WAEC 2011 Chemistry · Question 21

Which of the following processes does not involve the use of limestone?

Options

A.Extraction of iron in the blast furnance
B.Manufacture of tetraoxosulphate (VI) acid by Contact process
C.Production of washing soda by Solvay process
D.Production of cement

Answer: B. Manufacture of tetraoxosulphate (VI) acid by Contact process

Explanation written with AI and checked against the answer key

Analyze the question: We need the process where limestone (calcium carbonate, CaCO₃) is NOT used.

Concept: Limestone is used as a raw material or flux in several industries. Let's check each option.

Checking each option:

A. Extraction of iron in the blast furnace: Limestone decomposes to CaO, which combines with silica impurities to form slag: CaCO₃ → CaO + CO₂ CaO + SiO₂ → CaSiO₃ (slag) So limestone is used.

B. Contact process for H₂SO₄: The raw materials are sulphur (or sulphur-containing ores), air, and water. S → SO₂ → SO₃ (with V₂O₅ catalyst) → oleum (H₂S₂O₇) → H₂SO₄. No limestone is involved, so limestone is not used.

C. Solvay process for washing soda (Na₂CO₃): Limestone is heated to give CO₂ and CaO. The CO₂ reacts with brine and ammonia, and the CaO is used to recover the ammonia. So limestone is used.

D. Cement production: Limestone (a source of calcium) is heated with clay or shale. So limestone is used.

Answer: The Contact process is the only one that does not use limestone, so the answer is B.

Tip: Link limestone with the "3 Cs": Cement, Carbonate (Solvay), and Cast iron (blast furnace). The Contact process is about sulphur, air, and a V₂O₅ catalyst, so there is no calcium carbonate involved.

AI can make mistakes. Report anything that looks wrong.