O Level Chemistry 5070 Paper 41, May/June 2024

Fig. 1.1 shows the apparatus the student uses to measure $25.0{\text{ cm}}^3$ of aqueous sodium hydroxide. Name the apparatus shown in Fig. 1.1.

Name a more suitable piece of apparatus to measure $25.0{\text{ cm}}^3$ of aqueous sodium hydroxide.

Fig. 1.2 shows the apparatus used to determine the volume of $\text{HA(aq)}$ at the end of the experiment. Name the apparatus shown in Fig. 1.2.

The initial reading on this apparatus is $1.0{\text{ cm}}^3$. Use Fig. 1.2 to determine the volume of $\text{HA(aq)}$ used in the titration. volume of $\text{HA(aq)}={\text{.................................................. cm}}^3$

The student washes the apparatus in Fig. 1.2 before it is used. State the substance used to wash the apparatus.

Describe the colour change of the methyl orange at the end-point. from ................................................................ to ................................................................

State the value in Table 2.1 which the student records to an incorrect degree of precision.

The temperatures for $\mathbf{\text{D}}$ are shown in Fig. 2.1. Record these temperatures in Table 2.1. Calculate and record the temperature increases for $\mathbf{\text{B}}$ and $\mathbf{\text{D}}$ in Table 2.1.

The equation for the reaction between $\mathbf{\text{B}}$ and aqueous copper(II) sulfate is shown. $$\text{B(s)}+{\text{CuSO}}_4\text{(aq)}\to {\text{BSO}}_4\text{(aq)}+\text{Cu(s)}$$ Copper(II) sulfate is a blue solution. At the end of the experiment, the student observes a colourless solution, a grey solid and a brown solid. Explain how these observations show that $\mathbf{\text{B}}$ is in excess in this reaction.

Using the equation in (iii), write the formula for: • the colourless solution • the grey solid • the brown solid. colourless solution ............................................................................................................. grey solid ........................................................................................................................... brown solid ........................................................................................................................

Use your results to arrange $\mathbf{\text{A}}$, $\mathbf{\text{B}}$, $\mathbf{\text{C}}$ and $\mathbf{\text{D}}$ in decreasing order of reactivity. Explain how the results give this order of reactivity. most reactive ...................... ...................... ...................... least reactive ...................... explanation ...............................................................................................................................

A student repeats the experiment using a fifth metal. This metal is the second most reactive of the five metals. Suggest a temperature increase for this experiment.

The temperature increases measured are less than the true values for these experiments. Suggest a reason for this. Describe an improvement to the method which makes the results closer to the true values. reason ....................................................................................................................................... improvement .............................................................................................................................

State and explain the effect of using half the concentration of aqueous copper(II) sulfate on the temperature increase for metal $\mathbf{\text{A}}$. effect ......................................................................................................................................... explanation ...............................................................................................................................

The student leaves a wooden splint with one end dipped into $\mathbf{\text{R}}$ for ten minutes. The student then places the damp end of the wooden splint into a blue Bunsen burner flame. The flame briefly shows a shade of red and then turns yellow. State two possible conclusions from this observation.

Explain why it is difficult to make a definite conclusion from the observation in (a)(i).

The student adds dilute nitric acid to $\mathbf{\text{R}}$, followed by aqueous barium nitrate. The student concludes that $\mathbf{\text{R}}$ does not contain sulfate ions. State the observation which allows the student to make this conclusion.

The student adds dilute nitric acid to $\mathbf{\text{R}}$, followed by aqueous silver nitrate. The student observes a white precipitate. State a conclusion from this observation.

The student adds aqueous silver nitrate to aqueous sodium carbonate. A white precipitate forms. The student adds dilute nitric acid a drop at a time until no further change is seen. The white precipitate dissolves to form a colourless solution. Describe one other observation.

Suggest why it is important to add dilute nitric acid in (c).

The student adds a few drops of aqueous sodium hydroxide to $\mathbf{\text{R}}$. State the observation the student makes which suggests that $\mathbf{\text{R}}$ may contain ${\text{Ca}}^{2+}$.

Describe what else the student needs to do to confirm that ${\text{Ca}}^{2+}$ ions are present. State what the student observes. what the student does .............................................................................................................. observation ...............................................................................................................................

The student warms the solution from (e). The student concludes that ammonia gas is produced. State the observation the student makes which confirms that ammonia gas is produced.

Identify a cation, other than calcium, present in $\mathbf{\text{R}}$.

Solution $\mathbf{\text{R}}$ is made from a mixture of two different ionic compounds. Suggest the names of these two compounds.