Answer the following.
\nQuestion 1.
\nWhat are the main sources of water?
\nAnswer:
\nSurface water is found in the oceans, seas, rivers, lakes, streams, etc. Sources of groundwater include springs and wells.<\/p>\n
Question 2.
\nWater dissolves all nitrate salts and most chloride salts. True or false?
\nAnswer:
\nTrue.<\/p>\n
Question 3.
\nDifferentiate between miscible and immiscible liquids.
\nAnswer:
\nLiquids that dissolve in water are called miscible liquids that do not dissolve in water are called immiscible liquids.<\/p>\n
Question 4.
\nWhat type of solution is sugar in water – homogeneous or heterogeneous?
\nAnswer:
\nA solution of sugar in water is a homogeneous mixture.<\/p>\n
Question 5.
\nCan you see the particles of a suspension?
\nAnswer:
\nThe particles of suspensions can be seen with the naked eye.<\/p>\n
Check Your Progress (Page 107)<\/span><\/p>\n Answer these following. Question 2. Question 3. Question 4. Question 5. A. Tick the most appropriate answer<\/span><\/p>\n Question 1. Question 2. Question 3. Question 4. Question 5. Question 6. B. Fill in the blanks.<\/span><\/p>\n Question 1. Question 2. Question 3. Question 4. Question 5. Question 6. Question 7. C. Write true or false. Correct the false statements.<\/span><\/p>\n Question 1. Question 2. Question 3. Question 4. Question 5. Question 6. Question 7. D. Write the chemical equations for the following.<\/span><\/p>\n Question 1. Question 2. Question 3. Question 4. Question 5. E. Match the columns<\/span><\/p>\n Answer:<\/p>\n F. Answer the following in short.<\/span><\/p>\n Question 1. Question 2. Question 3. Question 4. Question 5. Question 6. Question 7. Question 8. G Answer the following in detail<\/span><\/p>\n Question 1. Question 2. Question 3. Question 4. Permanent hardness of water cannot be removed by boiling as it is caused due to chlorides and sulphates of calcium and magnesium. As these salts are stable to heat, permanent hardness can be removed by addition of compounds like washing soda (sodium carbonate). Washing soda reacts with chlorides and sulphates of calcium and magnesium to form their respective insoluble carbonates. The insoluble carbonates can be filtered out and the water becomes soft. Question 5. Hard water also has some disadvantages compared to soft water. For example, hard water unsuitable for washing. More soap is needed to produce lather. With soap, it forms scum that causes wastage of soap. The scum produced spoils the appearance of Think And Answer<\/span><\/p>\n Question 1. Question 2. Question 3. Question 4.
\nQuestion 1.
\nCalcium chloride is a hygroscopic substance. True or false?
\nAnswer:
\nTrue.<\/p>\n
\nWhat will happen when sodium reacts with cold water?
\nAnswer:
\nSodium react with cold water to liberate hydrogen gas and form the corresponding metal hydroxide.
\n![\"ICSE](\"https:\/\/i1.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/ICSE-Class-8-Chemistry-Notes-Chapter-8-Water-1.png?resize=370%2C78&ssl=1\")
<\/p>\n
\nWhat is the chemical formula of aluminium oxide?
\nAnswer:
\nThe chemical formula of aluminium oxide is Al2<\/sub>O3<\/sub>.<\/p>\n
\nWrite the reaction between magnesium oxide and water.
\nAnswer:
\n![\"ICSE](\"https:\/\/i2.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/ICSE-Class-8-Chemistry-Notes-Chapter-8-Water-2.png?resize=296%2C66&ssl=1\")
<\/p>\n
\nWhat are the types of hardness of water?
\nAnswer:
\nThere are two types of hardness of water :<\/p>\n\n
\nWhich of the following exists in three different states in natural conditions on the earth?
\na. soil
\nb. water
\nc. oxygen
\nd. salt
\nAnswer:
\nb. water<\/p>\n
\nWhich of the following does not dissolve in water?
\na. sand
\nb. sugar
\nc. salt
\nd. vinegar
\nAnswer:
\na. sand<\/p>\n
\nWhat type of solution is milk?
\na. homogeneous solution
\nb. suspension
\nc. colloid
\nd. none of these
\nAnswer:
\nc. colloid<\/p>\n
\nWhich of the following is an anhydrous salt?
\na. copper sulphate pentahydrate
\nb. calcium chloride hexahydrate
\nc. Magnesium sulphate heptahydrate
\nd. sodium nitrate
\nAnswer:
\nd. sodium nitrate<\/p>\n
\nWhich gas is evolved during the reaction of water with metals?
\na. carbon dioxide
\nb. hydrogen
\nc. oxygen
\nd. nitrogen
\nAnswer:
\nb. hydrogen<\/p>\n
\nBy which of the following can temporary hardness of water be removed from hard water?
\na. boiling
\nb. freezing
\nc. melting
\nd. none of these
\nAnswer:
\na. boiling<\/p>\n
\nWater is called the solvent as it dissolves many substances.
\nAnswer:
\nWater is called the universal solvent as it dissolves many substances.<\/p>\n
\nThe particles of are bigger than those of a colloid.
\nAnswer:
\nThe particles of suspension are bigger than those of a colloid.<\/p>\n
\nA is a heterogeneous solution in which the solute particles are larger than those of a solution and smaller than those of a suspension.
\nAnswer:
\nA colloid is a heterogeneous solution in which the solute particles are larger than those of a solution and smaller than those of a suspension.<\/p>\n
\nIn a solution, no more solute can dissolve at a given temperature.
\nAnswer:
\nIn a saturated solution, no more solute can dissolve at a given temperature.<\/p>\n
\nThe process in which the crystals of a solute are separated on cooling a hot saturated solution is called
\nAnswer:
\nThe process in which the crystals of a solute are separated on cooling a hot saturated solution is called crystallization.<\/p>\n
\nA substance that contains water of crystallization is called a substance
\nAnswer:
\nA substance that contains water of crystallization is called a hydrated substance.<\/p>\n
\nMetal oxides that are soluble in water dissolve in it to form
\nAnswer:
\nMetal oxides that are soluble in water dissolve in it to form alkalis.<\/p>\n
\nLiquids such as petrol and vegetable oil are miscible.
\nAnswer:
\nTrue<\/p>\n
\nChalk powder in water is an example of suspension.
\nAnswer:
\nTrue<\/p>\n
\nBlue copper sulphate crystals are anhydrous.
\nAnswer:
\nFalse; Blue copper sulphate crystals are hydrated.<\/p>\n
\nSilica gel .is a desiccant
\nAnswer:
\nTrue<\/p>\n
\nThe reaction of iron with steam is reversible.
\nAnswer:
\nTrue<\/p>\n
\nHard water gives rich lather with soap.
\nAnswer:
\nFalse; Soft water gives rich lather with soap.<\/p>\n
\nLimescale is produced when hard water is heated.
\nAnswer:
\nTrue<\/p>\n
\nSodium oxide reacting with water
\nAnswer:
\n![\"Living](\"https:\/\/i2.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-1.png?resize=407%2C48&ssl=1\")
<\/p>\n
\nPotassium reacting with cold water
\nAnswer:
\n![\"Living](\"https:\/\/i2.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-2.png?resize=395%2C74&ssl=1\")
<\/p>\n
\nAluminium reacting with steam
\nAnswer:
\n![\"Living](\"https:\/\/i1.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-3.png?resize=393%2C73&ssl=1\")
<\/p>\n
\nHeating calcium bicarbonate
\nAnswer:
\n![\"Living](\"https:\/\/i1.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-4.png?resize=446%2C75&ssl=1\")
<\/p>\n
\nCalcium chloride reacting with sodium carbonate
\nAnswer:
\n![\"Living](\"https:\/\/i1.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-5.png?resize=439%2C70&ssl=1\")
<\/p>\n\n\n
\n 1. Universal solvent<\/td>\n a. Calcium oxide<\/td>\n<\/tr>\n \n 2. Desiccant<\/td>\n b. Calcium bicarbonate<\/td>\n<\/tr>\n \n 3. Hygroscopic salt<\/td>\n c. Water<\/td>\n<\/tr>\n \n 4. Magnesium sulphate heptahydrate<\/td>\n d. Phosphorus pentoxide<\/td>\n<\/tr>\n \n 5. Temporary hardness of water<\/td>\n e. Potassium nitrate<\/td>\n<\/tr>\n \n 6. Anhydrous substance<\/td>\n f. Hydrated substance<\/td>\n<\/tr>\n \n <\/td>\n g. Magnesium oxide<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n\n
\n 1. Universal solvent<\/td>\n c. Water<\/td>\n<\/tr>\n \n 2. Desiccant<\/td>\n d. Phosphorus pentoxide<\/td>\n<\/tr>\n \n 3. Hygroscopic salt<\/td>\n d. Phosphorus pentoxide<\/td>\n<\/tr>\n \n 4. Magnesium sulphate heptahydrate<\/td>\n f. Hydrated substance<\/td>\n<\/tr>\n \n 5. Temporary hardness of water<\/td>\n b. Calcium bicarbonate<\/td>\n<\/tr>\n \n 6. Anhydrous substance<\/td>\n e. Potassium nitrate<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\nWhy is water called the universal solvent?
\nAnswer:
\nWater can dissolve many substances to form aqueous solutions. It can dissolve more substances than any other liquid. Therefore, it is called the universal solvent.<\/p>\n
\nWhat happens when a carbonated drink bottle is opened?
\nAnswer:
\nCarbonated drinks contain carbon dioxide dissolved in water at a high pressure. On opening a bottle of a carbonated drink, the dissolved carbon dioxide escapes with a \u2018fizz\u2019.<\/p>\n
\nWhat is a suspension?
\nAnswer:
\nA suspension is a heterogeneous mixture in which small solid particles are suspended.<\/p>\n
\nDifferentiate between a saturated solution and an unsaturated solution.
\nAnswer:
\nA saturated solution is a solution in which no more solute can dissolve at a given temperature. An unsaturated solution is a solution in which more of the solute can dissolve at a given temperature.<\/p>\n
\nWhat is crystallization?
\nAnswer:
\nThe process in which the crystals of a solute are separated on cooling a hot saturated solution is called crystallization.<\/p>\n
\nWhat do you mean by water of crystallization?
\nAnswer:
\nWater of crystallization is the definite number of water molecules chemically combined with a salt in its crystalline form.<\/p>\n
\nWhat happens when metal oxides dissolve in water?
\nAnswer:
\nMetal oxides that are soluble in water dissolve in it to form metal hydroxides.<\/p>\n
\nWhat are the causes of hardness of water?
\nAnswer:
\nHardness of water is caused by dissolved salts of calcium and magnesium such as bicarbonates, chlorides and sulphates.<\/p>\n
\nDifferentiate between a suspension and a colloid.
\nAnswer:
\nA suspension is a heterogeneous mixture in which small solid particles are suspended. The particles of suspensions can be seen with the naked eye. The particles of a suspension are bigger than those of a solution. Chalk powder in water, flour in milk, smoke emitted by moving vehicles and some medicines are examples of suspensions. A colloid is a heterogeneous solution in which the solute particles are large than those of a solution and smaller than those of a suspension. Milk, cream, toothpaste, blood and ink
\nare examples of colloids.<\/p>\n
\nHow can a saturated solution be converted into an unsaturated one?
\nAnswer:
\nA saturated solution can also be converted to an unsaturated solution by heating the solution gradually or by adding more of the solvent to it.<\/p>\n
\nExplain the reactions of water with metals with the help of examples.
\nAnswer:
\nReactions of metals with water Many metals react with water to produce metal hydroxides or metal oxides and hydrogen gas. With cold water active metals such as potassium, sodium and calcium react with cold water to liberate hydrogen gas and form the corresponding metal hydroxides.
\n![\"Living](\"https:\/\/i1.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-6.png?resize=400%2C156&ssl=1\")
\n![\"Living](\"https:\/\/i2.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-7.png?resize=418%2C72&ssl=1\")
\nWith hot water : Magnesium reacts with hot water to form magnesium hydroxide and hydrogen. But, the reaction is slow.
\n![\"Living](\"https:\/\/i0.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-8.png?resize=421%2C75&ssl=1\")
\nWith steam : When steam is passed over heated magnesium, aluminium, zinc or iron, the corresponding metal oxides and hydrogen gas are produced.
\n![\"Living](\"https:\/\/i0.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-9.png?resize=413%2C294&ssl=1\")
<\/p>\n
\nHow can hardness of water be removed? Explain with the help of examples.
\nAnswer:
\nRemoval of hardness of water Temporary hardness of water can be removed by boiling. The soluble bicarbonates of calcium decompose on boiling to form insoluble carbonates. These insoluble salts can be separated from water by filtration and the water then becomes soft.
\n![\"Living](\"https:\/\/i1.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-10.png?resize=459%2C71&ssl=1\")
\n![\"Living](\"https:\/\/i1.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-11.png?resize=448%2C78&ssl=1\")
<\/p>\n
\n![\"Living](\"https:\/\/i1.wp.com\/icsesolutions.com\/wp-content\/uploads\/2021\/03\/Living-Science-Chemistry-Class-8-ICSE-Solution-Chapter-8-Water-12.png?resize=458%2C146&ssl=1\")
<\/p>\n
\nState the advantages and disadvantages of hard water.
\nAnswer:
\nAdvantages and disadvantages of hard water Hard water has some advantages compared to soft water. For example, the dissolved calcium compounds in hard water can improve the taste of the water. The ions of calcium and magnesium are good for the development and maintenance of bones and teeth. These can help to reduce heart disease.<\/p>\n
\nbaths and shower screens. The scum also sticks to clothes, resulting in the poor washing of the clothes.<\/p>\n
\nThe components of a solution cannot be separated by filtration. Explain.
\nAnswer:
\nThe particles of the solute in a solution are very small and Arundeep’s Living Sci. Chemistry-8th 184
\ncannot be seen with the naked eye. They are not visible even under a powerful microscope. Solutions are clear and transparent and their components cannot be separated by filtration.<\/p>\n
\nFilter paper can be used to separate the components of a suspension. Why?
\nAnswer:
\nThe particles of a suspension do not pass through filter paper. Thus, filter paper can be used to separate the components of a suspension.<\/p>\n
\nThe permanent hardness of water cannot be removed by boiling. Why?
\nAnswer:
\nThe permanent hardness of water cannot be removed by boiling as it is caused due to chlorides and sulphates of calcium and magnesium. As these salts are stable to heat, permanent hardness can be removed by addition of compounds like washing soda (sodium carbonate).<\/p>\n
\nTemporary hardness can reduce the heating efficiency of utensils, industrial boilers and hot water pipes. Explain.
\nAnswer:
\nTemporary hardness can reduce the heating efficiency of utensils, industrial boilers and hot water pipes. This is because limescale that contains calcium carbonate is produced when hard water is heated. Limescale coats the heating areas in utensils and the inside of boilers and hot water pipes. Because of this, more heat energy is needed to heat water. Pipes may become blocked by limescale causing the heating system to break down.<\/p>\n