Required Practicals

Question 1

How would you use a titration to find out the concentration of a solution?

Answer 1

1. A known volume of solution of an acid is measured out with a pipette and placed in a conical flask
2. A few drops of indicator (phenolphthalein) are added
3. The other solution is added from the burette until the indicator changes colour
4. The volume added from the burette is recorded, and the experiment optionally repeated
5. Work out the moles of the solution whose concentration is known (m=cv)
6. Use molar ratios to work out the moles of the other solution
7. Calculate the concentration of the other solution using c=m/v

Question 2

How would you prepare a pure dry sample of a soluble salt from an insoluble oxide or carbonate?

Answer 2

1. Measure 25cm^3 of dilute acid (usually sulphuric) in a conical flask
2. Warm the dilute acid with a Bunsen burner and add the carbonate, stirring until it’s in excess
3. Filter the solution
4. Heat the new solution
5. Cool and crystallise
6. Filter and dry the crystals

Question 3

How would you investigate what happens when aqueous solutions are electrolysed using inert electrodes?

Answer 3

1. Pour approximately 50cm^3 of copper (II) chloride solution into a beaker
2. Place a plastic petri dish over the beaker
3. Insert a graphite rod into each hole (graphite is inert and will not react)
4. Connect the rods to the terminals of a low-voltage power supply
5. Select 4V on the power supply and turn it on
6. Chlorine gas will be released at the cathode and copper will form on the anode. You can verify the identity of the chlorine gas with litmus paper

Question 4

How would you investigate the variables that affect temperature change in a neutralisation reaction?

Answer 4

1. Measure out 25cm^3 of 1mol/dm^3 sodium hydroxide and place it in a polystyrene cup
2. Fill a burette with 1mol/dm^3 hydrochloric acid
3. Measure and record the temperature of the sodium hydroxide
4. Add 5cm^3 of hydrochloric acid from the burette and record the temperature.
5. Repeat Step 4 until 40cm^3 of hydrochloric acid has been added
6. Repeat the experiment

Question 5

How would you investigate how changes in concentration affect the rate of reaction by measuring the volume of a gas produced?

Answer 5

1. Use a measuring cylinder to place 50cm^3 of hydrochloric acid into a conical flask
2. Attach the conical flask to a bung and a delivery tube
3. Place the delivery tube into a container filled with water
4. 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
7. Every ten seconds, measure the volume of hydrogen gas in the measuring cylinder and continue until no more hydrogen is given off
8. Repeat using different concentrations of hydrochloric acid

Question 6

How would you investigate how changes in concentration affect the rate of reaction by methods involving colour change or turbidity?

Answer 6

1. Place 25cm^3 of sodium thiosulfate in a conical flask on top of a piece of paper with a cross drawn on it
2. Add 25cm^3 of hydrochloric acid to the conical flask
3. Swirl the solution and start the stopwatch
4. Stop the stopwatch when the cross is no longer visible
5. Repeat the experiment with lower concentrations of sodium thiosulfate
6. Repeat the entire experiment again and calculate mean values (do not include anomalous results)

Question 7

How would you use paper chromatography to tell the difference between different coloured solutions?

Answer 7

1. Draw a base line on the chromatography paper 1.5cm from the bottom using a pencil (ink would dissolve into the water)
2. Place a concentrated drop of each solution to be tested on the base line
3. Tape the chromatography paper to a glass rod which is suspended over a beaker of 1cm deep water
4. Add a lid to the beaker and make sure the paper isn’t touching the sides of the beaker
5. After the water soaks up the paper, dry it and spray it with sodium hydroxide solution
6. Use the solvent front and the distances travelled by the chemicals to calculate Rf values (Rf = Distance of substance / Distance of solvent)

Question 8

How would you check the purity of a sample of water?

Answer 8

1. Use a pipette to place a drop of the water onto a strip of universal indicator paper
2. If the paper turns green, the water has a neutral pH (but might not still be pure)
3. Use a balance to weigh an empty evaporating basin and record the mass
4. Fill the evaporating basin with water and place it on a tripod and gauze
5. Use a bunsen burner to heat the water until it completely evaporates
6. Weigh the evaporating basin again. If the weight has increased, the water contained dissolved solids

Question 9

How would you purify water through distillation?

Answer 9

1. Set up the equipment: A conical flask on top of a tripod and gause with a bung and a collecting tube. The collecting tube leads to a test tube inside a beaker of icy water.
2. Gently boil the water, causing it to evaporate and form steam
3. The steam will travel down the collecting tube and condense in the test tube, forming distilled water