Class 10th science last 10 year papers chapter wise chapter 1 chemical reaction and equation part 3

 30. What is redox reaction? Identify the substance oxidised and the substance reduced in the following reactions.

(i)2PbO + C —–> 2Pb + CO2
(ii)MnO2 + 4HCl —–> MnCl2 + 2H20 + Cl2
Answer. Those reactions in which oxidation and reduction takes place simultaneously are called redox reactions.
(i) PbO is getting reduced and C is getting oxidised.
(ii) MnOs is getting reduced and HCl is getting oxidised.

31. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
Thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
Answer.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-23
It is a displacement reaction because A1 is displacing Fe from Fe2O3.
Molten iron is used’for repairing broken railway tracks.


32. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction?
Answer.

chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-24.
It is a double displacement reaction. It is also a precipitation reaction as AgCl is a white precipitate.

Very Short Answer Type Questions [1 Mark] -Year 2011

33.State one basic difference between a physical change and a chemical change.
Answer. In physical change, no new substance is formed, whereas in a chemical change, new substance(s) is/are formed.

34 What is meant by a chemical reaction?
Answer. The reaction representing a chemical change is called a chemical reaction.

35.AgN03(aq) + NaCl(aq)——————– > AgCl(s)4↓ + NaN03(aq)
FeS + H2S04————- > FeS04 + H2S↑
Consider the above mentioned two chemical equations with two different kinds of arrows (↑and ↓) along with product. What do these two different arrows indicate?
Ans,↑shows the gas is evolved whereas ↓shows insoluble substance (precipitate) is formed.

36. Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why?
Answer. It is because properties of compound (H2O) are different from properties of its constituting elements, i.e. H2and O2.

Short Answer Type Questions[l] [2 Marks] -Year 2011

37.Using a suitable chemical equation, justify that some chemical reactions are determined by:
(i) change in colour, (ii) change in temperature.
Answer.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-25
38.(a) A solution of substance ‘X’ is used for white washing. What is the substance ‘X’? State the chemical reaction of ‘X’ with water.
(b) Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer.
(a) ‘X’ is calcium oxide (CaO).
CaO(s) + H2O(l) —–> Ca(OH)2(aq) + heat
(a) It is because iron displaces copper from CuS04 to form FeS04 which is pale green.
Fe(s) + CUS04 (aq)—–> FeS04(aq) + Cu(s)
Blue                       Pale green

39.Balance the following chemical equations.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-26
Answer.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-27

40.Write the balanced equation for the. following reaction and identify the type of reaction in each case.
(i) Potassium bromide + Barium iodide—-> Potassium iodide + Barium bromide.
(ii) Hydrogen(g) + Chlorine(g)—-> Hydrogen chloride(g)
Answer.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-28

41. A zinc plate was put into a solution of copper sulphate kept in a glass container. It was found that blue colour of the solution gets fader and fader with the passage of time. After few days, when zinc plate was taken out of the solution, a number of holes were observed on it.
(i) State the reason for changes observed on the zinc plate.
(ii) Write the chemical equation for the reaction involved.
Answer.
(i) It is because zinc has displaced copper from CuS04. Zinc metal has been used to form zinc sulphate, therefore, number of holes were observed.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-29

42. A white salt on heating decomposes to give brown fumes and a residue is left behind.
(i) Name the salt.
(ii) Write the equation for the decom-position reaction.
Answer.
(i) Lead nitrate is white salt.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-30

43. When a solution of potassium iodide is added to a solution of lead nitrate in a test tube, a reaction takes place.
(a) What type of reaction is this?
(b) Write a balanced chemical equation to represent the above reaction.
Answer.
(a) Double displacement as well as precipitation reaction.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-31

44. Define combination reaction. Give one example of a combination reaction which is also exothermic.
Answer. A reaction in which two elements or compounds combine to form a single compound is called combination reaction.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-32
It is also an exothermic reaction along with a combination reaction because heat is evolved.

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