Required Practical: Analysing and Purifying Water
Chemistry: AQA GCSE Higher, topic 10.1.5
Method 1: Analysing Water Samples (PH and Dissolved Solids)
This experiment aims to test water samples from different sources for pH and dissolved solids.
Apparatus
- Water samples (A, B, C, D)
- Universal indicator paper or pH meter
- Evaporating basin
- Mass balance
- Measuring cylinder
- Bunsen burner
Method
- Use a universal indicator or a pH meter to measure the pH of each water sample.
- Weigh an empty evaporating basin accurately.
- Add 25 cm3 of the water sample to the basin.
- Heat gently over a Bunsen burner until most of the water evaporates.
- Once cooled, reweigh the basin and calculate the mass of solid left behind.
Reminders
- Avoid overheating:
- Some solids may decompose, giving false results.
- The mass of residue shows how much dissolved solids the water contained.
Analysis
- Compare pH and solid content between samples.
- High solid content or very low pH suggests poorer water quality.
- Results can indicate where the water might have come from:
- For example, the sea, river, rain
- Compare results to safe drinking water standards.
Hazards and precautions
- Acidic or alkaline water samples:
- Some samples may cause irritation to the eyes or skin.
- Rinse immediately if contact occurs.
- Heated apparatus:
- Touching hot apparatus may cause burns.
- Allow them to cool before holding.
Test yourself on Required Practical: Analysing and Purifying Water
Why should hot apparatus be allowed to cool before it is touched?
Why is the evaporating basin weighed both before and after heating?
Why is the boiling point and pH of the distillate measured after distillation?
Why does a large mass of solid residue left after evaporation suggest that a water sample is of poor quality?
Why are a water sample's pH and dissolved solid results compared with safe drinking water standards?