Properties of water1

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Properties of water1

  1. 1. Surface Tension Colour Cohesion Properties of Water WJEC GCE BIOLOGY Latent heat State at room temp. Specific heat capacity Density Next
  2. 2. Properties of Water WJEC GCE BIOLOGY Match the property of water with the corresponding significance for life and correctly fill in the table START
  3. 3. Property of water Ice is less dense than water High surface tension 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) Significance for life Answers The high surface tension of water means that it can form a habitat on the surface of the water Can be used for cooling organisms by evaporation of for example sweat 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
  4. 4. Property of water Significance for life 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 Strong cohesive properties and high tensile strength Water can be pulled through plants in a column as the water molecules are held together by H-bonds Properties of Water Light can pass through cells for photosynthesis Liquid at room temperature WJEC GCE BIOLOGY Colourless with a high transmission 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
  5. 5. 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 Back
  6. 6. 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% 13% Properties of Water WJEC GCE BIOLOGY Sun light Light absorbed by leaves (typical values): Near IR 15% Red 82% Green 80% Blue 84% 9% 8% 7% 7% 32% Transmitted through leaves Back Back
  7. 7. 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 Back
  8. 8. 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 LIQ melt SO LI D Properties of Water WJEC GCE BIOLOGY UID • Water has a large latent heat of vaporisation, and therefore absorbs a large amount of heat energy while changing from water to vapour. solidify time Back Back
  9. 9. State at room temperature • Water is a liquid at room temperature. However, all other similar molecules are gases. δ+ H O H Hydrogen bonds form because of polar covalent bonding between the oxygen and hydrogen atoms δ+ 2δ- Properties of Water WJEC GCE BIOLOGY δ+ H O H δ+ δ+ H O H δ+ 2δ- 2δ- δ+ H O 2δ- H δ+ • Hydrogen bonds act between the water molecules, and they attract them enough so that it behaves as a liquid. Back Back
  10. 10. Specific Heat Capacity • The heat needed to raise the temperature of 1kg of water by 1°C is termed the Specific Heat Capacity. Properties of Water WJEC GCE BIOLOGY thermometer • Water has a large specific heat capacity, and therefore can absorb large amounts of heat energy before its temperature raises a significant amount. 1kg of water Back Back
  11. 11. Density of water • Unlike other substances, water expands as it freezes. H Ice Water H H O H O H H O H O H H H O H Water molecules are able to approach one another quite closely Properties of Water WJEC GCE BIOLOGY O H H H H O H O 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 H H H H O O H H • 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. Back Back

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