Required Practicals (Paper 2)

Question 1

Describe a method that can be used to find the rate of reaction between sodium thiosulfate and hydrochloric acid at different temperatures [6]

Answer 1

Measure 10cm3 of sodium thiosulfate and pour into conical flask above a large cross [1]
Measure 40cm3 of water and pour in the flask [1]
Measure 10cm3 of HCl and pour into the flask [1]
Start a stopwatch and immediately begin swirling the flask [1]
Stop the stopwatch when the large cross is no longer visible [1]
Repeat with different concentrations of sodium thiosulfate and calculate a mean. [1]

Question 2

State 2 independant variables that can be changed to affect rate of reaction [2]

Answer 2

Temperature [1]
Concentration [1]

Question 3

Describe an experiment to identify the various substances within ink [6]

Answer 3

Draw a pencil line 1cm from the bottom of the chromatography paper [1]
Place a spot of the ink onto the pencil line [1]
Add 0.5cm of water to the beaker, up to the pencil line [1]
Allow the water to rise up the paper and separate the ink [1]
Measure the distance from the pencil line to the solvent front and the middle of each spot [1]
Use these to calculate an Rf value. [1]

Question 4

Describe an experiment to obtain pure salt crystals from sea water [5]

Answer 4

Set up a bunsen burner on a heatproof mat with a tripod [1]
Measure 5cm3 of sea water into a glass dish [1]
Heat up a watch bath with 200cm3 of water inside, and place the dish on top [1]
Heat the sample until all water has evaporated [1]
Collect the sample of pure salt crystals and meaure its mass. [1]

Question 5

Why should the water not touch the baseline of pencil? [2]

Answer 5

The water would mix with the pencil [1] therefore results are inaccurate [1]

Question 6

Why shoudl you add a lid to your chromatography beaker? [1]

Answer 6

To prevent the solvent evaporating [1]