ijmb model questions vol1 2020 chemistry | Practical

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Question 1 View Details
A mass‑spectrometer was used to analyse a pure sample of an unknown element X. The instrument gave the following mass‑to‑charge (m/z) values and relative intensities: | m/z (amu) | Relative intensity (%) | |-----------|------------------------| | 32 | 95 | | 34 | 5 | The spectrometer was calibrated using a standard of known mass‑to‑charge ratio, and the detector response was linear over the range of interest.
Question Parts
(a)
State the approximate mass numbers of the isotopes of element X that are responsible for the observed peaks.
(b)
Calculate the average atomic mass of element X from the data given. Show all steps.
(c)
Identify element X and write its atomic number and group number in the periodic table. Justify your identification using the calculated average atomic mass.
(d)
List two possible sources of error that could affect the accuracy of the average atomic mass obtained from this experiment.
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Question 2 View Details
During a flame‑test investigation, three unknown solid samples (A, B and C) were introduced separately into a non‑luminous Bunsen‑burner flame using clean nichrome wires. The observed flame colours were recorded as follows: - Sample A: bright orange‑red flame - Sample B: lilac flame - Sample C: brick‑red flame All other experimental conditions (wire cleaning, flame temperature, ambient lighting) were kept constant.
Question Parts
(a)
Identify the metal ion present in each sample based on the flame colour observed.
(b)
Arrange the three identified metal ions in order of increasing first ionisation energy. Provide the approximate first ionisation energy values you used and justify the order using periodic trends.
(c)
It is suspected that sample B contains a mixture of two metal ions, one of which gives a lilac flame and the other a yellow‑orange flame (characteristic of sodium). Propose a practical method to separate the two ions before performing the flame test.
(d)
State two precautions that should be observed to avoid cross‑contamination between successive flame‑test samples.
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Question 3 View Details
A student synthesises a metal chloride by reacting excess dry chlorine gas with a clean piece of metal M weighing 0.250 g in a sealed glass tube. The tube is then sealed and the reaction is allowed to proceed to completion. After the reaction the solid product is cooled, removed and weighed, giving a mass of 0.726 g. The decrease in mass of the chlorine‑containing vessel is recorded as follows: initial mass (vessel + chlorine) = 150.000 g, final mass (vessel after reaction) = 149.524 g. The product is dissolved in distilled water and a conductivity test shows that the solution conducts electricity. The metal is known to form only one type of chloride.
Question Parts
(a)
Determine the empirical formula of the metal chloride formed.
(b)
From the formula obtained, calculate the oxidation state of the metal in the chloride.
(c)
Suggest the type of chemical bond (ionic or covalent) present in the chloride and justify your answer using the experimental observations.
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Question 4 View Details
An unknown aromatic compound (X) is suspected to have the empirical formula C₆H₅. To determine its molecular formula, a freezing‑point‑depression experiment is carried out using benzene as the solvent (K_f = 5.12 °C kg mol⁻¹). 1.00 g of X is dissolved in 50.0 g of benzene. The freezing point of pure benzene is 5.5 °C, whereas the solution freezes at 4.84 °C. The density of benzene is 0.877 g cm⁻³. All measurements are made at 25 °C and atmospheric pressure.
Question Parts
(a)
Calculate the molar mass of the unknown compound X from the data given.
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