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GCE A-Level (Singapore) Acid-Base Equilibria — practice questions — page 2

Explore 65 free Acid-Base Equilibria questions in GCE A-Level (Singapore) Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Acid-Base Equilibria questions and exercises with answers

Showing questions 31–60 of 65.

Equal amounts of a weak acid and a strong base are mixed. What is the resulting solution like?Read the answer and worked solution →Roughly what concentration of hydrochloric acid does the stomach hold to help digestion?Read the answer and worked solution →Which side effect is linked to a magnesium hydroxide antacid rather than an aluminium hydroxide one?Read the answer and worked solution →Handbooks list Kb for ammonia as 1.8 x 10^-5 but no Ka for ammonium. How is the missing value found?Read the answer and worked solution →Aniline has Kb = 4.3 x 10^-10. What is the pH of a 0.233 M solution of aniline hydrochloride?Read the answer and worked solution →Sodium acetate is dissolved in water. What does the acetate ion do?Read the answer and worked solution →Acetic acid has Ka = 1.8 x 10^-5. What is Kb for the acetate ion at 25 degrees Celsius?Read the answer and worked solution →A solution has 0.050 M acetate and 2.5 x 10^-6 M hydroxide, with Kb = 5.6 x 10^-10. What is the acetic acid concentration?Read the answer and worked solution →Why is an aqueous solution of potassium bromide neutral?Read the answer and worked solution →Why do solutions of many metal salts turn out acidic?Read the answer and worked solution →The hydrated aluminium ion has Ka = 1.4 x 10^-5. What is the pH of 0.10 M aluminium chloride?Read the answer and worked solution →How does the acidity of a hydrated metal ion depend on the ion itself?Read the answer and worked solution →Which hydrated metal ions do not give acidic solutions in water?Read the answer and worked solution →For a diprotic acid, how do the two ionisation steps compare?Read the answer and worked solution →A saturated solution has 0.033 M carbonic acid with Ka1 = 4.3 x 10^-7. What is the hydronium concentration?Read the answer and worked solution →Why is the carbonate ion described as a diprotic base?Read the answer and worked solution →What mixture makes up a buffer solution?Read the answer and worked solution →An acetate buffer is 0.10 M in acetic acid and 0.10 M in sodium acetate, with Ka = 1.8 x 10^-5. What is its pH?Read the answer and worked solution →A buffer is needed to hold a solution at pH 9.5. Which pair should be chosen?Read the answer and worked solution →Which expression is the Henderson and Hasselbalch equation?Read the answer and worked solution →Which pair is chiefly responsible for buffering human blood?Read the answer and worked solution →How large a shift in blood pH is described as likely to be fatal?Read the answer and worked solution →Who introduced the pH scale, and in which year?Read the answer and worked solution →What is the equivalence point of a titration?Read the answer and worked solution →At what pH does the equivalence point fall when a strong acid is titrated with a strong base?Read the answer and worked solution →12.50 mL of 0.100 M NaOH is added to 25.00 mL of 0.100 M HCl. What is the pH?Read the answer and worked solution →37.50 mL of 0.100 M NaOH is added to 25.00 mL of 0.100 M HCl. What is the pH now?Read the answer and worked solution →What is the pH of 0.100 M acetic acid before any base is added, given Ka = 1.8 x 10^-5?Read the answer and worked solution →Half the base needed for equivalence has been added to a weak acid. What is the pH of the mixture?Read the answer and worked solution →What colour is phenolphthalein in a solution of pH below 8.3?Read the answer and worked solution →

Worked practice questions

Equal amounts of a weak acid and a strong base are mixed. What is the resulting solution like?

  1. Weakly acidic, from the cation left behind
  2. Weakly basic, from the anion left behind
  3. Exactly neutral, since both are used up
  4. Strongly acidic, from the leftover acid
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Correct answer: B. Weakly basic, from the anion left behind

1. The cation here is the conjugate acid of a strong base, which has no measurable acidity. 2. The anion is the conjugate base of a weak acid, so it is itself a weak base. 3. That anion takes protons from water and raises the hydroxide concentration. 4. The solution is therefore weakly basic even though the amounts were stoichiometric. 5. Sodium acetate from acetic acid and sodium hydroxide is the standard example. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.4 Hydrolysis of Salt Solutions_

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Roughly what concentration of hydrochloric acid does the stomach hold to help digestion?

  1. About 0.03 M
  2. About 0.30 M
  3. About 3.0 M
  4. About 0.003 M
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Correct answer: A. About 0.03 M

1. The stomach lining secretes hydrochloric acid to help break down food. 2. The working concentration is roughly 0.03 mol per litre. 3. Heartburn happens when some of this acid leaks up into the unprotected oesophagus. 4. An antacid is a base taken to neutralise that excess acid. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.4 Hydrolysis of Salt Solutions_

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Which side effect is linked to a magnesium hydroxide antacid rather than an aluminium hydroxide one?

  1. It tends to cause constipation instead
  2. It can act as a laxative on the user
  3. It releases carbon dioxide as it works
  4. It leaves a strongly basic stomach behind
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Correct answer: B. It can act as a laxative on the user

1. Magnesium hydroxide is a sparingly soluble base that supplies hydroxide ions. 2. Those ions react with stomach hydronium ions to form water, so no gas is released. 3. Antacids containing magnesium can have a laxative effect on the user. 4. Aluminium hydroxide has the opposite tendency and can cause constipation. 5. Some products combine the two so that the side effects offset one another. 6. Carbon dioxide comes from carbonate antacids such as calcium carbonate instead. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.4 Hydrolysis of Salt Solutions_

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