Chapter 15

(a) Is the compound \(\mathrm{H}_{2} \mathrm{SO}_{4}\) molecular or ionic? (b) How did you decide on your answer to part (a)? (c) Based on your answer to part (a), would you call \(\mathrm{H}_{2} \mathrm{SO}_{4}\) an electrolyte or a nonelectrolyte? (d) An aqueous solution of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) causes a light bulb to light. What does this tell you about \(\mathrm{H}_{2} \mathrm{SO}_{4} ?\)

Indicate whether each compound is an electrolyte or a nonelectrolyte in water: (a) \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\) (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{O}\) (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) (d) \(\mathrm{CH}_{3} \mathrm{OH}\) (e) \(\mathrm{CuSO}_{4}\) (f) \(\mathrm{KBr}\) (g) \(\mathrm{HBr}\)

(a) Draw a beaker containing water and show what ions, if any, are present when ammonium bromide, \(\mathrm{NH}_{4} \mathrm{Br}\), dissolves. (b) Does the \(\mathrm{NH}_{4} \mathrm{Br}\) dissociate? What does the fact that it does or does not dissociate tell you regarding electrolyte/nonelectrolyte classification for this compound? (c) Add to your drawing from part (a) a light bulb attached to positive and negative wires. Indicate which way the dissolved species move.

True or false? If a compound is a molecular substance and an acid in water, it must also be an electrolyte.

Write a balanced dissociation equation for carbonic acid in water that shows the maximum number of \(\mathrm{H}_{3} \mathrm{O}^{+}\) ions the acid can yield.

Your answer to Practice Problem \(15.5\) shows the dissociation yielding 2 moles of protons per mole of acid, but this reaction actually produces fewer protons. Write the two balanced equilibrium equations for the dissociation of carbonic acid in water.

What salt forms when sulfuric acid completely neutralizes sodium hydroxide? Give both name and formula for the salt.

How many moles of \(\mathrm{NaOH}\) would it take to neutralize 1 mole of hydrochloric acid? How many moles of \(\mathrm{NaOH}\) would it take to neutralize 1 mole of sulfuric acid? Why aren't the answers to these two questions the same?

How many moles of \(\mathrm{Ba}(\mathrm{OH})_{2}\) would it take to neutralize \(0.1\) mole of hydrochloric acid?

In the reaction $$ \mathrm{NH}_{3}+\mathrm{PH}_{3} \rightarrow \mathrm{NH}_{2}^{-}+\mathrm{PH}_{4}^{+} $$ which reactant is the Bronsted-Lowry acid and which is the Bronsted-Lowry base?

In Reaction \(15.7\), water is shown acting as a base. How is water behaving in the following reaction? $$ \mathrm{NH}_{2}^{-}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{NH}_{3}+\mathrm{OH}^{-} $$ Explain your answer.

Aniline, \(\mathrm{C}_{6} \mathrm{H}_{7} \mathrm{~N}\), is a molecular compound that is a weak base. The molecule has a lone pair of electrons on the \(\mathrm{N}\) atom. (a) Why can aniline act as a base? (b) Write the equilibrium expression that shows how aniline in water makes the solution basic. (Be careful about the relative lengths of the two arrows you show in the expression.)

In the presence of water, the bicarbonate ion, \(\mathrm{HCO}_{3}^{-}\), can be either a BronstedLowry acid or a Bronsted-I.owry base. Write both equilibrium equations.

In the example we worked above, the concentration of \(\mathrm{H}_{3} \mathrm{O}^{+}\) was \(2.56 \mathrm{M}\) and that of \(\mathrm{OH}^{-}\) was \(3.91 \times 10^{-15} \mathrm{M}\). Suppose you must multiply these values together but are forbidden to use a calculator or a pencil. What is their product?

The OH concentration of an aqueous solution is \(0.000155 \mathrm{M}\). (a) Is the solution acidic or basic? Explain how you know. (b) What is the molar \(\mathrm{H}_{3} \mathrm{O}^{+}\) concentration?

Suppose \(1.00\) mole of \(\mathrm{HCl}\) is dissolved in enough water to give \(500.0 \mathrm{~mL}\) of solution. (a) What is the \(\mathrm{H}_{3} \mathrm{O}^{+}\) concentration? (Hint: When 1 mole of \(\mathrm{HCl}\) dissociates, we get 1 mole of \(\mathrm{H}_{3} \mathrm{O}^{+}\) ions because the acid is strong and monoprotic. Your answer should be in moles of \(\mathrm{H}_{3} \mathrm{O}^{+}\) per liter of solution.) (b) What is the \(\mathrm{OH}^{-}\) concentration? (Hint: Use the \(K_{\mathrm{w}}\) relationship.)

Suppose \(0.0100\) mole of \(\mathrm{Ba}(\mathrm{OH})_{2}\) is dissolved in enough water to give \(500.0 \mathrm{~mL}\) of solution. (a) What is the \(\mathrm{OH}^{-}\) concentration? (Hint: Remember that every time \(1 \mathrm{~mole}\) of \(\mathrm{Ba}(\mathrm{OH})_{2}\) dissociates, we get 2 moles of \(\mathrm{OH}^{-}\) ions.) (b) What is the \(\mathrm{H}_{3} \mathrm{O}^{+}\) concentration? (Hint: Use the \(K_{w}\) relationship.)

What is the base- 10 logarithm of \(0.0010 ?\)

What is the logarithm of \(10,000 ?\)

What is the logarithm of \(10 ?\) The logarithm of \(10^{1}\) is the same. Why?

What is the logarithm of \(0.01\) ? The logarithm of \(10^{-2}\) is the same. Why?

What is the base- 10 logarithm of \(10^{3}\) ?

What is the logarithm of \(1.0 \times 10^{-11}\) and of \(10^{-11} ?\)

What is the negative logarithm, \(-\log\), of \(10^{-7}\) ? (Hint: The minus sign in -log means you must put a minus sign in front of the number you get for the logarithm.)

Which solution is less acidic, solution \(A\) with \(\mathrm{pH} 2\) or solution \(\mathrm{B}\) with \(\mathrm{pH} 6\), and by how much?

Basic solution \(A\) has \(\mathrm{pH}=9 .\) Basic solution \(\mathrm{B}\) is ten times more basic than \(\Lambda\). What is the \(\mathrm{pH}\) of solution \(\mathrm{B}\) ?

\(A\) basic solution has a pH of \(9.8\). What is its molar \(\mathrm{H}_{3} \mathrm{O}^{+}\) concentration?

What is the \(\mathrm{H}_{3} \mathrm{O}^{+}\) concentration in a solution that is 100 times less acidic than one having a \(\mathrm{pH}\) of \(2.56 ?\)

What is the \(\mathrm{OH}^{-}\) concentration in a solution having a pH of \(5.55\) ? (Hint: Use the \(K_{w}\) expression.)

(a) Show how \(\mathrm{HCO}_{3}^{-}\) can act as a weak acid. (b) Show how \(\mathrm{HCO}_{3}^{-}\) can act as a weak base. (c) Since \(\mathrm{HCO}_{3}^{-}\) can act as either an acid or a base, can it be its own conjugate?

If \(\mathrm{HCO}_{3}^{-}\) is considered a weak acid, what is its conjugate base?

If \(\mathrm{HCO}_{3}^{-}\) is considered a weak base, what is its conjugate acid?

Ammonium ion, \(\mathrm{NH}_{4}^{+}\), is a weak acid. Write the equation for its reaction with water.

Ammonia, \(\mathrm{NH}_{3}\), is a weak base. Write the equation for its reaction with water.

What do you call an aqueous solution that contains a large amount of dissolved \(\mathrm{NH}_{4} \mathrm{Cl}\) and \(\mathrm{NH}_{3}\) ? Explain.

List the three criteria early chemists used to classify a compound as an acid.

List the three criteria early chemists used to classify a compound as a base.

To be an indicator, what must a compound do? Give an example of one and explain how it behaves.

What is an electrolyte? What is a nonelectrolyte? Give some examples of each.

Describe an experimental setup to determine whether a compound is an electrolyte or a nonelectrolyte. What would you look for?

Ethanol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\), dissolves in water. So does magnesium chloride, \(\mathrm{MgCl}_{2}\). Yet there is a fundamental difference in the way these two substances dissolve. What is this fundamental difference?

What is the difference between just dissolving versus dissolving and dissociating? Give an example of each.

If an ionic compound is water-soluble, it is an electrolyte. Explain why.

True or false? Because the solid phase of a molecular compound does not consist of ions, the compound cannot dissociate into ions when it dissolves in water. Back up your answer with an explanation and an example.

Electricity can be defined as charged particles in motion. Using this definition, explain how an aqueous solution of an electrolyte conducts electricity.

The molecular compound \(\mathrm{HCl}\) is an electrolyte. (a) What do we mean when we say that \(\mathrm{HCl}\) is a molecular compound? (b) Is it incorrect to call HCl an ionic compound? (c) What must a molecular compound like \(\mathrm{HCl}\) do when dissolved in aqueous solution in order to function as an electrolyte?

The compound \(\mathrm{NaCl}\) is an electrolyte. (a) Is it incorrect to call \(\mathrm{NaCl}\) a molecular compound? Explain. (b) Why is \(\mathrm{NaCl}\) expected to be an electrolyte?

Explain why this statement is true: Water-soluble compounds that consist of one or more metal atoms combined with one or more nonmetal atoms are electrolytes.

Characterize the following as electrolytes or nonelectrolytes: (a) Calcium bromide, \(\mathrm{CaBr}_{2}\) (b) Bromine, \(\mathrm{Br}_{2}\) (c) Hydrogen, \(\mathrm{H}_{2}\)

Write a balanced equation to show what happens to \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) when it dissolves in water. Use the \((a q)\) symbol when necessary.