1.3.10Chemical Substances, Reactions and Essential Resources
Benefits and Drawbacks of Hard Water
5 min read 7 parts Lesson 32 of 46 Unit quiz
Section 1 of 7Benefits of hard water
Healthy bones and teeth
- Healthy bones and teeth Dissolved calcium compounds are a useful source of calcium in the diet,
- and calcium is needed to build and maintain strong bones and teeth.
- People who live in hard-water areas therefore take in a little extra calcium every time they drink tap water.
Heart health
- Heart health The calcium in hard water is linked with a lower risk of heart and cardiovascular disease.
- This is a link found in population studies, so it is described as a possible benefit rather than a proven cure.
Taste and brewing
- Taste and brewing Many people prefer the taste of hard water because the dissolved minerals give it a fuller flavour than very pure water.
- Some brewers believe that hard water makes better beer, and certain traditional brewing towns grew up where the local water was hard.
Section 2 of 7Drawbacks of hard water
Problems for homes and industry
Poor lather
- Poor lather Calcium and magnesium ions react with soap, so soap is used up before it can form a lather.
- More soap is needed to wash, and household costs rise.
Scum
- Scum Soap reacts with the ions to give an insoluble scum,
- which looks unpleasant, floats on the water and leaves a grey ring on baths and basins.
- It can also mark clothes.
Scale in appliances
- Scale in appliances Scale deposits in kettles, washing machines and boilers slow down heat transfer,
- so the appliances work less efficiently and waste energy.
Blocked pipes
- Blocked pipes Hot-water pipes can 'fur up' as scale builds on the inside, narrowing the bore until they are partly or completely blocked and need expensive repair or replacement.
Section 3 of 7How scale leads to higher costs
1Water is heated
- Water is heated Temporary hardness (dissolved calcium hydrogencarbonate) decomposes on heating to form calcium carbonate, water and carbon dioxide.
2Scale builds up
- Scale builds up The insoluble solid coats heating elements and the insides of pipes, layer after layer, every time the water is heated.
3Efficiency falls
- Efficiency falls Scale is a poor conductor of heat.
- It insulates the element, so more energy is needed to heat the same amount of water.
4Costs rise
- Costs rise Energy bills increase and appliances or pipes may need descaling or replacing, which costs both time and money.
Section 4 of 7Comparing hardness: a soap test
1
Measure the same volume of each water sample, for example 50 cm3, into separate conical flasks. Use distilled water as a soft-water control.
2
Add soap solution from a burette or dropper in small, equal portions, such as 1 cm3 at a time.
3
After each portion, put a stopper on the flask and shake it for a set time, such as 10 seconds, then look for a lather that lasts for 30 seconds.
4
Record the total volume of soap solution needed to produce a permanent lather in each sample.
5
Compare the results: the more soap solution needed, the harder the water. Repeat each test and calculate a mean to improve reliability.
6
Boil a second portion of each sample, let it cool, then repeat the test. If less soap is needed afterwards, the sample contained temporary hardness.
Section 5 of 7Using the ideas in an evaluation answer
Give both sides
- Give both sides A question that says 'evaluate' or 'discuss' needs at least one benefit and at least one drawback, each explained rather than just listed.
Link cause and effect
- Link cause and effect Do not just write 'scale is bad'.
- Say that scale insulates the element, so more energy is needed, so bills rise.
Reach a conclusion
- Reach a conclusion Finish with a judgement.
- For example, hard water is useful for health but costly for households, which is why many people fit a water softener.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Hard water | Water with high concentrations of dissolved calcium and magnesium ions. |
| Scale | A hard deposit of calcium carbonate formed when hard water is heated. |
| Scum | Insoluble solid produced when soap reacts with hardness ions. |
| Lather | The foam produced when soap mixes with water. |
| Heat transfer | The movement of thermal energy, for example from an element into water. |
| Temporary hardness | Hardness caused by dissolved calcium hydrogencarbonate, which is removed by boiling. |
Section 7 of 7Exam technique
1
Writing that hard water is unhealthy; its calcium content has health benefits.
2
Saying scale makes kettles heat faster - it insulates the element and makes heating less efficient.
3
Describing only drawbacks when the question asks for an evaluation; include benefits too.
4
Confusing scum (from soap and hardness ions) with scale (from heating temporary hardness).
5
Forgetting to keep the volume of water and the shaking time the same in the soap test, which makes the comparison unfair.