3.6 To discus the advantages of water as a solvent

Natural sciences

The earth and beyond

Form, reaction and alteration of materials

Educator section

Memorandum

THE VALUE OF WATER.

• Medium in which animals and plants can live because oxygen is soluble in water.
  • General solvent
• Keeps nature clean (“washes” nature)
• Medium in which processes in the body take place (the contents of our bodies would not interact in powder form.)
• Doesn’t change temperature quickly (has to gain or lose a lot of heat to raise or lower its temperature by 10 C. This enables us to maintain a constant body temperature.).

Leaner section

Content

Activity: to discus the advantages of water as a solvent [lo 2.1, lo 2.3]

Advantages:

• Many aquatic animals are dependent on the oxygen in water. Natural water in rivers and lakes contains oxygen. When the water is colder or when it flows over waterfalls, more gases dissolve into the water. This explains why fish that live in rivers cannot survive in a fish tank at home – there is not enough oxygen.
• Carbon dioxide is soluble in water. An example of this is the gas used in fizzy drinks.
• Medicinal substances (solids or liquids) are dissolved in water to be taken as medicines.
• Dirt in our clothes can be dissolved in water when our clothes are washed.
• We wash ourselves with water every day.
• Sugar, salt and other flavourants dissolve in water. We can use this to flavour foods.
• Dyes are soluble in water.

Disadvantages:

• Poisons can be dissolved in water.
• Too much water in the ground can dissolve the salts and sink deeper into the ground. The soil then has too few minerals.
• Some dyes are soluble in water. When the clothes are washed the colours fade, or the dissolved dyes stain other clothes.

Write a paragraph about the value of water in nature.

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Assessment

Learning Outcome 2: Learners know, interpret and apply scientific, technological and environmental knowledge.

Assessment Standard 2.1: We know this when the learner recalls meaningful information: at the minimum, describes the features which distinguish one category of thing from another;

Assessment Standard 2.3: We know this when the learner interprets information: at the minimum, interprets information by using alternative forms of the same information.