prep of ethyne

• CaC2 + 2H2O ----> C2H2 + Ca(OH)2
• calcium dicarbide


  grey, lumpy solid

  IMPURITIES

  -calcium sulphide

  -calcium nitride

  -calcium phosphide
• ethyne


  colourless gas

  pure covalent

  IMPURITIES

  -hydrogen suphide

  -ammonia

  -phosphine
• calcium hydroxide


  white precipitate forms on calcium dicarbide
• reaction type

  addition

  hydrolysis

  exothermic
• acidified copper sulphate


  removes impurities from ethyne
• precautions

  CaC2 very reactive -moisture on skin burns -use spatula

  ethyne is explosive in air -safety screen

  discard first testubes as they contain expanded air
• observations

  bubbles of ethyne

  white precipitate on CaC2

  bottom of buchner flask heats
• flame

  normal: luminous smokey sooty flame

  -large proportion of unburnt carbon

  a lot of controlled o2

  -bright white very hot flame