Chemical Reactions and Equations: Practice Time

 

PART A                                                                                              1 MARK QUESTIONS

 

Q1. Which of the following gas is used in the storage of fat and oil containing foods for a long time?

a)    Carbon dioxide

b)    Oxygen

c)    Nitrogen

d)    Neon

Q2.Name the gas evolved when zinc reacts with dil. HCl.

Q3. Represent decomposition of ferrous sulphate with the help of balanced chemical equation.

Q4. X + Y SO₄ → X SO₄ + Y
Y + X SO₄ → No reaction
Of the two elements T and Y which is more reactive and why?

Q5. On which chemical law, balancing of chemical equation is based?

 

PART B                                                                                              2 MARK QUESTIONS

Q6.What is a balanced chemical equation?

 

Q7. Which among the following are physical or chemical changes?
(a) Evaporation of petrol
(b) Burning of Liquefied Petroleum Gas (LPG)
(c) Heating of an iron rod to red hot
(d) Curdling of milk
(e) Sublimation of solid ammonium chloride

Q8. What is lime water test for the detection of carbon dioxide?

Q9. State conditions necessary for rusting of iron.

Q10.Deepa has been collecting silver coins and copper coins. One day she observed a black coating on silver coin and a green coating on copper coins.

a)    Which chemical phenomenon is responsible for these coating?

b)    Write the chemical name of black and green coatings?

Q11.Balance the following equations:
(a) Bacl₂ + H₂SO₄ → BaSO₄ + HCl
(b) CH₄ + O₂ → CO₂ + H₂O
Q12. 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 

PART C                                                                                              3 MARK QUESTIONS

 

Q13. Why respiration is considered as an exothermic reaction? Explain.

Q14.Give the characteristics gas for the following gases:

a)    SO2

b)    O2

c)    H2

Q15. Identify the oxidising agent (oxidant) in the following reactions:
(a) Pb₃O₄ + 8HCl → 3PbCl₂ + Cl₂ + 4H₂O
(b) 2Mg + O₂ → 2MgO
(c) CuSO₄ + Zn → Cu + ZnSO₄
(d) V₂O₅ + 5Ca → 2V + 5CaO
(e) 3Fe + 4H₂O → Fe₃O₄ + 4H₂
(f) CuO + H₂ → Cu + H₂O

Q16. Explain the following terms with suitable examples.
(a) Oxidation(b) Reduction

Q17. A brown substance ‘X’ on heating in air forms a substance ‘Y’. When hydrogen gas is passed over heated ‘Y’, it again changes back into ‘X’.
(i) Name the substances X and Y.
(ii) Name the chemical processes occurring during both the changes.
(iii) Write the chemical equations.

Q18.What happens when zinc granules are treated with dilute solution of H2SO4 and NaOH, also write the chemical equations if reaction occurs.

 

PART D                                                                                  4 MARK QUESTIONS

 

Q19. 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. 

Q20. Observe the following activity and identify the following:

(a) Type of chemical reaction.
(b) Write a chemical equation to represent the above change.
(c) Name the gas evolved in the above reaction.
(d) Do you observe any colour change in the above reaction? If yes, mention the colour change.
(e) Name the coloured substance formed.

 

 

 

 

 

 

Answer1: C) Nitrogen

Answer2: Hydrogen gas is evolved.

Answer3:2FeSO₄ (s) → Fe₂O₃ (s) + SO₂ (g) + SO₃ (g)

Answer4: ‘X’ is more reactive than ‘Y since it has displaced ‘Y’ in the displacement reaction.

Answer5:Balancing of a chemical equation is based on the law of conservation of mass.

 

Answer6: 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, 2Mg+O2⟶Δ2MgO

Answer7:
(a) Physical change
(b) Chemical change
(c) Physical change
(d) Chemical change

Answer8: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)

Answer9: Conditions necessary for rusting:

·         Open surface of the metal

·         Presence of air (oxygen)

·         Presence of moisture (water).

Answer10:

a) The phenomenon responsible for the changes seen is CORROSION.

b) Black coating is Ag2S or silver sulphide and Green coating is Cu(OH)2 + CuCO3 that is copper carbonate and copper hydroxide.

Answer11:
(a) Bacl₂ + H₂SO₄ → BaSO₄ + 2HCl
(b) CH₄ + 2O₂ → CO₂ + 2H₂O

Answer12:
(a) endothermic
(b) exothermic
(c) exothermic
(d) endothermic.

Answer13: An exothermic reaction is a reaction in which energy is liberated out.Respiration is considered as exothermic reaction because energy is released in this process.Glucose combines with oxygen present in our cells to form carbon dioxide and water along with energy.
C₆H₁₂O₆ + 6O₂ ----> 6CO₂ + 6H₂O + energy

Answer14:

a) SO2:
 Sulphur dioxide is a odorless and pungent gas. 
Test : Sulphur dioxide gas turns acidified potassium dichromate solution from orange to green colour.

b) H2 gas:
If a burning match stick is brought near Hydrogen, the match stick burns with POP sound.

c) O2 gas :
O2 gas is a good supporter of Combustion. So if a burning match stick is brought near the gas it burns more vigorously.

Answer15:
(a) Pb₃O₄
(b) O₂
(c) CuSO₄
(d) V₂O₅
(e) 4H₂O
(f) CuO

Answer16:
(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.

Answer17:
(i) The substance X is copper and Y is copper (II) oxide or CuO.
(ii) The process of change of X into Y is oxidation. The process of change of Y into X is reduction.
(iii) The chemical equations are:

 

 

 

 

 

Answer18:

Hydrogen gas and zinc sulphate are formed when zinc granules are treated with sulphuric acid.

Zn + H₂SO₄ ⇨ ZnSO₄ + H₂

 

Sodium zincate and hydrogen gas are formed when zinc granules are treated with sodium hydroxide and water.

Zn + 2H₂O + 2NaOH ⇨ Na₂Zn(OH)₄ + H₂

 

Answer19:

 

 

 

 

 

 

Answer20:
(a) Decomposition reaction.
(b) 2Pb(NO₃)₂ (s) → 2PbO (s) + 4NO₂ (g) + O₂ (g)
(c) Reddish brown fumes of nitrogen dioxide along with oxygen gas is evolved.
(d) The colour of the substance changes from white to yellow due to formation of lead oxide.
(e) Lead oxide which is yellow coloured