The Finkelstein reaction is a nucleophilic substitution reaction in which a halogen atom in a halogenoalkane is replaced by another halogen atom. The reaction is carried out using dry propanone as a solvent. One example of the Finkelstein reaction is given. CH3CH2CH2Br + NaI ⇌ CH3CH2CH2I + NaBr (pr) = substance is dissolved in propanone The student plans to record the time it takes for the solid formed to obscure a cross on a piece of paper below the conical flask, as shown. [Figure X.X] To carry out this experiment, the following materials are available. • CH3CH2CH2Br(l) • NaI(s) • dry propanone, CH3COCH3(l) • usual laboratory apparatus

1. (a)(i)Explain why it is important for dry propanone to be used as a solvent for this reaction.[1]
2. (a)(ii)The solubilities of NaBr and NaI in propanone are shown. compound solubility at 25 °C in g/100 g of propanone NaBr 0.00841 NaI 39.9 Use this information to explain why, although the reaction between CH3CH2CH2Br and NaI is reversible, the reaction produces a very high yield.[2]
3. (b)Some safety information for the organic compounds used in this reaction is shown. • 1-bromopropane is highly flammable and moderate health hazard. It is irritating to eyes, the respiratory system and skin. • 1-iodopropane is flammable and moderate health hazard. It is irritating to eyes, the respiratory system and skin. • Propanone is highly flammable and moderate health hazard. It is irritating to eyes, and may cause dizziness and drowsiness. Identify two different precautions, other than using protective equipment such as gloves, a lab coat or eye protection, that should be taken when carrying out this experiment. Explain each answer. 1 precaution explanation 2 precaution explanation[2]
4. (c)(i)Calculate the masses of NaI(s) and CH3COCH3(l) that would be needed to make 150 cm³ of 0.50 mol dm⁻³ NaI(pr). Assume 150 cm³ of propanone are required. Give your answers to one decimal place. The density of CH3COCH3(l) is 0.79 g cm⁻³. [Aᵣ: Na, 23.0; I, 126.9] mass of NaI(s) = ................................. g mass of CH3COCH3(l) = ................................. g[2]
5. (c)(ii)Part of the table the student used to record data is given. Complete the table with appropriate volumes that the student could have used in four further experiments. volume of volume of volume of total volume time 0.50 mol dm⁻³ CH3CH2CH2Br(l) CH3COCH3(l) NaI(pr)/cm³ /cm³ /cm³ /cm³ /s 10.0 2.0 30.0 42.0 [2]
6. (c)(iii)The student uses the same experimental set-up each time. In this experiment, identify the dependent variable.[1]
7. (c)(iv)Write an expression to show how the student could calculate the rate of the reaction.[1]
8. (c)(v)Identify the major source of inaccuracy of measurement in this reaction. Suggest an improvement to the experiment to make it more accurate. inaccuracy improvement[2]
9. (d)The reaction between CH3CH2CH2Br and NaI proceeds via an SN2 mechanism. The student repeated the experiment in (c) using an isomer of CH3CH2CH2Br that reacts via both SN1 and SN2 mechanisms. State and explain whether the student will be able to show that the rate of this reaction is proportional to the concentration of NaI.[1]

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