And so attracts both. Once the ions have separated they are prevented from rejoining by water molecules clustering round each of them. Therefore water is an extremely good solvent from which ionic solids and polar molecules easily dissolve in it. This property is very important in every day life. Wherever water goes , in the ground or through our bodies it is able to carry along valuable chemicals, minerals and nutrients. It is also of great biological importance because all the chemical reactions that take place in cells do so in aqueous solution. Carbon dioxide also dissolves in water to form a weak carbonic acid.
The heat capacity of Water
Heat capacity is defined as the amount of heat required to raise the temperature of 1gram by 1C. Water has a very high heat capacity compared with other liquids it therefore changes temperature more slowly than other compounds that gain or lose energy. The heat capacity of water is directly linked to its hydrogen bond structure. Although hydrogen bonds are weak, their combined effect however is much stronger. When heat is added to ice or liquid water, the energy first breaks the hydrogen bonds, which allows the molecule to move freely. Since the temperature is a measure of the average kinetic energy of the molecules, the temperature of water rises slowly with the addition of heat. When the temperature of water drops slightly, many additional hydrogen bonds form and release a considerable amount of energy in the form of heat.
This is why water is so valuable to industries and in cars radiators as a coolant. As it takes so long to heat up it also helps to regulate the rate at which air changes temperature, which is why the temperature between seasons is very gradual, especially near the oceans. This is due to the fact that the ocean can absorb and store a huge amount of energy heat from the sun during the daytime and summers. This resistance water has to sudden change makes it an excellent habitat because organisms adapted to narrow temperature ranges may die if the temperature fluctuates widely. The heat requiring and retaining properties of water provide a much more stable environment than is found on land.
This property of water is also vital for living organisms which need particular temperatures to optimize enzyme activity.When more water is present in the cells and tissues a constant temperature is more eadily maintained which is also why water is so important. Because of its high specific heat capacity it is also able to remain a liquid over a huge temperature range which is essential for metabolism and aquatic organisms which avoid freezing, it also has a very high boiling point of 100C
The surface tension of water
Surface tension is force acting within the surface of a liquid that causes it to contract so that it occupies the least possible area. This is caused by the inward-acting cohesive forces between the molecules at the surface, which is caused by the polarity of the molecule. Water has a greater surface tension than all other liquids except mercury.at the point where water and air meets (interphase) is an ordered arrangement of water molecules which are hydrogen bonded to one another. The result is an interfase under tension.
This also plays an important part in the movement of molecules across it, also plays an important part in the movement of water up the capillary like vessels and tracheids in the stems of plants, and it enables the surface to support and provide a habitat for certain aquatic organisms. Aquatic organisms have evolved adaptions that allow them to spread their body weight over a large surface area to prevent breaking water’s surface tension.The air water interface forms a special habitat for organisms adapted to living in this surface where tension is big.Water’s high surface tension serves as a supporting surface for many organisms.
The hydrophobic effect, or the exclusion of compounds containing carbon and hydrogen (non polar compounds) is another unique property of water caused by the hydrogen bonds. The hydrophobic effect is particularly important in the formation of cell membranes. Water pushes the non polar molecules together (see diagram 3)
Diagram 3 The phospholipid bilayer making up the cell surface membrane
Most materials are transparent to some sort of wavelengths of electromagnetic radiation. Materials absorb radiation either by making the atoms vibrate, or by exciting electrons into different energy levels. However only one particular wavelengths will do this and the ones that cant passes straight through. It so happens that for water these wavelengths correspond to the visible wavelengths – light. That is why water is transparent.
Water as a solid , liquid and gas.
Water is the only natural substance that is found in all three states liquid, solid (ice) and gas (steam).Water turns to a gas when enough energy is given to break the strong bonds in the liquid and turn it into gas. AT a 100C is when this happens (boiling point). Water is very different to other liquids in the fact that when it freezes it is less dense, than a liquid. Most liquids contract when they solidify but water expands. This property is due to the hydrogen bonding. Water starts to freeze at 0C and the molecule no longer moves vigorously enough to break their hydrogen bonds. The water molecules become locked into a crystalline lattice, and each water molecule is bonded to a maximum of four partners. (see diagram4).
Diagram 4 The arrangement of water molecules in ice
This often happens on lakes, where temperatures go below 0C, this causes ice to form at the top of the lake. The ice becomes an insulating layer on the surface of the lake, it reduces heat loss from the water below and enables life to continue in the lake. When ice absorbs enough heat for its temperature to raise above 0C, the hydrogen bonds can be broken and allow the water molecules to slip closer together. The ice stays at the top, and doesn’t sink because its density is almost ten times lighter than liquid water
Water has many unique properties which is vital for our every day life, and as shown there is many processes of benefit to humans and other organisms, all because wateris present.
