Paper 2 Required Practicals

Question 1

Describe how to carry out a practical investigation to explore the effect of concentration on the rate of reaction.

Answer 1

This is the Disappearing cross reaction:
Sodium thiosulfate solution + hydrochloric acid = sulfur(solid)

The sulphur makes the solution go cloudy(turbidity)

1. First use a meshing cylinder to put 10cm^3 of sodium thiosulfate solution into a conical flask.
2. The place the flask on a printed black cross.
3. Then add 10cm^3 into the conical flask and swirl the solution and start the timer.
4. Then look through the top of the flask and after a certain of time it will turn cloudy.
   Stop the timer when you can no longer see the cross.
5. Repeat the experiment using lower concentrations of sodium thiosulfate solution.
6. Finally

Question 2

Describe how to carry out a practical investigation to explore the effect of concentration on the rate of reaction: Second Method

Answer 2

Magnesium + hydrochloric acid = magnesium chloride + hydrogen

This allows us to measure the volume of hydrogen produced.

1. Use a measuring cylinder to place 50cm^3 of hydrochloric acid into a conical flasks
2. Then attach the flask to a bung and delivery tube
3. Place the tube into a container filled with water
4. Then place an upturned measuring cylinder also filled with water over the delivery tube.
5. Add a 3cm strip of magnesium to the hydrochloric acid and start a stopwatch.
6. The reaction produces hydrogen gas which is trapped in the measuring cylinder. Every 10 seconds, measure the volume of hydrogen gas in the measuring cylinder. Continue until no more hydrogen is given off.

Question 3

Chromatography: Part 1

Answer 3

Question 4

Chromatography: Part 2

Answer 4

The unknown colour has separated into three spots, telling us that this is a mixture into 3 colours.

The spots in colours A, C and D line up with the spots in the unknown colour. This tells us the unknown colour is a mixture of A, C and D and the unknown colour does not contain B

Question 5

How do we identify the chemicals?

Answer 5

If we want to identify the chemicals we need to calculate the Rf value.

Rf = 0.2

We can now look this Rf value up in a database and that will tell us the identity of the chemical.

Several different chemicals could have this Rf value. We might need to repeat this experiment using a different solvent to narrow it down further.

Question 6

How to use chemical tests to identify ions in unknown compounds

Question 1) Compound A produced a lilac flame test.
A sample of compound A was reacted with silver nitrate solution and dilute nitric acid. A yellow precipitate was formed.
Identify Compound A

Answer 6

A lilac test tells us that compound A contains the potassium ion
The fact that it produced a yellow precipitate tells us that it contains the iodide ion.
A is potassium Iodide.

Question 7

Describe how to :

- Analyse a sample of water for purity

Answer 7

Pure water has a Ph of 7(neutral)

1. We are given a sample of water and we have to find out whether it is pure or not
2. We first need to check it’s Ph. We do this by placing a small amount of water onto a piece of universal indicator(UI) paper. UI is green if the pH is 7.
   - If the pH is not 7 then the water sample contains dissolved acid or alkali and therefore not pure.
   - But even if the pH is 7 it does not mean the water is pure. The water could still contain dissolved solid
3. So to test for this we first use a balance to weigh an empty evaporating basin. We need to record the mass
4. Then we need to fill the evaporating basin with our water sample and place this on a tripod and gauze and use the Bunsen burner to gently heat the water until it has all evaporated.
5. Then we allow the basin to cool and reweight it and if the water contained any dissolved material then the mass of the empty basin should have increased.
6. The dissolved solids will have formed crystals on the surface of the evaporating basin.

If the mass of the basin did not increase the water could be pure.

Question 8

Describe how to:

Purify a sample of water by distillation

Answer 8

1. using a measuring cyclinder pour 10 ml of water sample 1 into a conical flask, and set up the apparatus for distillation (shown above)
2. heat the water until it boils, then reduce the heat so it boils gently
3. heat the water until about 1 cm depth of water is collected in the test tube
4. analyse the water you have distilled by determining its boiling point
5. repeat steps 1-4 for water samples 2 and 3