Analysing Water Samples

Topic 10 - Using Resources
Written by Atheridge Tuition

Plan an investigation to determine the pH and mass of dissolved solids in a sample of water.

[AQA Required Practical - 6 marks]

Visual Mark Scheme Breakdown

1. Test pH

    • Dip universal indicator paper into the water sample using clean forceps. Compare the resulting colour with a pH colour chart to determine the pH.

    • Different water samples may have different pH values. In this example, the indicator paper turns green, showing a neutral pH of 7.

Forceps holding universal indicator paper dipped into a water sample to test its pH in the AQA GCSE Chemistry required practical.
Green universal indicator paper removed from a water sample and compared with a pH colour chart, showing a neutral pH of 7.

2. Test Mass of Solids

    • Weigh the evaporating basin on a digital balance and record the mass

    • Use a measuring cylinder to pour a set amount of the sample into the basin

Vector graphic showing digital balance with evaporating basin on top. Text reads: record mass of evaporating basin.
Vector graphic showing water sample being poured using a measuring cylinder into the evaporating basin. Text reads: Pour 25cm^3 of water sample.

    • Wear safety goggles to protect eyes from spitting solids.

    • Gently heat the evaporating basin using a water bath until the water evaporates.

Vector graphic showing the evaporating basin with water sample suspended above a water bath above a bunsen burner flame. Text reads: Heat basin and contents.

    • Remove the evaporating basin carefully and let it cool.

    • Weigh it.

    • Keep heating it until the mass of the evaporating basin and its contents is constant.

Vector graphic showing evaporating basin with contents on a digital balance. Text reads: Weigh. Keep heating until mass is constant.

  • Carry out the following calculation:

    Mass of basin and contents - mass of evaporating basin = mass of dissolved solids

Vector graphic showing evaporating basin with contents minus evaporating basin alone, equals contents (water sample alone). Text reads: mass of basin & contents - mass of basin = mass of dissolved solids.
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