Chapter 12

Classify the following as solutions or heterogeneous mixtures: (a) \(\mathrm{A}\) hot cup of instant coffee (b) Chicken vegetable soup (c) Unfiltered blood (d) Filtered blood plasma (e) A chromium-plated steel automobile bumper (f) A stainless steel automobile bumper (stainless steel is prepared by combining iron, Fe, up to \(30 \%\) chromium, \(\mathrm{Cr}\), and smaller amounts of nickel, \(\mathrm{Ni}\), and carbon, \(C\), and heating the mixture until it becomes molten)

Identify the solvent and solute or solutes in each solution: (a) Nail-polish remover ( \(30 \%\) acetone in water) (b) Humid air (c) Stainless steel (see Practice Problem 12.1) (d) Aqueous solution of aspirin

The "proof" value of any liquor is equal to twice the percentage of alcohol; for example, a 50-proof liquor is \(25 \%\) alcohol in water. Vodka is normally sold between 80 and 100 proof, but suppose you came across a bottle of 135 -proof vodka. Would you be justified in calling the alcohol the solvent and the water the solute? Explain.

Consider the ionic compound magnesium chloride, \(\mathrm{MgCl}_{2}\). Do you think the hydration energy for this compound is greater than, less than, or about equal to that of \(\mathrm{NaCl}\) ?

Imagine you are trying to dissolve \(\mathrm{NaCl}\) in liquid carbon tetrachloride, \(\mathrm{CCl}_{4}\). Would the energy released in the solvation step be greater than, less than, or about equal to that released when NaCl dissolves in water? Explain.

Based on the answer to Practice Problem \(12.4\), is the energy required for solute separation greater for \(\mathrm{NaCl}\) or \(\mathrm{MgCl}_{2}\) ? Explain.

For a given solute in water, the energy changes are \(\Delta E_{\text {solute separation }}=835 \mathrm{~kJ}\), \(\Delta E_{\text {solvent separation }}=98 \mathrm{~kJ}\), and \(\Delta E_{\text {solvation }}=-805 \mathrm{~kJ} .\) Will this solute dissolve in water? Explain your answer, both numerically and in terms of the three-step model for a solute's dissolving in a solvent.

Suppose we want to dissolve a gaseous solute in water. Would you expect \(\Delta E_{\text {solute separation }}\) to be larger for the gaseous solute or for a solid ionic solute? Explain.

The more negative \(\Delta E_{\text {solvation }}\) is, the more likely a solute will dissolve. Explain.

Suppose you want to dissolve some \(\mathrm{MgCl}_{2}\) in water. (a) How do we know that magnesium cations have a \(+2\) charge? (b) \(\Delta E_{\text {solute separation }}\) for \(\mathrm{MgCl}_{2}\) is much more positive than \(\Delta E_{\text {solute separation }}\) for \(\mathrm{NaCl}\). Explain what this means and why it might be so. (c) \(\mathrm{MgCl}_{2}\) is more soluble in water than \(\mathrm{NaCl}\). Explain how this is possible in light of the information given in (b).

How many grams of sucrose will it take to saturate 1 ton of water at \(20.0^{\circ} \mathrm{C} ?(1\) ton \(=2000 \mathrm{lb} ; 1 \mathrm{lb}=453.6 \mathrm{~g})\)

How many grams of potassium chloride, \(\mathrm{KCl}\), will it take to prepare a saturated solution in \(500.0 \mathrm{~mL}\) of boiling water? (The solubility of \(\mathrm{KCl}\) at \(100^{\circ} \mathrm{C}\) is \(56.7 \mathrm{~g} / 100.0 \mathrm{~g}\) water; assume the density of water is \(1.000 \mathrm{~g} / \mathrm{mL}\).)

On the basis of the three steps involved in the formation of a solution, what is the biggest difference between dissolving a gas and dissolving a solid?

How many milliliters of a \(1.500 \mathrm{M}\) solution of \(\mathrm{NaCl}\) do you need to obtain \(100.0 \mathrm{~g}\) of \(\mathrm{NaCl} ?\)

How many milliliters of a 2.55 M solution of glucose, \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\), molar mass \(=180.155 \mathrm{~g} / \mathrm{mol}\), do you need to obtain \(25.0 \mathrm{~g}\) of glucose?

How many grams of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\), are there in \(200.0 \mathrm{~mL}\) of a \(2.00 \mathrm{M}\) aqueous solution of ethanol?

What mass of solid NaCl do you need to prepare \(400.0 \mathrm{~mL}\) of a \(2.00 \mathrm{M} \mathrm{NaCl}\) solution from scratch? How much water do you add to the \(\mathrm{NaCl}\) ?

You have 1 L of a \(3.00 \mathrm{M}\) stock solution of \(\mathrm{NaCl}\) and need to prepare \(400.0 \mathrm{~mL}\) of a \(2.00 \mathrm{M}\) solution. Describe how you would do it.

A solution is prepared by dissolving \(25.0 \mathrm{~g}\) of sucrose in \(175.0 \mathrm{~g}\) of water. Characterize its concentration by the appropriate percent composition.

Gasohol is a solution of gasoline and ethanol. Every liter of gasohol contains \(90.0 \mathrm{~mL}\) of ethanol dissolved in gasoline. Characterize the solute concentration by the appropriate percent composition. (Hint: Assume you have 1 L of gasohol solution.)

How many moles of \(\mathrm{CaF}_{2}\) are there in \(25.0 \mathrm{~mL}\) of \(0.350 \mathrm{M} \mathrm{CaF}_{2}(a q) ?\)

What volume of \(0.350 \mathrm{M} \mathrm{CaF}_{2}\) solution is required to obtain \(0.00875\) mole of \(\mathrm{CaF}_{2} ?\)

How many moles of glucose are there in \(255.0 \mathrm{~mL}\) of a \(0.998 \mathrm{M}\) solution of glucose?

What volume of \(0.350 \mathrm{M} \mathrm{BaCl}_{2}\) solution is required to obtain \(0.500\) mole of \(\mathrm{BaCl}_{2}\) ?

What volume of \(0.350 \mathrm{M} \mathrm{BaCl}_{2}\) solution is required to obtain \(0.500 \mathrm{~mole}\) of \(\mathrm{Cl}^{-}(a q) ?\)

How would you prepare \(9.70 \mathrm{~g}\) of \(\mathrm{PbCl}_{2}(\mathrm{~s})\) from a \(0.100 \mathrm{M}\) solution of \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}\) and a \(0.200 \mathrm{M}\) solution of \(\mathrm{CaCl}_{2}\) ?

How would you prepare \(20.0 \mathrm{~g}\) of iron(III) hydroxide from a \(0.250 \mathrm{M}\) solution of \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}\) and a \(0.150 \mathrm{M}\) solution of \(\mathrm{Ba}(\mathrm{OH})_{2} ?\) How much product would you have isolated if your percent yield were \(67.5 \% ?\)

A \(30.00-\mathrm{mL}\) volume of aqueous sulfuric acid, \(\mathrm{H}_{2} \mathrm{SO}_{4}\), is titrated using \(0.200 \mathrm{MaOH}\) and an indicator that turns color only after all the sulfuric acid protons have reacted with \(\mathrm{OH}^{-}\) ions. The solution turns color when \(48.32 \mathrm{~mL}\) of base has been added. What is the molar concentration of the sulfuric acid?

A \(50.00-\mathrm{mL}\) volume of aqueous phosphoric acid, \(\mathrm{H}_{3} \mathrm{PO}_{4}\), is titrated using \(0.100 \mathrm{M}\) \(\mathrm{NaOH}\) and an indicator that turns color only after all the phosphoric acid protons have reacted with \(\mathrm{OH}^{-}\) ions. The solution turns color when \(38.60 \mathrm{~mL}\) of base has been added. What is the molar concentration of the phosphoric acid?

A 1.65-g sample of an acid that has one acidic proton per molecule is dissolved in water to give \(25.00 \mathrm{~mL}\) of solution. It takes \(27.48 \mathrm{~mL}\) of \(1.000 \mathrm{M} \mathrm{NaOH}\) to neutralize the acid. (a) What is the molar concentration of the acid? (b) What is the molar mass of the acid? (c) The empirical formula of the acid is \(\mathrm{CH}_{2} \mathrm{O}\). What are the molecular formula and name of the acid?

A solution is prepared at sea level (external pressure = \(1 \mathrm{~atm}\) ) by dissolving \(100.0 \mathrm{~g}\) of calcium nitrate in \(450.0 \mathrm{~g}\) of water. At what temperature will this solution have a vapor pressure of \(760 \mathrm{~mm} \mathrm{Hg}\) ? (Hint: What does an aqueous solution at sea level do when its vapor pressure is \(760 \mathrm{~mm} \mathrm{Hg}\) ?)

A student dissolves \(45.0 \mathrm{~g}\) of an unknown solid in \(225.0 \mathrm{~g}\) of cyclohexane. It is known to dissolve without dissociating. She cools the solution and finds that the temperature remains at \(2.70^{\circ} \mathrm{C}\) while the solution changes phase from liquid to solid. What is the molar mass of the solid?

Define the terms solute, solvent, and solution.

Suppose you mixed a small amount of table sugar with a large amount of flour and then spent hours grinding the mixture to a very fine powder. Is this mixture a solution? Explain.

Both a soft drink and the atmosphere we breathe are properly called solutions. For each, state why this is true, and also state the solvent for each.

Suppose there is a dust storm due to the winds blowing dry soil into the air. Would a sample of this dusty atmosphere be a mixture? Would it be a solution? Explain.

Vinegar is a common household solution that we consume. What is the solvent and what is the solute in vinegar?

What is a solid solution? Give some examples.

Classify the following as solutions or heterogeneous mixtures: (a) 14 karat gold (prepared by mixing 10 parts molten copper with 14 parts molten gold and then allowing the substance to cool until it solidifies) (b) Filtered ocean water (c) A piece of wood (d) Your exhaled breath (e) A bottle of salad oil and vinegar shaken extremely well

Suppose you had a \(50: 50\) homogeneous mixture of oxygen gas in helium gas. Which would you call the solvent and which would you call the solute?

A solution of table salt and table sugar in water is allowed to evaporate, leaving behind the two solid solutes. Is what remains a solution or a heterogeneous mixture? Explain your answer.

What evidence is there in your everyday experience to indicate that intermolecular attractive forces must exist between water molecules?

If there were no attractive forces between water molecules, what phase or phases of water would you expect to be prevalent at room temperature? Explain your answer.

Why does it take such a high temperature to melt \(\mathrm{NaCl}\) but a much lower temperature to dissolve it in water?

When an ionic substance such as \(\mathrm{NaCl}\) dissolves, the crystal lattice has to break apart to release the individual ions into the solution. Does this part of the dissolving process absorb energy or release energy? Explain your answer.

In dissolving any solute, room must be made in the solvent to accommodate solute particles. Does making this room absorb energy or release energy? Explain why.

Consider the process known as hydration during aqueous solution formation. (a) What is hydration? (b) Does it release or absorb energy? Explain.

Anhydrous calcium sulfate [CaSO \(\left._{4}\right] ;\) anhydrous means without any water in its lattice, will absorb water (will hydrate) to give calcium sulfate hydrate. The water molecules end up in "holes" or spaces in the ionic lattice. This process releases a considerable amount of energy in the form of heat. Explain why.

When \(\mathrm{NaCl}\) dissolves, what helps keep the dissolved \(\mathrm{Na}^{+}\) and \(\mathrm{Cl}^{-}\) ions from coming back together and reforming the lattice, precipitating the solid?

What is the name of the attractive force between dissolved \(\mathrm{Na}^{+}\) ions and water molecules? Diagram this force, showing how a water molecule would approach an \(\mathrm{Na}^{+}\) ion. Do the same for a \(\mathrm{Cl}^{-}\) ion.