WAEC 2017 Chemistry · Question 3

Which of the following statements is NOT a chemical property of an acid?

Options

A.Evolution of ammonia when heated with ammonium salts
B.Evolution of carbon dioxide gas when added to a trioxocarbonate (IV) salt
C.Formation of salt and water with alkalis
D.Formation of salt and hydrogen gas with reactive metals

Answer: A. Evolution of ammonia when heated with ammonium salts

Explanation written with AI and checked against the answer key

Analyze the question: We need the statement that is NOT a chemical property of acids. Three options describe typical acid reactions, and one describes something else.

Concept: Typical chemical reactions of acids:

Acid + reactive metal → salt + hydrogen gas
Acid + base/alkali → salt + water (neutralization)
Acid + carbonate/hydrogen carbonate → salt + water + carbon dioxide

Checking each option:

A. Evolution of ammonia when heated with ammonium salts. This is a property of alkalis (bases), not acids. When an ammonium salt is heated with an alkali such as NaOH, ammonia is released: NH₄Cl + NaOH → NaCl + H₂O + NH₃↑ This is the standard test for ammonium ions. Acids do not do this, so it is not an acid property.

B. Evolution of CO₂ with a trioxocarbonate(IV) salt. This is an acid property: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑

C. Salt and water with alkalis. This is neutralization, which is an acid property: HCl + NaOH → NaCl + H₂O

D. Salt and hydrogen with reactive metals. This is an acid property: Zn + 2HCl → ZnCl₂ + H₂↑

Answer: The statement that is NOT a chemical property of an acid is A.

Exam tip: Remember that ammonia is a basic gas. Anything about releasing NH₃ points to an alkali reacting with an ammonium salt, not to an acid. For "acid properties" questions, think of the three reactions: metals, bases and carbonates.

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