O Level Chemistry 5070 Paper 42, Oct/Nov 2023

Name apparatus X.

Give a reason why iron electrodes are not used during this electrolysis.

Chlorine gas is produced at the anode during this electrolysis. Describe and explain one safety precaution the student takes during this electrolysis. safety precaution ...................................................................................................................... explanation ...............................................................................................................................

A different gas is produced at the cathode during this electrolysis. Name the gas produced. Describe a test and its result to confirm the identity of the gas. name of gas .............................................................................................................................. description of test and result ..................................................................................................... ...................................................................................................................................................

Complete Table 2.1 by filling in the three missing values.

Parts of the thermometer used in Experiment 3 are shown in Fig. 2.1. The liquid levels inside the thermometer are missing. Complete Fig. 2.1 by drawing in the liquid level to show: • the initial temperature in Experiment 3 • the highest temperature reached in Experiment 3.

Draw a graph of temperature rise against volume of $\mathbf{Q}$ on the grid in Fig. 2.2. You should: • plot the point (0,0) as there is no temperature rise when no $\mathbf{Q}$ is added • plot the temperature rises and volumes of $\mathbf{Q}$ from Table 2.1 • draw a straight line of best fit for the first four points • draw a straight line of best fit for the last three points • extend the lines so that they intersect.

The point where the two lines intersect indicates the volume of $\mathbf{Q}$ that exactly neutralises $25.0\mathrm{c}{\mathrm{m}}^3$ of $\mathbf{P}$. Determine the volume of $\mathbf{Q}$ where the two lines on the graph intersect. volume of $\mathbf{Q}$ .................................................. $\mathrm{c}{\mathrm{m}}^3$

$\mathbf{P}$ is $1.25\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}\mathrm{d}{\mathrm{m}}^3$ aqueous sodium hydroxide. Use your answer to (d) to calculate the concentration of sulfuric acid in $\mathbf{Q}$. $$2\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}+{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4\to \mathrm{N}{\mathrm{a}}_2\mathrm{S}{\mathrm{O}}_4+2{\mathrm{H}}_2\mathrm{O}$$ concentration of sulfuric acid in $\mathbf{Q}$ .......................................... $\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}\mathrm{d}{\mathrm{m}}^3$

Describe and explain what happens to the gradient of the straight line for the first four points on the graph if a metal cup is used instead of a plastic cup.

A burette may be used instead of a measuring cylinder to measure the volume of water in these experiments. Suggest how this improves the experiments.

State the dependent variable in this set of experiments.

Solid $\mathbf{Y}$ is white and contains carbonate ions. The tests the student does on $\mathbf{Y}$ are shown in Table 3.1. Some of the observations for these tests are also shown. Predict the identity of the gas produced in test 1. Describe how the student tests the gas to confirm its identity. gas .................................................................................................................................... test and observation .......................................................................................................... ...........................................................................................................................................

The solution produced in test 1 contains an anion. Name a reagent that reacts with this anion to form a white precipitate when added to the solution produced in test 1 after the addition of dilute nitric acid.

The observations for test 3 are incomplete. State one other observation the student makes in test 3.

Solid $\mathbf{Y}$ contains only one cation. The student cannot identify the cation from the observations in Table 3.1. Use Table 3.1 to name the two cations which could be present in $\mathbf{Y}$.

Describe an additional test the student does on the solution produced in test 1 to identify the cation in $\mathbf{Y}$.

Solution $\mathbf{Z}$ contains one cation and one anion. The cation contains two non-metals. The student adds aqueous sodium hydroxide to $\mathbf{Z}$ in a boiling tube. Describe how the student completes this test to identify the cation in $\mathbf{Z}$.

The student adds dilute nitric acid and then aqueous silver nitrate to $\mathbf{Z}$. A precipitate is formed. It is difficult to tell if the precipitate is white or cream in colour. Describe how the student uses separate aqueous solutions of a chloride and a bromide to decide the colour of the precipitate.

The student adds dilute nitric acid and then aqueous barium nitrate to $\mathbf{Z}$. Predict the expected observation.