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WATER AND HYDROGEN
The uses of water include drinking, washing, cooling, generation of steam to drive turbines and as a solvent. In this subtopic we will study some of the physical and chemical properties of water.Water is very important in Chemistry. Water reacts with both metals and non metals.
SOURCES OF WATER
Water is the most abundant substance on earth. About 70% of the earth surface is covered with water.The sources of water are rain, rivers, lakes,oceans and wells.
By the end of the lesson you should be able to
a) State the sources of water
b) Describe an experiment to show water is a product of burning organic matter
c) State the products of reactions of cold water and steam with different metals
PRODUCTS OF A BURNING CANDLE
The products of a burning candle can be investigated using the set up below. The candle is lit and the sunction pump is turned on.Observe the following animation and carefully and note what happens.
The candle burns in air to form a colourless gas that forms a white precipitate with calcium hydroxide solution. The white precipitate is Calcium Carbonate.
The candle also produces vapour which condenses to colourless liquid in the beaker containing ice cold water.
TEST FOR COLOURLESS LIQUID
The colourless liquid can be tested by dividing it into two portions.To the first portion a few drops of the colourless liquid are added to white anhydrous Copper (II) Sulphate. To the second portion, blue Cobalt (II) Chloride paper is immersed. Observe what happens carefully and note the colour changes.
The change of colour of anhydrous Copper (II) Sulphate and dry cobalt (II) chloride paper indicate that the colourless liquid is water.
Water turns white anhydrous Copper (II) Sulphate blue.
The colourless gas produced forms a white precipitate with calcium hydroxide.
The gas is Carbon (IV) Oxide.
From the above observations we can conclude that candle wax is made up of hydrogen and carbon only.
REACTION OF METALS WITH WATER
Some metals react with water.The experiment below investigates the reaction of sodium with cold water. Observe what happens when Sodium metal is immersed into a trough containing cold water.Note the colour of red and blue litmus paper.
Sodium metal melts to a silvery ball, darts on the water surface and gradually becomes smaller as the reaction continues. The solution formed turns red litmus paper blue while the blue litmus remains blue. Therefore, the solution formed is alkaline. Sodium hydroxide and hydrogen gas are formed from this reaction.
Calcium reacts with cold water slowly. Observe what happens carefully
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