2.2- Properties of water Flashcards
What does water have that s essential to life?
Water has many properties that are essential for life, many of which depend on the polar nature of the water molecules an on hydrogen bonding between water molecules.
How is liquid a property of water?
As in any liquid, water molecules constantly move around. Unlike other liquids, as they move they continually make and break hydrogen bonds.
- The hydrogen bonds between water molecules makes it more difficult for them to escape to become a gas. By contrast, other less polar but similarly sized molecules (H2S) are gases at room temperature. Even with hydrogen bonds, water has quite a low viscosity, which means it can flow easily.
What can water do when liquid is at room temperature?
Because it is a liquid at room temperature, water can:
- Provide habitats for living things in river, lakes and seas -Form a major component of the tissues in living organisms.
- Provide a reaction medium for chemical reactions
- Provide an effective transport medium, e.g. in blood and vascular tissue
How is density a property of water?
The density of water provides an ideal habitat for living things. If water was less dense, aquatic organisms would find it very difficult to float.
-When most liquids get colder, they become more dense. If this were the case with water, then water at the top of the pond would freeze and sink. The water replacing it at the top, would do the same, until the pond will be full of ice. But water behavers differently. It becomes more dense as it gets colder until about 4 degrees . As it goes from 4 degrees to freezing point, because of its polar nature, the water molecules align themselves in a structure which is less dense than liquid water.
what happens to water as ice is less dense?
Because ice is less dense than water:
- Aquatic organism have a stable environment in which to live through 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
How is solvent a property of water?
Water is a good solvent for many substances found in living things. This includes ionic solutes such as sodium chloride and covalent solutes such as glucose. Because the water is polar the positive and negative parts of water molecules are attracted to the negative and positive parts of the solute. The water molecules cluster around the charged parts of the solute molecules or ions and will help to separate them and keep them apart. At this point they dissolve and a solution is formed.
What happens in the solvent?
Because water is a good solvent:
- Molecules and ions can move around and react together in water. Many such reactions happen in the cytoplasm of cells which is over 70% water.
- Molecules and ions can be transported around living things whilst dissolved in water.
How is cohesion and surface tension a property of water?
A drop of water on a flat surface does not spread out, but can look almost spherical. This is because hydrogen bonding between the molecules pulls them together. The water molecules demonstrate cohesion.
- This happens at the surface of water as well. The water molecules at the surface are all hydrogen bonded to the molecule beneath them, and hence more attracted to the water molecules beneath than to the air molecules above. This means the surface of the water contracts (because the molecules are being pulled inwards) and it gives the surface of the water an ability to resist force applied on it. This is known as surface tension
Because of cohesion and surface tension:
- Columns of water in plant vascular tissue are pulled up the xylem tissue together from the roots.
- Insects like pond skaters can walk on water
How is high specific heat capacity a property of water?
Water temperature is a measure of the kinetic energy of the water molecules. Water molecules are held together quite tightly by hydrogen bonds. Therefore you have to put in a lot of heat energy to increase their kinetic energy and temperature. The amount of heat energy required is known as the specific heat capacity (4.2kJ of energy to raise temperature of 1kg of water by 1 degrees) . This means that water does heat up or cool down easily.
Because the main component of many livings thing is water, and many organism live in water, its high specific heat capacity is important:
- Living things, including prokaryotes and eukaryotes, need a stable temperature for enzymes controlled reactions to occur.
- Aquatic organisms need a stable environment in which to live
How is heat latent heat of vaporisation a property of water?
When water evaporates, heat energy known as the latent heat of vaporisation, help molecules to break away from each other to become gas. Because the molecules are held together by hydrogen bonds, a relatively large amount of energy is needed for water molecules to evaporate. Therefore, water can help to cool living things and keep their temperature stable. For example, mammals are cooled when sweat evaporates and plants are cooled when water evaporates from mesophyll cells.
How is reactant a property of water?
Water is also a reactant in reactions such as photosynthesis and in hydrolysis reactions such as digestion of starch, proteins and lipids. Its properties as a reactant do not directly draw on its polarity, but its role as a is extremely important for digestion and synthesis of large biological molecules.
