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

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 1–30 of 65.

Under the Bronsted and Lowry definition, what makes a compound an acid?Read the answer and worked solution →What is left behind when a Bronsted and Lowry acid gives up its proton?Read the answer and worked solution →What name is given to a reaction in which one molecule ionises by reacting with another of its own kind?Read the answer and worked solution →What is the value of the ion product constant for water at 25 degrees Celsius?Read the answer and worked solution →What are the hydronium and hydroxide concentrations in pure water at 25 degrees Celsius?Read the answer and worked solution →The ion product of water at 80 degrees Celsius is 2.4 x 10^-13. What is the hydronium concentration in pure water there?Read the answer and worked solution →A solution at 25 C has a hydronium concentration of 2.0 x 10^-6 M. What is its hydroxide concentration?Read the answer and worked solution →What word describes a species that can either gain or lose a proton?Read the answer and worked solution →The hydrogen sulfite ion reacts with hydroxide ion. Which products form?Read the answer and worked solution →How is the hydronium ion molarity recovered once the pH of a solution is known?Read the answer and worked solution →Pure water at 80 degrees Celsius has pH 6.31. Is it acidic there?Read the answer and worked solution →Stomach acid has a hydronium ion concentration of 1.2 x 10^-3 M. What is its pH?Read the answer and worked solution →Blood has a pH of 7.3. What is its hydronium ion concentration?Read the answer and worked solution →Air saturated water has a hydronium concentration of 2.0 x 10^-6 M from dissolved carbon dioxide. What is its pH?Read the answer and worked solution →What are the pOH and pH of a 0.0125 M solution of potassium hydroxide at 25 degrees Celsius?Read the answer and worked solution →What pH marks rainwater as acid rain rather than as normal rain?Read the answer and worked solution →Which set lists six common strong acids?Read the answer and worked solution →Which set lists six common strong bases?Read the answer and worked solution →How does the acid ionisation constant of an acid relate to its strength?Read the answer and worked solution →How does the percent ionisation of a given weak acid change as its solution is made more concentrated?Read the answer and worked solution →A 0.125 M solution of nitrous acid has pH 2.09. What is its percent ionisation?Read the answer and worked solution →What is the product of Ka for an acid and Kb for its conjugate base?Read the answer and worked solution →The nitrite ion has Kb = 2.17 x 10^-11. What is Ka for nitrous acid, its conjugate acid?Read the answer and worked solution →At equilibrium an acetic acid solution has 0.0787 M acid and 0.00118 M each of hydronium and acetate. What is Ka?Read the answer and worked solution →Caffeine at equilibrium is 0.050 M with 5.0 x 10^-3 M conjugate acid and 2.5 x 10^-3 M hydroxide. What is Kb?Read the answer and worked solution →A 0.0516 M solution of nitrous acid has pH 2.34. What is Ka for the acid?Read the answer and worked solution →Formic acid has Ka = 1.8 x 10^-4. What is the pH of a 0.534 M solution?Read the answer and worked solution →Trimethylamine has Kb = 6.3 x 10^-5. What is the pH of a 0.25 M solution of it?Read the answer and worked solution →Hydrogen chloride, bromide and iodide all appear equally strong in water. What is this effect called?Read the answer and worked solution →Down group 17 the acids run HF, HCl, HBr, HI. Which trend in acid strength is seen and why?Read the answer and worked solution →

Worked practice questions

Under the Bronsted and Lowry definition, what makes a compound an acid?

  1. It releases a hydroxide ion into the water
  2. It accepts a proton from another compound
  3. It donates a proton to another compound
  4. It accepts an electron pair from a partner
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Correct answer: C. It donates a proton to another compound

1. This definition centres on the proton, which is a hydrogen ion. 2. The compound that hands a proton over is the acid, the proton donor. 3. The compound that takes the proton up is the base, the proton acceptor. 4. Releasing hydroxide is the older Arrhenius picture of a base, not this one. 5. Accepting an electron pair belongs to the more general model introduced later. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.1 Brønsted-Lowry Acids and Bases_

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What is left behind when a Bronsted and Lowry acid gives up its proton?

  1. Its conjugate acid, able to accept a proton
  2. A neutral salt with no acid or base behaviour
  3. Its conjugate acid, able to donate a proton
  4. Its conjugate base, able to accept a proton
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Correct answer: D. Its conjugate base, able to accept a proton

1. An acid is defined by the fact that it can hand over a proton. 2. What remains once the proton has gone is called the conjugate base of that acid. 3. It counts as a base because it can take the proton back and re-form the acid. 4. A conjugate acid is what forms when a base gains a proton, which is the mirror case. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.1 Brønsted-Lowry Acids and Bases_

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What name is given to a reaction in which one molecule ionises by reacting with another of its own kind?

  1. Neutralisation of the two molecules
  2. Hydrolysis of one of the molecules
  3. Autoionisation of that substance
  4. Disproportionation of the species
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Correct answer: C. Autoionisation of that substance

1. In pure water a few molecules pass protons to other water molecules. 2. The products are the hydronium ion and the hydroxide ion. 3. A reaction between two molecules of the same substance that yields ions is autoionisation. 4. Neutralisation needs a separate acid and base, so it does not describe this case. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.1 Brønsted-Lowry Acids and Bases_

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