Water Properties of Water Water Cycle Water Treatment Hard/Soft Water Electrolysis of Water

Water is a compound made up of the elements hydrogen and oxygen. Each molecule of water has two hydrogen atoms bonded to one central oxygen atom. (H2O) Cobalt chloride paper is used to test for the presence of water . Cobalt chloride turns from Blue to Pink when water is present

To Test for the Presence of Water Water will turn anhydrous (without water) copper sulfate from white to blue.

Water expands as it freezes!!! All other liquids contract when they freeze to a solid and take up less space!! Water changes to ice and floats on water as ice is less dense than water. Density of ice = 0.9 g/cm3 Density of water is 1 g/cm3

Water is an excellent solvent. This allows blood (mainly water) to carry substances like glucose in it. Water carries dissolved solids and gases in it ( Fish need it!!)

Electrolysis The use of electricity to bring about a chemical reaction. A Hoffmann Voltameter is used to pass a current through water causing it to break down into hydrogen and oxygen

A small amount of sulfuric acid is added to the water to help it conduct electricity Platinum electrodes are used. Hydrogen collects at the negative electrode which is called the cathode Oxygen collects at the positive electrode called the anode Note that twice as much hydrogen as oxygen is produced because each molecule of water has two hydrogen atoms for every one oxygen atom.

The Water Cycle

Stages of the Water Cycle Heat from the sun causes water to evaporate from the oceans and transpiration from plants adds water vapour to the air. Water vapour cools and condenses into tiny droplets forming clouds Further cooling causes the droplets to join up making bigger droplets which fall as rain or snow Rainwater soaks through the ground and seeps into streams and rivers. Rivers carry the water back to the seas and oceans.

Desalination In countries where fresh water is scarce, salt water is desalinised. Desalinised is water that has salt removed from it. Desalination is a separation technique made up of evaporation followed by condensation