PROPERTIES OF WATER ALL YOU NEED TO KNOW ABOUT WATER

DID YOU KNOW? Pure water has a pH of 7 97% of the earth’s surface water is contained in the oceans Water is often referred to as the universal solvent The human body is 70% water Water is the only substance which naturally occurs as a solid, a liquid and a gas on earth Ice is less dense than water

THE CHEMISTRY OF WATER WATER IS MADE UP OF TWO HYDROGEN ATOMS COVALENTLY BONDED TO EACH OTHER. THIS PRODUCES A V-SHAPED MOLECULE

COVALENT BONDING A COVALENT BOND OCCURS WHEN ATOMS SHARE ELECTRONS IN ORDER TO FILL THEIR OUTER ELECTRON SHELL HYDROGEN SHARES ONE OF THE ELECTRONS IN THE OUTER SHELL OF THE CARBON ATOM TO FILL ITS OUTER SHELL CARBON NEEDS TWO ELECTRON S TO FILL ITS OUTER SHELL SO IT SHARES THE ELECTRON OF TWO HYDROGEN ATOMS

WATER IS POLAR If the electrons in the covalent bond spend more time with the oxygen atom than with the hydrogen atom then the hydrogen atoms will have a partial positive charge The oxygen atom will have a partial negative charge as sharing the hydrogen electrons means that the oxygen will be sharing/have more electrons than protons. This means that water has a positive and negative end

Water is a polar molecule (Ie it has a positive and negative end). This allows water to create hydrogen bonds with other water molecules. Hydrogen bonds are weak bonds that result from the attraction of the partial positive hydrogen to the partially negative oxygen atom of another water molecule. MOVIE!

Water molecules cling together through hydrogen bonding creating properties such as surface tension, adhesion and capillary action. Hydrogen bonding also explains why water expands when it freezes, why it has such a high boiling point and why it is such a good solvent.

SURFACE TENSION, ADHESION AND CAPILLARY ACTION

ADHESION Water sticks to itself because the water molecules are polar This leads to the formation of water drops and is why a tap has a stream of water and water droplets form on leaves, glass and other surfaces.

SURFACE TENSION Water has a high surface tension caused by the strong attraction/cohesion between water molecules. As long as the surface is not broken this surface tension is very strong

CAPILLARY ATTRACTION Capillary action refers to the process of water moving up a narrow tube against the force of gravity It occurs because water is attracted/adheres to the sides of the tube and the water is pulled up the tube as the water molecules stick to each other.

WATER AS A SOLVENT Water is a very strong solvent and is often referred to as the universal solvent as so many different substances will dissolve in water Substances that mix and dissolve in water are called hydrophilic (water loving) and those that do not mix and dissolve in water are called Hydrophobic (water hating)

TO DISSOLVE OR NOT Whether a substance will dissolve or not depends on whether the water is attracted to that substance or not. If the substance to be dissolved is attracted to the water (eg another polar substance) then the water molecules will allow the substance to dissolve.

If the substance does not attract the water molecules ( such as oil) then the water molecules will “push out” the substance and it will not dissolve.

WHY DOES ICE FLOAT?

In liquid water, the molecules are constantly moving around each other As the water cools the movement of the water molecules slows down so that the molecules do not slip past each other as easily. At 4 o c the water molecules will occupy the least amount of space so water is at its most dense at this temperature.

WHY ICE FORMS CRYSTALS After 4 o c the water molecules arrange themselves into a regular lattice structure which leads to the formation of ice crystals. This regular lattice structure means that there are empty spaces within the ice structure which means that as the ice crystals form the ice expands.

LIQUID WATER REGULAR LATTICE FOUND IN ICE Hydrogen bond Empty space Hydrogen atoms Oxygen atom

The lattice structure means that the same amount of water now take up more space This makes the same amount of water less dense when its frozen than when it’s a liquid. If ice is less dense than liquid water then ice will float on water.

Water cycle Water is naturally found on earth as a solid a liquid and a gas. Steam geysers at Rotoru, New Zealand Liquid water Ice berg in the polar Ice caps.

There is a finite amount of water present on earth Water is therefore moving through each of the three states (ice, liquid, water vapour) in a never-ending cycle called the water cycle. solid liquidgas sublimation condensation evaporation melting freezing sublimation

Water in the environment. Water is essential for life. Water’s ability to dissolve many substances means that it has a vital role to play in transporting these substances around the body of humans and other living organisms. Water is also used in many chemical reactions within the body Water is a reactant in the process of photosynthesis which is the basis of all food chains. For many organisms the water is their home environment and they have adapted many stratagies for living in this environment. Water quality is essential if water is to perform these tasks - polluted water is as dangerous as no water.