Mandatory Experiment 5.2Preparation and properties of ethyneStudent MaterialTheoryCalcium dicarbide reacts with water producing ethyne and calcium hydroxide:CaC2+ 2H2O → C2H2+ Ca(OH)2The gas usually contains hydrogen sulfide and phosphine as impurities, caused by thehydrolysis of traces of calcium sulfide and calcium phosphide present in the calciumdicarbide. The impurities, which cause an unpleasant odour, can be removed by bubblingthe gas through acidified copper sulfate solution.Chemicals and ApparatusCalcium dicarbideWaterAcidified copper(II) sulfate solutionnLimewateriAcidified potassium manganate(VII) solutioniBromine waterTeat-pipetteTest tubes, solid stoppers and stoppers with two holesDelivery tubesTroughRetort stands and clampsProcedureNB: Wear your safety glasses.(1) Preparation1.Place 2-3 pieces of calcium dicarbide in a test tube and set up the apparatus as inthe diagram.1
2.Add water from the teat-pipette, a few drops at a time, until all the calciumdicarbide has reacted. The gas produced is collected in test tubes by displacementof water, the test tubes being stoppered under water when filled with gas. The firsttest tube filled can be discarded, as it contains a mixture of air and ethyne.(2) Investigation of Properties1.Ignite the gas in one of the test tubes. Describe the flame. Add a few drops oflimewater to the test-tube and shake well. Describe what happens.2.Add a few drops of a solution of bromine water to a test tube of gas, stopper quicklyand shake well. Describe what you see.3.Add a few drops of acidified potassium manganate solution to a test tube of gas,stopper quickly and shake well. Describe what you see.Questions relating to the experiment1.Write an equation for the combustion of ethyne, and select a productthat may have caused a colour change in the limewater.