Chemistry Paper 1

Question 1

Analysis and purification of water samples from different sources

Answer 1

1. Use a pH probe or suitable indicator to analyse the pH of the sample
2. Set up distillation equipment (draw a diagram)
3. Heat a volume to 100°C so water changes from a liquid to a gas
4. Water collects in condenser and changes from a gas to a liquid. Collect pure water in a beaker.
5. When all all water has evaporated measure the mass of the solid left behind.

Question 2

Titration.

Answer 2

1. Wash and rinse a pipette with the alkali being used.
2. Use the pippette to measure out an accurate amount of the alkali.
3. Place the alkali in a clean, dry conical flask.
4. Add a suitable indicator (phenolphtalein)
5. Place flask on a white tile so the colour can be seen clearly
6. Place the acid in a burette, carefully washed and rinsed with the acid.
7. Take a reading of the volume of acid in the burette, make sure to read from meniscus
8. Carefully add acid to the alkali, swirling the conical flask to mix
9. Continue until the indicator changes colour, the end point.
10. Take a reading of the volume of acid in the burette.
11. Calculate volume of acid added.

Question 3

Obtaining a soluble saly from an insoluble oxide or carbonate.

Answer 3

1. Add the metal oxide or carbonate to a warm solution of acid until no more will react.
2. Filter the excess metal oxide or carbonate to leave a solution of salt.
3. Gently warm salt solution so water evaporates and crystals are formed.

Question 4

Electrolysis with aqueous solutions

Answer 4

1. Set up equipment needed (draw a diagram)
2. Pass electric current through aqueous solution.
3. Observe products formed at each electrode.