Water of Crystallization Reaction of Metals Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-8 Unit-2

Water of Crystallization Reaction of Metals Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-8 Unit-2(Water of Crystallisation and Reaction of Metals with Water). We Provide Step by Step Answers of Objectives, True and False, Incorrect and Correct, Definitions, Match the followings and Short/Long Question Type answers of Ch-8 (Water) Unit-2(Water of Crystallisation and Reaction of Metals with Water). Visit official Website  CISCE  for detail information about ICSE Board Class-8

Water of Crystallization and Reaction of Metals with Water Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-8 Unit-2

Board ICSE
Class 8th
Subject Chemistry
Book Name Goyal Brothers
Chapter-8 Water
Unit-2

Water of Crystallisation and Reaction of Metals with Water

Topic Solution of exercise questions
Session 2023-24

OBJECTIVE TYPE QUESTIONS

Water of Crystallization Reaction of Metals Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-8 Unit-2

Que: A. Fill in the blank spaces by choosing the correct words from the given list :

List : soft, hydrated, crystallisation, water, activity

1. The fixed number of water molecules, that are in loose combination with one molecules of a salt, is called water of crystallisation.

2. Hydrated copper sulphate contains water.

3. Crystal of some substance have fixed number of water molecules, such substances are known as hydrated substances.

4. The list of metals arranged in the order of their chemical activity, is called metal activity series.

5. A sample of groundwater, which freely lathers with soap solution, is called soft.

Que: B. Statements given below are incorrect. Write the correct statements :

Question: 1. On strong heating, white powder of copper sulphate changes into blue crystal.

Answer: On strong heating, white powder of copper sulphate changes into blue crystal.

Question: 2. The anhydrous substance does not change its original colour on the addition of water.

Answer: The anhydrous substance does not change its original colour on the addition of water.

Question: 3. Hygroscopic substances absorb water and change their state.

Answer: Hygroscopic substances absorb water and change their state.

Question: 4. Metals like potassium, sodium and calcium on heating react with steam to form their respective oxides and hydrogen gas.

Answer: Metals like potassium, sodium and calcium on heating react with steam to form their respective oxides and hydrogen gas.

Question: 5. Water containing calcium hydrogen carbonate or magnesium hydrogen carbonate is known as permanent hard water.

Answer: Water containing calcium hydrogen carbonate or magnesium hydrogen carbonate is known as permanent hard water.

Que: C. Match the statements in Column A, with those in Column B :

Column A Column B
1. The substance left after heating a hydrated substance. (a) Hard water
2. The substance which absorbs moisture from air, but does not change its state. (b) Potassium, calcium and sodium
3. The metals which react with cold water. (c) Anhydrous substance
4. The metals which do not react with water. (d) Hygroscopic substance
5. The water which forms sticky scum with soap solutions. (e) Copper, silver and gold

Answer : 

Column A Column B
1. The substance left after heating a hydrated substance. (a) Anhydrous substance
2. The substance which absorbs moisture from air, but does not change its state. (b) Hygroscopic substance
3. The metals which react with cold water. (c) Potassium, calcium and sodium
4. The metals which do not react with water. (d) Copper, silver and gold
5. The water which forms sticky scum with soap solutions. (e) Hard water

Que: D. Write ‘True’ or ‘False’ for the following statements :

Statements  True/False
1. On strong heating crystals crumble to form powdery mass. T
2. Crystals having fixed number of water molecules are known as anhydrous substances. F
3. Some substances have a tendency to absorb moisture from air and change into solution. T
4. Sodium is the most reactive metal among the metals. T
5. Hard water is unfit for drinking purposes, as it upsets stomach. F

Que: E. Tick (√) the most appropriate answer :

1. The fixed number of water molecules attached loosely with one molecule of a substance is known as water of 

(a) activation

(b) crystal

(c) evaporation

(d) crystallisation

Answer: option (d) crystallisation is correct.

2. Crystals having fixed number of water molecules are known as

(a) anhydrous substances

(b) hydrated substances

(c) deliquescent substances

(d) hygroscopic substances

Answer: option (b) hydrated substances is correct.

3. The substances which absorb moisture from air, but do not change their state are called 

(a) crystals

(b) deliquescent substances

(c) hygroscopic substances

(d) hydrated substances

Answer: option (c) hygroscopic substances is correct.

4. Metals like magnesium, zinc and iron on heating react with steam to form hydrogen gas and their respective

(a) hydroxides

(b) oxides

(c) hydrides

(d) none of these

Answer: option (b) oxides is correct.

5. If water has magnesium chloride dissolved in it, for examining its cleansing action, it is to be considered as

(a) soft water

(b) permanent hard water

(c) temporary hard water

(d) hard water

Answer: option (b) permanent hard water is correct.

STUDY QUESTIONS

Water of Crystallization Reaction of Metals Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-8 Unit-2

Question: 1. (a) What is meant by water of crystallisation?

Answer: Water of crystallization is the amount of water molecules which are present in one formula unit of salt. We can also say that the water molecules which form part of a structure of a crystal are called water of crystallization. They give the crystals their shape and crystal.

(b) How would you show that copper sulphate crystals contain water of crystallisation?

Answer: As the blue colour of the crystals disappeared on heating, we can conclude that the colour was due to water crystallisation. This proves that blue copper sulphate crystals contain water of crystallisation.

Question: 2. By giving two examples define the following terms :

(a) Hydrated substance

Answer: Hydrated substance :

  • Hydrated substances is any compound containing water in the form of H2O molecules, usually, but not always, with a definite content of water by weight.
  • The best-known hydrates are crystalline solids that lose their fundamental structures upon removal of the bound water.

(b) Anhydrous substance

Answer: Anhydrous substance :

  • Substances without water or substances that do not contain water are called anhydrous.
  • The word means absence of water.

(c) Hygroscopic substance

Answer: Hygroscopic substance :

  • The absorption and adsorption of water from the surrounding environment by the matter is called hygroscopy.
  • The substances which cause the hygroscopic effect are called hygroscopic substances.

Question: 3. Write balanced equations when 

(a) sodium metal is dropped in cold water.

Answer: Na(s) + H2O(l) → NaOH(aq) + H2(g)

(b) calcium metal is dropped in cold water.

Answer: Ca + 2H2O → CaOH2 + H2

(c) steam is passed over heated magnesium metal 

Answer: Mg(s) + H2O (g) → MgO (s) + H2 (g)

(d) steam is passed over heated iron metal

Answer: 3Fe(s) + 4H2O(aq) → Fe3O4 (s) + 4H2(g)

Question: 4. Define the following terms :

(a) Soft water

Answer: Soft water that is free from dissolved salts of such metals as calcium, iron, or magnesium, which form insoluble deposits such as appear as scale in boilers or soap curds in bathtubs and laundry equipment.

(b) Hard water

Answer: Hard water is a term that denotes water having a very high mineral content (the term is the opposite of ‘soft water’).

(c) Temporary hard water

Answer: Water that contains only hydrogen carbonates salt of Calcium and Magnesium is called temporary hard water.

(d) Permanent hard water

Answer: Hard water contains soluble salts of calcium and magnesium that are present in the form of sulfides, nitrates, or chlorides are called permanent hardness of the water.

Question: 5. (a) Name two chemicals which are responsible for temporary hardness of water.

Answer: Salts of Calcium and Magnesium dissolved in water are responsible for the temporary hardness of water.

(b) Name four chemicals which are responsible for permanent hardness of water.

Answer: CaCl2, MgCl2, CaSO4, and MgSO4 are responsible for permanent hardness of water.

Question: 6. How does water get temporary hard in nature?

Answer: Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate). The presence of the metal cations makes the water hard.

Question: 7. (a) How can you remove temporary hardness of water? Write relevant chemical equation in support of your answer.

Answer: In this case, the hardness in water can be removed by boiling the water. When we boil water, the soluble salts of Mg(HCO3)2 are converted to Mg(OH)2, which is insoluble, and hence gets precipitated and is removed.

(b) How can you remove permanent hardness of water? Write relevant chemical equation in support of your answer.

Answer: The presence of magnesium and calcium carbonates in water makes it temporarily hard. Hardness of water can be removed by boiling the water. When we boil the water the soluble salts of Mg(HCO3)2 is converted to Mg(OH)2 which is insoluble and hence gets precipitated and is removed. To remove hardness by boiling the bicarbonates changes to insoluble carbonate and water becomes soft.

 — : end of Water of Crystallization Reaction of Metals Class-8th Goyal Brothers ICSE Chemistry Solutions Ch-8 Unit-2 :–

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