CHAPTER – 1: CHEMICAL REACTIONS AND EQUATIONS

VOLUME – 1 (Study Capsule)

Multiple Choice Questions

Balanced form of hydrogen + oxygen → water is:
a) \( H_2 + O_2 \rightarrow H_2O \)
b) \( 2H_2 + O_2 \rightarrow 2H_2O \)
c) \( H_2O \rightarrow H_2 + O_2 \)
d) \( 2H_2O \rightarrow 2H_2 + O_2 \)
Answer: b
Which is a combination reaction?
a) \( CaO + H_2O \rightarrow Ca(OH)_2 \)
b) \( CaCO_3 \rightarrow CaO + CO_2 \)
c) \( Zn + CuSO_4 \rightarrow ZnSO_4 + Cu \)
d) \( FeSO_4 \rightarrow Fe_2O_3 + SO_2 + SO_3 \)
Answer: a
Which of the following is the chemical formula of quick lime?
a) \( CaCO_3 \) b) \( CaO \) c) \( Ca(OH)_2 \) d) \( CuO \)
Answer: b
Which of the following is the chemical formula of Slaked lime?
a) \( CaCO_3 \) b) \( CaO \) c) \( Ca(OH)_2 \) d) \( CuO \)
Answer: c
When carbon dioxide is passed through lime water:
(a) Calcium hydroxide is formed
(b) A white precipitate of CaO is formed
(c) Lime water turns milky
(d) Color of lime water disappears.
Answer: (c) Lime water turns milky
On immersing an iron nail in \( CuSO_4 \) solution for few minutes, you will observe:
(a) no reaction takes place
(b) the color of the solution fades away
(c) the surface of iron nails acquire a black coating
(d) the color of the solution changes to green
Answer: (d) the color of the solution changes to green
Reaction between potassium iodide and lead nitrate forms \( PbI_2 + KNO_3 \). This is a type of:
a) Combination reaction
b) Decomposition reaction
c) Double displacement (precipitation) reaction
d) Oxidation-reduction reaction
Answer: c
What type of reaction is \( CuO + H_2 \rightarrow Cu + H_2O \)?
a) Neutralization b) Decomposition c) Oxidation-reduction d) Combustion
Answer: c
Identify the substance getting oxidised in the following reaction:
\[ 2PbO(s) + C(s) \rightarrow 2Pb(s) + CO_2(g) \]
(a) PbO (b) C (c) Pb (d) CO2
Answer: (b)
Which gas is used to prevent rancidity in chips?
a) Oxygen b) Nitrogen c) Carbon dioxide d) Helium
Answer: b
Fatty foods become rancid due to the process of:
(a) oxidation (b) corrosion (c) reduction (d) hydrogenation
Answer: (a) oxidation
In which of the following, heat energy will be evolved?
(a) Electrolysis of water
(b) Dissolution of \( NH_4Cl \) in water
(c) Burning of L.P.G.
(d) Decomposition of AgBr in the presence of sunlight
Answer: (c) Burning of L.P.G.

Very Short Answer Type Questions (2 Marks)

Q13. Write balanced chemical equations for the following chemical reactions and also mention its type: Iron + Copper Sulphate → Iron Sulphate + Copper

Answer:

\[ Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s) \]

It is a displacement reaction in which one element replaces another element within a compound.

Q14. Differentiate between decomposition and combination reaction.

Combination Reactions	Decomposition Reactions
In a combination reaction two reactants are combining to create one product.	A single compound breaks down to produce two or more simpler substances.
Generally exothermic.	Generally endothermic.

Q15 (Based on text flow). Differentiate Displacement and Double Displacement Reaction.

Displacement Reaction	Double Displacement Reaction
In this reaction, one element replaces another element within a compound.	In this reaction, two compounds exchange ions, resulting in the formation of two new compounds.
Example: \( Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s) \) Iron (Blue) → Iron sulphate (Green) + Copper	Example: \( Pb(NO_3)_2(aq) + 2KI(aq) \rightarrow PbI_2(s) + 2KNO_3(aq) \) Lead Nitrate + Potassium Iodide → Lead Iodide (Yellow ppt)

Q16. What do you mean by a precipitation reaction? Explain by giving examples.

Answer: Precipitation reaction is a type of reaction where soluble reactants combine to form an insoluble solid called a precipitate.

Example:

\[ AgNO_3(aq) + KCl(aq) \rightarrow AgCl(s) + KNO_3(aq) \]

(White ppt)

Q17. Define rusting. How it can be prevented?

Answer: Rusting is a chemical process where iron corrodes due to oxidation when exposed to oxygen and moisture. Paint does not allow iron articles to come in contact with air, water and saves iron articles from rusting.

Short Answer Type Questions (3 Marks)

Q18. A solution of a substance ‘X’ is used for white washing.

(i) Name the substance ‘X’
(ii) Write its chemical formula.
(iii) Write the reaction of the substance ‘X’ named in (i) above with water.

Answer:

(i) The substance is calcium oxide (or quick lime).
(ii) Its formula is \( CaO \).
(iii) \( CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) \)

Q19. Define Decomposition reaction. Give one example each of decomposition reaction where light, heat and electricity is used.

Answer: In a decomposition reaction, a single compound breaks down to produce two or more simpler substances.

Heat (Thermal Decomposition): \[ CaCO_3(s) \xrightarrow{\text{Heat}} CaO(s) + CO_2(g) \]
Light (Photochemical Decomposition): \[ 2AgBr(s) \xrightarrow{\text{Light}} 2Ag(s) + Br_2(g) \]
Electricity (Electrolytic Decomposition): \[ 2H_2O(l) \xrightarrow{\text{Electricity}} 2H_2(g) + O_2(g) \]

Diagram representation of decomposition of silver chloride by sunlight.

Q20. Lead nitrate solution is added to a test tube containing potassium iodide solution.

Answer:

(a) Yellow precipitate of lead iodide is formed.
(b) Balanced Equation: \[ Pb(NO_3)_2(aq) + 2KI(aq) \rightarrow PbI_2(s) \downarrow + 2KNO_3(aq) \]
(c) Type: Precipitation reaction and Double displacement reaction.

Q21. 2 g of silver chloride is taken in a China dish and placed in sunlight.

Answer: Silver chloride will change into slightly grey or black colour.

\[ 2AgCl(s) \rightarrow 2Ag(s) + Cl_2(g) \]

It is a Photo chemical decomposition.

Q22. Differentiate between exothermic reaction and endothermic reaction.

Exothermic Reaction	Endothermic Reaction
These reactions release energy, usually as heat. Makes the surroundings warmer.	These reactions absorb energy from the surroundings. Causes the surroundings to cool down.
Examples: 1. \( CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + \text{Heat} \) 2. Burning of a candle 3. Respiration	Examples: 1. Melting of ice 2. Dissolving ammonium chloride in water

Long Answer / Application Based Questions

Q23. What happens when food materials containing fats and oils are left for a long time?

Answer: Rancidity is the process where fats and oils in food oxidize.

Changes: 1. Change in smell. 2. Change in taste.

Prevention: 1. Vacuum packing. 2. Refrigeration. 3. Placing food away from direct sunlight.

Q24. Translate and Balance:

a) Hydrogen gas combines with nitrogen to form ammonia.
Ans: \( 3H_2 + N_2 \rightarrow 2NH_3 \)
b) Hydrogen sulphide gas burns in air to give water and Sulphur dioxide.
Ans: \( 2H_2S + 3O_2 \rightarrow 2H_2O + 2SO_2 \) (Note: Source text has a typo repeating H2S, corrected here based on context).
c) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Ans: \( Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \)

Q24(2). Oil and fat containing food items are flushed with nitrogen. Why?

Ans: Nitrogen, being an inert gas acts as an antioxidant preventing the rancidity of food items with oils and fats.

Q25. In the reaction: \[ MnO_2 + 4HCl \rightarrow MnCl_2 + H_2O + Cl_2 \]

a) Name the substance oxidised: Ans: \( HCl \) is oxidised to \( Cl_2 \).
b) Name the oxidising agent: Ans: \( MnO_2 \).
c) Name the reducing agent: Ans: \( HCl \).

Why is a Combustion reaction an oxidation reaction?
Ans: Because it is always carried out in the presence of oxygen and oxygen is added to a compound. Example: \( CH_4 + O_2 \rightarrow CO_2 + H_2O \).

Case Based Questions

Q26. Meena heats a small amount of powder of metal ‘X’ (reddish brown). It becomes coated with black substance ‘Y’.

(a) Identify X and Y: X is Copper (Cu), Y is Copper oxide (CuO).
(b) Why is Y formed? The black substance (CuO) is due to oxidation of copper.
(c) Chemical Equation: \[ 2Cu + O_2 \xrightarrow{\text{Heat}} 2CuO \]
(d) How to turn black coating back to reddish brown? Pass hydrogen gas over hot material. \[ CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O \]

Q27. Oxidation and Reduction Concepts

(a) Substance getting oxidised: \( H_2S + Cl_2 \rightarrow S + 2HCl \)
Ans: \( H_2S \)
(b) Identify oxidising/reducing agent: \( Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3 \)
Ans: \( Fe_2O_3 \) is Oxidising agent; \( Al \) is Reducing agent.
(c) Oxidation and reduction reaction always occurs together.
Ans: Yes, because for one substance to lose O or H, another substance must accept it, hence the paired nature (Redox) of these reactions.

WORKSHEET: CHAPTER 1

1. What is formed at the cathode during the electrolysis of water?
Answer: B) Hydrogen

2. In a double displacement reaction, the exchange of which of the following takes place?
Answer: B) Ions

3. What type of reaction is: \( AgNO_3 + NaCl \rightarrow AgCl\downarrow + NaNO_3 \)?
Answer: D) Double displacement

4. Assertion (A): Magnesium ribbon burns with a dazzling white flame. Reason (R): Magnesium reacts with oxygen to form magnesium oxide.
Answer: a) Both A and R are true and R is the correct explanation of A

5. Balance following equation: \( H_2O \rightarrow H_2 + O_2 \)
Answer: \( 2H_2O \rightarrow 2H_2 + O_2 \)

6. Identify oxidising and reducing agent: \( MnO_2 + 4HCl \rightarrow MnCl_2 + Cl_2 + 2H_2O \)
Answer: Oxidizing agent: \( MnO_2 \); Reducing agent: \( HCl \)

7. Define 'rancidity'. Prevention?
Answer: Oxidation of fats and oils when exposed to air, making food smell and taste bad. Prevention: Airtight containers, antioxidants, refrigeration, nitrogen packing.

8. Write balanced equations:

(a) Iron reacts with steam: \[ 3Fe + 4H_2O(g) \rightarrow Fe_3O_4 + 4H_2 \] (Combination/Displacement)
(b) Decomposition of lead nitrate: \[ 2Pb(NO_3)_2 \rightarrow 2PbO + 4NO_2 + O_2 \] (Thermal decomposition)
(c) Sodium with water: \[ 2Na + 2H_2O \rightarrow 2NaOH + H_2 \] (Exothermic, displacement)

9. Silver chloride exposed to sunlight turns grey.
Equation: \( 2AgCl \xrightarrow{\text{Sunlight}} 2Ag + Cl_2 \)
Type: Photochemical decomposition.
Use: Black-and-white photography.

10. Case Study: Iron nails in copper sulphate.

Type: Displacement reaction.
Equation: \( Fe + CuSO_4 \rightarrow FeSO_4 + Cu \)
Observation: Blue color fades to green (formation of \( FeSO_4 \)); Brown coating on nail (Copper).
Reactivity: Iron is more reactive than Copper.

CHAPTER – 1: CHEMICAL REACTIONS AND EQUATIONS