Note: These questions are given in between different sections of a chapter in NCERT Text Book. A proper understanding of these questions will help you in having a crystal clear concept of the lesson.
Write the balanced equation for the following chemical reactions.
Hydrogen + Chlorine ⇨ Hydrogen Chloride
Answer: H2 + Cl2 ⇨ 2HCl
Barium chloride + Aluminium sulphate ⇨ Barium sulphate + Aluminium chloride
Answer: 3BaCl+ Al2(SO4 )3 ⇨ 3BaSO4 + 2AlCl3
Sodium + Water ⇨ Sodium hydroxide + Hydrogen
Answer: 2Na + 2H2O ⇨ 2NaOH + H2
Question 1: Write a balanced chemical equation with state symbols for the following reactions.
(a) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
Answer: BaCl2 (aq) + Na2SO4 ⇨ BaSO4 (s) + 2NaCl (aq)
(b) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Answer: NaOH (aq) + HCl ⇨ NaCl (aq) + H2O (l)
Question 2: A solution of a substance ‘X’ is used for white washing.
(a) Name the substance ‘X’ and write its formula.
Answer: The chemical name of substance, which is used for white washing is Calcium oxide. Its common name is lime or quick lime. The chemical formula of Calcium Oxide is CaO.
(b) Write the reaction of the substance ‘X’ named in (i) above with water.
Answer: CaO + H2O ⇨ Ca(OH)2
When calcium oxide reacts with water it forms calcium hydroxide. Calcium hydroxide is also known as slaked lime.
Question 3: Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.
Answer: (Hydrolysis of water has been performed in the activity 1.7 in the text book.) When electric current is passed through water it decomposes into its constituent components, i.e. hydrogen and oxygen gases. During electrolysis of water hydrogen gas collected in one test tube and has double amount than oxygen collected in another test tube. This is because a water molecule is formed by the combination of hydrogen and oxygen in the ratio of 2:1.
Question 4: Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer: The colour of copper sulphate solution is blue. When an iron nail is dipped in the solution of copper sulphate, it displaces copper from copper sulphate to form ferrous sulphate. The colour of ferrous sulphate is green. That's why blue colour disappears and the solution becomes green.
Question 5: Give an example of a double displacement reaction other than the one given in Activity 1.10.
Answer: When lead nitrate reacts with potassium iodide, potassium nitrate and lead iodide is formed. In this reaction the both the reactants exchange their ions after reaction. This type of reaction is known as double displacement reaction.
Pb(NO3 )2 (aq) + KI (aq) ⇨ KNO3 + PbI2
Question 6: Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(a) 4Na (s) + O2 (g) ⇨ 2NaO (s)
Answer: In this reaction sodium is getting oxidised because oxygen is added to it, or a non-metal is added to it. Moreover, oxygen is getting reduced because metal is added to it.
(b) CuO (s) + H2 (g) ⇨ Cu (s) + H2O (l)
Answer: In this reaction, Hydrogen is oxidised because oxygen is added to it or a non-metal is added to it. Copper oxide is getting reduced because oxygen is removed from it or a non-metal is removed from it.
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