Chapter 11

How do solutions differ from compounds? From other mixtures?

When \(\mathrm{KNO}_{3}\) is dissolved in water, the resulting solution is significantly colder than the water was originally. (a) Is the dissolution of \(\mathrm{KNO}_{3}\) an endothermic or an exothermic process? (b) What conclusions can you draw about the intermolecular attractions involved in the process? (c) Is the resulting solution an ideal solution?

Give an example of each of the following types of solutions: (a) a gas in a liquid (b) a gas in a gas (c) a solid in a solid

Predict whether each of the following substances would be more soluble in water (polar solvent) or in a hydrocarbon such as heptane ( \(\mathrm{C}_{7} \mathrm{H}_{16}\), nonpolar solvent): (a) vegetable oil (nonpolar) (b) isopropyl alcohol (polar) (c) potassium bromide (ionic)

Heat is released when some solutions form; heat is absorbed when other solutions form. Provide a molecular explanation for the difference between these two types of spontaneous processes.

Solutions of hydrogen in palladium may be formed by exposing Pd metal to \(\mathrm{H}_{2}\) gas. The concentration of hydrogen in the palladium depends on the pressure of \(\mathrm{H}_{2}\) gas applied, but in a more complex fashion than can be described by Henry's law. Under certain conditions, 0.94 g of hydrogen gas is dissolved in 215 g of palladium metal (solution density \(=10.8 \mathrm{g} \mathrm{cm}^{3}\) ). (a) Determine the molarity of this solution. (b) Determine the molality of this solution. (c) Determine the percent by mass of hydrogen atoms in this solution.

Explain why the ions \(\mathrm{Na}^{+}\) and \(\mathrm{Cl}^{-}\) are strongly solvated in water but not in hexane, a solvent composed of nonpolar molecules.

Explain why solutions of HBr in benzene (a nonpolar solvent) are nonconductive, while solutions in water (a polar solvent) are conductive.

Consider the solutions presented: (a) Which of the following sketches best represents the ions in a solution of \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}(a q) ?\) (b) Write a balanced chemical equation showing the products of the dissolution of \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}\)

What is the expected electrical conductivity of the following solutions? (a) \(\mathrm{NaOH}(a q)\) (b) \(\mathrm{HCl}(a q)\) (c) \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q)\) (glucose) (d) \(\mathrm{NH}_{3}(a q)\)

Why are most solid ionic compounds electrically nonconductive, whereas aqueous solutions of ionic compounds are good conductors? Would you expect a liquid (molten) ionic compound to be electrically conductive or nonconductive? Explain.

Suppose you are presented with a clear solution of sodium thiosulfate, \(\mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3}\). How could you determine whether the solution is unsaturated, saturated, or supersaturated?

Suggest an explanation for the observations that ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\), is completely miscible with water and that ethanethiol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{SH},\) is soluble only to the extent of \(1.5 \mathrm{g}\) per \(100 \mathrm{mL}\) of water.

At \(0^{\circ} \mathrm{C}\) and \(1.00 \mathrm{atm},\) as much as \(0.70 \mathrm{g}\) of \(\mathrm{O}_{2}\) can dissolve in \(1 \mathrm{L}\) of water. At \(0^{\circ} \mathrm{C}\) and \(4.00 \mathrm{atm},\) how many grams of \(\mathrm{O}_{2}\) dissolve in 1 L of water?

The Henry's law constant for \(\mathrm{CO}_{2}\) is \(3.4 \times 10^{-2} \mathrm{M} / \mathrm{atm}\) at \(25^{\circ} \mathrm{C}\). Assuming ideal solution behavior, what pressure of carbon dioxide is needed to maintain a \(\mathrm{CO}_{2}\) concentration of \(0.10 \mathrm{M}\) in a can of lemon-lime soda?

The Henry's law constant for \(\mathrm{O}_{2}\) is \(1.3 \times 10^{-3} \mathrm{M} /\) atm at \(25^{\circ} \mathrm{C}\). Assuming ideal solution behavior, what mass of oxygen would be dissolved in a 40-L aquarium at \(25^{\circ} \mathrm{C}\), assuming an atmospheric pressure of \(1.00 \mathrm{atm}\), and that the partial pressure of \(\mathrm{O}_{2}\) is 0.21 atm?

What are the mole fractions of \(\mathrm{HNO}_{3}\) and water in a concentrated solution of nitric acid \(\left(68.0 \% \mathrm{HNO}_{3} \mathrm{by}\right.\) mass)? (a) Outline the steps necessary to answer the question. (b) Answer the question.

Calculate the mole fraction of each solute and solvent: (a) \(583 \mathrm{g}\) of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) in \(1.50 \mathrm{kg}\) of water \(-\) the acid solution used in an automobile battery (b) \(0.86 \mathrm{g}\) of \(\mathrm{NaCl}\) in \(1.00 \times 10^{2} \mathrm{g}\) of water \(-\) a solution of sodium chloride for intravenous injection (c) \(46.85 \mathrm{g}\) of codeine, \(\mathrm{C}_{18} \mathrm{H}_{21} \mathrm{NO}_{3},\) in \(125.5 \mathrm{g}\) of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (d) \(25 \mathrm{g}\) of \(\mathrm{I}_{2}\) in \(125 \mathrm{g}\) of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\)

Calculate the mole fraction of each solute and solvent: (a) \(0.710 \mathrm{kg}\) of sodium carbonate (washing soda), \(\mathrm{Na}_{2} \mathrm{CO}_{3},\) in \(10.0 \mathrm{kg}\) of water \(-\) a saturated solution at \(0^{\circ} \mathrm{C}\) (b) \(125 \mathrm{g}\) of \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) in \(275 \mathrm{g}\) of water \(-\) a mixture used to make an instant ice pack (c) \(25 \mathrm{g}\) of \(\mathrm{Cl}_{2}\) in \(125 \mathrm{g}\) of dichloromethane, \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) (d) \(0.372 \mathrm{g}\) of tetrahydropyridine, \(\mathrm{C}_{5} \mathrm{H}_{9} \mathrm{N},\) in \(125 \mathrm{g}\) of chloroform, \(\mathrm{CHCl}_{3}\)

Calculate the mole fractions of methanol, \(\mathrm{CH}_{3} \mathrm{OH} ;\) ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} ;\) and water in a solution that is \(40 \%\) methanol, 40\% ethanol, and 20\% water by mass. (Assume the data are good to two significant figures.)

What is the molality of phosphoric acid, \(\mathrm{H}_{3} \mathrm{PO}_{4}\), in a solution of \(14.5 \mathrm{g}\) of \(\mathrm{H}_{3} \mathrm{PO}_{4}\) in \(125 \mathrm{g}\) of water? (a) Outline the steps necessary to answer the question. (b) Answer the question.

Calculate the molality of each of the following solutions: (a) \(583 \mathrm{g}\) of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) in \(1.50 \mathrm{kg}\) of water - the acid solution used in an automobile battery (b) \(0.86 \mathrm{g}\) of \(\mathrm{NaCl}\) in \(1.00 \times 10^{2} \mathrm{g}\) of water \(-\) a solution of sodium chloride for intravenous injection (c) \(46.85 \mathrm{g}\) of codeine, \(\mathrm{C}_{18} \mathrm{H}_{21} \mathrm{NO}_{3}\), in \(125.5 \mathrm{g}\) of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (d) 25 g of I_ \(_{2}\) in 125 g of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\)

Calculate the molality of each of the following solutions: (a) \(0.710 \mathrm{kg}\) of sodium carbonate (washing soda), \(\mathrm{Na}_{2} \mathrm{CO}_{3},\) in \(10.0 \mathrm{kg}\) of water \(-\) a saturated solution at \(0^{\circ} \mathrm{C}\) (b) \(125 \mathrm{g}\) of \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) in \(275 \mathrm{g}\) of water \(-\) a mixture used to make an instant ice pack (c) \(25 \mathrm{g}\) of \(\mathrm{Cl}_{2}\) in \(125 \mathrm{g}\) of dichloromethane, \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) (d) 0.372 g of tetrahydropyridine, \(\mathrm{C}_{5} \mathrm{H}_{9} \mathrm{N}\), in 125 \(\mathrm{g}\) of chloroform, \(\mathrm{CHCl}_{3}\)

Assuming ideal solution behavior, what is the osmotic pressure of an aqueous solution of \(1.64 \mathrm{g}\) of \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\) in water at 25 ^ C? The volume of the solution is 275 mL. (a) Outline the steps necessary to answer the question. (b) Answer the question.

A solution contains 5.00 g of urea, CO(NH_2)2, a nonvolatile compound, dissolved in 0.100 kg of water. If the vapor pressure of pure water at \(25^{\circ} \mathrm{C}\) is 23.7 torr, what is the vapor pressure of the solution (assuming ideal solution behavior)?

Arrange the following solutions in order by their decreasing freezing points: \(0.1 \mathrm{m} \mathrm{Na}_{3} \mathrm{PO}_{4}, 0.1 \mathrm{m} \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) \(0.01 \mathrm{m} \mathrm{CO}_{2}, 0.15 \mathrm{m} \mathrm{NaCl},\) and \(0.2 \mathrm{m} \mathrm{CaCl}_{2}\).

A sample of sulfur weighing 0.210 g was dissolved in 17.8 g of carbon disulfide, \(C S_{2}\left(K_{b}=2.43^{\circ} \mathrm{C} / m\right)\). If the boiling point elevation was \(0.107^{\circ} \mathrm{C},\) what is the formula of a sulfur molecule in carbon disulfide (assuming ideal solution behavior)?

Lysozyme is an enzyme that cleaves cell walls. A 0.100-L sample of a solution of lysozyme that contains \(0.0750 \mathrm{g}\) of the enzyme exhibits an osmotic pressure of \(1.32 \times 10^{-3}\) atm at \(25^{\circ} \mathrm{C}\). Assuming ideal solution behavior, what is the molar mass of lysozyme?

The osmotic pressure of a solution containing \(7.0 \mathrm{g}\) of insulin per liter is 23 torr at \(25^{\circ} \mathrm{C}\). Assuming ideal solution behavior, what is the molar mass of insulin?

The vapor pressure of methanol, \(\mathrm{CH}_{3} \mathrm{OH}\), is 94 torr at \(20^{\circ} \mathrm{C}\). The vapor pressure of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\), is 44 torr at the same temperature. (a) Calculate the mole fraction of methanol and of ethanol in a solution of \(50.0 \mathrm{g}\) of methanol and \(50.0 \mathrm{g}\) of ethanol. (b) Ethanol and methanol form a solution that behaves like an ideal solution. Calculate the vapor pressure of methanol and of ethanol above the solution at \(20^{\circ} \mathrm{C}\). (c) Calculate the mole fraction of methanol and of ethanol in the vapor above the solution.

A sample of \(\mathrm{HgCl}_{2}\) weighing \(9.41 \mathrm{g}\) is dissolved in \(32.75 \mathrm{g}\) of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\left(K_{\mathrm{b}}=1.20^{\circ} \mathrm{C} / \mathrm{m}\right)\). The boiling point elevation of the solution is \(1.27^{\circ} \mathrm{C} .\) Is \(\mathrm{HgCl}_{2}\) an electrolyte in ethanol? Show your calculations.

Distinguish between dispersion methods and condensation methods for preparing colloidal systems.

How do colloids differ from solutions with regard to dispersed particle size and homogeneity?

Explain the cleansing action of soap.

How can it be demonstrated that colloidal particles are electrically charged?