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10.E: Acids and Bases (Exercises)

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    10.1 Arrhenius Definition of Acids and Bases

    1. Give two examples of Arrhenius acids.

    2. List the general properties of acids.

    3. Name each compound. (For acids, look up the name in Table 10.1.1. For bases, use the rules for naming ionic compounds from Chapter 3.)

      1. HBr(aq)
      2. Ca(OH)2(aq)
      3. HNO3(aq)
      4. Fe(OH)3(aq)

    Answers

    1. HCl and HNO3 (answers will vary)

    2. sour taste, react with metals, react with bases, and turn litmus red

      1. hydrobromic acid
      2. calcium hydroxide
      3. nitric acid
      4. iron(III) hydroxide

    10.2 Brønsted-Lowry Definition of Acids and Bases

    Exercises

    1. Label each reactant as a Brønsted-Lowry acid or a Brønsted-Lowry base.

      HCl(aq) + NH3(aq) → NH4+(aq) + Cl−(aq)

    2. Explain why a Brønsted-Lowry acid can be called a proton donor

    3. Write the chemical equation of the reaction of ammonia in water and label the Brønsted-Lowry acid and base.

    4. Demonstrate that the dissolution of HNO3 in water is actually a Brønsted-Lowry acid-base reaction by describing it with a chemical equation and labeling the Brønsted-Lowry acid and base.

    5. Write the chemical equation for the reaction that occurs when cocaine hydrochloride (C17H22ClNO4) dissolves in water and donates a proton to a water molecule. (When hydrochlorides dissolve in water, they separate into chloride ions and the appropriate cation.)

    Answers

    1. HCl: Brønsted-Lowry acid; NH3: Brønsted-Lowry base

    2. A Brønsted-Lowry acid gives away an H+ ion—nominally, a proton—in an acid-base reaction.

    3. NH3 + H2O → NH4+ + OH− (here NH3 = Brønsted-Lowry base; H2O = Brønsted-Lowry acid)

    4. HNO3 + H2O → H3O+ + NO3− (here NO3 = Brønsted-Lowry acid; H2O = Brønsted-Lowry base)

    5. C17H22NO4+ + H2O → H3O+ + C17H21NO4

    10.3 Water: Both an Acid and a Base

    Exercises

    1. Is H2O(ℓ) acting as an acid or a base?

      H2O(ℓ) + NH4+(aq) → H3O+(aq) + NH3(aq)

    2. Why is pure water considered neutral?

    Answers

    1. base

    2. When water ionizes, equal amounts of H+ (acid) and OH− (base) are formed, so the solution is neither acidic nor basic: H2O(ℓ) → H+(aq) + OH−(aq)

    [SIDE NOTE: It is rare to truly have pure water. Water exposed to air will usually be slightly acidic because dissolved carbon dioxide gas, or carbonic acid, decreases the pH slightly below 7. Alternatively, dissolved minerals, like calcium carbonate (limestone), can make water slightly basic.]

    10.4 The Strengths of Acids and Bases

    Concept Review Exercises

    1. Explain the difference between a strong acid or base and a weak acid or base.
    2. Explain what is occurring when a chemical reaction reaches equilibrium.
    3. Define pH.

    Answers

    1. A strong acid or base is 100% ionized in aqueous solution; a weak acid or base is less than 100% ionized.

    2. The overall reaction progress stops because the reverse process balances out the forward process.

    3. pH is a measure of the hydrogen ion concentration.

    Exercises

    1. Give an example of a strong acid and a weak acid.

    2. Is each compound a strong acid or a weak acid? Assume all are in aqueous solution.

      1. HF
      2. HC2H3O2
      3. HCl
      4. HClO4

    3. Is each compound a strong base or a weak base? Assume all are in aqueous solution.

      1. NH3
      2. NaOH
      3. Ca(OH)2

    Answers

    1. strong acid: HCl; weak acid: HC2H3O2 (answers will vary)

    2. weak, weak, strong, strong

    3. weak, strong, strong

    10.5: Buffers

    Concept Review Exercise

    1. Explain how a buffer prevents large changes in pH.

    Answer

    1. A buffer has components that react with both strong acids and strong bases to resist sudden changes in pH.

    Exercises

    1. Describe a buffer. What two related chemical components are required to make a buffer?

    2. Which solute combinations can make a buffer? Assume all are aqueous solutions.

      1. HCl and NaCl
      2. HNO2 and NaNO2
      3. NH4NO3 and HNO3
      4. NH4NO3 and NH3

    Answers

    1. A buffer resists sudden changes in pH. It has a weak acid or base and a salt of that weak acid or base.

    2. not a buffer, buffer, not a buffer, buffer

    10.6: Chapter Summary

    Additional Exercises

    1. The properties of a 1.0 M HCl solution and a 1.0 M HC2H3O2 solution are compared. Measurements show that the hydrochloric acid solution has a higher osmotic pressure than the acetic acid solution. Explain why.
    2. Of a 0.50 M HNO3 solution and a 0.50 M HC2H3O2 solution, which should have the higher boiling point? Explain why.
    3. The reaction of sulfuric acid [H2SO4(aq)] with sodium hydroxide [NaOH(aq)] can be represented by two separate steps, with only one hydrogen ion reacting in each step. Write the chemical equation for each step.
    4. The reaction of aluminum hydroxide [Al(OH)3(aq)] with hydrochloric acid [HCl(aq)] can be represented by three separate steps, with only one hydroxide ion reacting in each step. Write the chemical equation for each step.
    5. A friend brings you a small sample of an unknown chemical. Assuming that the chemical is soluble in water, how would you determine if the chemical is an acid or a base?
    6. A neutral solution has a hydrogen ion concentration of about 1 × 10−7 M. What is the concentration of the hydroxide ion in a neutral solution?
    7. The Lewis definitions of an acid and a base are based on electron pairs, not protons. A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor. Use Lewis diagrams to show that

      H+(aq) + OH−(aq) → H2O(ℓ)

      is an acid-base reaction in the Lewis sense as well as in the Arrhenius and Brønsted-Lowry senses.

    8. Given the chemical reaction

      NH3(g) + BF3(g) → NH3—BF3(s)

      show that the reaction illustrated by this equation is an acid-base reaction if we use the Lewis definitions of an acid and a base (see Exercise 7). The product contains a bond between the N and B atoms.

    Answers

    1. HCl is a strong acid and yields more ions in solution. HC2H3O2 is a weak acid and undergoes partial ionization in solution.
    2. HNO3 is a strong acid while HC2H3O2 is a weak acid. HNO3 dissociates 100% and its solution contains more ions.  The more ions the solution contains the lower is its vapor pressure; the higher temperature is required for it to boil.
    3. H2SO4 + NaOH → NaHSO4 + H2O; NaHSO4 + NaOH → Na2SO4 + H2O
    4. Al(OH)3 + HCl  → Al(OH)2Cl + H2O; Al(OH)2Cl + HCl → Al(OH)Cl2 + H2O; Al(OH)Cl2 + HCl → AlCl3 + H2O
    5. One way is to add it to NaHCO3; if it bubbles, it is an acid. Alternatively, add the sample to litmus and look for a characteristic color change (red for acid, blue for base).
    6. In a neutral solution, [OH-] = [H+] = 1.0 x 10-7 M
    7. The O atom is donating an electron pair to the H+ ion, making the base an electron pair donor and the acid an electron pair acceptor.
    8. The N atom is donating a lone pair to B in BF3,  Hence NH3 is the Lewis base and BF3 is the Lewis acid.

     

    10.E: Acids and Bases (Exercises) is shared under a CC BY-SA license and was authored, remixed, and/or curated by LibreTexts.

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