Class 10 Ncert intext Question Answers of chapter Chemical reaction and equations

Q1. Why should a magnesium ribbon be cleaned before burning in air

Ans:- magnesium ribbon should be cleaned with burning in air in order to remove the white layer of magnesium oxide (mgo) from its surface which hinders the burning of magnesium
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Q2. 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) to balance a chemical equation
         Hydrogen+ chlorine ----> hydrogen chloride

STEP1: writing the skeletel chemical equation :
      H2 + c1 2 ----->HC1
STEP2: balancing the equation
H2+c12----->2HC1

(ii) to balance a chemical equation :
   Barium chloride + Aluminium sulphate ------> barium sulphate + Aluminium chloride
Step 1---> writing the skeletal chemical equation :
Bac12+Al2(so4) 3 ------> BaSo4  + A1c13
Step2-----> balancing the equation :
       3BACI2 + AL2(SO4)3------>3BaSO4 + 2AICI3
(III) to balance a chemical equation :
Sodium + water----->sodium hydroxide + hydrogen

Step1----> writing the skeletal chemical equation :
2na + 2h2o ------>2Naoh+ h2
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Q3--- write a balanced chemical equation with state chemical symbols for the following reactions:
(I) solution of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride .

(II) sodium hydroxide solution reacts with hydrochloric acid solution to produce sodium chloride solution and water

Ans (I) to balance a chemical equation
Barium chloride + sodium sulphate ----->
                        Barium sulphate+ sodium chloride

Step 1----->  writing the skeletal chemical equation
BaCI2 (AQ) + Na2 so4(AQ)------> baso4(s) + 2NaCI(AQ)
(II) to balance a chemical equation
            Sodium hydroxide + hydrochloric acid -----> sodium chloride + water
Step1----> write the skeletal chemical equation NaOh (AQ) + hci (AQ)------> NaCi
(AQ) + h2o(l)
Step2 balancing the equation
   NaOh (AQ) + HCI (AQ) ------> NaCi (AQ) + h2o (l)
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Q1-- A solution of a substance 'x' is used for whitewashing
(I) name the substance 'x' is write its formula .
(II) write the reaction of substance 'X' named in (I) above the water .
Ans---> (I)for whitewashing a solution quicklime and its formula is CaO [calcium oxide]
(II) when quick lime react with water the following reaction takes place :
CaO(s) + H2O(l) -----> ca(Oh)2 (aq)
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Q2 why is the amount of gas collected in one of the test tubes on your book activity 1.7 double of the amount collected in the other ? Name this gas
Ans----> during electrolysis, water decomposes to form hydrogen and oxygen gases
2H2O(l)-------> in the above reaction the balanced chemical equation shows that on electrolysis the water decomposes to form hydrogen and oxygen in the ratio of 2:1 by volume .
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Q1---> Why does the colour of copper sulphate solution change when an iron nail dipped in it ??
Ans--->iron is more reactive element than copper when an iron nail is dipped in copper sulphate solution which is blue in colour , iron being more reactive than copper displaces copper from copper sulphate and forms iron (II) sulphate which is green in  colour .
Cuso4 (aq) + Fe (s) -------> feso4 (AQ) + cu(s)
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Q2----> give an example of a double displacement reaction other than the one given in activity 1.10
Ans---> AgNo3(aq) +. NaCI(aq)-------> AgCi (s) + NaNo3(aq)
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Q3----identify the substances that are oxidised and the substances that are reduced in the following reactions
(I) 4Na(s) + O2(g) -----> 2Na2 O(s) (II) CuO(S) + H2(g)----> Cu(s) + h2O(l)

Ans----> (I) 4Na(s) + O2(g) -----> 2Na2O (s)
Na has gained oxygen and forms Na2O
So, Na is Oxidised and O2 is reduced
(II) CuO(s) + H2(g) -----> Cu(s) + H2O(l)
CuO has lost oxygen and forms Cu so CuO is reduced and H2  which has gained oxygen and oxidised .

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