Water Chapter 33

Water What is water? Water is a compound made up of the two elements hydrogen and oxygen.

Test for Water Water turns blue cobalt chloride paper pink.

Properties of Water Pure water has a freezing point of 0⁰C and a boiling point of 100⁰C. Water expands when it freezes.

Properties of water When water freezes it expands, the water becomes less dense, therefore ice floats on water.

Properties of Water Water is an excellent solvent. Many substances easily dissolve in water e.g. Salt in Water forms a solution.

The Water Cycle

The Water Cycle 5 stages: Evaporation: Heat from the sun causes water in oceans and lakes to evaporate. Condensation: This water cools and condenses into tiny droplets which form clouds. When clouds cool further the water droplets join up to make rain or snow.

The Water Cycle Rain water seeps through the ground into rivers and streams. The rivers and streams carry the water back to oceans and lakes.

Water Treatment

Stages in Water Treatment Screening: The water is passed through wire mesh or screen to remove any large floating material. Settling: Water is then stored in large settling tanks or reservoirs where large and medium sized, insoluble particles settle to the bottom.

Stages in Water Treatment Filtration: The water is filtered through beds of sand and gravel. Any remaining insoluble particles stick to the sand and gravel and are removed this way. Chlorination: Chlorine is added to the water in small amounts to kill any bacteria present.

Stages in Water Treatment Fluoridation: Fluorine is added to help prevent tooth decay.

Hardness Hardness is formed by calcium ions dissolved in water. Hard water is formed when slightly acidic rainwater reacts with limestone rocks (calcium carbonate)

Ion Exchange Hardness from water is removed by the process of ion exchange.

Advantages of Hard Water

Disadvantages of Hard Water

Electrolysis Electrolysis is the production of a chemical reaction using electricity. A Hoffman Voltameter is used to pass electricity through water.

Electrolysis of Water

Electrolysis of Water A small amount of sulfuric acid is added to help the water conduct electricity. Platinum electrodes were used. Hydrogen collects at negative electrode. Oxygen collects at positive electrode.

Electrolysis of Water Water is split up into the elements hydrogen and oxygen. Twice as much Hydrogen as oxygen is produced.