Neco 2020 Chemistry Question 3

Three unknown solid samples labelled X, Y and Z are subjected to a series of qualitative tests in the chemistry laboratory. The observations obtained are recorded in the table below. | Test | Sample X | Sample Y | Sample Z | |------|----------|----------|----------| | (i) Solubility in 100 mL of water (2.0 g sample) | Completely soluble | Insoluble | Slightly soluble | | (ii) Conductivity of the resulting solution (if any) | Conducts electricity | No conductivity (dry sample) | Does not conduct electricity | | (iii) Melting point (°C) | 801 | 660 | 120 | | (iv) Reaction with dilute HCl (excess) | No visible reaction | Bubbles of gas evolve rapidly | No visible reaction | Using the above data, answer the following questions. (a) State the type of chemical bonding present in each of the three samples. (b) For each test (i)–(iv), explain how the observation helps to identify the type of bonding. (c) Suggest a possible chemical formula for each sample consistent with the identified bond type. (d) Propose one practical precaution that should be observed when performing test (iv).