Igcse Model Questions Vol1 2023 Chemistry Question 3

You are given four solid compounds labelled A, B, C and D. Their identities are unknown to you. The compounds are: sodium chloride (NaCl), copper(II) sulphate pentahydrate (CuSO₄·5H₂O), glucose (C₆H₁₂O₆) and ammonia solution (NH₃(aq)). Using the apparatus listed, you will investigate the electrical conductivity of each compound in aqueous solution and, where possible, in the molten state. Apparatus: conductivity meter with cell constant 1.0 cm⁻¹, beakers (250 mL), distilled water, Bunsen burner, crucible, tongs, thermometer, balance (0.01 g), safety goggles and lab coat. Procedure (summarised): 1. Weigh 2.00 g of each solid (A–D) and record the masses. 2. Dissolve each solid in 100 mL of distilled water in separate beakers, stirring until completely dissolved. 3. Rinse the conductivity probe with distilled water and blot dry before each measurement. 4. Record the conductivity (µS cm⁻¹) of each solution. 5. For the solids that melt on heating (A and B), transfer a small amount to a clean crucible, heat gently over the Bunsen burner until a clear melt is obtained, and immediately insert the probe to record the conductivity of the molten material. 6. Clean the probe between measurements to avoid cross‑contamination. Answer the following questions: