Water CHEMISTRY 2 Additional Science Chapter 8. The Importance of Water Water is essential to life on Earth Water is used widely as a solvent in industrial.

WaterWaterCHEMISTRY 2CHEMISTRY 2

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The Importance of WaterThe Importance of Water

Water is essential to life on Earth

Water is used widely as a solvent in industrial

processes

Water is used widely as a coolant in industrial

processes

75% of the world’s surface is covered by

water

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The public water supplyThe public water supply

Water from river, lake or underground well stored in a reservoir

Solids allowed to settle

Filtration to remove smaller particles

Cl17

35

Chlorination to kill bacteria

Storage in tank or water tower before use by schools. Factories etc.This is the process that takes place to ensure that we have a

supply of drinking water. Some water authorities add other chemicals to drinking water e.g. many add fluoride ions which prevent tooth decay at controlled levels.

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Hard waterHard water

As rain water flows through rocks, it picks up calcium and magnesium ions. The result is - hard water.

Hard water forms scale (calcium carbonate) in pipes, and restricts water flow.

Hard water doesn’t produce soap suds easily.

This fact can be used to prove for water hardness, and to compare the hardness of different samples.

Hard water mixes with soap to form calcium or magnesium stearate which is insoluble – this is why soap scum forms.

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Types of hardnessTypes of hardness

Reason:-

Presence of calcium or magnesium carbonate in the water

Temporary hardness

Solution:-

Boiling the water. The hydrocarbonates decompose, leaving insoluble calcium carbonate or magnesium carbonate – this is the scale found in kettles and boilers.

Equation:-

Ca(HCO3)2 Ca CO3 + CO2 + H2O

Permanent hardness

Reason:-

Presence of calcium or magnesium sulphate in the water.

Solution:-

Soften the water by adding sodium carbonate or by ion exchange.

Equation:-

Na2CO3 + CaSO4 Ca CO3 + Na2SO4

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Hard waterHard water

AdvantagesAdvantages DisadvantagesDisadvantages

It produces boiler scale

Uses more energy to boil the water

More soap has to be used, resulting in soap scum

in the wash. Modern detergents are used instead

of soap in washing machines.

Removing boiler

scale is expensive

Reduces the efficiency of

kettles, boilers, coffee

machines etc.

Hard water tastes better than soft water. Beer production often involves artificially hardening the water.

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Solubility curves

water

sugar

The sugar doesn’t dissolve in the water any longer – you have a saturated saturated solution.solution.

TermsTerms

Solute – the substance thatdissolves (sugar).

Solvent– the liquid doing the dissolving (water).

Solubility – mass of solute that dissolves in a certain mass of solvent.

Usually the solubility of a solute increases with an increase in temperature

potassium chlorate

sodium chloride

Temperature °C

So

lub

ility

/

g p

er

10

0g

of

wa

ter Solubility curve

Can you think which solute’s solubility is

most affected?

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