8. Chemical Analysis (Paper 2)

Question 1

Plan an investigation to find the total mass of dissolved solids in a 100 cm3 sample of the drinking water. Your investigation should produce valid results.

Answer 1

Level 2: The design/plan would lead to the production of a valid outcome. All key steps are identified and logically sequenced.
3–4
Level 1: The design/plan would not lead to a valid outcome. Some relevant steps are identified, but links are not made clear.
1-2

•    weigh (evaporating) basin / dish
•    add measured volume of water
•    weigh (evaporating) basin / dish and water
•    heat to evaporate water
•    reweigh
•    repeat heating until constant mass obtained
•    subtract mass of (evaporating) basin / dish from mass
•    repeat and calculate a mean, discarding anomalous results
•    calculate the mass in 100 cm3 water if necessary