1. Water on Earth

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

1.1 - Define the terms solute, solvent and solution

Solute: Substance that is dissolved in a solution - it is the substance to be dissolved

Solvent: Substance that can dissolve a solute - it is the substance doing the dissolving

Solution: A homogeneous mixture of a solute dissolved in a solvent

Solute + Solvent = Solution

1.2 - Identify the importance of water as a solvent

Water is capable of dissolving a very wide variety of substances, and is able to dissolve more substances than any other liquid

It is essential as a reactant to recycle elements throughout nature

It allows biological processes to occur in aqueous solutions, serving as a transport system for nutrients and waste products in living organisms

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

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1.4 - Outline the significance of the different states of water on Earth in terms of water as: a constituent of cells and its role as both a solvent and a raw material in metabolism, a habitat in which temperature extremes are less than nearby terrestrial habitats, an agent of weathering of rocks both as liquid and solid, a natural resource for humans and other organisms

Water as a Constituent of Cells

Water takes part in many metabolic reactions of cells, which are vital for all living organisms on earth

As a raw material, it takes part in photosynthesis as a reactant, and respiration as a product, both of which are necessary for life to be possible

Photosynthesis: 6CO2 + 6H2O --> C6H12O6 + 6O2

Respiration: C6H12O6 + 6O2 --> 6CO2 + 6H2O

It is also incredibly useful and necessary as a solvent in its liquid state, as it is the medium fro various chemical and enzymatic reactions

In animals, it moves nutrients, hormones, antibodies and oxygen through the bloodstream

Water as a Habitat

All living organisms are composed of cells, which host a huge range of chemical reactions, catalysed by enzymes

Water serves as a natural habitat for many organisms, providing them with a stable, consistent temperature range which does not fluctuate easily, as water has a high heat capacity

This allows for the enzymes in the cells to function, and life to exist

Water as a weathering agent

Weathering is the physical and chemical breakdown and decay of rocks

Physically, rocks are broken down by the constant motion of the water wearing away at rock surfaces, and the expansion of water as it freezes between cracks in rocks

Chemically, water dissolves and reacts with some minerals present in rocks

The movement of water also produces landforms such as ocean cliffs, beaches and rock platforms

Water in the form of ice glaciers are also responsible for the production of rich soils by gradually grinding away at rocks underneath

Water for humans and organisms

Water is critical for humans and organisms, taking part in respiration and photosynthesis

It is used for drinking, washing, agriculture, industrial processes, and is a source of entertainment and leisure

It also serves as a medium for transport systems

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1.1P - Perform an investigation involving calculations of the density of water as a liquid and a solid using: density = mass/volume

Density = mass/volume, measured in kg/m^3 or g/cm^3

As temperature increases, volume generally increases as particles gain kinetic energy

However the mass remains the same as no particles are added or lost, leading to a decrease in density

As the mass remains constant, but the volume increases, the density decreases

As the temperature of water decreases down to 4 degrees, its density increases

However as its temperature decreases from 4 degrees down to 0 degrees, its density does not continue to increase, but decreases as it expands due to the intermolecular forces in water causing molecules to arrange themselves in a particular way

This allows ice to float on water