Biological molecules - water

physical and chemical properties of water.

Properties of water

Polar molecule

cohesion

adhesion

high specific heat capacity

high latent heat for vaporisation

ice is less dense

universal solvent for life

Polar molecule

It has uneven number of charges

the O atom is slightly negative
the H atom is slightly positive

The number of hydrogen bonds a water molecule can form…

…upto four neighbours

Hydrogen bonds form, break and reform…

…at great frequency

Numerous hydrogen bonds makes it a…

…very stable structure

Cohesion

Water molecules are attracted to each other and form hydrogen bonds

they move together as a chain

Adhesion

Water molecules stick to surfaces

due to the polarity it gets attracted to other charged or polar substances

Surface tension

a measure of the force necessary to stretch or break the surface of a liquid

Water behaves as if…

…it is covered by invisible film

High specific heat capacity

The amount of heat that may be absorbed or lost for 1 kg of a substance to change its temperature by 1’C

Water has a specific heat capacity of…

…4200J/kg’C

Water doesnt change temperature drastically so…

…this can be used to maintain a suitable temperature

Water can absorb/release relatively large amounts of heat…

…with only a slight change in its temperature

High latent heat of vaporisation

the thermal energy required to convert a specific amount of a substance from a liquid to a gas at a constant temperature and pressure

This is responsible for…

moderating earths climate

stabalising temperature in aquatic ecosystems

preventing organisms from overheating

Density

The mass of a substance per unit volume

most dense at 4’C
expands from 4’C to 0’C

Ice forms from…

…top to bottom

Solution

solute and solvent

Aqueous solution

solution in which water is the solvent

Hydrophilic

form hydrogen bonds with water

Hydrophobic

cant from bonds with water

hydrocarbons