chemistry class 10 chapter 7 important questions

• Important Multiple Choice Questions of Chapter Number 15: Water of Chemistry class 10th Urdu Medium.
• Important Short Questions of Chapter Number 15: Water of Chemistry class 10th Urdu Medium.
• "Soft water Soft water is that water which produces good lather with soap".
• "Hard water Hard water is that water which does not produce lather with soap'. Causes of hardness in water. The rain water while coming down absorbs carbon dioxide from the atmosphere. The water mixed with carbon dioxide, when passes through the beds of the soil, converts insoluble carbonates of calcium and magnesium into soluble bicarbonates. It may also dissolve chlorides and sulphates of calcium and magnesium. These salts make the water hard.
• Types of Hardness of Water Hardness is of two types: (i) Temporary hardness is because of presence of bicarbonates of calcium and magnesium. (ii) Permanent hardness is because of presence of sulphates and chlorides of calcium and magnesium.
• Disadvantages of Hard Water:  (i) Hard water consumes large amount of soap in washing purposes. (ii) Drinking hard water causes stomach disorders. (iii) Hard water is unfit for use in steam engines, boilers and turbines because insoluble calcium and magnesium salts deposit inside. They are called scales. They are bad conductors of heat and hence more fuel is used. Insoluble calcium and magnesium sulphates not only reduce the efficiency of the engine but also cause the boiler to burst.
• WATER POLLUTION: Water pollution is a contamination of water bodies (e.g. lakes, rivers, oceans and ground water). Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds.
• Q: Hard water hampers the cleaning action of soap?
• Soap is the sodium salt of a long chain carboxylic acid (fatty acid). Hard water contains salts of magnesium and calcium. These ions react with the soap molecule to form an insoluble precipitate of calcium and magnesium salts of fatty acids called scum. As a result, a large amount of soap is wasted in scum formation. Thus, it reduces the efficiency of soap.
• Industrial Effluents: Industrial units are installed to produce the desired substances (chemicals, cloth, leather goods, paper, plastic items, petrochemicals and rubber items) on commercial scale to meet the needs of the society. But unfortunately all the industrial units discharge their wastes (chemicals and solid materials) either to open ground or to water channels. This is called industrial effluent. The industrial effluent may be highly toxic organic chemicals, inorganic salts, heavy metals, mineral acids, oil and greases, etc. On the other hand, water used as cleaning agent in industries is directly discharged out. This water contains all kinds of toxic chemicals and detergents.
• Domestic Effluents: Use of detergents is increasing day by day for cleaning purposes in houses and industries. It is because, detergents have strong cleaning action than that of soap even in hard water. They can work even in acidic solutions. But they have a major disadvantage over the soaps, as some of the detergents are non-biodegradable (cannot be decomposed by microorganisms like bacteria). When household water containing these detergents is discharged in streams, ponds, lakes and rivers, it causes water pollution.
• Agricultural Effluents: Water pollution due to agricultural waste is because of use of fertilizers and pesticides. Fertilizers are used to make up the deficiency of nitrogen, phosphorus, etc. of the soil because of intensive cultivation of crops in the recent years. On the other hand, pesticides are used either directly to kill or control the growth of pests. Pests may be weeds, herbs, insects, fungi, viruses, etc. They all damage crops and transmit diseases both to human beings and animals. 
• Which salts are responsible for hardness of water?
• Explain the chemistry of removing the temporary hardness by boiling water.
• What is the principle of removing permanent hardness of water?
• How does addition of Na2 CO3 remove permanent hardness of water?
• How does sodium zeolite soften water?
• What do you mean by boiler scales? How are they removed?