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:

check Describing acids and bases

check Identifying conjugate acids and conjugate bases

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

check Doing stoichiometry of titrations

check 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:

check Know the strong acids and strong bases.

check Dimensional analysis helps in calculating the concentration.

check Use the stoichiometry when doing calculations.

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

check Calculations involving weak acids or bases always involve an equilibrium constant, Ka or Kb. Strong acids and bases do not have K’s.

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

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

check There’s only one way to write a Ka or a Kb 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?

HNO2, HNO3, NH3, KOH, CH3OH

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

HNO2, HNO3, NH3, KOH, CH3OH

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

HNO2, HNO3, NH3, KOH, CH3OH

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

HNO2, HNO3, NH3, KOH, CH3OH

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

HNO2, HNO3, NH3, KOH, CH3OH

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

HNO2, HNO3, CH3NH2, CsOH, C2H5OH

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 9781118549322-eq14001.eps?

920. What is the conjugate acid of NH3?

921. What is the conjugate base of NH3?

922. What is the conjugate base of H3PO4?

923. What is the conjugate acid of H2SO4?

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

Cl, HPO42–, Fe3+, AsO43–, Mg2+

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 HNO3 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 (HC2H3O2) solution? Ka = 1.7 × 10–5.

934. What is the pH of a 1.0-M nitrous acid (HNO2) solution? Ka = 5.0 × 10–4.

935. What is the pOH of a 1.0-M ammonia (NH3) solution? Kb = 1.8 × 10–5.

936. What is the pH of a 0.100-M hydrocyanic acid (HCN) solution? Ka = 6.2 × 10–10.

937. What is the pH of a 0.20-M acetic acid (HC2H3O2) solution? Ka = 1.7 × 10–5.

938. What is the pH of a 0.0015-M periodic acid (HIO4) solution? Ka = 2.8 × 10–2.

939. What is the pH of a 0.0025-M chlorous acid (HClO2) solution? Ka = 1.1 × 10–2.

940. What is the pOH of a 1.0-M pyridine (C5H5N) solution? Kb = 1.7 × 10–9.

941. What is the pH of a 0.15-M ammonia (NH3) solution? Kb = 1.8 × 10–5.

942. What is the pH of a 2.5-M methylamine (CH3NH2) solution? Kb = 5.2 × 10–4.

943. What is the pH of a 0.20-M chlorous acid (HClO2) solution? Ka = 1.1 × 10–2.

944. What is the pH of a 0.015-M cyanic acid (HOCN) solution? pKa = 3.46.

945. What is the pOH of a 1.0-M methylamine (CH3NH2), solution? pKb = 3.28.

946. What is the pH of a 0.25-M sodium hydrogen sulfate (NaHSO4) solution? The Ka of 9781118549322-eq14002.eps is 1.1 × 10–2.

947. What is the pH of a 0.50-M calcium acetate (Ca(C2H3O2)2) solution? The Ka of HC2H3O2 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

9781118549322-eq14003.eps

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

9781118549322-eq14004.eps

950. What is the molarity of a chlorous acid (HClO2) 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

9781118549322-eq14005.eps

951. How many moles of lithium hydroxide, LiOH, will react with 25.00 mL of 0.2500-M sulfuric acid (H2SO4) solution?

The reaction is

9781118549322-eq14006.eps

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 (HNO3) solution?

The reaction is

9781118549322-eq14007.eps

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 (H3PO4) solution?

The reaction is

9781118549322-eq14008.eps

954. How many moles of nitrous acid (HNO2) 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 (H2SO4) solution?

956. What is the molarity of a phosphoric acid (H3PO4) 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 (NH3) solution if 50.00 mL of the solution reacts with 47.98 mL of a 0.3215-M sulfuric acid (H2SO4) solution?

958. How many grams of acetic acid (HC2H3O2) 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 (NH3) 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 (NaNO2) solution?

CH3OH, KNO2, NaOH, HNO2, or KCl

961. Which of the following compounds would create a buffer when added to an ammonia (NH3) solution?

CH3OH, (NH4)2SO4, NaOH, CH3NH2, or KCl

962. Which of the following compounds would create a buffer when added to a sodium ­carbonate (Na2CO3) solution?

CH3OH, KHCO3, NaOH, CaCO3, or NaCl

963. What is the pH of a buffer solution that is 0.75 M in acetic acid (HC2H3O2) and 0.50 M in sodium acetate? The pKa of acetic acid is 4.76.

964. What is the pOH of a buffer solution that is 0.25 M in ammonia (NH3) and 0.35 M in ammonium chloride (NH4Cl)? The pKb 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 pKa of hydrofluoric acid is 3.17.

966. What is the pOH of a buffer solution that is 0.75 M in methylamine (CH3NH2) and 0.50 M in methylammonium chloride (CH3NH3Cl)? The pKb of methylamine is 3.28.

967. What is the pH of a buffer solution that is 0.35 M in ammonia (NH3) and 0.25 M in ammonium chloride (NH4Cl)? The pKb of ammonia is 4.75.

968. What is the pH of a buffer solution that is 0.50 M in methylamine (CH3NH2) and 0.25 M in methylammonium chloride (CH3NH3Cl)? The pKb 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 pKa of hydrofluoric acid is 3.17.

970. What is the pH of a buffer solution formed by mixing 0.75 mol of ammonia (NH3) and 0.25 mol of hydrochloric acid (HCl) in enough water to make a liter of solution? The pKb 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 (HC2H3O2) solution. What was the initial pH of the acetic acid solution? The pKa of acetic acid is 4.76, and the reaction is

9781118549322-eq14009.eps

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 (NH3) solution. What was the initial pH of the ammonia solution? The pKb of ammonia is 4.75, and the reaction is

9781118549322-eq14010.eps

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

9781118549322-eq14011.eps

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 (HC2H3O2) solution. What was the pH of the solution after he added 11.00 mL of base? The pKa of acetic acid is 4.76, and the reaction is

9781118549322-eq14012.eps

975. A student prepares to do a titration by adding 0.05000-M sulfuric acid (H2SO4) to 25.00 mL of a 0.08800-M ammonia (NH3) solution. What was the pH of the solution after she added 11.00 mL acid? The pKb of ammonia is 4.75, and the reaction is as follows. Ignore hydrolysis of the sulfate ion.

9781118549322-eq14013.eps

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 (HC2H3O2) solution. What was the pH of the solution after she added 20.00 mL of base? The pKaof acetic acid is 4.76, and the reaction is

9781118549322-eq14014.eps

977. A student prepares to do a titration by adding 0.05000-M sulfuric acid (H2SO4) to 25.00 mL of a 0.08800-M ammonia (NH3) solution. What is the pH of the solution after he adds 17.00 mL of acid? The pKb of ammonia is 4.75, and the reaction is as follows. Ignore hydrolysis of the sulfate ion.

9781118549322-eq14015.eps

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 (HC2H3O2) solution. What was the pH of the solution at the equivalence point? The pKa 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 (HC2H3O2) solution. What was the pH of the solution at the equivalence point? The pKa of acetic acid is 4.76.

980. A student prepares to do a titration by adding 0.06000-M sulfuric acid (H2SO4) to 25.00 mL of a 0.09800-M ammonia (NH3) solution. What was the pH of the solution at the equivalence point? The pKb of ammonia is 4.75. Ignore hydrolysis of the sulfate ion.