Edexcel Jun 2017 (IAL) Paper 3 Q2

Answers available below

2 1-bromobutane may be prepared by heating a mixture of butan-1-ol, sodium bromide and 50% concentrated sulfuric acid. C4H9OH + NaBr + H2SO4C4H9Br + NaHSO4 + H2O The preparation is carried out in eight stages. Stage 1 The reagents are heated in the apparatus shown in Diagram 1 for 45 minutes. Stage 2 Stage 3 Stage 4 Stage 5 Stage 6 Stage 7 Stage 8 Impure 1-bromobutane is extracted from the reaction mixture and is then transferred to the round bottom flask in the apparatus shown in Diagram 2. A mixture of 1-bromobutane and water is obtained when the impure 1-bromobutane is heated using the apparatus shown in Diagram 2. The mixture from Stage 3 is transferred to a separating funnel. This mixture consists of two layers, an aqueous layer and a layer containing impure 1-bromobutane. The two layers are separated. The impure 1-bromobutane is washed with concentrated hydrochloric acid and the resulting two layers are separated. The 1-bromobutane layer from Stage 5 is washed with sodium hydrogencarbonate solution, and any gas formed released. The 1-bromobutane layer is collected in a conical flask and anhydrous solid calcium chloride is added. The calcium chloride is filtered off and the filtrate is transferred to the apparatus shown in Diagram 2. On heating, pure 1-bromobutane is collected. The sample is weighed and the yield of the product calculated. Some information on 1-bromobutane, C4H9Br Density = 1.3 g cm3 Immiscible with water *P48384A0620*<br /> (a) Give the names of the practical techniques carried out using the apparatus shown in Diagram 1 and Diagram 2. (2) Diagram 1 Diagram 2 Awater in Bwater out Diagram 1:Diagram 2:(b) (i) Describe, in terms of changes of state, what is happening when reagents are heated in the apparatus shown in Diagram 1. (1)(ii) Explain why the reagents are heated in the apparatus shown in Diagram 1 for such a long time. (1)*P48384A0720* Turn over<br /> (c) (i) On the diagram of the separating funnel used in Stage 4, show the 1-bromobutane and aqueous layers. Label each layer. (1) (ii) The product is washed with concentrated hydrochloric acid in Stage 5 to remove any unreacted butan-1-ol. The acid donates a proton to the butan-1-ol. Suggest why this makes washing with acid more effective than washing with water. (1)(iii) What is the purpose of adding anhydrous solid calcium chloride in Stage 7? (1)(iv) How can you tell when Stage 7 is complete? (1)*P48384A0820*<br /> (d) In a preparation, 14.80 g of butan-1-ol formed 17.81 g of 1-bromobutane. (i) Calculate the volume of butan-1-ol, in cm3, that is used in the reaction mixture. The density of butan-1-ol is 0.810 g cm3. (ii) Calculate the number of moles of butan-1-ol in 14.80 g. [Molar mass of butan-1-ol = 74 g mol1] (1) (1) (iii) Calculate the mass of 1-bromobutane that would be formed if all the butan-1-ol is converted into 1-bromobutane. [Molar mass of 1-bromobutane = 137 g mol1] (iv) Calculate the percentage yield of 1-bromobutane in this preparation. (1) (1) *P48384A0920* Turn over<br /> (e) Suggest two reasons why the actual yield of 1-bromobutane was lower than the maximum theoretical yield. (2) Reason 1:Reason 2:(Total for Question 2 = 14 marks) 10 *P48384A01020*<br />

Show answer