igcse model questions vol1 2019 chemistry | Practical

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Question 1 View Details
A student carries out an experiment to determine the relative atomic mass of magnesium. A clean, dry piece of magnesium ribbon weighing 0.500 g is placed in a conical flask containing excess 1.0 M hydrochloric acid. The hydrogen gas produced is collected over water in an inverted graduated cylinder. The temperature of the water bath is 25 °C, the atmospheric pressure is 760 mm Hg and the water‑vapour pressure at 25 °C is 23.8 mm Hg. The volume of gas collected is 620 mL.
Question Parts
(a)
Write the balanced chemical equation for the reaction between magnesium and hydrochloric acid.
(b)
Calculate the number of moles of hydrogen gas collected, correcting for the water vapour pressure.
(c)
Using the result from part (b), determine the relative atomic mass of magnesium obtained in the experiment.
(d)
State 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 carries out a flame‑test investigation using a Bunsen burner. Small amounts of the following solid salts are placed separately on a clean platinum wire loop and introduced into the flame: • Sodium chloride (NaCl) • Potassium chloride (KCl) • Calcium chloride (CaCl₂) • Barium chloride (BaCl₂) The observed flame colours are recorded. An unknown solid sample is then tested in the same way and produces an orange‑red flame.
Question Parts
(a)
State the characteristic flame colour expected for each of the four known salts.
(b)
Based on the observed colour of the unknown sample, suggest which metal ion(s) are most likely present.
(c)
Explain, in terms of electron transitions, why different metal ions give different flame colours.
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Question 3 View Details
Three unknown solid samples labelled X, Y and Z have been supplied. Using appropriate laboratory techniques you are required to investigate the type of chemical bonding present in each sample.
Question Parts
(a)
Describe a suitable procedure for testing the electrical conductivity of aqueous solutions of the three samples. Include the apparatus required and the method of recording the observation.
(b)
Predict the observations you would expect for each sample in terms of (i) solubility in water, (ii) conductivity of the resulting solution and (iii) flame colour (if any). Present your answer in a table.
(c)
Using the predicted observations, deduce the most likely type of bonding (ionic, covalent or metallic) for each sample and justify your conclusion.
(d)
Identify two possible sources of error in the conductivity test and suggest how each could be minimised.
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Question 4 View Details
A 0.250 g sample of an unknown metal was reacted with excess dilute hydrochloric acid in a gas‑collection apparatus at 298 K and 100 kPa. The volume of hydrogen gas collected was 112.0 mL.
Question Parts
(a)
Outline the experimental arrangement required to collect the hydrogen gas over water. Name the main pieces of apparatus and describe briefly how the set‑up works.
(b)
Calculate the number of moles of hydrogen gas produced. Show all steps and use the appropriate gas constant.
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