igcse model questions vol1 2018 chemistry | Practical

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Question 1 View Details
A mass‑spectrometer was used to analyse a sample of an unknown element. The instrument gave the following data for the isotopes present:
Question Parts
(a)
Calculate the average atomic mass of the unknown element using the data in the table.
(b)
Using the periodic table, identify the element whose standard atomic mass is closest to your calculated value. State its chemical symbol and the group number of the element.
(c)
List two possible sources of error that could affect the accuracy of the mass‑spectrometer data.
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Question 2 View Details
A student performed flame tests on three unknown solid samples (A, B and C). The observations are recorded in the table below:
Question Parts
(a)
Identify the metal ion most likely responsible for each observed flame colour, giving the element name and its chemical symbol.
(b)
For each identified element, state its group number on the periodic table and one characteristic property of that group that explains the observed flame colour.
(c)
Predict which of the three elements would be most reactive with dilute hydrochloric acid at room temperature, and justify your answer using periodic trends.
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Question 3 View Details
You are given three white crystalline solids labelled X, Y and Z. Each sample is about 2 g. Your task is to determine the type of chemical bond present in each substance (ionic, covalent or metallic) using simple laboratory techniques.
Question Parts
(a)
Suggest a practical procedure that will allow you to distinguish between ionic, covalent and metallic substances. State the equipment required and the observations you would expect for each type of bond.
(b)
You performed the procedure and recorded the following observations: - Sample X dissolved readily in water and the bulb lit brightly. - Sample Y did not dissolve; the bulb remained off. - A small piece of Sample Z placed directly in the circuit caused the bulb to light, but when dissolved in water the bulb stayed off. Identify the type of bond present in each sample.
(c)
Suggest one likely source of error in the experiment and how it could be minimised.
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Question 4 View Details
A 0.500 g sample of a commercial sodium carbonate (Na₂CO₃) preparation is dissolved in 100 cm³ of water. The solution is then acid‑titrated with 0.100 mol dm⁻³ hydrochloric acid (HCl) until the endpoint is reached. The volume of HCl used is recorded as 23.5 cm³. The same sample is also heated in a test tube, and the volume of carbon dioxide gas (CO₂) produced at 25 °C and 1.00 atm is measured as 12.0 cm³.
Question Parts
(a)
Calculate the number of moles of Na₂CO₃ present in the sample based on its mass. (Molar mass of Na₂CO₃ = 106.0 g mol⁻¹)
(b)
From the titration data, determine the number of moles of Na₂CO₃ that reacted with HCl. (Balanced equation: Na₂CO₃ + 2 HCl → 2 NaCl + H₂O + CO₂)
(c)
Using the gas‑collection data, calculate the number of moles of CO₂ produced. (Assume ideal gas behaviour; R = 0.0821 L atm mol⁻¹ K⁻¹, temperature = 298 K.)
(d)
Based on the mass of the sample (a) and the moles of Na₂CO₃ that actually reacted (b), calculate the percent purity of the commercial sample.
(e)
Suggest one probable source of error that could account for the low calculated purity and propose a way to reduce it.
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