with $5.00 \times 10^{-4}$ mol of fluorine, and $9.00 \times 10^{-6} \mathrm{mol}$ of xenon was found in excess. What are the mass percents of each
xenon fluoride in the product mixture?

Katherine M.

### Problem 131

Hemoglobin is 6.0$\%$ heme $\left(\mathrm{C}_{34} \mathrm{H}_{32} \mathrm{FeN}_{4} \mathrm{O}_{4}\right)$ by mass. To remove the heme, hemoglobin is treated with acetic acid and
$\mathrm{NaCl},$ which forms hemin $\left(\mathrm{C}_{34} \mathrm{H}_{32} \mathrm{O}_{4} \mathrm{O}_{4} \mathrm{FeCl}\right) . \mathrm{A}$ blood sample from a crime scene contains 0.65 $\mathrm{g}$ of hemoglobin. (a) How many grams of heme are in the sample? (b) How many moles of heme?
(c) How many grams of Fe? (d) How many grams of hemin could be formed for a forensic chemist to measure?

Stephen H.

### Problem 132

Manganese is a key component of extremely hard steel. The element occurs naturally in many oxides. A 542.3 -g sample of a manganese oxide has an Mn/O ratio of 1.00$/ 1.42$ and con-
sists of braunite $\left(\mathrm{Mn}_{2} \mathrm{O}_{3}\right)$ and manganosite $(\mathrm{MnO}) .(\mathrm{a})$ How many grams of braunite and of manganosite are in the ore? (b) What is
the $\mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}$ ratio in the ore?

Katherine M.

### Problem 133

The human body excretes nitrogen in the form of urea, $\mathrm{NH}_{2} \mathrm{CONH}_{2} .$ The key step in its biochemical formation is the reaction of water with arginine to produce urea and ornithine:
(a) What is the mass $\%$ of nitrogen in urea, in arginine, and in
ornithine? (b) How many grams of nitrogen can be excreted as
urea when 135.2 $\mathrm{g}$ of ornithine is produced?

Katherine M.

### Problem 134

Aspirin (acetylsalicylic acid, $\mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O}_{4} )$ is made by reacting
salicylic acid $\left(\mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}_{3}\right)$ with acetic anhydride $\left[\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O} ] :$
$$\mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}_{3}(s)+\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}(l) \longrightarrow \mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O}_{4}(s)+\mathrm{CH}_{3} \mathrm{COOH}(l)$$
In one preparation, 3.077 g of salicylic acid and 5.50 $\mathrm{mL}$ of acetic anhydride react to form 3.281 $\mathrm{g}$ of aspirin. (a) Which is the limiting reactant $(d \text { of acetic anhydride }=1.080 \mathrm{g} / \mathrm{mL})$ ? (b) What is the percent yield of this reaction? (c) What is the percent atom economy of this reaction?

Katherine M.

### Problem 135

The rocket fuel hydrazine $\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)$ is made by the three-step
Raschig process, which has the following overall equation:
$\mathrm{NaOCl}(a q)+2 \mathrm{NH}_{3}(a q) \longrightarrow \mathrm{N}_{2} \mathrm{H}_{4}(a q)+\mathrm{NaCl}(a q)+\mathrm{H}_{2} \mathrm{O}(l)$
What is the percent atom economy of this process?

Katherine M.

### Problem 136

Lead(Il) chromate $\left(\mathrm{PbCrO}_{4}\right)$ is used as the yellow pigment for marking traffic lanes but is banned from house paint because of the risk of lead poisoning. It is produced from chromite (FeCr_a $\mathrm{O}_{4} )$ an ore of chromium:
$$4 \mathrm{FeCr}_{2} \mathrm{O}_{4}(s)+8 \mathrm{K}_{2} \mathrm{CO}_{3}(a q)+7 \mathrm{O}_{2}(g) \longrightarrow$$
$$2 \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+8 \mathrm{K}_{2} \mathrm{CrO}_{4}(a q)+8 \mathrm{CO}_{2}(g)$$
Lead(II) ion then replaces the $\mathrm{K}^{+}$ ion. If a yellow paint is to have 0.511$\% \mathrm{PbCrO}_{4}$ by mass, how many grams of chromite are needed per kilogram of paint?

Katherine M.

Stephen H.

### Problem 138

When powdered zinc is heated with sulfur, a violent reaction occurs, and zinc sulfide forms:
$$\mathrm{Zn}(s)+\mathrm{S}_{8}(s) \longrightarrow \mathrm{ZnS}(s)[\text { unbalanced }]$$
Some of the reactants also combine with oxygen in air to form zinc oxide and sulfur dioxide. When 83.2 $\mathrm{g}$ of $\mathrm{Zn}$ reacts with 52.4 $\mathrm{g}$ of $\mathrm{S}_{8}, 104.4 \mathrm{g}$ of $\mathrm{ZnS}$ forms.
(a) What is the percent yield of ZnS?
(b) If all the remaining reactants combine with oxygen, how many grams of each of the two oxides form?

Katherine M.

### Problem 139

Cocaine $\left(\mathrm{C}_{17} \mathrm{H}_{21} \mathrm{O}_{4} \mathrm{N}\right)$ is a natural substance found in coca leaves, which have been used for centuries as a local anesthetic
and stimulant. Illegal cocaine arrives in the United States either as the pure compound or as the hydrochloride salt $\left(\mathrm{C}_{17} \mathrm{H}_{21} \mathrm{O}_{4} \mathrm{NHCl}\right)$
At $25^{\circ} \mathrm{C},$ the salt is very soluble in water $(2.50 \mathrm{kg} / \mathrm{L}),$ but cocaine is much less so $(1.70 \mathrm{g} / \mathrm{L})$
(a) What is the maximum mass $(\text { g) of the salt that can dissolve in }$ 50.0 $\mathrm{mL}$ of water?
(b) If this solution is treated with NaOH, the salt is converted to cocaine. How much more water (L) is needed to dissolve it?

Stephen H.

### Problem 140

High-temperature superconducting oxides hold great promise in the utility, transportation, and computer industries
(a) One superconductor is $\mathrm{La}_{2-x} \mathrm{Sr}_{x} \mathrm{CuO}_{4}$ . Calculate the molar
masses of this oxide when $x=0, x=1,$ and $x=0.163$
(b) Another common superconducting oxide is made by heating a mixture of barium carbonate, copper(II) oxide, and ytrium(III) oxide, followed by further heating in $\mathrm{O}_{2}$ :
$$4 \mathrm{BaCO}_{3}(s)+6 \mathrm{CuO}(s)+\mathrm{Y}_{2} \mathrm{O}_{3}(s) \longrightarrow$$
$$2 \mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{65}(s)+4 \mathrm{CO}_{2}(g)$$
$$2 \mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{6.5}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7}(s)$$
When equal masses of the three reactants are heated, which reactant is limiting?
(c) After the product in part (b) is removed, what is the mass $\%$ of each reactant in the remaining solid mixture?

Katherine M.