O Level Chemistry 5070 Paper 42, May/June 2024

Fig. 1.1 shows the apparatus the student uses to measure the volume of dilute sulfuric acid. Name the apparatus shown in Fig. 1.1.

Explain why the student does not need to use a volumetric pipette to measure the volume of dilute sulfuric acid.

Describe how the student uses the volumetric pipette to measure $25.0{\text{ cm}}^3$ of aqueous iron(II) sulfate safely.

Name the apparatus the student uses to add the aqueous potassium manganate(VII) to the flask.

State why the student does not need to add an indicator to this titration.

Explain how the student knows when they have done enough titrations.

Fig. 2.1 shows the results for $120\text{ s}$ and $300\text{ s}$. Record the values from Fig. 2.1 to the nearest $0.5{}^{\circ }\text{C}$ in Table 2.1.

Calculate the maximum temperature change in the investigation. maximum temperature change ..................................................... ${}^{\circ }\text{C}$

Describe the trends shown in the results in Table 2.1.

Suggest the temperature of the mixture if it is left for 60 minutes. Explain your answer. temperature after 60 minutes .............................. ${}^{\circ }\text{C}$ explanation ........................................................................................................................ ...........................................................................................................................................

Describe the energy change when the solid dissolves in water. Explain how the results in Table 2.1 support your answer. description ................................................................................................................................ explanation ............................................................................................................................... ...................................................................................................................................................

Explain why it is important for the student to stir the mixture.

The maximum temperature change calculated is not the true value for this investigation. This may be because the volume of water and the temperature are not measured precisely. Explain how to obtain a more precise temperature measurement.

The maximum temperature change calculated is less than the true value for this investigation. Suggest a reason for this, other than the precision of measurements. Describe an improvement to the method which reduces this error. reason ....................................................................................................................................... ................................................................................................................................................... improvement ............................................................................................................................. ...................................................................................................................................................

The student leaves a wooden splint with one end dipped into R for ten minutes. The student then places the damp end of the wooden splint into the flame of a Bunsen burner with the air hole open. The student concludes that R contains sodium ions. State the observation which allows the student to make this conclusion.

Explain why the air hole on the Bunsen burner must be open when doing this flame test.

The student adds dilute nitric acid to R. The student observes effervescence of a colourless gas which turns limewater milky. State the conclusions from these observations.

The student adds aqueous barium nitrate to some of the mixture from (b)(i). The student concludes that R contains sulfate ions. State the observation which allows the student to make this conclusion.

The student adds aqueous silver nitrate to some of the mixture from (b)(i). The student observes a colourless solution. State a conclusion from this observation.

The student adds aqueous sodium hydroxide to R and warms the mixture. Describe a test and observation to show that R does not contain ammonium ions. test .................................................................................................................................... observation ......................................................................................................................... ...........................................................................................................................................

Solution R is made from a mixture of two different ionic compounds. Suggest the names of these two compounds.

The student tests a different solution, P, and finds it difficult to decide whether the solution contains chloride ions or bromide ions. The student also has aqueous potassium chloride and aqueous potassium bromide. Suggest how the student could use the aqueous potassium chloride and aqueous potassium bromide to make it easier to decide whether P contains chloride ions or bromide ions.

The student adds dilute hydrochloric acid to another solution and a gas is produced. The gas is passed through limewater. Describe how the gas can be passed through limewater. You may draw a labelled diagram to help answer the question.