CBSE Class 10 Chemistry Chemical Reactions And Equations Worksheet Set C

ONE MARK QUESTIONS

Question: What happens chemically when quick lime is added to water filled in a bucket?
Answer: Calcium hydroxide (Slaked lime) is formed with evolution of heat and hissing sound.
CaO(s) + H₂O(l) → Ca(OH)₂(aq)

Question: Which one is a chemical change: fermentation of fruit juice or diluting fruit juice?
Answer: Fermentation of fruit juice is a chemical change.

Question: Balance the given chemical equation:
FeSO₄(s) ^Heat→ Fe₂O₃(s) + SO₂(g) + SO₃(g)
Answer: 2FeSO₄(s) ^Heat→ Fe₂O₃(s) + SO₂(g) + SO₃(g)

Question: Define oxidation and reduction.
Answer: Oxidation is a process in which oxygen is added or loss of electrons take place. Reduction is a process in which hydrogen is added or gain of electrons takes place.

Question: State the main difference between endothermic reaction and an exothermic reaction.
Answer: In endothermic reaction, heat is absorbed. In exothermic reaction, heat is evolved. 

Question: What change in colour is observed when white silver chloride is left exposed to sunlight? State the type of chemical reaction in this change.
Answer: Grey coloured silver metal is formed and pungent smelling chlorine gas is evolved.

2AgCl(s) sunlight → 2Ag(s) + Cl₂(g)
It is photochemical decomposition reaction.

Question: Write a balanced equation for the chemical reaction that can be characterised as precipitation reaction.
Answer: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
It is a precipitation reaction.

Question: On what basis is a chemical reaction balanced?
Answer: Chemical equation is balanced on the basis of law of conservation of mass.

Question: Complete and balance the following equation:
Fe₂O₃ + Al →
Answer: Fe₂O₃ + 2Al → 2Fe + Al₂O₃

Question: Identify the type of reaction in the following example:
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
Answer: Displacement reaction.

Question: N2(g) + 3H2(g) ↓ 2NH3(g), name the type of reaction.
Answer: Combination reaction.

Question: On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue green. Predict the new compound formed which imparts a blue green colour to the solution.
Answer: CuO + 2HCl → CuCl₂ + 2H₂O
Copper chloride solution imparts blue green colour to the solution.

Question: Write a balanced chemical equation for the reaction between sodium chloride and silver nitrate indicating the physical state of the reactants and the products.
Answer: AgNO (aq) + NaCl (aq) →^Heat AgCl (s) + NaNO (aq) 
^{(Silver Nitrate) (Sodium Chloride) (Silver Chloride) (Sodium NItrate)}

Question: Give an example of double displacement reaction (only with complete balanced equation).
Answer: BaCl₂(aq) + H₂SO₄(dil.) → BaSO₄(s) + 2HCl(aq)
It is a double displacement reaction.

Question: Balance the given chemical equation:
Al(s) + CuCl₂(aq) → AlCl₃(aq) + Cu(s)
Answer: 2Al(s) + 3CuCl2(aq)→ 2AlCl₃(aq) + 3Cu(s)

Question: Identity the type of reaction in the following example:
Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄ → + 2NaCl(ag)
Answer: Double displacement reaction.

Question: Identify the type of reaction in the following example:
2H₂(g) + O₂(g)→ 2H₂O(l)
Answer: Combination reaction.

Question: Balance the following chemical equation:
Pb(NO₃)₂ → PbO + NO₂ + O₂
Answer: 2Pb(NO₃)2 → ^Heat2PbO + 4NO₂ + O₂

TWO MARKS QUESTIONS

Question: Write the essential condition for the following reaction to take place:
2AgBr→ 2Ag + Br₂
Write application of this reaction.
Answer: The reaction will take place in presence of sunlight.
This reaction is used in black and white photography.

Question: List two observations that are noticed when an iron nail is put inside copper sulphate solution. Write the chemical equation for the reaction that occurs.
Answer: The blue coloured solution will become pale green. Reddish brown metal will get deposited.
Fe(s)+ CuSO₄ (aq)→ FeSO₄ (aq)+ → Cu(s)
(Blue) (Pale Green) (Reddish brown)

Question: Write balanced chemical equation for the following reactions:
a. Hydrogen sulphide burns in air to give water and sulphur dioxide.
b. Barium chloride reacts in aqueous solution with zinc sulphate to give zinc chloride and barium sulphate.
Answer: a. 2H₂S(g) + 3O₂(g) → 2H₂O(l) + 2SO₂(g)
b. BaCl(aq) + ZnSO(aq) → BaSO₄ (s) + ZnCl₂(aq)

Question: “We need to balance a skeleton chemical equation”. Give reason to justify the statement.
Answer: We must balance a skeletal equation so as to ensure that the reaction follows ‘Law of conservation of mass’. The total mass of reactants must be equal to the total mass of products, that is why all reactions should he balanced.

Question: Name the reducing agent in the following reaction:
3MnO₂ + 4A1 → 3Mn + Al₂O₃
State which is more reactive, Mn or Al and Why?
Answer: Al is the reducing agent. Al is more reactive than Mn.
Reason: It is because Al is displacing Mn from MnO₂.

Question: Giving an example list two important information which makes a chemical equation more useful (informative).
Answer: a. It should include physical states of reactants and products.
b. It should specify conditions under which reaction takes place e.g.,
 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)
^(Cold)
H2(g) + Cl₂(g) → ^sunlight 2HCl(g)

Question: Consider the following chemical equation:
X + Barium chloride → Y + Sodium chloride
(White ppt)
Identify (a) X and Y (b) The type of reaction.
Answer: (a) X is silver nitrate, Y is silver chloride.
2AgNO₃ (aq) BaCl₂ (aq)→ 2AgCl ↓+Ba(3NO₃ )₂ (aq)
^{(White ppt)}
(b) The reaction is an example of double displacement
(precipitation) reaction.

Question: (a) Complete the following equation for the chemical reaction:
FeSO₄(s)→ ^Heat Fe₂O₃ + ___ +___
(b) What happens when water is added to quicklime (CaO)? Write the chemical equation.
Answer: (a) 2FeSO₄(s) → ^Heat Fe₂O₃(s) + SO₂(g) + SO₃(g)
(b) Slaked lime Ca(OH)₂ is formed. Hissing sound and lot of heat is also produced:
CaO(s) + H₂O(l) → Ca(OH)2(aq)

Question: (a) Write a balanced chemical equation for the process of photosynthesis.
(b) When do desert plant take up carbon dioxide and perform photosynthesis.
Answer: a. 6CO₂(g) + 6H₂O(l) ^chlorophyll→ _sunlight C₆H₁₂O₆(aq) + 6O₂(g)
b. Desert plant take up carbon dioxide and perform photosynthesis at night.

Question: A metal is treated with dilute H₂SO₄. The gas evolved is collected by the method as shown in figure. Answer the following questions:
a. Name the gas liberated.
b. Name the method used for collection of gas.
c. Is the gas soluble or insoluble in water?
d. Is the gas lighter or heavier than air?
Answer: a. The gas liberated is H₂.
b. It is collected by downward displacement of water.
c. The gas is insoluble in water.
d. Hydrogen gas is lighter than air.

Question:On heating copper powder in air, the surface of copper powder becomes coated with black CuO. How can this black coating be converted into brown copper? Write chemical equation for the reaction that occurs during the colour change.
Answer:
2Cu + O₂ → ^Heat 2CuO
^(Black)
Copper oxide on heating with H₂ will change back to reddish brown copper metal.
CuO(s) + H₂(g) → ^Heat Cu(s) + H₂O(g)

Question: What is observed when a solution of potassium iodide is added to a solution of lead nitrate? Name the type of reaction. Write a balanced chemical equation to represent the above chemical reaction.
Answer: Yellow precipitate is formed due to formation of lead iodide.
It is a precipitation as well as double displacementreaction.
Pb(NO₃ ) (aq)+ 2KI (ag) → PbI₂ (s) 2KNO₃ (aq)
^{Yellow ppt}

Question: Identify the type of reaction from the following equations:
a. CH₄ + 2O₂ → CO₂ + 2H₂O
_{b. Pb(NO3)2 + 2KI → PbI2 + 2KNO}3
c. CaO + H₂O → Ca(OH)₂
d. CuSO₄ + Zn → ZnSO₄ + Cu
Answer: a. Oxidation reaction
b. Double displacement reaction
c. Combination reaction
d. Displacement reaction

Question: Two reactions are given below:
a. 2KI + Cl₂ → 2KCl + I₂
b. 2K + Cl₂ → 2KCl
Identify the type of reaction, giving justification in each case.
Answer: a. Displacement reaction because Cl₂ is displacing I2 from KI solution.
b. Combination reaction because K reacts with Cl₂ to form potassium chloride.

Question: Consider the chemical equations given below and answer the questions which follow:
(i) CuO + H2 → ^Heat Cu + H₂O
(ii) ZnO + C →^Heat Zn + CO
a. Name the substances that are oxidised and reduced respectively in each case,
b. Identify the reducing agent in each case.
Answer: a. H₂ is getting oxidised to H₂O, CuO getting reduced to Cu.
b. H₂ is reducing agent in (i) reaction whereas C is reducing agent in second reaction.

Question: Translate the following statement into chemical equation and then balance it. “A metal in the form of ribbon burns with a dazzling white flame and changes into white powder.”
Answer: 2Mg(s) + O₂(g) → ^Burning 2MgO(s) + Light + Heat

Question: It has been found that marble of Taj is getting corroded due to development of industrial areas around it. Explain this fact giving a chemical equation.
Answer: Taj is made up of CaCO3 which reacts with acid formed by pollution of SO₂(g) and NO2 from Mathura refinery and other industries.
CaCO₃ + 2H₂SO₄ → CaSO4 + CO₂ + 2H₂O
CaCO₃ + 2HNO₃ → Ca(NO3)₂ + H₂O + CO₂

Question: Reaction of compound X with aluminium is used to join railway tracks or cracked machine parts.
a. Identify the compound.
b. Name the reaction.
c. Write a balanced chemical equation for the reaction.
Answer: a. The compound X is Fe₂O₃ (Ferric oxide) or Iron (III) oxide.
b. It is called Thermite Reaction.
c. 2Al(s) + Fe₂O₃(s)→ ^Heat Al₂O₃(s) + 2Fe(l)

Question: What is a redox reaction? Identify the substances oxidised and the substance reduced in the following reactions:
a. MnO₂+ 4HCl → MnCl₂ + Cl₂ + H₂O
b. CuO + H₂ → Cu + H₂O
Answer: Redox reaction is a reaction in which oxidation and reduction takes place simultaneously.
c. HCl is the substance oxidised, MnO₂ is the substance getting reduced.
d. H₂ is getting oxidised, CuO is getting reduced.

Question: Give an example each for thermal decomposition and photochemical decomposition reactions. Write balanced chemical equation also.
Answer: Thermal decomposition:
ZnCO₃(s) →Heat ZnO(s) + CO₂(g)
Photochemical decomposition:
2AgI(s) →^sunlight 2Ag(s) + I₂(g)

Question: Write balanced chemical equations for the following reactions:
a. Silver bromide on exposure to sunlight decomposes into silver and bromine.
b. Sodium metal reacts with water to form sodium hydroxide and hydrogen gas.
Answer: a. 2AgBr(s)→ ^sunlight 2Ag(s)+ Br₂(g)
b. 2Na(s) + 2H₂O(l) → 2NaOH(l) + H2(g)

Question: Using balanced chemical equation explain the difference between a displacement reaction and a double displacement reaction.
Answer: Displacement reaction: A reaction in which a more reactive element displaces a less reactive element from its salt solution e.g.,
2KBr(aq) + Cl₂(g) → 2KCl(aq) + Br₂(aq)
Double displacement reaction: A reaction in which
two compounds exchange their ions to form two new
compounds e.g.,
KOH + HNO₃ → KNO₃ + H₂O

Question: a. What is colour of ferrous sulphate crystals? How does this colour change after heating?
b. Name the products formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change?
Answer: a. FeSO₄ ·7H₂O → crystals are pale green in colour. They become dirty white on heating.
b. Ferric oxide, sulphur dioxide and sulphur trioxide are formed:
2FeSO₄(s)→ ^Heat Fe₂O₃(s) + SO₂(g) + SO₃(g)
It is a decomposition reaction.

THREE MARKS QUESTIONS

Question: In the electrolysis of water:
a. Name the gas collected at the cathode and anode respectively.
b. Why is volume of gas collected at one electrode double than that at the other? Name this gas.
c. How will you test this gas?
Answer: a. Hydrogen is collected at the cathode, oxygen is collected at the anode.
b. It is because H₂O contains hydrogen and oxygen in the ratio 2 : 1.
c. Bring a burning matchstick near the gas, if the gas burns with ‘pop’ sound, the gas is H₂.

Question: (a) Why is it necessary to balance a chemical equation?
(b) Write the balanced chemical equation for the following reactions:
(i) Natural gas burns in air to form carbon dioxide and water.
(ii) During respiration, glucose combines with oxygen and forms carbon dioxide and water along with the release of energy.
Answer: 
a. Chemical equation must be balanced so as to follow the law of conservation of mass.
b. (i) CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)
(ii) C₆H₁₂O₆(s) 6O₂(g) 6CO₂(g) 6H₂O(l) Heat

Question: Decomposition reactions require energy either in the form of heat, light or electricity for breaking down the reactants. Write an equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity.
Answer: 
a. CaCO3(s) → Heat CaO(s) + CO₂(g)
b. 2AgBr(s) → ^sunlight 2Ag(s) + Br₂(g)
c. 2H₂O(l) → ^Electricity 2H₂(g) + O₂(g)

Question: Name the type of reactions represented by the following equations:
a. CaO + H₂O → Ca(OH)₂
b. 3BaCl₂ + Al₂(SO₄) → 3BaSO₄ + 2AlCl₃
c. 2FeSO_4→ ^Heat Fe₂O₃ + SO₂ + SO₃
Answer: 
a. Combination reaction,
b. Double displacement reaction,
c. Decomposition reaction.

Question: Write balanced chemical equations for the following reactions:
a. Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
b. Barium chloride reacts with zinc sulphate to give zinc chloride and barium sulphate.
c. Natural gas bums in air to form carbon dioxide and water.
Answer: 
a. 2H₂S(g) + 3O₂(g) → 2H₂O(l) + 2SO₂(g)
b. BaCl₂(aq) ZnSO₄(aq) → BaSO₄(s) ZnCl₂(aq) 
c. CH₄(g) + 2O₂ → CO₂(g) + 2H₂O(l)

 Question: State one example each characterised by following along with suitable chemical equation.
a. Change in state,
b. Evolution of gas,
c. Change in temperature.
Answer:
a. Change in state:
AgNO₃(aq) + HCl(aq)→ AgCl(s) + HNO₃(aq)
b. Evolution of gas:
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CaCO₃ (s) +2HCl dil →CaCl₂ aq H₂O(1)+ CO₂ (g) 
c. Change in temperature:
d. CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) + Heat

Question: In a schematic diagram for the preparation of hydrogen
gas as shown in the figure. What would happen if the following changes are made
a. In place of zinc granules, same amount of zinc dust is taken in the test tube?
b. Instead of dilute sulphuric, dilute hydrochloric acid is taken?
c. Sodium hydroxide is taken in place of dilute sulphuric acid and the flask is heated?
Answer:
a. Zinc dust will react faster, H₂(g) will be liberated at a faster rate.
b. Same volume of H₂(g) will be formed.
c. On heating Zn with NaOH, hydrogen gas will be formed at a faster rate.

FIVE MARKS QUESTIONS

Question: Write balanced chemical equation for the following statements:
a. NaOH solution is heated with zinc granules.
b. Excess of carbon dioxide is passed through lime water.
c. Dilute sulphuric acid is added to sodium carbonate.
d. Egg shell is dropped in hydrochloric acid,
e. Copper (II) oxide reacts with dilute hydrochloric acid.
Answer: 
a. Zn(s) + 2NaOH → Na₂ZnO₂ + H₂
b. Ca(OH)₂ + ₂CO₂ → Ca(HCO₃)₂
c. Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂
d. CaCO₃(s) + 2HCl(dil) → CaCl₂ + H₂O + CO₂
e. CuO(s) + 2HC1 → CuCl₂ + H₂O

Question: Identify the type of chemical reaction in the following statement and define each of them:
a. Digestion of food in our body.
b. Rusting of iron.
c. Heating of manganese dioxide with aluminium powder.
d. Blue colour of copper sulphate solution disappears when iron filings are added to it.
e. Dilute hydrochloric acid is added to sodium hydroxide solution to form sodium chloride and water.
Answer: a. Decomposition reaction: It is a process in which a compound is broken down into simple substances.
b. Oxidation: The process in which oxygen is added or electrons are lost.
c. Displacement reaction: The reaction in which a more reactive element can displace a less reactive element from its salt solution. Oxidation and Reduction are taking place simultaneously in rusting of iron. Download more materials in free at : 
d. Displacement reaction: The reaction in which a more reactive element can displace a less reactive element.
e. Neutralisation reaction: The reaction in which acid reacts with base to form salt and water.