Chapter 12

What do we mean when we say that solute particles diffuse through a solution?

You have two solutions, one \(1.50 \mathrm{M}\) sodium sulfide and the other \(1.00 \mathrm{M} \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\). (a) Write a net ionic equation for the precipitation reaction that occurs when these solutions are combined. (b) How many milliliters of the solutions must be combined to prepare \(10.00 \mathrm{~g}\) of precipitate? (c) Suppose you filter off the precipitate and find that your percent yield is \(50.0 \%\). What volumes of the solutions should you have combined to isolate \(10.00 \mathrm{~g}\) of precipitate?

You have two solutions, one \(0.755 \mathrm{M}\) barium nitrate and the other \(1.250 \mathrm{M}\) calcium hydroxide. (a) Write a net ionic equation for the precipitation reaction that occurs when these solutions are combined. (b) How many milliliters of the two solutions must be combined to prepare \(5.00 \mathrm{~g}\) of precipitate? (c) Suppose you filter off the precipitate and find that your percent yield is \(85.0 \%\). What volumes of the solutions should you have combined to isolate \(5.00 \mathrm{~g}\) of precipitate?

You have two solutions, one \(0.650 \mathrm{M}\) iron(III) nitrate and the other \(1.500 \mathrm{M}\) ammonium carbonate. (a) Write a net ionic equation for the precipitation reaction that occurs when these solutions are combined. (b) If you pour \(200.0 \mathrm{~mL}\) of each solution into the same flask, what is the theoretical yield of the precipitate in grams? (c) What is the molar concentration of the excess reactant ion?

You have two solutions, one \(0.800 \mathrm{M}\) sodium. phosphate and the other \(0.800 \mathrm{M}\) lead(II) acetate. (a) Write a net ionic equation for the precipitation reaction that occurs when these solutions are combined. (b) If you pour \(100.0 \mathrm{~mL}\) of the sodium phosphate solution and \(50.0 \mathrm{~mL}\) of the lead(II) acetate solution into the same flask, what is the theoretical yield of the precipitate in grams? (c) What is the molar concentration of the excess reactant ion?

A \(25.00 \mathrm{~mL}\) sample of aqueous hydrobromic acid of unknown concentration is neutralized by \(43.28 \mathrm{~mL}\) of \(0.1001 \mathrm{M} \mathrm{NaOH}(a q)\) (a) Write a net ionic equation for this acid-base neutralization reaction. (b) How many moles of \(\mathrm{NaOH}\) did it take for the neutralization? (c) How many moles of hydrobromic acid were neutralized? (d) What is the molar concentration of the hydrobromic acid?

A \(25.00 \mathrm{~mL}\) sample of aqueous sulfuric acid of unknown concentration is neutralized by \(27.55\) \(\mathrm{mL}\) of \(1.0002 \mathrm{M} \mathrm{NaOH}(a q)\) (a) Write a net ionic equation for this acid-base neutralization reaction. (b) How many moles of \(\mathrm{NaOH}\) did it take for the neutralization? (c) How many moles of sulfuric acid were neutralized? (d) What is the molar concentration of the sulfuric acid?

Propionic acid has one acidic proton per molecule. A solution is prepared by dissolving \(0.273 \mathrm{~g}\) of propionic acid in enough water to yield \(100.0 \mathrm{~mL}\) of solution. This solution is neutralized by \(36.82 \mathrm{~mL}\) of \(0.1001 \mathrm{M} \mathrm{NaOH}(a q)\). (a) What is the molar concentration of the propionic acid? (b) What is the molar mass of propionic acid?

When it is warmed, a piece of plastic changes from a solid phase in which its molecules are positioned in an ordered arrangement to a solid phase in which its molecules are arranged randomly. How could you determine the temperature at which this phase change occurs?

When water boils, its temperature does not increase even though it is being heated. If the heat energy isn't being used to increase the temperature of the water, what is it being used for?

If liquid water is introduced into an evacuated (zero pressure) flask, the pressure will begin to rise. (a) Eventually, the pressure will stop rising and reach a constant value. Why does it stop rising? (b) What do we call this pressure? (c) What will happen to this pressure if we increase the temperature of the flask? Why does it happen?

Define vapor pressure and include the word equilibrium in your definition.

Hexane, which is a liquid at room temperature, is more volatile than water. (a) What does this mean? (b) Which liquid has the higher vapor pressure at a given temperature? (c) Which liquid most likely has the higher boiling point? (d) Why is hexane more volatile than water?

How could you make water boil at \(20^{\circ} \mathrm{C}\) (approximately room temperature)?

Use the dueling-arrows model to explain what heating does to a liquid that eventually causes the liquid to boil.

What does the word colligative mean when referring to colligative properties of a substance? Also, give three examples of colligative properties.

A student dissolves \(28.7 \mathrm{~g}\) of \(\mathrm{NaCl}(s)\) in \(2.00 \mathrm{~kg}\) of water. How many grams of sucrose, \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\), would she have to dissolve in \(2.00 \mathrm{~kg}\) of water to make the sucrose solution have the same freezing point as the \(\mathrm{NaCl}\) solution?

A student dissolves \(36.9 \mathrm{~g}\) of calcium nitrate in \(500.0 \mathrm{~g}\) of water. How many grams of glucose, \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\), would he have to dissolve in \(500.0 \mathrm{~g}\) of water to make the glucose solution have the same boiling point as the calcium nitrate solution?

What are (a) the boiling point and (b) the freezing point of a solution made by dissolving \(5.75 \mathrm{~g}\). of solid cetyl alcohol, \(\mathrm{C}_{16} \mathrm{H}_{34} \mathrm{O}\), in \(100.0 \mathrm{~mL}\) of benzene? (The density of benzene is \(0.874 \mathrm{~g} / \mathrm{mL}\).)

A solution is prepared by dissolving \(5.00 \mathrm{~g}\) of caffeine in \(100.0 \mathrm{~g}\) of carbon tetrachloride. The solution is cooled and the temperature plotted over time: (a) What is the molar mass of caffeine? (b) Combustion analysis reveals that the empirical formula of caffeine is \(\mathrm{C}_{4} \mathrm{H}_{5} \mathrm{~N}_{2} \mathrm{O}\). What is the molecular formula?

When soap molecules are dissolved in water in a pool, the soap molecules migrate to the surface of the water and actually coat the surface, with the polar heads being dissolved in the water and the non-polar tails sticking out into the air above the surface of the water. (a) Draw the scenario just described. (b) Using the rule of thumb "like dissolves like," explain why the soap molecules at the water's surface align as described. (c) Water bugs can "walk" on the surface of a pool's water, but if you put soap in the water, they fall through. Why do you think this is?

Micelles are spherical, although they are usually drawn as a flat cross section (as shown on page 495). Why wouldn't micelles exist in water as flat, two-dimensional structures?

Soap molecules have a hydrophobic portion and yet they dissolve in water. Explain how they accomplish this.

Explain how soaps allow water to wash oily, nonpolar dirt off clothes and skin.

Which would you expect to release the most hydration energy when dissolved in water: \(\mathrm{KCl}(\mathrm{s}), \mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{~s})\), or \(\mathrm{CO}_{2}(g) ?\) Which would you expect to release the least hydration energy? Explain your answers.

Which would you expect to release the most hydration energy when dissolved in water: \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(\mathrm{I}), \mathrm{CH}_{3} \mathrm{Cl}(l)\), or \(\mathrm{C}_{8} \mathrm{H}_{18}(I) ?\) Which would you expect to release the least hydration energy? Explain your answers.

The ionic lattice in which compound requires the most energy to break: \(\mathrm{KCl}, \mathrm{Mg}(\mathrm{OH})_{2}\), or \(\mathrm{NaNO}_{3}\) ? Explain your answer.

Which one of the following steps in the dissolving process must have a negative value for \(\Delta E\) ? Explain your answer. (a) The physical separation of solute particles (b) The formation of solvent-solute interactions (c) The physical separation of solvent particles (d) None of the above

Which one of the following statements is true? (a) Gases are more soluble in liquids when the pressure is decreased. (b) Pressure has no effect on how soluble a gas is in a liquid. (c) Gases are more soluble in liquids when the pressure is increased (d) Gases are less soluble in liquids when the pressure is increased.

How many moles of potassium permanganate, \(\mathrm{KMnO}_{4}\), are there in \(28.86 \mathrm{~mL}\) of a \(5.20 \times 10^{-3} \mathrm{M}\) solution of \(\mathrm{KMnO}_{4} ?\)

(a) How many grams of \(\mathrm{NaOH}\) are needed to prepare \(500.0 \mathrm{~mL}\) of a \(0.300 \mathrm{M} \mathrm{NaOH}\) solution? (b) Describe how you would make this solution, including the equipment needed.

How would you prepare \(250.0 \mathrm{~mL}\) of a \(0.350 \mathrm{M}\) \(\mathrm{NaOH}\) solution from a \(6.00 \mathrm{M} \mathrm{NaOH}\) stock solution?

Calculate the number of moles of each ion present in \(2.00 \times 10^{2} \mathrm{~cm}^{3}\) of (a) \(0.200 \mathrm{M} \mathrm{NaCl}\), (b) \(0.350 \mathrm{M} \mathrm{K}_{3} \mathrm{PO}_{4}\) (c) \(1.44 \mathrm{M} \mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\)

\(4.70 \mathrm{~g}\) of \(\mathrm{CuSO}_{4}\) is added to enough water to make \(150.0 \mathrm{~cm}^{3}\) of solution. (a) What is the molarity of the solution? (b) How many moles of \(\mathrm{CuSO}_{4}\) are there in \(1.00\) \(\mathrm{mL}\) of this solution? (c) What is the percent by mass of \(\mathrm{CuSO}_{4}\) of this solution? (The density of the solution is \(1.01 \mathrm{~g} / \mathrm{mL}) .\)

Combustion analysis reveals vitamin \(\mathrm{C}\) to be \(40.9 \%\) by mass \(\mathrm{C}\) and \(4.58 \%\) by mass \(\mathrm{H}\). The only other element present is oxygen. A solution of \(19.40 \mathrm{~g}\) of vitamin \(\mathrm{C}\) in \(100.0 \mathrm{~g}\) of water freezes at \(22.05^{\circ} \mathrm{C}\). What is the molecular formula of vitamin \(C\) ?

The freezing point of a solution prepared by dissolving \(0.200\) mole of \(\mathrm{HF}(g)\) in \(2.00 \mathrm{~kg}\) of water is \(-0.19{ }^{\circ} \mathrm{C}\). Is HF primarily intact in solution, existing as \(\mathrm{HF}(a q)\), or has it dissociated to \(\mathrm{H}^{+}(a q)\) and \(\mathrm{F}^{-}(a q)\) ions? Does this mean \(\mathrm{HF}\) is a weak or a strong acid?

How many gallons of 24 -proof wine would you have to drink to consume \(0.100\) gallon of alcohol?

Draw pictures illustrating the solute-solvent interactions and the solvent- solvent interactions for methanol, \(\mathrm{CH}_{3} \mathrm{OH}\), in water. Is this a case of like dissolves like? Explain.

After \(125.0 \mathrm{~mL}\) of water is added to \(50.0 \mathrm{~mL}\) of a \(0.250 \mathrm{M}\) solution of ammonium phosphate, (a) what is the molar concentration of ammonium phosphate in the diluted solution? Once in solution, the ammonium phosphate exists not as intact ammonium phosphate but rather as ammonium ions and phosphate ions. What are the molar concentrations (b) of ammonium ions in the diluted solution and (c) of phosphate ions in the diluted solution?

After \(50.0 \mathrm{~mL}\) of a \(0.250 \mathrm{M}\) solution of calcium nitrate is combined with \(100.0 \mathrm{~mL}\) of a \(0.835 \mathrm{M}\) solution of calcium nitrate, \((\) a) what is the molar concentration of \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}(a q)\) in the combined solution? Once in solution, the calcium nitrate exists not as intact calcium nitrate but rather as calcium ions and nitrate ions. What are the molar concentrations (b) of \(\mathrm{Ca}^{2+}(a q)\) in the combined solution and (c) of \(\mathrm{NO}_{3}^{-}(a q)\) in the combined solution?

Suppose \(250.0 \mathrm{~mL}\) of a \(0.600 \mathrm{M}\) solution of barium nitrate is combined with enough \(0.500 \mathrm{M}\) sodium sulfate solution to precipitate the maximum amount of barium sulfate. What volume of the sodium sulfate solution is required?

A bottle contains \(1.00 \mathrm{~L}\) of a stock solution of \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}\) of unknown concentration. A lab technician dilutes \(5.00 \mathrm{~mL}\) of the stock solution to \(100.0 \mathrm{~mL}\) with water. He then determines the \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}\) concentration of this solution to be \(0.0478 \mathrm{M}\). What is the \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}\) concentration of the stock solution?

What volume of a \(0.245 \mathrm{M}\) solution of \(\mathrm{NaI}\) would you need to add to \(100.0 \mathrm{~mL}\) of a \(0.300 \mathrm{M}\) solution of lead acetate to precipitate out all the lead? Which ions are spectators?

Citric acid can produce \(3 \mathrm{H}^{+}(a q)\) ions per molecule. A solution of citric acid is prepared by dissolving \(0.177 \mathrm{~g}\) of solid citric acid in enough water to yield \(100.0 \mathrm{~mL}\) of solution. When this solution is titrated with \(0.1001 \mathrm{M} \mathrm{NaOH}(a q)\), the indicator turns color after \(27.55 \mathrm{~mL}\) of \(\mathrm{NaOH}(a q)\) has been added. (a) What is the molar concentration of citric acid? (b) What is the molar mass of citric acid?

A 25.00-mL sample of a hydrochloric acid solution of unknown concentration is titrated with \(0.1004 \mathrm{M}\) \(\mathrm{NaOH}\). However, before the acid is titrated, \(27.65\) mL of water is added to it. The phenolphthalein indicator turns red after \(28.70 \mathrm{~mL}\) of \(\mathrm{NaOH}\) has been added. What is the concentration of the \(25.00-\) \(\mathrm{mL}\) sample of hydrochloric acid?

Identify the solvent and the solute in each solution: (a) Brass, which is 60 to \(80 \% \mathrm{Cu}\), and 18 to \(40 \% Z n\) (b) Household ammonia cleaner, which is \(1 \%\) by mass ammonia gas in water (c) \(2.59 \mathrm{~g}\) of sucrose in \(1.00 \mathrm{~g}\) of water at \(50^{\circ} \mathrm{C}\)

Carbon dioxide, \(\mathrm{CO}_{2}\), is a compound of carbon and oxygen. Does this mean that a sample of pure carbon dioxide can be considered to be a solution of carbon dissolved in oxygen? Explain your answer.

Describe at the molecular level what is happening when solid iodine, \(\mathrm{I}_{2}(s)\), dissolves in carbon tetrachloride liquid, \(\operatorname{CCl}_{4}(l)\).

Would you expect solid iodine, \(\mathrm{I}_{2}(s)\), to be more or less soluble in \(\mathrm{CCl}_{4}(l)\) than in \(\mathrm{H}_{2} \mathrm{O}(l) ?\) Explain your answer in terms of energy.

What is the difference between hydration and solvation? Does one process always release more energy than the other? Explain.