Monday, November 28, 2011


1.            List the physical properties of water?
                Water is a colourless, tasteless and odourless liquid.
2.            Why is water called a universal solvent?
                Water can dissolve maximum number of solvents in it and hence is called a universal solvent.
3.            Mention any six substances that are insoluble in water?
                Sand, glass, wood, plastic, stone, metals, paper
4.            List any four substances that are soluble in water?
                Salt, sugar, bicarbonates
5.            Why do certain samples of water not readily give lather with soap?
                These samples contain soluble salts like carbonates and bicarbonates of magnesium and calcium that cause                 hardness in water and hence does not give lather with soap.
6.            What is soft water?
                Water that give lather easily with ordinary soap is called soft water.
1.            What is the nature of water that comes out of the permutit?
                The water that comes out of the permutit is soft, but not pure.
2.            Mention any two properties of pure water?
                Pure water is colourless and tasteless.
3.            How does water get its color, taste and odour?
                Water gets its colour, taste and odour by the impurities present in it.
4.            How is water classified? What is the basis for this classification?
                Water is classified as hard water and soft water based on the changes observes during its reaction with soap.
5.            What do you mean by conservation of water?
                The effort made by the society towards the rational use, prevention of pollution and recycling of water is called                 water conservation.
6.            Why should we soften hard water before it is used?
·         Hard water is not suitable for washing as there will be heavy wastage of soap and clothes are not washed properly and leave a yellow stain on the clothes.
·         Hard water consumes more fuel for cooking and the salts accumulate on the inner walls of the vessels making their cleaning difficult.
·         In industries, where boilers are used, it leaves a scale on the inner walls of the boiler and sometimes even causes foaming and explosion.
·         Hard water forms scales inside the pipes and corrodes the pipes
                Hence we should soften hard water before it is used.
7.            What is permutit? Mention two methods of preparing it?
·         Artificially prepared sodium aluminium silicate is called permutit.
·         It is prepared by heating quartz, sand, china clay and sodium carbonate.
·         It can also be prepared by fusing sodium silicate and sodium aluminate.
8. Name the simplest method of removing permanent hardness of water. On what principle does it work?
·         Distillation is the simplest methods of removing permanent hardness of water.
·         The condensation of water vapors produced is the principle involved in the process.
9. Mention two advantages and two disadvantages of permutit process of softening hard water?
a)      Advantages:
·         It is economical
·         It removes hardness more or less completely.
b)      Disadvantages:
·         It is not suitable, if water contains suspended impurities and sodium salts.
·         It does not remove lead, iron or manganese if present as impurities.
10  Describe briefly the two types of hardness in water?
·         Based on the negative ions present along with magnesium and calcium ions, hard water is grouped as temporary hard water and permanent hard water.
·         Water that contain bicarbonate ions along with magnesium and calcium ions and that can be softened by boiling is called temporary hard water.
·         Water that contains chloride and sulphate ions along with magnesium and calcium ions is called permanent hard water.
·         When all the ions are precipitated, water begins to give lather.
11.What is hard water? Describe briefly the soda process of removing hardness in water?
·         Water that forms an insoluble scum with soap before giving lather is called hard water.
·         Sodium carbonate is added to the hard water. It reacts with the salts that cause hardness and gives their respective carbonates that are insoluble. These insoluble carbonates are removed by filtration.

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