Chapter 1 Chemical Reactions and Equations Class 10 Science Extra Questions

Chapter 1 Chemical Reactions and Equations Class 10 Science Extra Questions

Chapter 1 Chemical Reaction and Equations Extra Questions and Answer

Chapter Name

Chemical Reaction and Equations Extra Questions 


CBSE Class 10

Textbook Name

NCERT Textbook Class 10 Science

Related Readings

  • Extra Questions for Class 10
  • Extra Question for Class 10 Science
  • NCERT Solutions for Chemical Reaction and Equations 

Question 1. How does the food become rancid?


Food becomes rancid when fat and oils present in the food are oxidised.

Question 2. A student burnt a metal A found in the form of ribbon. The ribbon burnt with a dazzling flame and a white powder B was formed which was basic in nature. Identify A and B. Write the balanced chemical equation.


X = Mg, Y = MgO, Mg + O2 → 2MgO

Question 3. What is a balanced chemical equation?


An equation that has equal number of atoms of each element on both the sides of the equation is called a balanced chemical equation, i.e., mass of the reactants is equal to mass of the products.
For example, 

Question 4. Write a balanced equation for a chemical reaction that can be characterised as precipitation.


BaCl2(aq) + Na2SO4 (aq) → BaSO4(s) + 2NaCl(aq)

Question 5. What is rust?


It is a brown mass known as hydrated ferric oxide. Its formula is Fe2O3. xH2O.

Question 6. A zinc rod is left for nearly 20 minutes in a copper sulphate solution. What change would you observe in the zinc rod?


The zinc rod will change into zinc sulphate.

Question 7. Name two salts that are used in black and white photography.


Both silver chloride and silver bromide are used in black and white photography.

Question 8. Which chemical process is used for obtaining a metal from its oxide?


The process is known as the reduction of metal oxide.

Question 9. If you collect silver coins and copper coins you may have seen that after some days a black coating forms on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of the black and green coatings.


Corrosion is responsible for the formation of this coating. Black coating is due to formation of Ag2S and green coating is due to formation of CuCO3.Cu(OH)2.

Question 10. When carbon dioxide is passed through lime water, it turns milky, why?


Lime water (calcium hydroxide) combines with carbon dioxide to form a suspension of calcium carbonate which makes lime water milky.
Ca(OH)2 + CO2 → CaCO3 + H2O

Question 11. Identify the most reactive and least reactive metal: Al, K, Ca, Au.


Most reactive metal: K(Potassium); least reactive metal: Au(gold).

Question 12. X + Y SO4 → X SO4 + Y
Y + X SO4 → No reaction
Of the two elements T and Y which is more reactive and why?


‘X’ is more reactive than ‘Y since it has displaced ‘Y’ in the displacement reaction.

Question 13. Why is it necessary to balance a chemical equation?


An equation is balanced in order to satisfy the law of conservation of mass according to which total mass of the reactants is equal to the total mass of the products, i.e., mass can neither be created nor be destroyed during any chemical change.

Question 14. During electrolysis of water, the gas collected in one test tube is double than the other, why?


On electrolysis, water decomposes into hydrogen and oxygen in the ratio 2 : 1 by volume so, H2 gas collected in one test tube is double than O2.

Question 15. Represent decomposition of ferrous sulphate with the help of balanced chemical equation.


2FeSO4 (s) → Fe2O3 (s) + SO2 (g) + SO3 (g)

Question 16. What is a chemical equation?


A chemical equation is a symbolic notation that uses formulae instead of words to represent a chemical equation.

Question 17. A teacher took a few crystals of sugar in a dry test tube and heated the test tube over a flame. The colour of sugar turned black. Explain why?


Sugar is a complex compound which on heating undergoes decomposition. Water gets evaporated thereby leaving behind black carbon in the test tube.

Question 18. Name two metals which do not get corroded.


Gold (Au) and platinum (Pt) do not get corroded.

Question 19. Identify the compound oxidised in the following reaction:
H2S (g) + Cl2 → S(s) + 2HCl (g)


H2S is oxidised.

Question 20. Why is a magnesium ribbon cleaned before burning?


Magnesium reacts with moist air and forms a layer of oxide, MgO (white), on its surface. So, a magnesium ribbon is cleaned to remove the oxide layer before burning.

Question 21. State the chemical change that takes place when limestone is heated.


Calcium carbonate decomposes on heating to give calcium oxide and carbon dioxide.

Question 22. On which chemical law, balancing of chemical equation is based?


Balancing of a chemical equation is based on the law of conservation of mass.

Question 23. Name the term used for the solution of the reactants or products when dissolved in water.



Question 24. What happens when magnesium ribbon burns in air?


When magnesium ribbon burns in air, it combines with the oxygen to form magnesium oxide.
2Mg(s) + O2(g) → 2MgO(s)

Question 25. Give an example of an exothermic reaction.


CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + Heat (evolved)

Question 26. What type of reaction is this: Na2SO4 + BaCl2 → BaSO4 + 2NaCl


It is a double displacement reaction.

Question 27. Give an example of exothermic reaction.


N2 (g) + O2 (g) → 2NO (g) – Heat (absorbed)

Question 28. A substance X used for coating iron articles is added to a blue solution of a reddish brown metal Y. The colour of the solution gets discharged. Identify X and Y and also the type of reaction.


X = Zn, Y = Cu, Displacement reaction.

Question 29. Name the gas evolved when zinc reacts with dil. HCl.


Hydrogen gas is evolved.

Short Answer Type

Question 1. You are given the following materials
(i) Marble chips
(ii) dilute hydrochloric acid
(iii) Zinc granules
Identify the type of reaction when marble chips and zinc granules are added separately to acid taken in two test tubes.


(i) Marble chips react with dilute hydrochloric acid to form calcium chloride and carbon dioxide. It is a double displacement reaction.
CaCO3 + 2HCl → CaCl2 + H2O + CO2

(ii) Zinc granules react with dilute hydrochloric acid to give hydrogen gas. It is a displacement reaction.
Zn (s) + 2HCl → ZnCl2 (aq) + H2 (g)

Question 2. What do you understand by precipitation reaction? Explain with suitable examples.


The reaction in which two compounds in their aqueous state react to form an insoluble compound. When two reactants react and product formed remains insoluble and settles as a solid it is substance (precipitate) is called a precipitation reaction.

For example,

(i) When aqueous solution of sodium sulphate is mixed with an aqueous solution or barium chloride, barium sulphate is obtained as a white precipitate.
Na2SO4 (aq) + BaCl2 (aq) → BaSO4 (s) + 2NaCl (ag)

(ii) When aqueous solution of sodium chloride is mixed with an aqueous solution of silver nitrate, silver chloride is obtained as a white precipitate.

Question 3. What happens when aqueous solutions of sodium sulphate and barium chloride are mixed? What type of reaction is it?


On mixing the solutions of sodium sulphate and barium chloride, a white precipitate of barium sulphate is obtained.

It is a double displacement reaction.

Question 4. Explain the following terms with suitable examples.
(a) Oxidation
(b) Reduction


(a) Oxidation is a process of addition of oxygen to a substance or removal of hydrogen from a substance, for example,

Copper is oxidised to CuO, as oxygen is added to copper.

(b) It is the process of removal of oxygen from a substance or addition of hydrogen to a substance, for example,

Copper oxide is reduced to copper as it involves removal of oxygen.

Question 5. Complete the missing components/variables given as x and y in the following reactions. [NCERT Exemplar]
(a) Pb(NO3)2 (aq) + 2Kl (aq) → PbI2 (x) + 2KNO3 (y)
(b) Cu (s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + x (s)
(c) Zn (s) + H2SO4 (aq) → ZnSO4 (x) + H2 (y)


(a) x = (s), y = (aq)
(b) x = 2Ag
(c) x = (aq); y = (g)
(d) x = heat

Question 6. An iron knife kept dipped in a blue copper sulphate solution turns the blue solution light green. Why?


We know that iron is more reactive than copper, so it displaces copper from copper sulphate solution and forms ferrous sulphate which is of light green colour.

Question 7. A, B and C are three elements which undergo chemical reactions in the following way.
A2O3 + 2B → B2O3 + 2A
3CSO4 + 2B → B2(SO4)3 + 3C
3CO + 2A → A2O3 + 3C
Answer the following:
(a) Which element is most reactive?
(b) Which element is least reactive?


(a) The most reactive element is ‘B’. It has displaced both ‘A’ and ‘C’ from their compounds.
(b) The least reactive element is ‘C’ as it has been displaced by both ‘A’ and ‘B’.

Question 8. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773 K to form ammonia gas.
(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H2SO4.
(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light. [NCERT Exemplar]


Question 9. What is lime water test for the detection of carbon dioxide?


When carbon dioxide gas is passed through lime water, it turns milky due to the formation of a milky suspension (precipitate) of calcium carbonate.
Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + CO2 (g)

Question 10. During the reaction of some metals with dilute hydrochloric acid, following observations were made,
(a) Silver metal does not show any change.
(b) The temperature of the reaction mixture rises when aluminium (Al) is added.
(c) The reaction of sodium metal is found to be highly explosive.
(d) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
Explain these observations giving suitable reasons. [NCERT Exemplar]


(a) No change takes place because silver metal does not react with hydrochloric acid in normal situations.
(b) The reaction between hydrochloric acid and aluminium is exothermic, thus the temperature of the reaction mixture rises when aluminium is added.
(c) Since, sodium is a highly reactive metal, thus it reacts with hydrochloric acid vigorously and produces a large amount of heat. Thus, the reaction is exothermic.
(d) Bubbles of hydrogen gas are formed when lead react with dilute hydrochloric acid.
Pb + 2HCl → PbCl2 + H2

Question 11. A copper coin is kept in a solution of silver nitrate for some time. What will happen to the coin and the colour of the solution?


We know that copper is more reactive than silver, so it will displace silver from its salt solution.
Cu(s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag (s)
So, the solution will turn blue due to the formation of copper nitrate.

Question 12. An aqueous solution of metal nitrate P reacts with sodium bromide solution to form yellow ppt. of compound Q which is used in photography. Q on exposure to sunlight undergoes decomposition reaction to form metal present in P along with reddish brown gas. Identify P and Q. Write the chemical reaction and type of chemical reaction.


P = AgNO3 , Q = AgBr
AgNO3 (aq) + NaBr (aq) → NaNO3 (aq) + AgBr (s); Double decomposition reaction
2AgBr (s) → 2Ag (s) + Br2 (g); Photochemical decomposition reaction

Question 13. What happens when iron nails are immersed in copper sulphate solution? What type of reaction is it?


When iron nails are immersed in copper sulphate solution, iron ions displace copper ions and a new compound ferrous sulphate is formed.

It is a diplacement reaction.

Question 14. Which of the following reaction is possible. Explain giving suitable reason.
(i) Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s)
(ii) Fe (s) + ZnSO4 (aq) → FeSO4 (aq) + Zn (s)
(iii) Zn (s) + FeSO4 (s) → ZnSO4 (aq) + Fe (s)


Reaction (i) and (iii) are possible.

Zinc is more reactive than copper, therefore, it can displace copper from copper sulphate solution.

(iii) Zn (s) + FeSO4 (aq) → ZnSO4 (aq) + Fe(s)
Zn is more reactive than Fe, therefore, it can displace iron from ferrous sulphate solution.

Reaction (ii) is not possible as iron is less reactive than zinc, hence, it cannot displace Zn.

Question 15. Which among the following changes are exothermic or endothermic in nature?
(a) Decomposition of ferrous sulphate
(b) Dilution of sulphuric acid
(c) Dissolution of sodium hydroxide in water
(d) Dissolution of ammonium chloride in water [NCERT Exemplar]


(a) endothermic
(b) exothermic
(c) exothermic
(d) endothermic.

Question 16. State one advantage and one disadvantage of corrosion.


Advantage. In some metals a protective layer is formed on its surface due to corrosion which prevent it from further corrosion.

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