WJEC GCSE Chemistry
WJEC GCSE Chemistry 1.3 Water Exam Questions
Free WJEC GCSE Chemistry revision for 1.3 Water: what you need to know, common mistakes and exam-style questions with answers. Covers water supply and treatment, fluoridation, desalination, distillation, solubility curves, hard and soft water and methods of softening water.
Practise 1.3 Water with past papers
Once you have learnt this topic, find the 1.3 Water questions in real WJEC GCSE Chemistry past papers and mark them with the mark scheme. Doing lots of real questions is the quickest way to learn how examiners ask about each idea.
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About WJEC GCSE Chemistry 1.3 Water
Water is a distinctive topic in WJEC GCSE Chemistry Unit 1, focusing on one of our most essential resources. You need to know what is dissolved in natural water, how a sustainable water supply is maintained and how water is treated to make it safe to drink, including the arguments for and against adding fluoride. The topic covers desalination and distillation, solubility and solubility curves, and the causes and removal of hardness in water. The specified practical compares the hardness of water samples using soap solution. Examiners often set solubility curve reading questions and ask you to evaluate fluoridation or desalination.
What you need to know
- Water treatment Water is treated by sedimentation, filtration and chlorination. Chlorine kills microbes. Fluoride may be added to reduce tooth decay; arguments against include individual choice and possible health effects of too much fluoride.
- Desalination Desalination produces drinkable water from sea water, for example by distillation. It needs a lot of energy, so it is expensive and is mainly used where fresh water is scarce.
- Solubility Solubility is the mass of solute that dissolves in 100 g of water at a given temperature. Solubility curves show how this changes with temperature; the mass of crystals formed on cooling is the difference between the two solubility values.
- Hard water Hard water contains dissolved calcium and magnesium ions, which react with soap to form scum and need more soap to lather. Temporary hardness is caused by hydrogencarbonates and is removed by boiling; permanent hardness is not removed by boiling.
- Softening water Washing soda (sodium carbonate) precipitates calcium and magnesium ions. Ion exchange resins swap calcium and magnesium ions for sodium or hydrogen ions. Hard water has benefits (calcium for teeth and bones, possibly less heart disease) and drawbacks (scale in kettles and pipes).
- Hardness practical Add soap solution in small volumes to a fixed volume of water and shake, recording the volume needed for a permanent lather. Compare samples before and after boiling to show temporary and permanent hardness.
Common mistakes in 1.3 Water
- Saying hard water contains calcium. It contains dissolved calcium and magnesium ions, which react with soap.
- Writing that boiling removes all hardness. Boiling removes only temporary hardness caused by hydrogencarbonates.
- Stating that chlorine is added to remove solids. Filtration removes solids; chlorine kills microbes.
- Reading solubility from the curve and forgetting the amount of water. Solubility is per 100 g of water, so scale your answer if the question uses a different mass of water.
Try three 1.3 Water exam-style questions
1. Explain why chlorine is added to drinking water. (1 mark)
Show the mark scheme answer
To kill microbes / bacteria.
2. The solubility of a salt is 80 g per 100 g of water at 60 °C and 30 g per 100 g of water at 20 °C. Calculate the mass of crystals formed when a saturated solution in 50 g of water is cooled from 60 °C to 20 °C. (2 marks)
Show the mark scheme answer
Per 100 g: 80 - 30 = 50 g; for 50 g of water = 25 g.
3. Describe how a student could show whether a sample of hard water contains temporary or permanent hardness. (4 marks)
Show the mark scheme answer
Add soap solution to a measured volume of water and shake, recording volume needed for a lather; boil a second sample and repeat; if less soap is needed after boiling, temporary hardness was present; if the same volume is needed, the hardness is permanent.
1.3 Water FAQs
What does WJEC GCSE Chemistry 1.3 Water cover?
It covers natural water, water treatment, fluoridation, desalination and distillation, solubility and solubility curves, and the causes, benefits, drawbacks and removal of hardness in water.
Which unit is Water examined in?
It is examined in Unit 1: Chemical Substances, Reactions and Essential Resources, a 1 hour 45 minute written paper worth 45% of the GCSE, sat at foundation or higher tier. The Unit 3 practical assessment draws on the same practical skills.
How do I evaluate fluoridation in an exam?
Give a balanced answer: for, it reduces tooth decay especially in children; against, it removes individual choice and too much fluoride can cause problems such as fluorosis. Finish with a judgement.
