Surface Tension Colour Cohesion Properties of Water WJEC

Surface Tension Colour Cohesion Properties of Water WJEC GCE BIOLOGY Latent heat State at room temp. Specific heat capacity Density Next

Properties of Water WJEC GCE BIOLOGY Match the property of water with the corresponding significance for life and correctly fill in the table START

Property of water Ice is less dense than water Significance for life Answers The high surface tension of water means that it can form a habitat on the surface of the water High surface tension Can be used for cooling organisms by evaporation of for example sweat Strong cohesive properties and high tensile strength Colourless with a high transmission Properties of Water WJEC GCE BIOLOGY Liquid at room temperature In order to evaporate it must absorb a large amount of energy (high latent heat of vaporisation) Water can absorb a lot of energy for only a small rise in temperature (high specific heat capacity) Ice forms an insulating layer over water Conditions are stable in cells and aquatic environments Can be used for transport and a medium for reactions Light can pass through cells for photosynthesis Water can be pulled through plants in a column as the water molecules are held together by H-bonds

Property of water Ice is less dense than water Ice forms an insulating layer over water High surface tension The high surface tension of water means that it can form a habitat on the surface of the water Properties of Water Strong cohesive properties and high tensile strength WJEC GCE BIOLOGY Significance for life Water can be pulled through plants in a column as the water molecules are held together by H-bonds Colourless with a high transmission Light can pass through cells for photosynthesis Liquid at room temperature Can be used for transport and a medium for reactions In order to evaporate it must absorb a large amount of energy (high latent heat of vaporisation) Can be used for cooling organisms by evaporation of for example sweat Water can absorb a lot of energy for only a small rise in temperature (high specific heat capacity) Conditions are stable in cells and aquatic environments Next

Surface Tension • • Properties of Water WJEC GCE BIOLOGY • • The surface of water can behave like an elastic sheet The molecules in the bulk of the liquid are effected by various intermolecular forces of attraction Those molecules in the surface are not effected by molecules above them, and therefore ‘pull’ together more strongly, effectively resembling a stretched membrane A habitat can therefore survive on the surface of the water Back

Colour – transmission of light • • Water is colourless and is therefore transparent to light This means that sunlight can reach the cells and pass through them so that photosynthesis may occur Reflected by leaves 53% 10% Properties of Water WJEC GCE BIOLOGY Sun light Light absorbed by leaves (typical values): Near IR 15% Red 82% Green 80% Blue 84% 13% 9% 8% 7% 7% 32% Transmitted through leaves Back

Cohesion • Water molecules show a strong attraction to one another, this is called cohesion. Properties of Water WJEC GCE BIOLOGY Droplets of water form spheres due to cohesion between water molecules Back

Latent heat • While changing state, a substance will take in heat energy (solid liquid gas), or expel heat energy (gas liquid solid) without a change in temperature. This is termed Latent Heat. temperature evaporate GAS condense LIQU LID melt Water has a large latent heat of vaporisation, and therefore absorbs a large amount of heat energy while changing from water to vapour. solidify SO Properties of Water WJEC GCE BIOLOGY ID • time Back

State at room temperature • Water is a liquid at room temperature. However, all other similar molecules are gases. + H H Hydrogen bonds form because of polar covalent bonding between the oxygen and hydrogen atoms + O 2 - Properties of Water WJEC GCE BIOLOGY + H H + + H H O O 2 - • + H H O 2 - + + Hydrogen bonds act between the water molecules, and they attract them enough so that it behaves as a liquid. Back

Specific Heat Capacity • The heat needed to raise the temperature of 1 kg of water by 1°C is termed the Specific Heat Capacity. • Water has a large specific heat capacity, and therefore can absorb large amounts of heat energy before its temperature raises a significant amount. Properties of Water WJEC GCE BIOLOGY thermometer 1 kg of water Back

Density of water • Unlike other substances, water expands as it freezes. H H H O H O H H Properties of Water H O • As water expands when it freezes, its density (mass per unit volume) will decrease. • This means that ice is less dense than water, and will therefore float on top of it. H H H O Water molecules in ice form a rigid structure so that there is more space between them, this is seen as expansion as a whole O H Water molecules are able to approach one another quite closely WJEC GCE BIOLOGY H O Ice Water H H O Back