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10.E: Acids and Bases (Exercises)

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    1. Give two examples of Arrhenius acids.

    2. Give two examples of Arrhenius bases.

    3. List the general properties of acids.

    4. List the general properties of bases.

    5. 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)
    6. Name each compound.

      1. HI(aq)
      2. Cu(OH)2(aq)
      3. H3PO4(aq)
      4. CsOH(aq)
    7. Write a balanced chemical equation for the neutralization of Ba(OH)2(aq) with HNO3(aq).

    8. Write a balanced chemical equation for the neutralization of H2SO4(aq) with Cr(OH)3(aq).

    9. How many moles of sodium hydroxide (NaOH) are needed to neutralize 0.844 mol of acetic acid (HC2H3O2)? (Hint: begin by writing a balanced chemical equation for the process.)

    10. How many moles of perchloric acid (HClO4) are needed to neutralize 0.052 mol of calcium hydroxide [Ca(OH)2]? (Hint: begin by writing a balanced chemical equation for the process.)

    11. Hydrazoic acid (HN3) can be neutralized by a base.

      1. Write the balanced chemical equation for the reaction between hydrazoic acid and calcium hydroxide.
      2. How many milliliters of 0.0245 M Ca(OH)2 are needed to neutralize 0.564 g of HN3?
    12. Citric acid (H3C6H5O7) has three hydrogen atoms that can form hydrogen ions in solution.

      1. Write the balanced chemical equation for the reaction between citric acid and sodium hydroxide.
      2. If an orange contains 0.0675 g of H3C6H5O7, how many milliliters of 0.00332 M NaOH solution are needed to neutralize the acid?
    13. Magnesium hydroxide [Mg(OH)2] is an ingredient in some antacids. How many grams of Mg(OH)2 are needed to neutralize the acid in 158 mL of 0.106 M HCl(aq)? It might help to write the balanced chemical equation first.

    14. Aluminum hydroxide [Al(OH)3] is an ingredient in some antacids. How many grams of Al(OH)3 are needed to neutralize the acid in 96.5 mL of 0.556 M H2SO4(aq)? It might help to write the balanced chemical equation first.

    Answers

    1. HCl and HNO3 (answers will vary)

     

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

     

    1.  

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

     

    7.  2HNO3(aq) + Ba(OH)2(aq) → Ba(NO3)2(aq) + 2H2O

     

    9.  0.844 mol

     

    11.    Part 1: 2HN3(aq) + Ca(OH)2 → Ca(N3)2 + 2H2O

    11.   Part 2:  268 mL

     

    13.   0.488 g

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

      H2O(ℓ) + N2H4(aq) → N2H5+(aq) + OH(aq)

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

    4. Explain why a Brønsted-Lowry base can be called a proton acceptor.

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

    6. Write the chemical equation of the reaction of methylamine (CH3NH2) in water and label the Brønsted-Lowry acid and base.

    7. 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.

    8. Identify the Brønsted-Lowry acid and base in the following chemical equation:

      C3H7NH2(aq) + H3O+(aq) → C3H7NH3+(aq) + H2O(ℓ)

    9. 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.)

    10. If codeine hydrobromide has the formula C18H22BrNO3, what is the formula of the parent compound codeine?

    Answers

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

     

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

     

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

     

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

     

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

      CH3(aq) + H2O(ℓ) → CH4(aq) + OH(aq)

    3. In the aqueous solutions of some salts, one of the ions from the salt can react with water molecules. In some C2H3O2 solutions, the following reaction can occur:

      C2H3O2(aq) + H2O(ℓ) → HC2H3O2(aq) + OH(aq)

      Is H2O acting as an acid or a base in this reaction?

    4. In the aqueous solutions of some salts, one of the ions from the salt can react with water molecules. In some NH4+ solutions, the following reaction can occur:

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

      Is H2O acting as an acid or a base in this reaction?

    5. Why is pure water considered neutral?

    Answers

    1. base

     

    1. acid

     

    5. 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. Name a strong acid and a weak acid. (Hint: use Table 10.4.1.)

    2. Name a strong base and a weak base. (Hint: use Table 10.4.1.)

    3. Is each compound a strong acid or a weak acid? Assume all are in aqueous solution.  (Hint: use Table 10.4.1.)

      1. HF
      2. HC2H3O2
      3. HCl
      4. HClO4
    4. Is each compound a strong acid or a weak acid? Assume all are in aqueous solution.  (Hint: use Table 10.4.1.)

      1. H2SO4
      2. HSO4
      3. HPO42−
      4. HNO3
    5. Is each compound a strong base or a weak base? Assume all are in aqueous solution. (Hint: use Table 10.4.1.)

      1. NH3
      2. NaOH
      3. Mg(OH)2
      4. Cu(OH)2
    6. Is each compound a strong base or a weak base? Assume all are in aqueous solution. (Hint: use Table 10.4.1.)

      1. KOH
      2. H2O
      3. Fe(OH)2
      4. Fe(OH)3
    7. Write the chemical equation for the equilibrium process for each weak acid in Exercise 3.

    8. Write the chemical equation for the equilibrium process for each weak acid in Exercise 4.

    9. Write the chemical equation for the equilibrium process for each weak base in Exercise 5.

    10. Write the chemical equation for the equilibrium process for each weak base in Exercise 6.

    11. Which is the stronger acid—HCl(aq) or HF(aq)?

    12. Which is the stronger base—KOH(aq) or Ni(OH)2(aq)?

    13. Consider the two acids in Exercise 11. For solutions that have the same concentration, which one would you expect to have a lower pH?

    14. Consider the two bases in Exercise 12. For solutions that have the same concentration, which one would you expect to have a higher pH?

    15. Consider the list of substances in Table \PageIndex3\PageIndex3.2"The pH Values of Some Common Solutions". What is the most acidic substance on the list that you have encountered recently?

    16. Consider the list of substances in Table \PageIndex3\PageIndex3.2"The pH Values of Some Common Solutions". What is the most basic substance on the list that you have encountered recently?

    Answers

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

     

    1.  

      1. weak
      2. weak
      3. strong
      4. strong

     

    1.  

      1. weak
      2. strong
      3. strong
      4. weak

     

    1. 3a: HF(aq) ⇆ H+(aq) + F(aq); 3b: HC2H3O2(aq) ⇆ H+(aq) + C2H3O2(aq)

     

    1. 5a: NH3(aq) + H2O ⇆ NH4+(aq) + OH(aq); 5d: Cu(OH)2(aq) ⇆ Cu2+(aq) + 2OH(aq)

     

    1. HCl(aq)

     

    1. HCl(aq)

     

    1. (answers will vary)

    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. Can a buffer be made by combining a strong acid with a strong base? Why or why not?

    3. 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
    4. Which solute combinations can make a buffer? Assume all are aqueous solutions.

      1. H3PO4 and Na3PO4
      2. NaHCO3 and Na2CO3
      3. NaNO3 and Ca(NO3)2
      4. HN3 and NH3
    5. For each combination in Exercise 3 that is a buffer, write the chemical equations for the reactions of the buffer components when a strong acid and a strong base is added.

    6. For each combination in Exercise 4 that is a buffer, write the chemical equations for the reaction of the buffer components when a strong acid and a strong base is added.

    7. The complete phosphate buffer system is based on four substances: H3PO4, H2PO4, HPO42−, and PO43−. What different buffer solutions can be made from these substances?

    8. Explain why NaBr cannot be a component in either an acidic or a basic buffer.

    9. Explain why Mg(NO3)2 cannot be a component in either an acidic or a basic buffer.

    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.

     

    1.  

      1. not a buffer
      2. buffer
      3. not a buffer
      4. buffer

     

    1. 3b: strong acid: H+ + NO2 → HNO2; strong base: OH + HNO2 → H2O + NO2; 3d: strong acid: H+ + NH3 → NH4+; strong base: OH + NH4+ → H2O + NH3

    1. Buffers can be made by combining H3PO4 and H2PO4, H2PO4 and HPO42−, and HPO42− and PO43−.

    1. Mg(NO3)2 includes two types of ions, Mg2+ and NO3. Mg(OH)2 is strong base and completely dissociates (100% falls apart), so Mg2+ will not react with any added base (0% combines with OH). HNO3 is strong acid and completely dissociates (100% falls apart), so NO3 will not react with any added acid (0% combines with H+). Because Mg(NO3)2 does will not react with any added base or acid, it does not resist change in pH and is not a 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.

     

    1. H2SO4 + NaOH → NaHSO4 + H2O; NaHSO4 + NaOH → Na2SO4 + H2O

     

    1. 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).

     

    1. 7.jpg

      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.