Required Practicals (Paper 2)
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Describe a method that can be used to find the rate of reaction between sodium thiosulfate and hydrochloric acid at different temperatures [6]
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]
State 2 independant variables that can be changed to affect rate of reaction [2]
Temperature [1] Concentration [1]
Describe an experiment to identify the various substances within ink [6]
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]
Describe an experiment to obtain pure salt crystals from sea water [5]
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]
Why should the water not touch the baseline of pencil? [2]
The water would mix with the pencil [1] therefore results are inaccurate [1]
Why shoudl you add a lid to your chromatography beaker? [1]
To prevent the solvent evaporating [1]