## 1,001 Chemistry Practice Problems For Dummies (2014)

### Part I. The Questions

### Chapter 14. Acids and Bases

Simply knowing the concentration of an acid or base is often insufficient to understand its actions. The pH relates to the concentration of hydrogen ions in a solution, and the pOH relates to the concentration of the hydroxide ions in the solution. Acids and bases may be strong or weak. There are only a few strong acids and bases, and calculations involving them are always simpler than calculations involving weak acids or bases. A buffer solution provides a means to control the pH of a solution.

*The Problems You’ll Work On*

In this chapter, you work with acids and bases in the following ways:

Describing acids and bases

Identifying conjugate acids and conjugate bases

Determining pH and pOH for strong and weak acid or base solutions

Doing stoichiometry of titrations

Completing buffer problems

** Note: **See the Appendix if you need to check the periodic table.

*What to Watch Out For*

Remember the following when working on acids and bases:

Know the strong acids and strong bases.

Dimensional analysis helps in calculating the concentration.

Use the stoichiometry when doing calculations.

At the equivalence point, the concentrations of the reactants are zero (other than through hydrolysis).

Calculations involving weak acids or bases always involve an equilibrium constant, *K*_{a} or *K*_{b}. Strong acids and bases do not have *K*’s.

Either a *K* or the Henderson-Hasselbalch equation works for a buffer solution.

Concentrations have units; pH and *K*’s do not.

There’s only one way to write a *K*_{a}* *or a *K*_{b} expression; any variation is wrong.

*Identifying Acids and Bases*

*912–917** Identify acids and bases.*

** 912. **Which member of the following set is a strong acid?

HNO_{2}, HNO_{3}, NH_{3}, KOH, CH_{3}OH

** 913. **Which member of the following set is a strong base?

HNO_{2}, HNO_{3}, NH_{3}, KOH, CH_{3}OH

** 914. **Which member of the following set is a weak acid?

HNO_{2}, HNO_{3}, NH_{3}, KOH, CH_{3}OH

** 915. **Which member of the following set is a weak base?

HNO_{2}, HNO_{3}, NH_{3}, KOH, CH_{3}OH

** 916. **Which member of the following set is neither an acid nor a base?

HNO_{2}, HNO_{3}, NH_{3}, KOH, CH_{3}OH

** 917. **Which member of the following set is a weak base?

HNO_{2}, HNO_{3}, CH_{3}NH_{2}, CsOH, C_{2}H_{5}OH

*Conjugate Acids and Bases*

*918–924** Identify conjugate acids and conjugate bases.*

** 918. **What is the conjugate base of HCl?

** 919. **What is the conjugate acid of ?

** 920. **What is the conjugate acid of NH

_{3}?

** 921. **What is the conjugate base of NH

_{3}?

** 922. **What is the conjugate base of H

_{3}PO

_{4}?

** 923. **What is the conjugate acid of H

_{2}SO

_{4}?

** 924. **Which of the following substances may serve both as a conjugate acid and as a conjugate base?

Cl^{–}, HPO_{4}^{2–}, Fe^{3+}, AsO_{4}^{3–}, Mg^{2+}

*Finding pH and pOH of Strong Acids and Bases*

*925–932** Determine the pH or pOH of a strong acid or base solution.*

** 925. **What is the pH of a 0.01-M HNO

_{3}solution?

** 926. **What is the pOH of a 0.001-M KOH solution?

** 927. **What is the pH of a 0.015-M NaOH solution?

** 928. **What is the pOH of a 0.0025-M HCl solution?

** 929. **What is the pH of a 0.003-M Ba(OH)

_{2}solution?

** 930. **What is the pH of a 1.0 × 10

^{–3}M Sr(OH)

_{2}solution?

** 931. **What is the pH of a 1.0-M HBr solution?

** 932. **What is the pH of a 15-M NaOH solution?

*Finding pH and pOH of Weak Acids and Bases*

*933–947** Determine the pH or pOH of the weak acid or weak base solution.*

** 933. **What is the pH of a 1.0-M acetic acid (HC

_{2}H

_{3}O

_{2}) solution?

*K*

_{a}= 1.7 × 10

^{–5}.

** 934. **What is the pH of a 1.0-M nitrous acid (HNO

_{2}) solution?

*K*

_{a}

*= 5.0 × 10*

^{–4}.

** 935. **What is the pOH of a 1.0-M ammonia (NH

_{3}) solution?

*K*

_{b}= 1.8 × 10

^{–5}.

** 936. **What is the pH of a 0.100-M hydrocyanic acid (HCN) solution?

*K*

_{a}

*= 6.2 × 10*

^{–10}.

** 937. **What is the pH of a 0.20-M acetic acid (HC

_{2}H

_{3}O

_{2}) solution?

*K*

_{a}

*= 1.7 × 10*

^{–5}.

** 938. **What is the pH of a 0.0015-M periodic acid (HIO

_{4}) solution?

*K*

_{a}

*= 2.8 × 10*

^{–2}.

** 939. **What is the pH of a 0.0025-M chlorous acid (HClO

_{2}) solution?

*K*

_{a}

*= 1.1 × 10*

^{–2}.

** 940. **What is the pOH of a 1.0-M pyridine (C

_{5}H

_{5}N) solution?

*K*

_{b}= 1.7 × 10

^{–9}.

** 941. **What is the pH of a 0.15-M ammonia (NH

_{3}) solution?

*K*

_{b}= 1.8 × 10

^{–5}.

** 942. **What is the pH of a 2.5-M methylamine (CH

_{3}NH

_{2}) solution?

*K*

_{b}

*= 5.2 × 10*

^{–4}.

** 943. **What is the pH of a 0.20-M chlorous acid (HClO

_{2}) solution?

*K*

_{a}= 1.1 × 10

^{–2}.

** 944. **What is the pH of a 0.015-M cyanic acid (HOCN) solution? p

*K*

_{a}= 3.46.

** 945. **What is the pOH of a 1.0-M methylamine (CH

_{3}NH

_{2}), solution? p

*K*

_{b}= 3.28.

** 946. **What is the pH of a 0.25-M sodium hydrogen sulfate (NaHSO

_{4}) solution? The

*K*

_{a}

*of is 1.1 × 10*

^{–2}.

** 947. **What is the pH of a 0.50-M calcium acetate (Ca(C

_{2}H

_{3}O

_{2})

_{2}) solution? The

*K*

_{a}

*of HC*

_{2}H

_{3}O

_{2}is 1.7 × 10

^{–5}.

*Stoichiometry of Titrations*

*948–959** Answer the questions on the stoichiometry of titrations.*

** 948. **How many moles of hydrochloric acid (HCl) will react with 25.00 mL of 0.1000-M sodium hydroxide (NaOH) solution?

The reaction is

** 949. **What is the molarity of a hypochlorous acid (HClO) solution if 25.00 mL of this solution reacts completely with 35.42 mL of a 0.1250-M potassium hydroxide (KOH) solution?

The reaction is

** 950. **What is the molarity of a chlorous acid (HClO

_{2}) solution if 25.00 mL of this solution reacts completely with 39.32 mL of a 0.1350-M sodium hydroxide (NaOH) solution?

The reaction is

** 951. **How many moles of lithium hydroxide, LiOH, will react with 25.00 mL of 0.2500-M sulfuric acid (H

_{2}SO

_{4}) solution?

The reaction is

** 952. **What is the molarity of a calcium hydroxide (Ca(OH)

_{2}) solution if 25.00 mL of this solution reacts completely with 37.24 mL of a 0.1275-M nitric acid (HNO

_{3}) solution?

The reaction is

** 953. **What is the molarity of strontium hydroxide (Sr(OH)

_{2}) solution if 25.00 mL of the solution reacts with 39.26 mL of a 0.2500-M phosphoric acid (H

_{3}PO

_{4}) solution?

The reaction is

** 954. **How many moles of nitrous acid (HNO

_{2}) will react with 35.00 mL of 0.1000-M potassium hydroxide (KOH)?

** 955. **What is the molarity of a rubidium hydroxide (RbOH) solution if 25.00 mL of this solution reacts completely with 43.29 mL of a 0.1235-M sulfuric acid (H

_{2}SO

_{4}) solution?

** 956. **What is the molarity of a phosphoric acid (H

_{3}PO

_{4}) solution if 100.0 mL of this solution titrates with 27.98 mL of a 0.1000-M calcium hydroxide (Ca(OH)

_{2}) solution?

** 957. **What is the molarity of an ammonia (NH

_{3}) solution if 50.00 mL of the solution reacts with 47.98 mL of a 0.3215-M sulfuric acid (H

_{2}SO

_{4}) solution?

** 958. **How many grams of acetic acid (HC

_{2}H

_{3}O

_{2}) are in a vinegar sample if the sample requires 39.95 mL of 0.09527-M sodium hydroxide (NaOH) to reach the endpoint of a titration? The molar mass of acetic acid is 60.52 g/mol.

** 959. **How many grams of ammonia (NH

_{3}) are in a sample of household cleaner if the sample requires 37.86 mL of 0.08271-M hydrochloric acid (HCl) to reach the endpoint of a titration? The molar mass of ammonia is 17.031 g/mol.

*Buffer Solutions*

*960–970** The following questions deal with buffer solutions.*

** 960. **Which of the following compounds would create a buffer when added to a sodium nitrite (NaNO

_{2}) solution?

CH_{3}OH, KNO_{2}, NaOH, HNO_{2}, or KCl

** 961. **Which of the following compounds would create a buffer when added to an ammonia (NH

_{3}) solution?

CH_{3}OH, (NH_{4})_{2}SO_{4}, NaOH, CH_{3}NH_{2}, or KCl

** 962. **Which of the following compounds would create a buffer when added to a sodium carbonate (Na

_{2}CO

_{3}) solution?

CH_{3}OH, KHCO_{3}, NaOH, CaCO_{3}, or NaCl

** 963. **What is the pH of a buffer solution that is 0.75 M in acetic acid (HC

_{2}H

_{3}O

_{2}) and 0.50 M in sodium acetate? The p

*K*

_{a}

*of acetic acid is 4.76.*

** 964. **What is the pOH of a buffer solution that is 0.25 M in ammonia (NH

_{3}) and 0.35 M in ammonium chloride (NH

_{4}Cl)? The p

*K*

_{b}of ammonia is 4.75.

** 965. **What is the pH of a buffer solution that is 0.25 M in hydrofluoric acid (HF) and 0.35 M in sodium fluoride (NaF)? The p

*K*

_{a}of hydrofluoric acid is 3.17.

** 966. **What is the pOH of a buffer solution that is 0.75 M in methylamine (CH

_{3}NH

_{2}) and 0.50 M in methylammonium chloride (CH

_{3}NH

_{3}Cl)? The p

*K*

_{b}of methylamine is 3.28.

** 967. **What is the pH of a buffer solution that is 0.35 M in ammonia (NH

_{3}) and 0.25 M in ammonium chloride (NH

_{4}Cl)? The p

*K*

_{b}of ammonia is 4.75.

** 968. **What is the pH of a buffer solution that is 0.50 M in methylamine (CH

_{3}NH

_{2}) and 0.25 M in methylammonium chloride (CH

_{3}NH

_{3}Cl)? The p

*K*

_{b}

*of methylamine is 3.28.*

** 969. **What is the pH of a buffer solution formed by mixing 1.00 mol of hydrofluoric acid (HF) with 0.25 mol of sodium hydroxide (NaOH) in enough water to make a liter of solution? The p

*K*

_{a}of hydrofluoric acid is 3.17.

** 970. **What is the pH of a buffer solution formed by mixing 0.75 mol of ammonia (NH

_{3}) and 0.25 mol of hydrochloric acid (HCl) in enough water to make a liter of solution? The p

*K*

_{b}of ammonia is 4.75.

*Titrations and pH Changes*

*971–980** Answer the questions on pH changes during titrations.*

** 971. **A student prepares to do a titration by adding 0.1000-M sodium hydroxide (NaOH) to 25.00 mL of a 0.08750-M acetic acid (HC

_{2}H

_{3}O

_{2}) solution. What was the initial pH of the acetic acid solution? The p

*K*

_{a}of acetic acid is 4.76, and the reaction is

** 972. **A student prepares to do a titration by adding 0.1000-M hydrochloric acid (HCl) to 25.00 mL of a 0.08750-M ammonia (NH

_{3}) solution. What was the initial pH of the ammonia solution? The p

*K*

_{b}of ammonia is 4.75, and the reaction is

** 973. **What is the pH at the equivalence point for the titration of 50.00 mL of a 0.5000-M sodium hydroxide (NaOH) solution with 0.7500-M hydrochloric acid (HCl)? The reaction is

** 974. **A student prepares to do a titration by adding 0.05000-M barium hydroxide (Ba(OH)

_{2}) to 25.00 mL of a 0.08800-M acetic acid (HC

_{2}H

_{3}O

_{2}) solution. What was the pH of the solution after he added 11.00 mL of base? The p

*K*

_{a}

*of acetic acid is 4.76, and the reaction is*

** 975. **A student prepares to do a titration by adding 0.05000-M sulfuric acid (H

_{2}SO

_{4}) to 25.00 mL of a 0.08800-M ammonia (NH

_{3}) solution. What was the pH of the solution after she added 11.00 mL acid? The p

*K*

_{b}

*of ammonia is 4.75, and the reaction is as follows. Ignore hydrolysis of the sulfate ion.*

** 976. **A student prepares to do a titration by adding 0.05000-M barium hydroxide (Ba(OH)

_{2}) to 25.00 mL of a 0.08800-M acetic acid (HC

_{2}H

_{3}O

_{2}) solution. What was the pH of the solution after she added 20.00 mL of base? The p

*K*

_{a}of acetic acid is 4.76, and the reaction is

** 977. **A student prepares to do a titration by adding 0.05000-M sulfuric acid (H

_{2}SO

_{4}) to 25.00 mL of a 0.08800-M ammonia (NH

_{3}) solution. What is the pH of the solution after he adds 17.00 mL of acid? The p

*K*

_{b}

*of ammonia is 4.75, and the reaction is as follows. Ignore hydrolysis of the sulfate ion.*

** 978. **A student prepares to do a titration by adding 0.05000-M barium hydroxide (Ba(OH)

_{2}) to 25.00 mL of a 0.08800-M acetic acid (HC

_{2}H

_{3}O

_{2}) solution. What was the pH of the solution at the equivalence point? The p

*K*

_{a}

*of acetic acid is 4.76.*

** 979. **A student prepares to do a titration by adding 0.4800-M barium hydroxide (Ba(OH)

_{2}) to 25.00 mL of a 0.7600-M acetic acid (HC

_{2}H

_{3}O

_{2}) solution. What was the pH of the solution at the equivalence point? The p

*K*

_{a}of acetic acid is 4.76.

** 980. **A student prepares to do a titration by adding 0.06000-M sulfuric acid (H

_{2}SO

_{4}) to 25.00 mL of a 0.09800-M ammonia (NH

_{3}) solution. What was the pH of the solution at the equivalence point? The p

*K*

_{b}of ammonia is 4.75. Ignore hydrolysis of the sulfate ion.