O Level Chemistry 5070 Paper 41, Oct/Nov 2025

State the name of the piece of apparatus labelled A in Fig. 1.1.

The student makes a mistake when assembling the apparatus. Describe this mistake.

When it is correctly assembled, the apparatus shown in Fig. 1.1 is used to separate petroleum into useful substances. State the name of this separation process.

State the property of these substances that allows them to be separated.

State the name of the piece of apparatus the student uses to safely heat the petroleum in Fig. 1.1. Explain why this piece of apparatus is suitable. piece of apparatus .................................................................................................................... explanation ............................................................................................................................... ...................................................................................................................................................

Complete Table 2.1. You should: • record the student’s results for $5.0{\text{ cm}}^3$ and $30.0{\text{ cm}}^3$ using Fig. 2.1 • subtract the initial temperature of $\mathbf{X}$ from each temperature recorded to determine the temperature change. All temperatures and temperature changes should be recorded to $+\mathrm{/}-0.5{}^{\circ }\text{C}$.

Plot a graph of the temperature change ($y$-axis) against the volume of $\mathbf{Y}$ ($x$-axis) on Fig. 2.2. Draw a line of best fit through the points where the temperature change is increasing. Draw a line of best fit through the points where the temperature change is decreasing. Extend both lines so that they cross.

Find the point on the graph where the two lines cross. Determine the volume of $\mathbf{Y}$ at this point. volume .................................................. ${\text{cm}}^3$

$\mathbf{X}$ is $1.60{\text{ mol/dm}}^3$ sodium hydroxide solution. The formula of sodium hydroxide is $\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}$. Calculate the number of moles of hydroxide ions, ${\mathrm{O}\mathrm{H}}^{-}$, in $25.0{\text{ cm}}^3$ of $\mathbf{X}$. number of moles .........................................................

The volume of $\mathbf{Y}$ in (c) is the volume needed to completely neutralise $25.0{\text{ cm}}^3$ of $\mathbf{X}$. Use your answers to (c) and (d) to calculate the concentration of hydrogen ions, ${\mathrm{H}}^{+}$, in $\mathbf{Y}$. $${\mathrm{H}}^{+}+{\mathrm{O}\mathrm{H}}^{-}\to {\mathrm{H}}_2\mathrm{O}$$ concentration .......................................... ${\text{mol/dm}}^3$

Suggest why $\mathbf{Y}$ is added to $\mathbf{X}$ using a burette and not a measuring cylinder.

Suggest why the temperatures are recorded after 30 seconds and not immediately after mixing.

Solution $\mathbf{Q}$ is acidic. Solution $\mathbf{Q}$ contains one cation and one anion. The tests the student does on $\mathbf{Q}$ are shown in Table 3.1. Some of the observations for these tests are also shown. Describe the expected colour change in test 1.

A gas is produced in test 2. Predict one other observation made by the student in test 2.

Predict the identity of the gas produced in test 2.

Describe a test to confirm the identity of this gas. Include the result of a positive test. test .................................................................................................................................... result .................................................................................................................................

Identify the cation and the anion in $\mathbf{Q}$. cation ......................................................... anion .........................................................

The tests the student does on $\mathbf{R}$ are shown in Table 3.2. Some of the observations for these tests are also shown. Describe how the student does a flame test.

Describe one additional observation expected in test 5 based on the observations in tests 4 and 5.

Describe one additional test to confirm the identity of the cation in $\mathbf{R}$. Include the result of a positive test. test .................................................................................................................................... ........................................................................................................................................... result .................................................................................................................................

Identify the cation in $\mathbf{R}$. cation ...........................................................................................................................