Chem – Preliminary – Water

Water is a habitat:
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Water bodies have the advantage that they show less temperature fluctuations than do land and air masses.

Define the terms solute, solvent and solution.

A Solute is the substance (solid) that is placed in a solvent (liquid), and dissolved to produce a solution (a combination of a dissolved solute and a solvent).

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It is a habitat for life forms such as fish, algae and bacteria – the place where they live.

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Sec 1 – Water is distributed on Earth as a solid, liquid and a gas

Water is a major weathering and eroding agent:
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Identify the importance of water as a solvent.

Rain and rivers wash loose material to lower altitudes and eventually to the sea.

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Many drinks that humans use are aqueous solutions, as there are many household products such as bleaches, disinfectants, cleaning agents and some medicines. Industry uses aqueous solutions of acids and alkalies and often makes or extracts products from aqueous solutions.

Glaciers cut a swathe from mountain tops through weaker rocks to the oceans, and

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Water is the most widely used solvent used by humans and by nature. In all living matter most of the chemical reactions responsible for life occur in water solutions or aqueous solutions as they are called. Water dissolves nutrients from soil and carries them in solution to living cells. Water also carries waste products away from cells.

A freeze-thaw mechanism sees liquid water seep into small cracks in rocks, freeze and expand and so widen the crack until large fragments of rock break away.

Water is a resource for humans to use:
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Water is a resource for humans. We drink water and it is essential. Most body substances are dissolved in water for diffusion across cells.

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Compare the state percentage and distribution of water in the biosphere, lithosphere, hydrosphere and atmosphere.

Zone

State of Water
Liquid
Liquid, solids

Percentage of
Earths water
0.0001%
99.4%

Percentage water in that zone
60-90%
99%

Biosphere
Hydrosphere
Lithosphere
Atmosphere

Liquid
Gas, liquid and solid

0.6%
0.001%

10%
0.5-5%

Distribution medium
In living things
Oceans, rivers, icecaps, glaciers Water in rocks
Water vapour, rain, hail, snow

As a working fluid in electricity generating stations and as a coolant in them and in many industries -

For generating electricity directly

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In industry as a reactant, solvent and cleaning agent and for waste disposal and settling dust

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Furthermore water expands upon freezing. This is when water gets trapped in rocks during the warmer temperatures but during the colder temperatures the water freezes and thus expands, breaking the rock. This is due to the large amounts of pressure exerted by water on the rock. Water also causes erosion. At beaches water erodes rocks. When frozen, in glacier form it erodes as it moves.

For irrigation of crops, and watering of livestock

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Water is an important solvents as it is able to dissolve numerous amounts of solutes. We are made of water and due to its good nature as a solvent, our bodily functions are performed. Water controls the temperature of an environments, this is because less temperature variations occur in water than in land.

For drinking, food preparation, washing and recreation

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As a mode of transport (now less used – planes and trains are more widely used).

Density

For density prac – look in theory book

Density is a relationship between mass and volume.

Note for antifreeze prac – look at prac book

Density is calculated using the formula
Density = mass / volume
D

=

m/V

Units = g/cm^3, where m is in grams
= g/mL, where v is in cm^3/mL
When most liquids freeze, they produce a solid that is more dense than the liquid.
Water on the other hand is most dense at 4C.
Therefore ice floats on water.

• outline the significance of