Here you will get answers of all the questions which are asked in the middle of the chapter 1 Chemical Reactions and Equations. Check Out all answers in simple words and learn easily.

Part I

1.Why should a magnesium ribbon be cleaned before burning in air?

Ans: Magnesium reacts with oxygen very easily, so we have to clean magnesium ribbon before burning as it's surface contains layer of oxides on it.

2. Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen

Ans: i) H2 + Cl2 -> HCl
After balancing we get : H2 + Cl2 -> 2HCl
ii) BaCl2 + Al2(SO4)3 -> BaSO4 + AlCl3
After balancing we get : BaCl2 + Al2(SO4)3 -> BaSO4 + AlCl3
iii) Na + H2O -> NaOH + H2
After balancing we get :2Na + 2H2O -> 2NaOH + H2

3. Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Ans: i) BaCl2(aq) + Na2SO4(aq) -> BaSO4(s) + NaCl(aq)
After balancing the equation: BaCl2(aq) + Na2SO4(aq) -> BaSO4(s) + 2NaCl(aq)
ii) NaOH(aq) + HCl(aq) -> NaCl(aq) + H2O(l)
Already balanced.

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Part II

1.A solution of a substance ‘X’ is used for whitewashing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

Ans: i)The substance used for whitewashing is Calcium oxide also known as quicklime. Its formula is CaO.
ii) CaO + H2O -> Ca(OH)2 + Heat This reaction is an example of exothermic reaction.

2. 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.

Ans: The two gases are hydrogen gas (H2) and oxygen gas (O2). As the water contains 2 Hydrogen atom and 1 Oxygen atom in each water molecule. So that is why  hydrogen gas will be more than oxygen gas.

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Part III

1.Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Ans: Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) Here, displacement reaction occurs as iron(Fe) is more reactive than Copper(Cu). So due to the replacement of copper from the solution the color changes.

2. Give an example of a double displacement reaction other than the one given in Activity 1.10.

Ans: KOH(aq) + H2SO4(aq) → K2SO4(aq) + H2O(l)
After Balancing Equation : 2KOH(aq) + H2SO4(aq) → K2SO4(aq) + 2H2O(l)

3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) 4Na(s) + O₂(g) → 2Na₂O(s)
(ii) CuO(s) + H₂(g) → Cu(s) + H₂O(l)

Ans: i) Na(Sodium) is gaining oxygen, so it is oxidised and O2 is reduced.
ii) Cu(copper) is loosing oxygen, so it is reduced and H2(hydrogen) is gaining Oxygen, so it is oxidised.