Chapter 12

How would you explain the fact that \(\mathrm{Na}_{3} \mathrm{PO}_{4}\) is quite soluble in water but \(\mathrm{AlPO}_{4}\) is essentially insoluble?

Consider dissolving these two molecules in water: Even though the solute-separation step for ethanol requires more energy than does the solute-separation step for diethyl ether, ethanol is more soluble in water. Explain why.

Whether or not a solute dissolves in a solvent is decided not only by changes in energy but also by changes in

If the dissolution of a particular solute in water is endothermic, what must be true about (a) \(\Delta E_{\text {total }}\) and (b) the change in entropy for the system as a result of the dissolution?

Henry's law tells us that the solubility \(s\) of a gas in a liquid increases as the pressure \(P\) of the gas increases. Which of the following mathematical expressions of Henry's law is correct? Explain your choice and explain why the other two expressions are incorrect. (Hint: The \(k\) is just a constant of proportionality and can be ignored.) (a) \(s=k P\) (b) \(s=k / P\) (c) \(s=k P / P\)

Why do most solids become more soluble in water with increasing temperature? (Hint: Think about what happens to the water molecules as temperature increases.)

When a small amount of soap is added to a beaker of water, the soap molecules end up positioning themselves at the surface (hence soaps are often called surfactants): Explain why the soap molecules migrate to the surface, and why they orient themselves with their hydrocarbon tails sticking out of the water.

Soap molecules not only form spherical micelles in water, they also form spherical vesicles, which you can picture as thick-walled hollow spheres. Here is a cross section of such a vesicle, with the blue regions representing water: Unlike a micelle, a vesicle traps water in its interior. What gives a vesicle this ability? (If you are having trouble with the difference between micelles and vesicles, think of a baseball and a hollow rubber ball. The baseball, with no empty space inside, is analogous to the micelle, and the hollow ball is analogous to the vesicle.)

A student dilutes \(75.0 \mathrm{~mL}\) of a \(2.00 \mathrm{M}\) solution of iron(III) nitrate with sufficient water to prepare \(2.00 \mathrm{~L}\) of solution. (a) What is the molar concentration of iron(III) nitrate in the diluted solution? Once in solution, the iron(III) nitrate exists not intact but rather as dissociated ions. What are the molar concentrations (b) of \(\mathrm{Fe}^{3+}(a q)\) in the diluted solution and (c) of \(\mathrm{NO}^{3-}(a q)\) in the diluted solution?

A student dilutes \(45.0 \mathrm{~mL}\) of a \(0.500 \mathrm{M}\) solution of aluminum sulfate with sufficient water to prepare \(1.50 \mathrm{~L}\) of solution. (a) What is the molar concentration of aluminum sulfate in the diluted solution? Once in solution, the aluminum sulfate exists not intact but rather as dissociated ions. What are the molar concentrations (b) of \(\mathrm{Al}^{3+}(a q)\) in the diluted solution and (c) of \(\mathrm{SO}_{4}^{2-}(a q)\) in the diluted solution?

A student combines \(60.0 \mathrm{~mL}\) of \(0.250 \mathrm{M} \mathrm{NaOH}\) with \(60.0 \mathrm{~mL}\) of \(0.125 \mathrm{M} \mathrm{NaOH}\). What is the \(\mathrm{NaOH}\) molar concentration in the resulting solution?

A student combines \(60.0 \mathrm{~mL}\) of \(0.250 \mathrm{M} \mathrm{NaOH}\) with \(60.0 \mathrm{~mL}\) of \(0.125 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\). What is the hydroxide ion molar concentration in the resulting solution?

What is the mass in grams of the nitrogen atoms in \(100.0 \mathrm{~mL}\) of \(1.00 \mathrm{M} \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) solution?

How many grams of \(\mathrm{NaOH}\) are needed to prepare \(500.0 \mathrm{~mL}\) of \(0.300 \mathrm{M} \mathrm{NaOH}\) solution?

What is the molarity of \(3.69 \mathrm{~mL}\) of solution containing \(0.0025\) mole of calcium chloride?

How many moles of potassium permanganate, \(\mathrm{KMnO}_{4}\), are there in \(28.68 \mathrm{~mL}\) of a \(5.20 \times 10^{-3} \mathrm{M}\) solution of \(\mathrm{KMnO}_{4} ?\)

What is the volume in milliliters of \(0.0150 \mathrm{M}\) \(\mathrm{NaOH}\) solution required to neutralize \(50.0 \mathrm{~mL}\) of \(0.0100 \mathrm{MHNO}_{3}(a q) ?\)

What is the volume in milliliters of \(0.0150 \mathrm{M}\) \(\mathrm{NaOH}\) solution required to neutralize \(50.0 \mathrm{~mL}\) of \(0.0100 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}(a q) ?\)

A \(50.00\) -mL sample of hydrochloric acid of unknown concentration was neutralized by \(47.35 \mathrm{~mL}\) of \(0.01020 \mathrm{M}\) sodium hydroxide solution. Calculate the concentration of the original HCl solution.

A solution is prepared by dissolving \(5.00 \mathrm{~g}\) of sucrose, \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\), in \(1.00 \mathrm{~L}\) of water. What is the percent by mass concentration of sucrose? (The density of water is \(1.00 \mathrm{~g} / \mathrm{mL}\) ).

A solution is prepared by combining \(4.00 \mathrm{~mL}\) of hexane with a sufficient volume of ethanol to obtain \(250.0 \mathrm{~mL}\) of solution. What is the percent by volume concentration of hexane?

Air is approximately \(21 \%\) by volume oxygen, \(\mathrm{O}_{2}\). How many grams of oxygen are present in \(200.0 \mathrm{~L}\) of air at \(1.00 \mathrm{~atm}\) and \(25^{\circ} \mathrm{C}\) ? (Hint: Use the ideal gas equation from Chapter \(11 .\) )

When \(5.00 \mathrm{~g}\) of a solute is dissolved in sufficient solvent to produce \(100.0 \mathrm{~mL}\) of solution, (a) What is the percent by mass/volume concentration of the solute? (b) What additional information do you need to calculate the percent by mass concentration of the solute, and how would you calculate that concentration once you had the missing information?

A sample of stainless steel, which is an alloy of iron, chromium, and minor amounts of other components, is \(11.5 \%\) by mass chromium. How many grams of chromium are there in \(250.0 \mathrm{lb}\) of stainless steel?

Your boss says, "Prepare \(0.5000 \mathrm{~kg}\) of a \(1.00 \%\) solution of hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right.\), a liquid) in dichloromethane \(\left(\mathrm{CH}_{2} \mathrm{Cl}_{2}\right.\), also a liquid). \({ }^{\prime}\) (a) What is wrong with his request? (b) How would you prepare this solution if he meant a \(1.00 \%\) by mass solution?

When \(26.5 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) is combined with \(49.8 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{NaF}\), (a) What is the theoretical yield of \(\mathrm{CaF}_{2}(\mathrm{~s})\) in grams? (b) What is the molar concentration of \(\mathrm{Ca}^{2+}(\) excess reactant \()\) in the combined solution?

Suppose \(200.0 \mathrm{~mL}\) of a \(2.50 \mathrm{M}\) solution of sodium hydroxide is combined with \(100.0 \mathrm{~mL}\) of a \(1.50 \mathrm{M}\) solution of iron(III) nitrate. (a) Write a net ionic equation for the formation of the expected precipitate. (b) What is the theoretical yield of precipitate in grams? (c) Suppose only \(10.95 \mathrm{~g}\) of precipitate is isolated. What is the percent yield for the reaction? (d) What is the molar concentration of the excess reactant in the combined solution?

Suppose \(20.0 \mathrm{~g}\) of \(\mathrm{NaBr}(\mathrm{s})\) is added to \(50.0 \mathrm{~mL}\) of a \(2.00 \mathrm{M}\) silver nitrate solution. (a) Write a net ionic equation for the formation of the expected precipitate. (b) What is the theoretical yield of precipitate in grams? (c) Suppose only \(15.0 \mathrm{~g}\) of precipitate is isolated. What is the percent yield for the reaction? (d) What is the molar concentration of the excess reactant in the combined solution?

In a titration of \(\mathrm{HCl}\) with \(\mathrm{NaOH}\), you read the buret to see how much base it took to neutralize the acid (turn the indicator pink). You do this titration to determine the molar concentration of the acid. Why is it important to accurately know the amount (volume) of acid that you originally put into the flask?

Calculate the molarity of pure water at \(4.0^{\circ} \mathrm{C}\). The density of water at \(4.0^{\circ} \mathrm{C}\) is \(1.0000 \mathrm{~g} / \mathrm{mL}\).

When methanol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right)\) dissolves in water, both initially at \(22{ }^{\circ} \mathrm{C}\), heat is released and the resulting solution is warmer than \(22{ }^{\circ} \mathrm{C}\). Explain why this is so. (What must be true?)

At \(0.00{ }^{\circ} \mathrm{C}\) and sea level, dry air can be assumed to have a molar volume of \(22.414 \mathrm{~L}\). Given that air is \(21.0 \%\) by volume oxygen, what is the molar concentration of oxygen in the atmosphere at sea level at \(0.00^{\circ} \mathrm{C}\) ?

The amount to which a solvent's boiling point is elevated and vapor pressure is lowered depends on the number per volume (concentration) and not the chemical identity of solute particles dissolved in it. Explain why this is so in terms of entropy.

The dissolving of a solute (like \(\mathrm{NaCl}\) ) into a solvent (like water) can be thought of as a threestep process. (a) Briefly name or describe these three steps. (b) What are the energy implications of each step? (exothermic, endothermic, depends on the particular solvent/solute) (c) Which of the three steps is primarily responsible for the "like dissolves like" rule for solubility?

The dissolving of a solute into a solvent can be thought of as a three-step process. The drinking alcohol, ethanol \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}-\mathrm{OH}\right)\), is infinitely soluble in water. However, another alcohol called pentanol, with the molecular formula \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2}-\mathrm{OH}\), is nearly insoluble in water. (a) Which of the three steps in the solubility model is most responsible for this difference in solubility? Describe the step you choose (specify its name). (b) Give a BRIEF explanation for your choice.

Our task is to measure the volume of blood in a live hippopotamus. One way to do this would be to drain its blood into a suitable container and measure its volume. Aside from the obviously disastrous effect this method would have on the hippo, it would not be very accurate since some blood would still remain behind in the tissues. Instead, we will inject the hippo with \(2.00 \mathrm{~mL}\) of a \(2.00 \mathrm{M}\) dye solution which the hippo will not appreciably metabolize or excrete in one hour, and then measure the dye concentration in the bloodstream after 30 minutes (which should be sufficient time for the dye to thoroughly mix in the bloodstream). After 30 minutes, the concentration of the dye in a \(78.0 \mathrm{~mL}\) blood sample was found to be \(0.0000125 \mathrm{M}\). What is the volume of blood in the hippo?