# CHEMISTRY: The Molecular Nature of Matter and Change 2016

## Educators

NV

### Problem 1

Describe how properties of seawater illustrate the two characteristics that define mixtures.

Ali D.

### Problem 2

What types of intermolecular forces give rise to hydration shells in an aqueous solution of sodium chloride?

NV
Nicole V.

### Problem 3

Acetic acid is miscible with water. Would you expect carboxylic acids with general formula $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{n} \mathrm{COOH}$ to become more or less water soluble as n increases? Explain.

Ali D.

### Problem 4

Which would you expect to be more effective as a soap, sodium acetate or sodium stearate? Explain.

Keenan M.
University of Miami

### Problem 5

Hexane and methanol are miscible as gases but only slightly soluble in each other as liquids. Explain.

Ali D.

### Problem 6

Hydrogen chloride (HCl) gas is much more soluble than propane gas $\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)$ in water, even though HCl has a lower boiling point. Explain.

Keenan M.
University of Miami

### Problem 7

Which gives the more concentrated solution, (a) $\mathrm{KNO}_{3}$ in $\mathrm{H}_{2} \mathrm{O}$ or ( b ) $\mathrm{KNO}_{3}$ in carbon tetrachloride $\left(\mathrm{CCl}_{4}\right) ?$ Explain.

Ali D.

### Problem 8

Which gives the more concentrated solution, stearic acid $\left[\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{COOH}\right]$ in $(\mathrm{a}) \mathrm{H}_{2} \mathrm{O}$ or $(\mathrm{b}) \mathrm{CCl}_{4} ?$ Explain.

Keenan M.
University of Miami

### Problem 9

What is the strongest type of intermolecular force between solute and solvent in each solution?

Ali D.

### Problem 10

What is the strongest type of intermolecular force between solute and solvent in each solution?
(a) $\mathrm{Cu}(s)$ in $\mathrm{Ag}(s)$ (b) $\mathrm{CH}_{3} \mathrm{Cl}(g)$ in $\mathrm{CH}_{3} \mathrm{OCH}_{3}(g)$
c) $\mathrm{CH}_{3} \mathrm{CH}_{3}(g)$ in $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}(l)$

Keenan M.
University of Miami

### Problem 11

What is the strongest type of intermolecular force between solute and solvent in each solution?
(a) $\mathrm{CH}_{3} \mathrm{OCH}_{3}(g)$ in $\mathrm{H}_{2} \mathrm{O}(I)$ (b) $\mathrm{Ne}(g)$ in $\mathrm{H}_{2} \mathrm{O}(l)$
(c) $\mathrm{N}_{2}(g)$ in $\mathrm{C}_{4} \mathrm{H}_{10}(g)$

Ali D.

### Problem 12

What is the strongest type of intermolecular force between solute and solvent in each solution?
(a) $\mathrm{C}_{6} \mathrm{H}_{14}(l)$ in $\mathrm{C}_{8} \mathrm{H}_{18}(l)$ (b) $\mathrm{H}_{2} \mathrm{C}=\mathrm{O}(g)$ in $\mathrm{CH}_{3} \mathrm{OH}( )$
(c) $\mathrm{Br}_{2}(l)$ in $\mathrm{CCl}_{4}(l)$

Keenan M.
University of Miami

### Problem 13

Which member of each pair is more soluble in diethyl ether? Why?

Keenan M.
University of Miami

### Problem 14

Which member of each pair is more soluble in water? Why?

Keenan M.
University of Miami

### Problem 15

A dictionary definition of homogeneous is “uniform in composition throughout.” River water is a mixture of dissolved compounds, such as calcium bicarbonate, and suspended soil particles. Is river water homogeneous? Explain.

Ali D.

### Problem 16

Gluconic acid is a derivative of glucose used in cleaners and in the dairy and brewing industries. Caproic acid is a carboxylic acid used in the flavoring industry. Although both are six-carbon acids (see structures below), gluconic acid is soluble in water and nearly insoluble in hexane, whereas caproic acid has the opposite solubility behavior. Explain

Keenan M.
University of Miami

### Problem 17

Name three intermolecular forces that stabilize the shape of a soluble, globular protein, and explain how they act.

Ali D.

### Problem 18

Name three intermolecular forces that stabilize the structure of DNA, and explain how they act.

Keenan M.
University of Miami

### Problem 19

How can relatively weak H bonds hold the double helix together yet allow DNA to function?

Ali D.

### Problem 20

Is sodium propanoate (the sodium salt of propanoic acid) as effective a soap as sodium stearate (the sodium salt of stearic acid)? Explain.

Keenan M.
University of Miami

### Problem 21

What intermolecular forces stabilize a lipid bilayer?

Ali D.

### Problem 22

In what way do proteins embedded in a membrane differ structurally from soluble proteins?

Keenan M.
University of Miami

### Problem 23

Histones are proteins that control gene function by attaching through salt links to exterior regions of DNA. Name an amino acid whose side chain is often found on the exterior of histones.

Ali D.

### Problem 24

What is the relationship between solvation and hydration?

Keenan M.
University of Miami

### Problem 25

For a general solvent, which enthalpy terms in the thermochemical solution cycle are combined to obtain $\Delta H_{\text { solvation }} ?$

Ali D.

### Problem 26

a) What is the charge density of an ion, and what two properties of an ion affect it?(b) Arrange the following in order of increasing charge density:
(c) How do the two properties in part (a) affect the ionic heat of hydration, $\Delta H_{\text { hydr }} ?$

Keenan M.
University of Miami

### Problem 27

For $\Delta H_{\text { soln to be very small, what quantities must be nearly }}$ equal in magnitude? Will their signs be the same or opposite?

Ali D.

### Problem 28

Water is added to a flask containing solid $\mathrm{NH}_{4} \mathrm{Cl}$ . As the salt dissolves, the solution becomes colder
(a) Is the dissolving of $\mathrm{NH}_{4} \mathrm{Cl}$ exothermic or endothermic?
(b) Is the magnitude of $\Delta H_{\text { latice }}$ of $\mathrm{NH}_{4}$ Cl larger or smaller than the combined $\Delta H_{\text { hydr }}$ of the ions? Explain.
(c) Given the answer to (a), why does $\mathrm{NH}_{4} \mathrm{Cl}$ dissolve in water?

Keenan M.
University of Miami

Ali D.

### Problem 30

Sketch an enthalpy diagram for the process of dissolving $\mathrm{KCl}(s)$ in $\mathrm{H}_{2} \mathrm{O}$ (endothermic).

Keenan M.
University of Miami

### Problem 31

Sketch an enthalpy diagram for the process of dissolving $\mathrm{NaI}(s)$ in $\mathrm{H}_{2} \mathrm{O}$ (exothermic).

Ali D.

### Problem 32

Which ion in each pair has greater charge density? Explain.
(a) ${Na}^{+}$ or ${Cs}^{+}$ (b) ${Sr}^{2+}$ or ${R} {b}^{+}$ (c) ${Na}^{+}$ or ${Cl}^{-}$
(d) ${O}^{2-}$ or ${F}^{-}$ (e) ${OH}^{-}$ or ${SH}^{-}$ (f) ${Mg}^{2+}$ or ${Ba}^{2+}$
(g) ${Mg}^{2+}$ or ${Na}^{+}$ (h) ${NO}_{3}^{-}$ or ${CO}_{3}^{2-}$

Keenan M.
University of Miami

### Problem 33

Which ion has the lower ratio of charge to volume? Explain.
(a) ${Br}^{-}$ or ${I}^{-}$ (b) ${Sc}^{3+}$ or ${Ca}^{2+}$ (c) ${Br}^{-}$ or ${K}^{+}$
(d) ${S}^{2-}$ or ${Cl}^{-}$ (e) ${Sc}^{3+}$ or ${Al}^{3+}$ (f) ${SO}_{4}^{2-}$ or ${ClO}_{4}^{-}$
(g) ${Fe}^{3+}$ or ${Fe}^{2+}$ (h) ${Ca}^{2+}$ or ${K}^{+}$

Ali D.

### Problem 34

Which ion of each pair in Problem 13.32 has the larger $\Delta H_{\mathrm{hydr}} ?$

Keenan M.
University of Miami

### Problem 35

Which ion of each pair in Problem 13.33 has the smaller $\Delta H_{\text { bydr }} ?$

Ali D.

### Problem 36

a) Use the following data to calculate the combined heat of hydration for the ions in potassium bromate (KBrO_ $_{3} ) :$
$$\Delta H_{\text { lattice}}=745 \mathrm{kJ} / \mathrm{mol} \quad \Delta H_{\mathrm{soln}}=41.1 \mathrm{kJ} / \mathrm{mol}$$
(b) Which ion contributes more to the answer for part (a)? Why?

Keenan M.
University of Miami

### Problem 37

(a) Use the following data to calculate the combined heat of hydration for the ions in sodium acetate $\left(\mathrm{NaC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)$
$$\Delta H_{\text { lattice }}=763 \mathrm{kJ} / \mathrm{mol} \quad \Delta H_{\mathrm{soln}}=17.3 \mathrm{kJ} / \mathrm{mol}$$
(b) Which ion contributes more to the answer for part (a)? Why?

Ali D.

### Problem 38

Keenan M.
University of Miami

### Problem 39

State whether the entropy of the system increases or decreases in each of the following processes:
(a) Pure gases are mixed to prepare an anesthetic.
(b) Electronic-grade silicon is prepared from sand
(c) Dry ice (solid $\mathrm{CO}_{2} )$ sublimes.

Ali D.

### Problem 40

Besides its use in making black-and-white film, silver nitrate $\left(\mathrm{AgNO}_{3}\right)$ is used similarly in forensic science. The NaCl left behind in the sweat of a fingerprint is treated with AgNO_ solution o form AgCl. This precipitate is developed to show the blackand-white fingerprint pattern. Given that $\Delta H_{\text { lattice }}=822 \mathrm{kJ} / \mathrm{mol}$ and $\Delta H_{\mathrm{hydr}}=$ $-799 \mathrm{kJ} / \mathrm{mol}$ for $\mathrm{AgNO}_{3},$ calculate its $\Delta H_{\mathrm{soln}}$

Keenan M.
University of Miami

### Problem 41

You are given a bottle of solid X and three aqueous solutions of X—one saturated, one unsaturated, and one supersaturated. How would you determine which solution is which?

Ali D.

### Problem 42

Potassium permanganate $\left(\mathrm{KMnO}_{4}\right)$ has a solubility of 6.4 $\mathrm{g} / 100 \mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}$ at $20^{\circ} \mathrm{C}$ and a curve of solubility vs. temperature that slopes upward to the right. How would you prepare a supersaturated solution of $\mathrm{KMnO}_{4} ?$

Keenan M.
University of Miami

### Problem 43

Why does the solubility of any gas in water decrease with rising temperature?

Ali D.

### Problem 44

For a saturated aqueous solution of each of the following at $20^{\circ} \mathrm{C}$ and 1 atm, will the solubility increase, decrease, or stay the same when the indicated change occurs?
(a) $\mathrm{O}_{2}(g),$ increase $P$ (b) $\mathrm{N}_{2}(g),$ increase $V$

Keenan M.
University of Miami

### Problem 45

13.45 For a saturated aqueous solution of each of the following at $20^{\circ} \mathrm{C}$ and 1 $\mathrm{atm}$ , will the solubility increase, decrease, or stay the same when the indicated change occurs?
(a) $\mathrm{He}(g),$ decrease $T$ (b) $\mathrm{RbI}(s),$ increase $P$

Ali D.

### Problem 46

The Henry's law constant $\left(k_{\mathrm{H}}\right)$ for $\mathrm{O},$ in water at $20^{\circ} \mathrm{C}$ is $1.28 \times 10^{-3} \mathrm{mol} / \mathrm{L} \cdot \mathrm{atm} .$ (a) How many grams of $\mathrm{O}_{2}$ will dissolve in 2.50 $\mathrm{L}$ of $\mathrm{H}_{2} \mathrm{O}$ that is in contact with pure $\mathrm{O}_{2}$ at 1.00 $\mathrm{atm}$ ? (b) How many grams of $\mathrm{O}_{2}$ will dissolve in 2.50 $\mathrm{L}$ of $\mathrm{H}_{2} \mathrm{O}$ that is in contact with air, where the partial pressure of $\mathrm{O}_{2}$ is 0.209 atm?

Keenan M.
University of Miami

### Problem 47

Argon makes up 0.93$\%$ by volume of air. Calculate its solubility $(\mathrm{mol} / \mathrm{L})$ in water at $20^{\circ} \mathrm{C}$ and 1.0 $\mathrm{atm}$ . The Henry's law contant for Ar under these conditions is $1.5 \times 10^{-3} \mathrm{mol} / \mathrm{L} \cdot \mathrm{atm}$ .

Ali D.

### Problem 48

Caffeine is about 10 times as soluble in hot water as in cold water. A chemist puts a hot-water extract of caffeine into an ice bath, and some caffeine crystallizes. Is the remaining solution saturated, unsaturated, or supersaturated?

Keenan M.
University of Miami

### Problem 49

The partial pressure of $\mathrm{CO}_{2}$ gas above the liquid in a bottle of champagne at $20^{\circ} \mathrm{C}$ is 5.5 $\mathrm{atm}$ . What is the solubility of $\mathrm{CO}_{2}$ in champagne? Assume Henry's law constant is the same for champagne as for water. at $20^{\circ} \mathrm{C}, k_{\mathrm{H}}=3.7 \times 10^{-2} \mathrm{mol} / \mathrm{L} \cdot$ atm.

Ali D.

### Problem 50

Respiratory problems are treated with devices that deliver air with a higher partial pressure of $\mathrm{O}_{2}$ than normal air. Why?

Keenan M.
University of Miami

### Problem 51

Explain the difference between molarity and molality. Under what circumstances would molality be a more accurate measure of the concentration of a prepared solution than molarity? Why?

Ali D.

### Problem 52

Which way of expressing concentration includes (a) volume of solution; (b) mass of solution; (c) mass of solvent?

Keenan M.
University of Miami

### Problem 53

A solute has a solubility in water of 21 g/kg solvent. Is this value the same as 21 g/kg solution? Explain.

Ali D.

### Problem 54

You want to convert among molarity, molality, and mole fraction of a solution. You know the masses of solute and solvent and the volume of solution. Is this enough information to carry out all the conversions? Explain.

Keenan M.
University of Miami

### Problem 55

When a solution is heated, which ways of expressing concentration change in value? Which remain unchanged? Explain.

Ali D.

### Problem 56

Calculate the molarity of each aqueous solution:
(a) 32.3 g of table sugar $\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)$ in $100 . \mathrm{mL}$ of solution
(b) 5.80 g of LiNO $_{3}$ in 505 mL of solution

Keenan M.
University of Miami

### Problem 57

Calculate the molarity of each aqueous solution:
(a) 0.82 g of ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ in 10.5 $\mathrm{mL}$ of solution
(b) 1.27 g of gaseous $\mathrm{NH}_{3}$ in 33.5 $\mathrm{mL}$ of solution

Ali D.

### Problem 58

Calculate the molarity of each aqueous solution:
(a) 78.0 $\mathrm{mL}$ of 0.240 $\mathrm{M} \mathrm{NaOH}$ diluted to 0.250 $\mathrm{L}$ with water
(b) 38.5 $\mathrm{mL}$ of 1.2 $\mathrm{M} \mathrm{HNO}_{3}$ diluted to 0.130 $\mathrm{L}$ with water

Keenan M.
University of Miami

### Problem 59

Calculate the molarity of each aqueous solution:
(a) 25.5 $\mathrm{mL}$ of 6.25 $\mathrm{M} \mathrm{HCl}$ diluted to 0.500 $\mathrm{L}$ with water
(b) 8.25 $\mathrm{mL}$ of $2.00 \times 10^{-2} \mathrm{M} \mathrm{KI}$ diluted to 12.0 $\mathrm{mL}$ with water

Ali D.

### Problem 60

How would you prepare the following aqueous solutions?
(a) 365 $\mathrm{mL}$ of $8.55 \times 10^{-2} \mathrm{M} \mathrm{KH}_{2} \mathrm{PO}_{4}$ from solid $\mathrm{KH}_{2} \mathrm{PO}_{4}$
(b) 465 mL of 0.335$M \mathrm{NaOH}$ from 1.25 $\mathrm{M} \mathrm{NaOH}$

Keenan M.
University of Miami

### Problem 61

How would you prepare the following aqueous solutions?
(a) 2.5 $\mathrm{L}$ of 0.65 $\mathrm{M}$ NaCl from solid $\mathrm{NaCl}$
(b) 15.5 $\mathrm{L}$ of 0.3$M$ urea $\left[\left(\mathrm{NH}_{2}\right), \mathrm{C}=\mathrm{O}\right]$ from 2.1 $\mathrm{M}$ urea

Ali D.

### Problem 62

How would you prepare the following aqueous solutions?
(a) 1.40 $\mathrm{L}$ of 0.288 M KBr from solid $\mathrm{KBr}$
(b) 255 $\mathrm{mL}$ of 0.0856 $\mathrm{M} \mathrm{LiNO}_{3}$ from 0.264 $\mathrm{M} \mathrm{LiNO}_{3}$

Keenan M.
University of Miami

### Problem 63

How would you prepare the following aqueous solutions?
(a) 57.5 $\mathrm{mL}$ of $1.53 \times 10^{-3} \mathrm{M} \mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3}$ from solid $\mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3}$
(b) $5.8 \times 10^{3} \mathrm{m}^{3}$ of 1.45 $\mathrm{M} \mathrm{NH}_{4} \mathrm{NO}_{3}$ from 2.50 $\mathrm{M} \mathrm{NH}_{4} \mathrm{NO}_{3}$

Ali D.

### Problem 64

Calculate the molality of the following:
(a) A solution containing 85.4 g of glycine $\left(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{COOH}\right)$ dissolved in 1.270 $\mathrm{kg}$ of $\mathrm{H}_{2} \mathrm{O}$
(b) A solution containing 8.59 g of glycerol $\left(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}_{3}\right)$ in 77.0 $\mathrm{g}$ of ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$

Keenan M.
University of Miami

### Problem 65

Calculate the molality of the following:
(a) A solution containing 174 $\mathrm{g}$ of $\mathrm{HCl}$ in 757 $\mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}$
(b) A solution containing 16.5 g of naphthalene $\left(\mathrm{C}_{10} \mathrm{H}_{8}\right)$ in 53.3 $\mathrm{g}$ of benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)$

Ali D.

### Problem 66

What is the molality of a solution consisting of 44.0 mL of benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6} ; d=0.877 \mathrm{g} / \mathrm{mL}\right)$ in 167 $\mathrm{mL}$ of hexane $\left(\mathrm{C}_{6} \mathrm{H}_{14}\right.$ $d=0.660 \mathrm{g} / \mathrm{mL} ) ?$

Keenan M.
University of Miami

### Problem 67

What is the molality of a solution consisting of 2.66 mL of carbon tetrachloride $\left(\mathrm{CCl}_{4} ; d=1.59 \mathrm{g} / \mathrm{mL}\right)$ in 76.5 $\mathrm{mL}$ of methylene chloride $\left(\mathrm{CH}_{2} \mathrm{Cl}_{2} ; d=1.33 \mathrm{g} / \mathrm{mL}\right) ?$

Ali D.

### Problem 68

How would you prepare the following aqueous solutions?
(a) $3.10 \times 10^{2}$ of 0.125$m$ ethylene glycol $\left(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}_{2}\right)$ from ethylene glycol and water
(b) 1.20 $\mathrm{kg}$ of 2.20 $\mathrm{mass} \% \mathrm{HNO}_{3}$ from 52.0 $\mathrm{mass} \% \mathrm{HNO}_{3}$

Keenan M.
University of Miami

### Problem 69

How would you prepare the following aqueous solutions?
(a) 1.50 $\mathrm{kg}$ of 0.0355 $\mathrm{m}$ ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ from ethanol and water
(b) 445 g of 13.0 mass $\%$ HCl from 34.1 mass $\% \mathrm{HCl}$

Ali D.

### Problem 70

A solution contains 0.35 mol of isopropanol $\left(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}\right)$ dissolved in 0.85 mol of water. (a) What is the mole fraction of isopropanol? (b) The mass percent? (c) The molality?

Keenan M.
University of Miami

### Problem 71

A solution contains 0.100 mol of NaCl dissolved in 8.60 mol of water. (a) What is the mole fraction of NaCl? (b) The mass percent? (c) The molality?

Ali D.

### Problem 72

What mass of cesium bromide must be added to 0.500 L of water (d 5=1.00 g/mL) to produce a 0.400 m solution? What are the mole fraction and the mass percent of CsBr?

Keenan M.
University of Miami

### Problem 73

What are the mole fraction and the mass percent of a solution made by dissolving 0.30 g of KI in 0.400 L of water (d = 1.00 g/mL)?

Ali D.

### Problem 74

Calculate the molality, molarity, and mole fraction of $\mathrm{NH}_{3}$ in ordinary household ammonia, which is an 8.00 $\mathrm{mass} \%$ aqueous solution $(d=0.9651 \mathrm{g} / \mathrm{mL})$

Keenan M.
University of Miami

### Problem 75

Calculate the molality, molarity, and mole fraction of $\mathrm{NH}_{3}$ in a 28.8 mass $\%$ aqueous solution $(d=1.280 \mathrm{g} / \mathrm{mL})$

Keenan M.
University of Miami

### Problem 76

Wastewater from a cement factory contains 0.25 $\mathrm{g}$ of $\mathrm{Ca}^{2+}$ ion and 0.056 g of $\mathrm{Mg}^{2+}$ ion per 100.0 $\mathrm{L}$ of solution. The solution density is 1.001 $\mathrm{g} / \mathrm{mL}$ . Calculate the $\mathrm{Ca}^{2+}$ and $\mathrm{Mg}^{2+}$ concentra-
tions in ppm (by mass).

Keenan M.
University of Miami

### Problem 77

An automobile antifreeze mixture is made by mixing equal volumes of ethylene glycol $(d=1.114 \mathrm{g} / \mathrm{mL} ; \mathscr{M}=62.07 \mathrm{g} / \mathrm{mol})$ and water $(d=1.00 \mathrm{g} / \mathrm{mL})$ at $20^{\circ} \mathrm{C}$ . The density of the mixture is 1.070 $\mathrm{g} / \mathrm{mL}$ . Express the concentration of ethylene glycol as:
(a) Volume percent (b) Mass percent (c) Molarity
(d) Molality (e) Mole fraction

Keenan M.
University of Miami

### Problem 78

The chemical formula of a solute does not affect the extent of the solution’s colligative properties. What characteristic of a solute does affect these properties? Name a physical property of a solution that is affected by the chemical formula of the solute.

Keenan M.
University of Miami

### Problem 79

What is a nonvolatile nonelectrolyte? Why is using this type of solute the simplest way to demonstrate colligative properties?

Ali D.

### Problem 80

In what sense is a strong electrolyte “strong”? What property of the substance makes it a strong electrolyte?

Keenan M.
University of Miami

### Problem 81

Express Raoult’s law in words. Is Raoult’s law valid for a solution of a volatile solute? Explain.

Ali D.

### Problem 82

What are the most important differences between the phase diagram of a pure solvent and the phase diagram of a solution of that solvent?

Keenan M.
University of Miami

### Problem 83

Is the composition of the vapor at the top of a fractionating column different from the composition at the bottom? Explain.

Keenan M.
University of Miami

### Problem 84

Is the boiling point of 0.01 m KF(aq) higher or lower than that of 0.01 m glucose(aq)? Explain.

Keenan M.
University of Miami

### Problem 85

Which aqueous solution has a boiling point closer to its predicted value, 0.050 m NaF or 0.50 m KCl? Explain.

Keenan M.
University of Miami

### Problem 86

Which aqueous solution has a freezing point closer to its predicted value, 0.01$m$ NaBr or 0.01$m \mathrm{MgCl}_{2}$ ? Explain.

Keenan M.
University of Miami

### Problem 87

13.87 The freezing point depression constants of the solvents cyclohexane and naphthalene are $20.1^{\circ} \mathrm{C} / m$ and $6.94^{\circ} \mathrm{C} / \mathrm{m},$ respectively. Which solvent would give a more accurate result if you are using freezing point depression to determine the molar mass of a substance that is soluble in either one? Why?

Keenan M.
University of Miami

### Problem 88

Classify the following substances as strong electrolytes, weak electrolytes, or nonelectrolytes:
(a) Hydrogen chloride (HCl) (b) Potassium nitrate $\left(\mathrm{KNO}_{3}\right)$
(c) Glucose $({C}_{6} {H}_{12} {O}_{6})$ (d) Ammonia$\left({NH}_{3}\right)$

Keenan M.
University of Miami

### Problem 89

Classify the following substances as strong electrolytes, weak electrolytes, or nonelectrolytes:
(a) Sodium permanganate $\left(\mathrm{NaMnO}_{4}\right)$
(b) Acetic acid $\left(\mathrm{CH}_{3} \mathrm{COOH}\right)$
(c) Mechanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right)$
(D) Calcium acetate $\left[\mathrm{Ca}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\right]$

Keenan M.
University of Miami

### Problem 90

How many moles of solute particles are present in 1 L of each of the following aqueous solutions?
a) 0.3$M \mathrm{KBr}$ b) 0.065$M \mathrm{HNO}_{3}$
c) $10^{-4} M \mathrm{KHSO}_{4}$ d) 0.06$M$ ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$

Keenan M.
University of Miami

### Problem 91

How many moles of solute particles are present in 1 mL of each of the following aqueous solutions?
a) 0.02$M \mathrm{CuSO}_{4}$ b) 0.004$M \mathrm{Ba}(\mathrm{OH})_{2}$
c) 0.08$M$ pyridine $\left(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}\right)$ d) 0.05$M\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}$

Keenan M.
University of Miami

### Problem 92

Which solution has the lower freezing point?
(a) 11.0 $\mathrm{g}$ of $\mathrm{CH}_{3} \mathrm{OH}$ in 100. g of $\mathrm{H}_{2} \mathrm{O}$ or 22.0 $\mathrm{g}$ of $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$ in $200 . \mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}$
(b) 20.0 $\mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O}$ in 1.00 $\mathrm{kg}$ of $\mathrm{CH}_{3} \mathrm{OH}$ or 20.0 $\mathrm{g}$ of $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$ in 1.00 $\mathrm{kg}$ of $\mathrm{CH}_{3} \mathrm{OH}$

Keenan M.
University of Miami

### Problem 93

Which solution has the higher boiling point?
(a) 38.0 $\mathrm{g}$ of $\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}_{3}$ in $250 .$ g of ethanol or
38.0 $\mathrm{g}$ of $\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}_{2}$ in $250 . \mathrm{g}$ of ethanol
(b) 15 $\mathrm{g}$ of $\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}_{2}$ in 0.50 $\mathrm{kg}$ of $\mathrm{H}_{2} \mathrm{O}$ or 15 $\mathrm{g}$ of $\mathrm{NaCl}$ in 0.50 $\mathrm{kg}$ of $\mathrm{H}_{2} \mathrm{O}$

Keenan M.
University of Miami

### Problem 94

Rank the following aqueous solutions in order of increasing (a) osmotic pressure; (b) boiling point; (c) freezing point; (d) vapor pressure at $50^{\circ} \mathrm{C}$ :
(1) 0.100 $\mathrm{m}$ NaNO,
(II) 0.100 $\mathrm{m}$ glucose
(III) 0.100 $\mathrm{m} \mathrm{CaCl}_{2}$

Keenan M.
University of Miami

### Problem 95

Rank the following aqueous solutions in order of decreasing (a) osmotic pressure; (b) boiling point; (c) freezing point; (d) vapor pressure at 298 K:
(1) 0.04 $m$ urea $\left[\left(\mathrm{NH}_{2}\right)_{2} \mathrm{C}=\mathrm{O}\right]$
(I) 0.01 $\mathrm{m} \mathrm{AgNO}_{3}$
(III) 0.03 $\mathrm{m} \mathrm{CuSO}_{4}$

Keenan M.
University of Miami

### Problem 96

Calculate the vapor pressure of a solution of 34.0 g of glycerol $\left(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}_{3}\right)$ in 500.0 $\mathrm{g}$ of water at 25 $\mathrm{C}$ . The vapor pressure of
water at $25^{\circ} \mathrm{C}$ is 23.76 torr. (Assume ideal behavior.)

Keenan M.
University of Miami

### Problem 97

Calculate the vapor pressure of a solution of 0.39 $\mathrm{mol}$ of cholesterol in 5.4 mol of toluene at $32^{\circ} \mathrm{C}$ . Pure toluene has a vapor pressure of 41 torr at $32^{\circ} \mathrm{C}$ . (Assume ideal behavior).

Keenan M.
University of Miami

### Problem 98

What is the freezing point of 0.251 m urea in water?

Keenan M.
University of Miami

### Problem 99

What is the boiling point of 0.200 m lactose in water?

Keenan M.
University of Miami

### Problem 100

The boiling point of ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ is $78.5^{\circ} \mathrm{C} .$ What is the boiling point of a solution of 6.4 $\mathrm{g}$ of vanillin $(\mathscr{M}=$
152.14 $\mathrm{g} / \mathrm{mol}$ ) in 50.0 $\mathrm{g}$ of ethanol $\left(K_{\mathrm{b}} \text { of ethanol }=1.22^{\circ} \mathrm{C} / \mathrm{m}\right) ?$

Keenan M.
University of Miami

### Problem 101

The freezing point of benzene is $5.5^{\circ} \mathrm{C}$ . What is the freezing point of a solution of 5.00 $\mathrm{g}$ of naphthalene $\left(\mathrm{C}_{10} \mathrm{H}_{8}\right)$ in 444 $\mathrm{g}$ of benzene $\left(K_{\mathrm{f}} \text { of benzene }=4.90^{\circ} \mathrm{C} / \mathrm{m}\right) ?$

Keenan M.
University of Miami

### Problem 102

What is the minimum mass of ethylene glycol $\left(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}_{2}\right)$ that must be dissolved in 14.5 $\mathrm{kg}$ of water to prevent the solution
from freezing at $-12.0^{\circ} \mathrm{F} ?$ (Assume ideal behavior.)

Keenan M.
University of Miami

### Problem 103

What is the minimum mass of glycerol $\left(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}_{3}\right)$ that must be dissolved in 11.0 mg of water to prevent the solution from freezing at $-15^{\circ} \mathrm{C} ?$ (Assume ideal behavior.)

Keenan M.
University of Miami

### Problem 104

A small protein has a molar mass of $1.50 \times 10^{4}$ g/mol. What is the osmotic pressure exerted at $24.0^{\circ} \mathrm{C}$ by 25.0 $\mathrm{mL}$ of an aqueous solution that contains 37.5 $\mathrm{mg}$ of the protein?

Keenan M.
University of Miami

### Problem 105

A 125-mL sample of an aqueous solution of the protein ovalbumin from chicken egg white contains 1.31 g of the dissolved protein and has an osmotic pressure of 4.32 torr at $25^{\circ} \mathrm{C}$ .
What is the molar mass of ovalbumin?

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### Problem 106

Assuming ideal behavior, find the freezing point of a solution made by dissolving 13.2 g of ammonium phosphate in 45.0 g of water

Keenan M.
University of Miami

### Problem 107

Assuming ideal behavior, find the boiling point of a solution made by dissolving 32.8 g of calcium nitrate in 108 g of water.

Keenan M.
University of Miami

### Problem 108

Calculate the molality and van’t Hoff factor (i) for the following aqueous solutions:
a) $1.00 \mathrm{mass} \% \mathrm{NaCl},$ freezing point $=-0.593^{\circ} \mathrm{C}$
b) 0.500 mass $\% \mathrm{CH}_{3}$ COOH, freezing point $=-0.159^{\circ} \mathrm{C}$

Keenan M.
University of Miami

### Problem 109

Calculate the molality and van’t Hoff factor (i) for the following aqueous solutions:
a) 0.500 mass $\% \mathrm{KCl}$ , freezing point $=-0.234^{\circ} \mathrm{C}$
b) 1.00 mass $\% \mathrm{H}_{2} \mathrm{SO}_{4},$ freezing point $=-0.423^{\circ} \mathrm{C}$

Keenan M.
University of Miami

### Problem 110

In a study designed to prepare new gasoline-resistant coatings, a polymer chemist dissolves 6.053 g of poly(vinyl alcohol) in enough water to make 100.0 $\mathrm{mL}$ of solution. At $25^{\circ} \mathrm{C},$ the osmotic pressure of this solution is 0.272 $\mathrm{atm}$ . What is the molar
mass of the polymer sample?

Keenan M.
University of Miami

### Problem 111

The U.S. Food and Drug Administration lists dichloromethane $\left(\mathrm{CH}_{2} \mathrm{Cl}_{2}\right)$ and carbon tetrachloride (CCl,) among the many cancer-causing chlorinated organic compounds. What are the partial pressures of these substances in the vapor above a solu-
tion of 1.60 $\mathrm{mol}$ of $\mathrm{CH}_{2} \mathrm{Cl}_{2}$ and 1.10 $\mathrm{mol}$ of $\mathrm{CCl}_{4}$ at $23.5^{\circ} \mathrm{C} ?$ The vapor pressures of pure $\mathrm{CH}_{2} \mathrm{Cl}_{2}$ and $\mathrm{CCl}_{4}$ at $23.5^{\circ} \mathrm{C}$ are 352 torr and 118 torr, respectively. (Assume ideal behavior.)

Keenan M.
University of Miami

### Problem 112

Is the fluid inside a bacterial cell considered a solution, a colloid, or both? Explain.

Keenan M.
University of Miami

### Problem 113

What type of colloid is each of the following?
(a) Milk (b) Fog (c) Shaving cream

Keenan M.
University of Miami

### Problem 114

What is Brownian motion, and what causes it?

Keenan M.
University of Miami

### Problem 115

In a movie theater, you can see the beam of projected light. What phenomenon does this exemplify? Why does it occur?

Keenan M.
University of Miami

### Problem 116

Why don’t soap micelles coagulate and form large globules? Is soap more effective in freshwater or in seawater? Why?

Keenan M.
University of Miami

### Problem 117

The three aqueous ionic solutions below have total volumes of 25. mL for A, 50. mL for B, and 100. mL for C. If each sphere represents 0.010 mol of ions, calculate: (a) the total molarity of ions for each solution; (b) the highest molarity of solute; (c) the lowest molality of solute (assuming the solution densities are equal); (d) the highest osmotic pressure (assuming ideal behavior).

Keenan M.
University of Miami

### Problem 118

An aqueous solution is $10 . \%$ glucose by mass $(d=$ 1.039 $\mathrm{g} / \mathrm{mL}$ at $20^{\circ} \mathrm{C}$ ). Calculate its freezing point, boiling point at $1 \mathrm{atm},$ and osmotic pressure.

Keenan M.
University of Miami

### Problem 119

Because zinc has nearly the same atomic radius as copper $\left(d=8.95 \mathrm{g} / \mathrm{cm}^{3}\right),$ zinc atoms substitute for some copper atoms in the many types of brass. Calculate the density of the brass with
(a) 10.0 atom $\% \mathrm{Zn}$ and (b) 38.0 atom $\% \mathrm{Zn}$ .

Keenan M.
University of Miami

### Problem 120

Gold occurs in seawater at an average concentration of $1.1 \times 10^{-2}$ ppb. How many liters of seawater must be processed to recover 1 troy ounce of gold, assuming 81.5$\%$ efficiency (d of
seawater $=1.025 \mathrm{g} / \mathrm{mL} ; 1$ troy ounce $=31.1 \mathrm{g} ) ?$

Keenan M.
University of Miami

### Problem 121

Use atomic properties to explain why xenon is 11 times as soluble as helium in water at $0^{\circ} \mathrm{C}$ on a mole basis.

Keenan M.
University of Miami

### Problem 122

Which of the following best represents a molecular-scale view of an ionic compound in aqueous solution? Explain.

Keenan M.
University of Miami

### Problem 123

Four 0.50 m aqueous solutions are depicted below. Assume that the solutions behave ideally.
(a) Which has the highest boiling point?
(b) Which has the lowest freezing point?
(c) Can you determine which one has the highest osmotic pressure? Explain.

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### Problem 124

Thermal pollution from industrial wastewater causes the temperature of river or lake water to increase, which can affect fish survival as the concentration of dissolved $O_{2}$ decreases. Use the following data to find the molarity of $\mathrm{O}_{2}$ at each temperature (assume the solution density is the same as water):

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### Problem 125

Pyridine (right) is an essential portion of many biologically active compounds, such as nicotine and vitamin $\mathrm{B}_{6}$ . Like ammonia, it has a nitrogen with a lone pair, which makes it act as a weak base. Because it is miscible in a wide range of solvents, from water to benzene, pyridine is one of the most important bases and solvents in organic syntheses. Account for its solubility behavior in terms of intermolecular forces.

Keenan M.
University of Miami

### Problem 126

A chemist is studying small organic compounds for their potential use as an antifreeze. When 0.243 g of a compound is dissolved in 25.0 $\mathrm{mL}$ of water, the freezing point of the solution
is $-0.201^{\circ} \mathrm{C} .$
(a) Calculate the molar mass of the compound (d of water $=$ 1.00 $\mathrm{g} / \mathrm{mL} )$
(b) Analysis shows that the compound is 53.31 mass $\% \mathrm{C}$ and 11.18 mass $\% \mathrm{H}$ , the remainder being $\mathrm{O}$ . Calculate the empirical and molecular formulas of the compound.
(c) Draw a Lewis structure for a compound with this formula that forms $\mathrm{H}$ bonds and another for one that does not.

Keenan M.
University of Miami

### Problem 127

Air in a smoky bar contains $4.0 \times 10^{-6} \mathrm{mol} / \mathrm{L}$ of $\mathrm{CO}$ . What
mass of $\mathrm{CO}$ is inhaled by a bartender who respires at a rate of 11 $\mathrm{L} / \mathrm{min}$ during an 8.0 -h shift?

Keenan M.
University of Miami

### Problem 128

Is 50$\%$ by mass of methanol dissolved in ethanol different from 50$\%$ by mass of ethanol dissolved in methanol? Explain.

Keenan M.
University of Miami

### Problem 129

Three gaseous mixtures of $\mathrm{N}_{2}$ (blue), $\mathrm{Cl}_{2}$ green), and Ne (purple) are depicted below. (a) Which has the smallest mole fraction of $\mathrm{N}_{2} ?(\mathrm{b})$ Which have the same mole fraction of Ne? (c) Rank all three in order of increasing mole fraction of $\mathrm{Cl}_{2}$ .

Keenan M.
University of Miami

### Problem 130

A water treatment plant needs to attain a fluoride concentration of $4.50 \times 10^{-5} M .(\text { a) What mass of NaF must be added to }$ 5000 . L of water in a blending tank? (b) What mass per day of
fluoride is ingested by a person who drinks 2.0 $\mathrm{L}$ of this water?

Keenan M.
University of Miami

### Problem 131

Four U tubes each have distilled water in the right arm, a solution in the left arm, and a semipermeable membrane between arms. (a) If the solute is KCl, which solution is most concentrated? (b) If each solute is different but all the solutions have the same molarity, which contains the smallest number of dissolved ions?

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### Problem 132

$\beta$ -Pinene $\left(\mathrm{C}_{10} \mathrm{H}_{16}\right)$ and $\alpha$ -terpineol $\left(\mathrm{C}_{10} \mathrm{H}_{18} \mathrm{O}\right)$ are used in cosmetics to provide a "fresh pine" scent. At 367 $\mathrm{K}$ , the pure substances have vapor pressures of 100.3 torr and 9.8 torr, respectively. What is the composition of the vapor (in terms of mole fractions) above a solution containing equal masses of these compounds at 367 K? (Assume ideal behavior.)

Keenan M.
University of Miami

### Problem 133

A solution of 1.50 g of solute dissolved in 25.0 mL of $\mathrm{H}_{2} \mathrm{O}$ at $25^{\circ} \mathrm{C}$ has a boiling point of $100.45^{\circ} \mathrm{C}$ (a) What is the molar mass of the solute if it is a nonvolatile nonelectrolyte and the solution behaves ideally $\left(d \text { of } \mathrm{H}_{2} \mathrm{O} \text { at } 25^{\circ} \mathrm{C}=0.997 \mathrm{g} / \mathrm{mL}\right)$ ?
(b) Conductivity measurements show that the solute is ionic with general formula $\mathrm{AB}_{2}$ or $\mathrm{A}_{2} \mathrm{B}$ . What is the molar mass if the solution behaves ideally? (c) Analysis indicates an empirical formula of $\mathrm{CaN}_{2} \mathrm{O}_{6}$ . Explain the difference between the actual formula mass and that calculated from the boiling point elevation. (d) Find the van't Hoff factor (i) for this solution.

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### Problem 134

A pharmaceutical preparation made with ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ is contaminated with methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right) .$ A sample of vapor above the liquid mixture contains a 97$/ 1 \mathrm{mass}$ ratio of
$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ to $\mathrm{CH}_{3} \mathrm{OH}$ . What is the mass ratio of these alcohols in the liquid? At the temperature of the liquid, the vapor pressure of $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ and $\mathrm{CH}_{3} \mathrm{OH}$ are 60.5 tor and 126.0 torr, respectively

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### Problem 135

Water treatment plants commonly use chlorination to destroy bacteria. A byproduct is chloroform $\left(\mathrm{CHCl}_{3}\right),$ a suspected carcinogen, produced when HOCl, formed by reaction of $\mathrm{Cl}_{2}$ and water, reacts with dissolved organic matter. The United States, Canada, and the World Health Organization have set a limit of $100 . \mathrm{ppb}$ of $\mathrm{CHCl}_{3}$ in drinking water. Convert this concentration into molarity, molality, mole fraction, and mass percent.

Keenan M.
University of Miami

### Problem 136

A saturated $\mathrm{Na}_{2} \mathrm{CO}_{3}$ solution is prepared, and a small excess of solid is
present (white pile in beaker). A seed crystal of $\mathrm{Na}_{2}^{14} \mathrm{CO}_{3}\left(^{14} \mathrm{C}\right.$ is a radioactive isotope of $^{12} \mathrm{C} )$ is added (small red piece), and
the radioactivity is measured over time. (a) Would you expect radioactivity in the solution? Explain. (b) Would you expect radioactivity in all the solid or just in the seed crystal? Explain.

Keenan M.
University of Miami

### Problem 137

A biochemical engineer isolates a bacterial gene fragment and dissolves a 10.0-mg sample in enough water to make 30.0 mL of solution. The osmotic pressure of the solution is 0.340 torr at $25^{\circ} \mathrm{C}(\text { a) What is the molar mass of the gene fragment? (b) If the }$ solution density is 0.997 $\mathrm{g} / \mathrm{mL}$ , how large is the freezing point depression for this solution $\left(K_{\mathrm{f}} \text { of water }=1.86^{\circ} \mathrm{C} / \mathrm{m}\right) ?$

Keenan M.
University of Miami

### Problem 138

A river is contaminated with 0.65 $\mathrm{mg} / \mathrm{L}$ of dichloroethylene $\left(\mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Cl}_{2}\right) .$ What is the concentration (in ng/L) of dichloroethylene at $21^{\circ} \mathrm{C}$ in the air breathed by a person swimming in the river
$\left(k_{\mathrm{H}} \text { for } \mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Cl}_{2} \text { in water is } 0.033 \mathrm{mol} / \mathrm{L} \cdot \mathrm{atm}\right) ?$

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### Problem 139

At an air-water interface, fatty acids such as oleic acid lie in a one-molecule-thick layer (monolayer), with the heads in the water and the tails perpendicular in the air. When 2.50 mg of oleic acid is placed on a water surface, it forms a circular monolayer 38.6 $\mathrm{cm}$ in diameter. Find the surface area (in $\mathrm{cm}^{2} )$ occupied by one molecule (} of oleic acid = 283 g/mol).

Keenan M.
University of Miami

### Problem 140

A simple device used for estimating the concentration of total dissolved solids in an aqueous solution works by measuring the electrical conductivity of the solution. The method assumes that equal concentrations of different solids give approximately the same conductivity, and that the conductivity is proportional to concentration. The table below gives some actual electrical conductivities (in arbitrary units) for solutions of selected solids at the indicated concentrations (in ppm by mass):
a) How reliable are these measurements for estimating concentrations of dissolved solids? (b) For what types of substances might this method have a large error? Why? (c) Based on this method, an aqueous $\mathrm{CaCl}_{2}$ solution has a conductivity of 14.0 units. Calculate its mole fraction and molality.

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### Problem 141

Two beakers are placed in a closed container (left). One beaker contains water, the other a concentrated aqueous sugar solution. With time, the solution volume increases and the water volume decreases (right). Explain on the molecular level.

Keenan M.
University of Miami

### Problem 142

The release of volatile organic compounds into the atmosphere is regulated to limit ozone formation. In a laboratory simulation, 5% of the ethanol in a liquid detergent is released. Thus, a “down-the-drain” factor of 0.05 is used to estimate ethanol emissions from the detergent. The $k_{\mathrm{H}}$ values for ethanol and 2 -butoxyethanol $\left(\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{OCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right)$ are $5 \times 10^{-6} \mathrm{atm} \cdot \mathrm{m}^{3} / \mathrm{mol}$and $1.6 \times 10^{-6}$ atm $\cdot \mathrm{m}^{3} / \mathrm{mol}$ , respectively. (a) Estimate a "down- the-drain" factor for 2 -butoxyethanol in the detergent. (b) What is the $k_{\mathrm{H}}$ for ethanol in units of $\mathrm{L}$ atm/mol? (c) Is this value consistent with a value given as 0.64 Pa'm $^{3} / \mathrm{mol} ?$

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### Problem 143

Although other solvents are available, dichloromethane $\left(\mathrm{CH}_{2} \mathrm{Cl}_{2}\right)$ is still often used to "decaffeinate" drinks because the solubility of caffeine in $\mathrm{CH}_{2} \mathrm{Cl}_{2}$ is 8.35 times that in water.
(a) A 100.0 -mL sample of cola containing 10.0 $\mathrm{mg}$ of caffeine is extracted with 60.0 $\mathrm{mL}$ of $\mathrm{CH}_{2} \mathrm{Cl}_{2}$ . What mass of caffeine remains in the aqueous phase?
(b) A second identical cola sample is extracted with two successive 30.0 -mL portions of ${CH}_{2} {Cl}_{2}$ . What mass of caffeine remains in the aqueous phase after each extraction?
(c) Which approach extracts more caffeine?

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### Problem 144

How do you prepare $250 .$ g of 0.150 m aqueous NaHCO$_{3} ?$

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### Problem 145

Tartaric acid occurs in crystalline residues found in wine vats. It is used in baking powders and as an additive in foods. It contains 32.3$\%$ by mass carbon and 3.97$\%$ by mass hydrogen; the balance is oxygen. When 0.981 g of tartaric acid is dissolved in 11.23 $\mathrm{g}$ of water, the solution freezes at $-1.26^{\circ} \mathrm{C}$ . Find the empirical and molecular formulas of tartaric acid.

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### Problem 146

Methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right)$ and ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ are miscible because the major intermolecular force for each is H bonding. In some methanol-ethanol solutions, the mole fraction of methanol is higher, but the mass percent of ethanol is higher. What is the range of mole fraction of methanol for these solutions?

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### Problem 147

A solution of 5.0 $\mathrm{g}$ of benzoic acid $\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right)$ in 100.0 $\mathrm{g}$ of carbon tetrachloride has a boiling point of $77.5^{\circ} \mathrm{C}$
(a) Calculate the molar mass of benzoic acid in the solution.
(b) Suggest a reason for the difference between the molar mass based on the formula and that found in part (a).

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### Problem 148

Derive a general equation that expresses the relationship between the molarity and the molality of a solution. Why are the numerical values of these two terms approximately equal for very dilute aqueous solutions?

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### Problem 149

A florist prepares a solution of nitrogen-phosphorus fertilizer by dissolving 5.66 $\mathrm{g}$ of $\mathrm{NH}_{4} \mathrm{NO}_{3}$ and 4.42 $\mathrm{g}$ of $\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}$ in enough water to make 20.0 $\mathrm{L}$ of solution. What are the molarities
of $\mathrm{NH}_{4}^{+}$ and of $\mathrm{PO}_{4}^{3-}$ in the solution?

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### Problem 150

Suppose coal-fired power plants used water in scrubbers to remove $\mathrm{SO}_{2}$ from smokestack gases (see Chemical Connections, p. 273 ). (a) If the partial pressure of $\mathrm{SO}_{2}$ in the stack gases is $2.0 \times 10^{-3}$ atm, what is the solubility of $\mathrm{SO}_{2}$ in the scrubber liquid $\left(k_{\mathrm{H}} \text { for } \mathrm{SO}_{2} \text { in water is } 1.23 \mathrm{mol} / \mathrm{L} \cdot \mathrm{atm} \text { at } 200 . \mathrm{C}\right) ?(\mathrm{b})$ From your answer to part (a), why are basic solutions, such as limewater slurries $\left[\mathrm{Ca (\mathrm{OH})_{2}\right],$ used in scrubbers?

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### Problem 151

Urea is a white crystalline solid used as a fertilizer, in the pharmaceutical industry, and in the manufacture of certain polymer resins. Analysis of urea reveals that, by mass, it is 20.1$\%$ . carbon, 6.7$\%$ hydrogen, 46.5$\%$ nitrogen, and the balance oxygen.
(a) Find the empirical formula of urea.
(b) $\mathrm{A} 5.0 \mathrm{g} / \mathrm{L}$ solution of urea in water has an osmotic pressure of
2.04 $\mathrm{atm}$ , measured at $25^{\circ} \mathrm{C}$ . What is the molar mass and molecular
formula of urea?

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### Problem 152

The total concentration of dissolved particles in blood is 0.30 M. An intravenous (IV) solution must be isotonic with blood, which means it must have the same concentration
(a) To relieve dehydration, a patient is given $100 . \mathrm{mL} / \mathrm{h}$ of $\mathrm{IV}$
glucose $\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)$ for 2.5 $\mathrm{h}$ . What mass (g) of glucose did she receive? (b) If isotonic saline (NaCl) is used, what is the molarity of the solution? (c) If the patient is given 150. mL/h of IV saline for 1.5 h, how many grams of NaCl did she receive?

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### Problem 153

Deviations from Raoult’s law lead to the formation of azeotropes, constant boiling mixtures that cannot be separated by distillation, making industrial separations difficult. For components A and B, there is a positive deviation if the A-B attraction is less than A-A and B-B attractions (A and B reject each other),
and a negative deviation if the A-B attraction is greater than A-A and B-B attractions. If the A-B attraction is nearly equal to the A-A and B-B attractions, the solution obeys Raoult’s law. Explain
whether the behavior of each pair will be nearly ideal, have a positive deviation, or a negative deviation:
(a) Benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)$ and methanol
(b) Water and ethyl acetate
(c) Hexane and heptane
(d) Methanol and water
(e) Water and hydrochloric acid

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### Problem 154

Acrylic acid $\left(\mathrm{CH}_{2}=\mathrm{CHCOOH}\right)$ is a monomer used to make superabsorbent polymers and various compounds for paint and adhesive production. At 1 atm, it boils at $141.5^{\circ} \mathrm{C}$ but is prone to polymerization. Its vapor pressure at $25^{\circ} \mathrm{C}$ is 4.1 mbar. What pressure (in mmHg) is needed to distill the pure acid at $65^{\circ} \mathrm{C} ?$

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### Problem 155

To effectively stop polymerization, certain inhibitors require the presence of a small amount of $\mathrm{O}_{2}$ . At equilibrium with 1 atm of air, the concentration of $\mathrm{O}_{2}$ dissolved in the monomer acrylic acid $\left(\mathrm{CH}_{2}=\mathrm{CHCOOH}\right)$ is $1.64 \times 10^{-3} M .$ (a) What is $k_{\mathrm{H}}(\mathrm{mol} / \mathrm{L} \cdot \mathrm{atm} \mathrm{m})$ for $\mathrm{O}_{2}$ in acrylic acid? (b) If 0.005 atm of $\mathrm{O}_{2}$ is sufficient to stop polymerization, what is the molarity of $\mathrm{O}_{2} ?$ (c) What is the mole fraction? (d) What is the concentration in ppm? (Pure acrylic acid is $14.6 M ; P_{\mathrm{O}_{2}}$ in air is 0.2095 $\mathrm{atm.}$ .

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### Problem 156

Volatile organic solvents have been implicated in adverse health effects in industrial workers. Greener methods are phasing these solvents out. Rank the solvents in Table 13.6 (p. 544) in terms of increasing volatility.

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### Problem 157

At ordinary temperatures, water is a poor solvent for organic substances. But at high pressure and above $200^{\circ} \mathrm{C}$ , water develops many properties of organic solvents. Find the minimum pressure needed to maintain water as a liquid at $200 .^{\circ} \mathrm{C}\left(\Delta H_{\mathrm{vap}}=\right.$ 40.7 $\mathrm{kJ} / \mathrm{mol}$ at $100^{\circ} \mathrm{C}$ and $1.00 \mathrm{atm} ;$ assume that this value remains constant with temperature).

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### Problem 158

In ice-cream making, the ingredients are kept below $0.0^{\circ} \mathrm{C}$ n an ice-salt bath. (a) Assuming that NaCl dissolves completely and forms an ideal solution, what mass of it is needed to lower the melting point of 5.5 $\mathrm{kg}$ of ice to $-5.0^{\circ} \mathrm{C} ?(\mathrm{b})$ Given the same assumptions as in part (a), what mass of $\mathrm{CaCl}_{2}$ is needed?

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### Problem 159

Perfluorocarbons (PFCs), hydrocarbons with all H atoms
replaced by F atoms, have very weak cohesive forces. One interesting consequence of this property is that a live mouse can breathe while submerged in $\mathrm{O}_{2}$ -saturated PFCs.
(a) At $298 \mathrm{K},$ perfluorohexane $\left(\mathrm{C}_{6} \mathrm{F}_{14}, \mathrm{M}=338 \mathrm{g} / \mathrm{mol} \text { and } d=\right.$ 1.674 $\mathrm{g} / \mathrm{mL}$ ) in equilibrium with $101,325 \mathrm{Pa}$ of $\mathrm{O}_{2}$ has a mole fraction of $\mathrm{O}_{2}$ of $4.28 \times 10^{-3} .$ What is $k_{\mathrm{H}}$ in mol/L $\cdot$ atm $?$
(b) According to one source, $k_{\mathrm{H}}$ for $\mathrm{O}_{2}$ in water at $25^{\circ} \mathrm{C}$ is 756.7 $\mathrm{L} \cdot \mathrm{atm} / \mathrm{mol}$ . What is the solubility of $\mathrm{O}_{2}$ in water at $25^{\circ} \mathrm{C}$ in ppm? (c) Rank the $k_{\mathrm{H}}$ values in descending order for $\mathrm{O}_{2}$ in water,
ethanol, $\mathrm{C}_{6} \mathrm{F}_{14},$ and $\mathrm{C}_{6} \mathrm{H}_{14} .$ Explain your ranking.

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### Problem 160

The solubility of $\mathrm{N}_{2}$ in blood is a serious problem for divers breathing compressed air $\left(78 \% \mathrm{N}_{2} \text { by volume) at depths }\right.$ greater than 50 $\mathrm{ft.}$
(a) What is the molarity of $\mathrm{N}_{2}$ in blood at 1.00 $\mathrm{atm}$ ?
(b) What is the molarity of $\mathrm{N}_{2}$ in blood at a depth of 50. ft?
(c) Find the volume (in $\mathrm{mL} )$ of $\mathrm{N}_{2},$ measured at $25^{\circ} \mathrm{C}$ and 1.00 $\mathrm{atm}$ ,released per liter of blood when a diver at a depth of 50 . ft rises to
the surface $\left(k_{\mathrm{H}} \text { for } \mathrm{N}_{2} \text { in water at } 25^{\circ} \mathrm{C} \text { is } 7.0 \times 10^{-4} \mathrm{mol} / \mathrm{L} \cdot \text { atm and }\right.$ at $37^{\circ} \mathrm{C}$ is $6.2 \times 10^{-4} \mathrm{mol} / \mathrm{L} \cdot$ atm; assume $d$ of water is 1.00 $\mathrm{g} / \mathrm{mL}$ ).

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### Problem 161

Figure 12.11 (p. 466) shows the phase changes of pure
water. Consider how the diagram would change if air were present at 1 atm and dissolved in the water.
(a) Would the three phases of water still attain equilibrium at some temperature? Explain.
(b) In principle, would that temperature be higher, lower, or the same as the triple point for pure water? Explain.
(c) Would ice sublime at a few degrees below the freezing point under this pressure? Explain.
(d) Would the liquid have the same vapor pressure as that shown in Figure 12.7$(\mathrm{p} .464)$ at 100 $\mathrm{C}$ ? At $120^{\circ} \mathrm{C} ?$

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### Problem 162

$\mathrm{KNO}_{3}, \mathrm{KClO}_{3}, \mathrm{KCl},$ and $\mathrm{NaCl}$ are recrystallized as follows: Step 1. A saturated aqueous solution of the compound is prepared at $50^{\circ} \mathrm{C}$
Step $2 .$ The mixture is filtered to remove undissolved compound.
Step $3 .$ The filtrate is cooled to $0^{\circ} \mathrm{C}$ .
Step $4 .$ The crystals that form are filtered, dried, and weighed.
(a) Which compound has the highest percent recovery and which the lowest (see Figure 13.19, p. 534)?
(b) Starting with 100. g of each compound, how many grams of neach can be recovered?

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### Problem 163

Eighty proof whiskey is 40$\%$ ethanol $\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)$ by volume. A man has 7.0 $\mathrm{L}$ of blood and drinks 28 $\mathrm{mL}$ of the whiskey,
of which 22$\%$ of the ethanol goes into his blood.
(a) What concentration (in g/mL) of ethanol is in his blood (d of ethanol = 0.789 g/mL)?
(b) What volume (in mL) of whiskey would raise his blood alcohol level to $8.0 \times 10^{-4}$ g/mL, the level at which a person is considered intoxicated?

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### Problem 164

Soft drinks are canned under 4 atm of $\mathrm{CO}_{2}$ and release $\mathrm{CO}_{2}$ when opened.
(a) How many moles of $\mathrm{CO}_{2}$ are dissolved in a $355-\mathrm{mL}$ can of
soda before it is opened?
(b) After it has gone flat?
(c) What volume (in L) would the released $\mathrm{CO}_{2}$ occupy at 1.00 $\mathrm{atm}$ and $25^{\circ} \mathrm{C}\left(k_{\mathrm{H}} \text { for } \mathrm{CO}_{2} \text { at } 25^{\circ} \mathrm{C} \text { is } 3.3 \times 10^{-2} \mathrm{mol} / \mathrm{L} \cdot \mathrm{atm} ; P_{\mathrm{CO}_{2}} \text { in air }\right.$ is $4 \times 10^{-4}$ atm $) ?$

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### Problem 165

Gaseous $\mathrm{O}_{2}$ in equilibrium with $\mathrm{O}_{2}$ dissolved in water at 283 $\mathrm{K}$ is depicted at right. (a) Which scene below represents the system at 298 $\mathrm{K} ?$ (b) Which scene represents the system when the pressure of $\mathrm{O}_{2}$ is increased by half?

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