Water purity

This topic is common to all specifications, it is expected that students know about the water cycle, the difference between hard and soft water, the effects of hard water and how to remove ions that cause hardness. This includes the relative solubility of different salts in water

There are good opportunities in this topic for students to carry out research and practical investigations.

Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance

 

Links and Resources

World Water

This is a series of eight resources which can be used to teach about world water supplies (some of these have cross-curricular links to biology topics, including micro-organisms and spread of disease).

You could introduce the lack of available 'clean' drinking water in certain parts of the world by using the video 'Safe Drinking Water' as a starter. This could then be followed by showing a sample of water in a bottle and asking the students if it is 'clean'. The definition of 'clean' could be discussed with students and what they mean by 'pure'. The point to make is that water does not have to be pure to be fit to drink but it has to be free from micro-organisms which would cause disease. Much of the water we drink is not pure because it contains dissolved salts.

The pack includes resources about how water is contaminated and how it is treated to make it safe for human consumprion e.g. filtration. This can support students independent research into water treatment methods - a visit to a local water treatment plant or sewage works would be ideal!.

An good practical activity would be getting the students to pass various solutions like orange juice, coke through separating columns filled with soil,  limestine and activated charcoal to find out how this affects the appearance and properties like pH. The use of activated charcoal in gas masks is an additional discussion point.

Water and waste engineers are responsible for using technologies in water treatment and 'Engineers can save lives'  highlights a potential career path which makes use of this branch of chemistry. 

publication year
2010 to date

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Drinking Water

This resource can be used by your students as part of a research project exploring the safety of drinking water in different parts of the world.

As a starter activity you can use a 'Reading Images' activity: show students various photographs or images of people in various countries and the water/sanitation conditions. Ask them to say what the pictures tell them, what they might infer from them and what questions they might want to ask the people in the pictures. This should prompt a discussion about whether people in different countries have access to safe drinking water.

An alternative way to approach this topic is to consider atronauts in space. The space shuttle can only take a limited supply of fresh water into space. What heppens when this runs out? This will take a while for the idea to register with the students as they realise what the astronauts will eventually be re-cycling!

Encourage the students to appreciate that the Earth is a closed system just like to space shuttle and that water needs to be re-cycled for use as drinking water. This should help them see the importance of water treatment technologies and provide relevance for their research.

publication year
2000 - 2009

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Water Supply and Developing Countries

Students may be surprised at how much water is used in manufacture of many materials. You could use available websites so that students can explore not only their own water footprint but the global footprint:

They could consider how much water they use for every day activities - shower/bath, washing, cooking cleaning their teeth and so on. They could consider how people manage when water is scarce and what they can do to reduce their water footprint.

This resource pack is very comprehensive and can be used to highlight issues such as global water scarcity, the challenges people face when sourcing water and maintaining a water supply in developing countries and the role of the engineers in solving these problems.

This could lead to an ethical debate about the amount of money spent on bottled water in affluent societies where tap water is freely avaiable and safe to drink.

 

publication year
2010 to date

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Chemical Filtration

This activity can be used as a follow up activity to students research. Pond or river water can filtered to remove solids. The resultant filtrate may look 'clean' but it still contains dissolved salts and microorganisms may be present.  Students could look at a sample of this water under a microscope to confirm the presence or absence of any microorganisms.

Filters with carbon and ion exchange resins can be used to remove some of the dissolved substances/salts in tap water to improve the taste and quality. Students could investigate the effects of using Brita filters on samples of water.

The use of chlorine for sterilisation purposesand the addition of fluorine to tap water also make interesting discussion points.

Pure water is produced by distillation - this again can be related to the re-cycling of water in the space shuttle and ensure students realise that pur water does not contain anything else.

Students may find the difference between adsorption and absorption confusing:

Adsorption: a gas, liquid or a dissolved substance is gathered on the surface of another substance, such as charcoal. Adsorption by charcoal is also used to remove unburned hydrocarbons from car exhausts, harmful gases from the air, and unwanted colours from certain products. The regulations that car manufacturers have to follow to avoid air pollution by exhaust emissions can be a point of discussion.

Absorption: a liquid is soaked up, as with a blotter. It is taken in completely and mixes with the absorbing material. You could make links here to help explain saturation to students.

 

publication year
2000 - 2009

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The Effect of Temperature on Solubility

Students should know that solids are generally more soluble in hot water than in cold water. The solubility of a solute in water (or another solvent) is usually given in grams of solute per 100 grams of water (or other solvent) at a particular temperature.

Students can carry out solubility experiments and plot solubility curves: solubility in grams of solute per 100g of water against temperature.

Students should be introduced to the term 'saturated solution' which is a solution in which no more solute will dissolve (for a given temperature).

A very visual demonstration showing a saturated solution is the sodium ethanoate stalagmite.  It shows that when a hot saturated solution is cooled, some of the solute may come out of solution vey dramatically with the introduction of a piece of dust.

Solubility curves can be used to show the temperature at which crystallisation will occur.

Follow up work could include identifying which type of substances are soluble and which are not.

publication year
2000 - 2009

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Testing Water Hardness

This experiment provides an opportunity for students to investigate the hardness of the water and link it to everyday activities, like the amount of soap/detergent needed for washing. Depending on the water hardness in your area, you can have a discussion about the effects of hard water on kettles and washing machines.

Rainwater, seawater and temporary hard water samples are used for the experiment, making reference to the water cycle and the effects of air poution on rain water which otherwise should be relatively pure.

Tap water in some parts of the country is very pure and is said to be ‘soft’ - it easily makes a lather with soap. Water from other parts may contain various dissolved impurities and is described as ‘hard’ water. Students may have noticed this if they have expereinced different areas from holidays.

You could discuss the range of mineral water available in the supermarkets and what the differences are between them. Why people buy them when drinkable water is available on tap?

 

publication year
2000 - 2009

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Water Treatment

If you are not able to take students on a field trip to a local water treatment plant then you could use this resources as a case study to highlight how water treatment is carried out in a specific context. Students explore the processes involved in making industrially contaminated water fit to drink.

The case study can provide background information for students to to use in a discussion/debate activity. Students can evaluate the implications and ethics of using a valuable and limited commodity, like water, in industrial processes when there are so many places in the world where water is scarce.

 

publication year
2010 to date

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