- Chapter 2.2 Water
- Water: The oxygen and the two hydrogen's are covalently bonded together. This is called an intramolecular force. Two water molecules are joined together by a hydrogen bond which is an intermolecular for.
- Properties of water
- High specific heat capacity: Water molecules are held together tightly by hydrogen bonds. A lots of heat energy is required to increase their kinetic energy and temperature. This means water does not heat up or cool down easily.
- High latent heat of vaporisation: When water evaporates, heat energy (the latent heat of vaporisation) helps the molecules to break away from each other to become a gas. The molecules are held together by hydrogen bonds so a large amount of energy is required for water to evaporate.
- Cohesion and surface tension: A drop of water on a flat surface does not spread out, but can look almost spherical. The hydrogen bonds between the molecules pull them together to demonstrate cohesion. The surface of the water can contract to give the surface of the water an ability to resist a force applied to it.
- Solvent: Water is a good solvent because water is polar, the positive and negative parts if the water molecules are attracted to the negative and positive parts of the solute. Water molecules cluster around the charged parts of the solute molecules or ions help separate them so they dissolve and form a solution.
- Reactant: Water is a reactant in photosynthesis and hydrolysis reactions such as digestion of starch, proteins and lipids. Water plays an important role in digestion and synthesis of large biological molecules.
- Density: When liquids get colder, they tend to get more dense, but water behaves differently. If water did behave this way water at the top of a pond would freeze and sink. The water replacing it on the top would do the same until the pond is full of ice. Ice is less then water due to its polar nature.
- Water is polar which means it has a slight charge called delta. Oxygen has a delta negative charge and hydrogen has a delta positive charge. Oxygen is attracted to hydrogen.
- The role water for living organisms
- High specific heat capacity: Living things need a stable temperature for enzyme-controlled reactions to work. Aquatic organisms need a stable environment to live in.
- High latent heat of vaporisation: It helps cool living organisms and keep their temperature stable. Mammals are cooled when sweat evaporates. Plants are cooled when water evaporates from mesophyll cells.
- Solvent: Molecules and ions can be transported around living organisms whilst dissolved in water.
- Density: Aquatic organisms have a stable environment in which to livet through the winter. Ponds and other bodies of water are insulated against extreme cold. The layer of ice reduces the rate of heat loss from the rest of the pond.
- Cohesion and surface tension: Columns of water in plant vascular tissue are pulled up to the xylem tissue together from the roots. Insects like pond-skaters are able to walk on water.
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