Water is not an organic molecule but is essential for life on this planet All cells are surrounded inside and out with water – anything that interacts with a cell must first be dissolved in water Physical properties: – colourless and transparent – liquid at room temperature – density = 1.0 g/mL – m.p. = 0 ℃ b.p = 100 ℃ water has LD, D-D forces, and H-bonding

Water has cohesive properties – the high number of intermolecular forces causes water molecules to ‘stick’ together Examples: – surface tension – beading of water – water striders – too light to break surface tension – transpiration in plants – transport in xylem tubes

Water has adhesive properties – it’s polar nature causes it to stick to other substances Examples: – capillary action – water ‘climbs’ up small diameter tubes, or ‘bleeds’ through the microscopic pores and channels in paper or other porous substances – this is due to the hydrogen bonding interactions between the water and the surface of the tube (either SiO 2 or the cellulose tubes of paper) – This helps to explain the meniscus inside a tube

Water has outstanding solvent properties Used to be called the ‘universal solvent’, but this is not a good name, since not everything dissolves in water The polar nature of water allows any other polar substance or any charged particle to dissolve easily The δ - will attract the δ + end of solutes, and this attraction will remain once the solute is dissolved. The same is true for ionic substances – the cation will be attracted to the δ - end of water, and the anion will be attracted to the δ + of water.

Water has a high specific heat capacity This is a measure of the amount of heat energy required to increase the temperature of a 1g of a substance by 1 ℃. c water = 4.18 J/g ‧℃ This is high compared to other substances: c copper = J/g ‧℃ c air = 1.00 J/g ‧℃ c glass = J/g ‧℃ c iron = J/g ‧℃ A metal pan absorbs heat energy quickly and loses it quickly. This makes metals useful for cooking. Water takes more energy to heat up – thus the time it takes to boil water in a pot.

Moderation of climate This property of water also helps to moderate temperature changes in cells

Water has a high latent heat of vaporization and fusion. Latent heat is the energy absorbed or released by a substance during a change of state. L f water = 334 J/g L v water = 2260 J/g Special Properties of water

Latent heat

Evaporative cooling relies on L v of water. Latent heat of vaporization

Tender fruit farmers take advantage of the latent heat of fusion of ice when there is a chance of frost On an evening when there is frost in the forecast, they spray water over their fruit, causing ice to form as the temperature drops below 0°C. How does this help to protect the fruit? Latent heat of fusion

Water’s density decreases as it changes from liquid to solid. This is because the distance between molecules in a crystal lattice (as ice) on average further than when in a liquid. Special Properties of water

HOMEWORK Read and Summarize Page: 195 “Salt and Ice” Pages: Unuaual Properties of Water Questions page 198 # 1,11