Chapter-1 Chemical Reactions and Equations
Important Questions

Topic-Wise Questions

Chemical Equations and Balancing

A 1.: What is a balanced chemical equation ? Why should chemical equations be balanced ?   [CBSE 2010]  [NCERT] 

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A 2.: Write the balanced chemical equations for the following reactions :   [CBSE 2020]  [NCERT]

  1. Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water 
  2. Zinc + Silver nitrate → Zinc nitrate + Silver
  3. Aluminum + Copper chloride → Aluminum chloride + Copper
  4. Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

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A 3.: Write the balanced chemical equations for the following reactions :   [CBSE 2023] 

  1. Nitrogen gas is treated with hydrogen gas to form ammonia gas. 
  2. Lead nitrate is heated strongly to form lead monoxide, nitrogen die oxide, and oxygen. 
  3. A copper wire is dipped in silver nitrate solution and a shining deposit of silver is produced. 

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A 4.: Translate the following statements into chemical equations and then balance them.     [NCERT]

  1. Hydrogen gas combines with nitrogen to form ammonia.
  2. Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
  3. Barium chloride reacts with aluminium sulphate to give aluminium chloride
    and a precipitate of barium sulphate.
  4. Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

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A 5.: Balance the following chemical equations.     [NCERT]

  1. HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
  2. NaOH + H2SO4 → Na2SO4 + H2O
  3. NaCl + AgNO3 → AgCl + NaNO3
  4. BaCl2 + H2SO4 → BaSO4 + HCl

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A 6.: Write the balanced chemical equation for the following and identify the type of reaction in each case.    [NCERT]

  1. Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) +
    Barium bromide(s)
  2. Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
  3. Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
  4. Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

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A 7.: Write a balanced chemical equation with state symbols for the
following reactions.    [NCERT]

  1. Solutions of barium chloride and sodium sulphate in water react
    to give insoluble barium sulphate and the solution of sodium
    chloride.
  2. Sodium hydroxide solution (in water) reacts with hydrochloric
    acid solution (in water) to produce sodium chloride solution and
    water. 

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A 8.: Write a balanced chemical equation for the reaction in which phosphorus burns in chlorine to form Phosphorous pentachloride.

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A 9.: Which among the following are physical or chemical changes?  [NCERT Exemplar]

  1. Evaporation of petrol
  2. Burning of Liquefied Petroleum Gas (LPG)
  3. Heating of an iron rod to red hot.
  4. Curdling of milk
  5. Sublimation of solid ammonium chloride.

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A 10.: Write a balanced chemical equation for each of the following reactions and also classify them.      [NCERT Exemplar]

  1. Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
  2. A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.
  3. Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
  4. Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.

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A 11.: Balance the following chemical equations and identify the type of chemical reaction.      [NCERT Exemplar]

(a) Mg(s) + Cl2 (g) → MgCl2 (s)

(b) HgO(s) → Hg(l) + O2 (g)

(c) Na(s) + S(s)  →  Na2S(s)

(d) TiCl4 (l) + Mg(s)  → Ti(s) + MgCl2 (s)

(e) CaO(s) + SiO2 (s)  → CaSiO3 (s)

(f) H2O2 (l)  → H2O(l) + O2 (g)

 

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Combination and Decomposition Reactions

B 1.: Give an example of an exothermic reaction.  [CBSE 2010]

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B 2.: Name the two salts that are used in black and white photography.  [CBSE 2010, 2011]

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B 3.: Why should a magnesium ribbon be cleaned before burning in air.    [CBSE 2010]  [NCERT]

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B 4.: A solution of a substance ‘X’ is used for whitewashing.    [CBSE 2010, 2011]  [NCERT]  

  1. Name the substance ‘X’ and write its formula.
  2. Write the reaction of the substance ‘X’ with water.

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B 5.: What does one mean by exothermic and endothermic reactions ? Give examples.  [CBSE 2012]  [NCERT]

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B 6.: Why is respiration considered an exothermic reaction ? Explain.  [CBSE 2012]  [NCERT]

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B 7.: Why are decomposition reactions called the opposite of combination reactions ? Write equations for these reactions.  [CBSE 2011]   [NCERT]

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B 8.: What is the colour of FeSO4.7H2O crystals? How does this colour change upon heating ? Give balanced chemical equation for the change.  [CBSE 2013]

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B 9.: An element ‘X’, when burnt in the presence of air burns with a dazzling light. It forms compound ‘Y’ which when dissolved in water forms compound ‘Z’. Identify ‘X’, ‘Y’, and ‘Z’.  [CBSE 2023]

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B 10.: Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.     [NCERT]

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B 11.: In the electrolysis of water,

  1. Name the gas collected at anode and cathode.
  2. Why is the volume of gas collected at one electrode is double than the other ?
  3. What would happen if dilute Sulphuric acid is not added to water ?

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B 12.: Translate the following reactions into balanced chemical equations:

  1. Manganese dioxide is heated with Aluminium powder.
  2. Iron is treated with steam. 

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B 13.: Give reason why :

  1. White coloured silver chloride turns grey when kept in sunlight.
  2. Sodium act as an reducing agent while chlorine act as an oxidising agent in the following reaction :  2Na + Cl2  →  2NaCl
  3. Why is decomposition reaction called the opposite of combination reaction ?

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B 14.: Why do we store silver chloride in dark coloured bottles ?       [NCERT Exemplar]

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B 15.: On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper (II) oxide (black), oxygen gas and a brown gas ‘X’ is formed.

  1. Write a balanced chemical equation of the reaction. 
  2. Identify the brown gas ‘X’ evolved.
  3. Identify the type of reaction. 
  4. What could be the pH range of aqueous solution of the gas ‘X’ ?

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B 16.: A Magnesium ribbon is burnt in oxygen to give a white compound ‘X’ accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and form compound ‘Y’. 

  1. Write the chemical formulae of ‘X’ and ‘Y’. 
  2. Write a balanced chemical equation when ‘X’ is dissolved in water. 

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B 17.: Give the characteristic test for the following gases :         [NCERT Exemplar]

  1. CO2
  2. O2
  3. SO2
  4. H2

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B 18.: A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.       [NCERT Exemplar]

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B 19.: Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why?       [NCERT Exemplar]

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B 20.: On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed.          [NCERT Exemplar]

  1. Write a balanced chemical equation of the reaction.
  2. Identity the brown gas X evolved.
  3. Identity the type of reaction.
  4. What could be the pH range of aqueous solution of the gas X?

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Displacement and Double-displacement Reactions

C 1.: Which characteristic change occurs in the following chemical reactions ?   [CBSE 2014]

  1. Dilute sulphuric acid is added to a barium chloride solution.
  2. Dilute sulphuric acid is added to a sodium carbonate solution.
  3. Quick lime is added to water.
  4. Aqueous solutions of lead nitrate and sodium iodide are mixed together.

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C 2.: Why does the colour of copper sulphate solution change when an iron nail is dipped in it?    [CBSE 2010, 2011]  [NCERT]

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C 3.: What is observed when aqueous solution of potassium iodide and lead nitrate are mixed together ? Name the type of reaction and write the chemical equation for the reaction that occurs.    [CBSE 2023]

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C 4.: When potassium iodide solution is added to a solution of lead (II) nitrate in a test tube, a precipitate is formed.    [CBSE 2013] 

  1. What is the colour of this precipitate?
  2. Name the compound precipitated.
  3. What a balanced chemical equation for this reaction?
  4. What type of reaction is this?

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C 5.: An Aluminium container was used to store ferrous sulphate. It is observed that in few days holds appeared in the container. Explain the observation and write chemical equation to support your answer.    [CBSE 2013]

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C 6.: What is the difference between displacement and double displacement reactions? Write equations for these reactions.    [NCERT]

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C 7.: In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.    [NCERT]

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C 8.: What do you mean by a precipitation reaction? Explain by giving examples.    [NCERT]

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C 9.: What happens when a piece of :     [NCERT Exemplar]

  1. Aluminum metal is added to dilute hydrochloric acid ?
  2. Zinc metal is added to copper sulphate solution ?
  3. Silver metal is added to copper sulphate solution ?

Also, write the balanced chemical reaction if the reaction occurs.

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C 10.: What happens when zinc granules are treated with dilute solution of H2SO4 , HCl , HNO3 , NaCl , and NaOH ? Also, write the chemical equations if reaction occurs.      [NCERT Exemplar]

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C 11.: 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?   [NCERT Exemplar]

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C 12.: Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.    [NCERT Exemplar]

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C 13.: During the reaction of some metals with dilute hydrochloric acid, following observations were made.

  1. Silver metal does not show any change
  2. The temperature of the reaction mixture rises when aluminium (Al) is added.
  3. The reaction of sodium metal is found to be highly explosive
  4. Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.

 Explain these observations giving suitable reasons.    [NCERT Exemplar]

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C 14.: On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained.       [NCERT Exemplar]

  1.  Write a balanced chemical equation of the reaction involve
  2. What other name can be given to this precipitation reaction? 
  3. On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?.   

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C 15.: You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO3 , ZnCl2 and H2O. In which of the above containers these solutions can be kept?      [NCERT Exemplar]

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Oxidation and Reduction Reactions

D 1.: Name a reducing agent that can be used to obtain manganese from manganese dioxide. Write a balanced chemical equation for the reaction.   [CBSE 2010]

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D 2.: Name the gas used to store potato chips for a long time.   [CBSE 2011]

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D 3.: Explain the following in terms of gain or loss of oxygen with two example each :   [CBSE 2011]   [NCERT]

  1. Oxidation 
  2. Reduction

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D 4.: A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.   [NCERT]

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D 5.: Why do we apply paint on iron articles ?    [NCERT]

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D 6.: Oil and fat containing food items are flushed with nitrogen. Why ?    [CBSE 2012]   [NCERT]

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D 7.: When copper powder is heated in a watch glass, a black substance is formed.    [CBSE 2023] 

  1. Why is this black substance formed ? Name it.
  2. How can this black substance be reversed to its original form ?

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D 8.: 1 gm of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equations of reactions, the name and the colour of the products formed in each case.    [CBSE 2019] 

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D 9.: Name the type of reaction for the following :  [CBSE 2014] 

  1. Vegetable matter changing into compost.
  2. Burning of natural gas.
  3. Silver items turning black when left exposed to air. 
  4. Change in blue colour of copper sulphate into green on dipping a iron nail in it.    

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D 10.: Explain the following terms with one example each.   [NCERT] 

  1. Corrosion
  2. Rancidity 

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D 11.: Identify the substances that are oxidised and the substances that are reduced in the following reactions.     [NCERT]
  1. 4Na(s) + O2 (g) → 2Na2O(s)
  2. CuO (s) + H2 (g) → Cu (s) + H2O (l).    

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D 12.: A metal ‘P’ when exposed to the moist air for longer period of time, loses its shiny brown surface and gain a green coat. Why has this happened ? Identify the metal. Write the name and chemical formula if this green coloured compound. List two ways to prevent this process.   

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D 13.: Which among the following changes are exothermic or endothermic in nature ?

  1. Decomposition of ferrous sulphate. 
  2. Dilution of Sulphuric acid.
  3. Dilution of sodium hydroxide (Caustic soda) in water
  4. Dilution of ammonium hydroxide in water. 

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D 13.: Identify the reducing agent in the following reactions :

  • 4NH3­ + 5O2 → 4NO + 6H2O
  • H2O + F2 → HF + HOF
  • Fe2O3 + 2CO → 2Fe + 3CO2
  • 2H2 + O2  →  2H2O

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D 13.: Identify the oxidising agent in the following reactions :

  • Pb3O4 + 8HCl → 3PbCl2 + Cl2 + 4H2O 
  • 2Mg + O2 →  2MgO
  • CuSO4 + Zn → Cu + ZnSO4
  • V2O5 + 5Ca → 2V + 5CaO
  • 3Fe + 4H2O → Fe3O4 + 4H2
  • CuO + H2 → Cu + H2O

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D 14.: A Silver article generally turn black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining. 

  1. Why do silver article turn black when kept in the open for a few days ? Name the phenomenon involved.
  2. Name the black substance formed and give its chemical formula. 

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D 15.: Why do fire flies glow at night?   [NCERT Exemplar]

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D 16.: Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?  [NCERT Exemplar]

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Case-Study / Passage-Based Questions

E 1.: —

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