Exam Style Question - 2

QuestionA student prepares 1-bromobutane by heating butan-1-ol with sodium bromide and concentrated sulfuric acid under reflux. The acid and sodium bromide react to make hydrogen bromide, which then reacts with the alcohol.CH₃CH₂CH₂CH₂OH + HBr → CH₃CH₂CH₂CH₂Br + H₂ODescribe how the crude 1-bromobutane is separated and purified. Explain the purpose of each step. (Density of 1-bromobutane = 1.27 g cm^-3; boiling temperature = 102 °C.)Answer1. Distil the crude product out of the reaction mixture, to separate it from the inorganic salts and acid.2. Put the distillate into a separating funnel and shake with water, then with sodium hydrogencarbonate solution, releasing the pressure often. Sodium hydrogencarbonate removes acidic impurities (HBr and H₂SO₄).3. 1-bromobutane is denser than water, so it forms the lower layer. Run off the lower layer and keep it.4. Add anhydrous calcium chloride and swirl until the liquid is clear, to remove water. Calcium chloride also removes unreacted butan-1-ol.5. Decant or filter the liquid into a clean flask and redistil it, collecting the fraction that boils close to 102 °C (for example 100 to 104 °C).Examiner tip: give the steps in the right order: distil, wash, separate, dry, redistil. If the final product boils over a wide range of temperatures, it is still impure.