Making coke

Making coke

ZIMSEC O Level Combined Science Notes: Experiment:Making coke and collecting the resulting gases

Aim: To make coke using coal and collect the gas and liquid by-products

Materials: crushed coal, test tubes, glass tubing, splints, lead ethanoate solution, filter paper, red and blue litmus paper, sodium hydroxide solution, beaker, water, trough, clamp stand


  1. Fill a hard glass test tube with crushed coal until it is about a quarter full and set up the equipment as shown in the diagram above
  2. Heat the coal steadly, gently at first but gradually increasing the temperature until the boiling test tube containing the coal is red hot
  3. Move the burner along the horizontal test tube to drive off any liquids
  4. Collect several test tubes of gas, rejecting the first one. Coal tar will collect in the water condenser and ammonia compounds will dissolve in the water
  5. Test the gas in the test tubes. First by holding a lighted splint to a test tube of the gas and secondly by lowering filter paper dipped in lead ethanoate solution into the gas
  6. Shake a small amount of water with the gas. Add blue litmus paper to the solution
  7. Test the contents of the water condenser. First add red litmus paper to the water solution at the top (aqueous solution/ammoniacal liquor). Next warm a little of the aqueous solution with aqueous sodium hydroxide and test the gas with we red/damp litmus paper.
  8. Dip the filter paper in the tar and ignite it. Do the smae with a clean filter paper and compare the flames
  9. Examine the solid residue once it has coed down and try to burn a small piece of the coke.

Results and Observations

  • Coal gas is evolved in the final test tube
  • When a lighted splint is used the coal gas burns with a blue flame (the flame is blue at the bottom)
  • Coal gas usually contains about 2% hydrogen  sulphide which turns the filter paper dipped in lead ethanoate brown-black
  • Some of the gases in coal gas are soluble resulting in acidic solution which turns blue litmus paper red
  • Ammoniacal liquor is alkaline and thus turns red litmus paper blue
  • When the ammoniacal liqour is mixed with sodium hydroxide and warmed ammonia gas is evolved, it turns damp red litmus paper blue
  • Filter paper dipped in tar burns with a faded red flame and gives of a lot of soot. Normal filter paper has an orange flame which is cleaner
  • When the coke is set alight it burns cleanly with no visible smoke


  • The above process turns the crushed coal into coke
  • It produces coal and several byproducts
  • These include: coal gas, benzol, tar and ammonia

To access more topics go to the Combined Science Notes page.