waec model questions vol1 2017 chemistry | Practical

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Question 1 View Details
A student is given three unknown solid samples labelled X, Y and Z. The following experimental procedures were carried out on each sample: 1. Flame test – the colour of the flame was observed. 2. Solubility test – a small amount of the sample was added to dilute hydrochloric acid (0.1 M HCl) and any observable reaction was recorded. Observations recorded: - Sample X: orange‑red flame; dissolves in HCl with effervescence (bubbling). - Sample Y: green flame; remains insoluble in HCl, no visible reaction. - Sample Z: violet flame; dissolves in HCl, no gas evolved.
Question Parts
(a)
Identify the most likely metal ion present in each sample (X, Y and Z) based on the observations.
(b)
Write the balanced chemical equation for the reaction that occurs when sample X is added to dilute HCl.
(c)
Suggest one source of experimental error that could affect the flame‑colour observation and propose a way to minimise it.
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Question 2 View Details
During a laboratory session the following first‑ionisation‑energy data (in kJ mol⁻¹) for the elements of period 2 were recorded: Li : 520  Be : 899  B : 801  C : 1086 N : 1402  O : 1314  F : 1681  Ne : 2080 Using this data answer the questions that follow.
Question Parts
(a)
Calculate the average first ionisation energy of the eight elements.
(b)
Identify the element with the highest first ionisation energy and give its value.
(c)
Explain the overall trend in ionisation energy across period 2, referring to electronic configuration where appropriate.
(d)
Based on the periodic trend, estimate the first ionisation energy of sodium (Na) and justify your estimate.
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Question 3 View Details
A student prepared magnesium oxide (MgO) by burning a clean piece of magnesium ribbon in air. The following data were recorded during the experiment:
Question Parts
(a)
Calculate the mass of MgO obtained after the reaction.
(b)
Using the masses of magnesium and oxygen in the product, determine the empirical formula of the compound formed.
(c)
Based on the empirical formula obtained and the observed physical properties (white solid, melting point ≈ 2850 °C, insoluble in water, conducts electricity when molten), state the type of chemical bond present in the compound and justify your answer.
(d)
Suggest one further qualitative test that could be performed to confirm the ionic nature of MgO.
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Question 4 View Details
An unknown metal carbonate (MCO₃) was reacted with excess dilute hydrochloric acid in a closed gas‑collection apparatus. The volume of carbon dioxide gas produced was measured over water.
Question Parts
(a)
Calculate the partial pressure of CO₂ in the collected gas.
(b)
Determine the number of moles of CO₂ collected at the experimental conditions (temperature = 298 K, volume = 320.0 mL).
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