igcse model questions vol1 2022 chemistry | Practical

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Question 1 View Details
A student determines the relative atomic mass of magnesium by reacting a known mass of magnesium ribbon with excess hydrochloric acid and collecting the hydrogen gas over water. Data recorded: - Mass of dry magnesium ribbon before reaction: 0.500 g - Mass of magnesium ribbon after reaction (dry): 0.380 g - Volume of gas collected over water: 125 mL - Temperature of the gas: 25 °C - Atmospheric pressure: 760 mmHg - Vapour pressure of water at 25 °C: 23.8 mmHg The reaction is: Mg + 2 HCl → MgCl₂ + H₂. Answer the following:
Question Parts
(a)
Calculate the pressure of the dry hydrogen gas collected (in mmHg and in atm).
(b)
Using the corrected pressure, calculate the amount of hydrogen gas collected in moles (use R = 0.0821 L·atm·mol⁻¹·K⁻¹).
(c)
From the reaction stoichiometry, state the number of moles of magnesium that have reacted.
(d)
Calculate the relative atomic mass of magnesium using the mass of magnesium that reacted.
(e)
Identify two possible sources of error in this experiment and suggest a method to reduce each error.
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Question 2 View Details
A student is given three unknown metal chloride samples labelled A, B and C. The following tests are carried out on each sample: 1. Flame test – the colour of the flame is observed. 2. Reaction with dilute hydrochloric acid (approximately 0.1 M) at room temperature. Observations recorded: - Sample A: bright yellow flame; vigorous effervescence on addition of HCl. - Sample B: lilac flame; vigorous effervescence on addition of HCl. - Sample C: orange‑red flame; no visible reaction with HCl. Using the periodic table and knowledge of periodic trends, answer the questions below:
Question Parts
(a)
Identify the metal present in each sample (A, B and C).
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Question 3 View Details
A student is given three unknown solid samples, labelled X, Y and Z, and is required to investigate the type of chemical bonding present in each sample using simple laboratory tests.
Question Parts
(a)
Outline the complete procedure the student should follow to test each sample for (i) solubility in water, (ii) electrical conductivity of the resulting solution, and (iii) flame colour.
(b)
The following observations were recorded: • Sample X: soluble, solution conducts electricity, flame shows no colour. • Sample Y: insoluble, solution does not conduct, flame is orange‑red. • Sample Z: soluble, solution does not conduct, flame is bright green. Identify the most likely type of bond (ionic, covalent or metallic) in each sample and justify your answer.
(c)
For sample X, 0.500 g is dissolved in 250 mL of water and is known to dissociate completely into two ions. Calculate the molarity of each ion in the solution. (Molar mass of X = 58.44 g mol⁻¹)
(d)
Suggest one source of error that could affect the conductivity test and state how it can be minimised.
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Question 4 View Details
A volatile liquid of unknown composition is to be investigated by the gas‑evolution method in order to determine its molar mass.
Question Parts
(a)
Describe a suitable experimental set‑up and the steps required to obtain the pressure of the vapour produced when a known mass of the liquid is vapourised in a sealed container.
(b)
The experiment gave the following data: mass of liquid = 0.250 g, volume of gas collected = 250 mL, total pressure = 750 mmHg, temperature = 298 K, water‑vapour pressure = 23 mmHg. Using R = 0.0821 L·atm·mol⁻¹·K⁻¹, calculate the number of moles of vapour present.
(c)
From the result obtained in part (b), calculate the molar mass of the liquid.
(d)
Discuss two possible systematic errors in this method and indicate how each would affect the calculated molar mass (whether it would be over‑ or under‑estimated).
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