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
- 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
- Heat the coal steadly, gently at first but gradually increasing the temperature until the boiling test tube containing the coal is red hot
- Move the burner along the horizontal test tube to drive off any liquids
- 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
- 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
- Shake a small amount of water with the gas. Add blue litmus paper to the solution
- 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.
- Dip the filter paper in the tar and ignite it. Do the smae with a clean filter paper and compare the flames
- 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.
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