Chemistry and Biology Assignments

Assignment 1. MCQ: Chemical Reactions and Equations

Q1. Before burning in air, the magnesium ribbon is cleaned by rubbing with a sand paper to:

a. Make the ribbon surface shinier
b. Remove the layer of magnesium oxide from the ribbon surface
c. Remove the layer of magnesium nitride from the ribbon surface
d. Remove the moisture from the ribbon surface

Answer: b. Remove the layer of magnesium oxide from the ribbon surface

Q2. In a chemical reaction between sulphuric acid and barium chloride solution the white precipitates formed are of:

a. Hydrochloric acid
b. Barium sulphate
c. Chlorine
d. Sulphur

Answer: b. Barium sulphate

Q3. The respiration process during which glucose undergoes slow combustion by combining with oxygen in the cells of our body to produce energy, is a kind of:

a. Exothermic process
b. Endothermic process
c. Reversible process
d. Physical process

Answer: a. Exothermic process

Q4. A chemical reaction does not involve:

a. Formation of new substances having entirely different properties than that of the reactant
b. Breaking of old chemical bonds and formation of new chemical bonds
c. Rearrangement of the atoms of reactants to form new products
d. Changing of the atoms of one element into those of another element to form new products

Answer: d. Changing of the atoms of one element into those of another element to form new products

Q5. It is necessary to balance a chemical equation in order to satisfy the law of:

a. Conservation of motion
b. Conservation of momentum
c. Conservation of energy
d. Conservation of mass

Answer: d. Conservation of mass

Q6. You are given the following chemical reaction:

This reaction represents:

a. Combination reaction as well as double displacement reaction
b. Redox reaction as well as displacement reaction
c. Double displacement reaction as well as redox reaction
d. Decomposition reaction as well as displacement reaction

Answer: b. Redox reaction as well as displacement reaction

Q7. When ferrous sulphate is heated strongly it undergoes decomposition to form ferric oxide as a main product accompanied by a change in colour from:

a. Blue to green.
b. Green to blue.
c. Green to brown.
d. Green to yellow.

Answer: c. Green to brown.

Q8. Following is given a diagram showing an experimental set-up:

The given set-up is used to carry out:

a. Distillation of water
b. Purification of water
c. Electrolysis of water
d. Hydrolysis

Answer: c. Electrolysis of water

Q9. The neutralization reaction between an acid and a base is a type of:

a. Double displacement reaction
b. Displacement reaction
c. Addition reaction
d. Decomposition reaction

Answer: a. Double displacement reaction

Q10. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is:

a. 1:1
b. 2:1
c. 4:1
d. 1:2

Answer: b. 2:1

Q11. Select the oxidising agent for the following reaction:

\( \text{H}_2\text{S} + \text{I}_2 \rightarrow 2\text{HI} + \text{S} \)

a. \( \text{I}_2 \)
b. \( \text{H}_2\text{S} \)
c. \( \text{HI} \)
d. \( \text{S} \)

Answer: a. \( \text{I}_2 \)

Q12. We store silver chloride in a dark coloured bottle because it is:

a. a white solid
b. undergoes redox reaction
c. to avoid action by sunlight
d. none of the above

Answer: c. to avoid action by sunlight

Assignment 2. Correct and balance the following equations:

(a) \( \text{Ca} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2 \)
Balanced equation: \( \text{Ca} + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2 \)

(b) \( \text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3 \)
Balanced equation: \( \text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3 \)

(c) \( \text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2 \)
Balanced equation: \( \text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2 \)

(d) \( \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \)
Balanced equation: \( \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \)

Assignment 3. Fill in the following blanks with suitable words:

1. Addition of hydrogen in a substance in a reaction is known as ___________ reaction.
Answer: reduction

2. In a ___________ reaction two or more substances combine to form a new single substance.
Answer: combination

3. Unbalanced reactions are also known as ___________.
Answer: skeletal reactions

4. Reactions in which heat is given out along with the products are called ___________ reactions.
Answer: exothermic

5. Reactions in which energy is absorbed are known as ___________ reactions.
Answer: endothermic

6. When an element displaces another element from its compound, a ___________ reaction occurs.
Answer: displacement

7. Those reactions, in which two compounds react by an exchange of ions to form two new compounds, are called ___________ reactions.
Answer: double displacement

8. Precipitation reactions produce ___________ salts.
Answer: insoluble

9. Reduction is the ___________ of oxygen or gain of hydrogen.
Answer: loss

10. The digestion of food in the body is an example of ___________ reaction.
Answer: decomposition

11. The addition of oxygen to a substance is called ___________.
Answer: oxidation

12. When calcium carbonate is heated, it decomposes to give ___________ and ___________.
Answer: calcium oxide, carbon dioxide

13. Chemical equations are balanced to satisfy the law of ___________.
Answer: conservation of mass

14. A solution made in water is known as an ___________ solution and indicated by the symbol ___________.
Answer: aqueous, (aq)

Assignment 4. True/False

1. The number of atoms of each element is conserved in any chemical reaction.
Answer: True

2. Oxidation is the loss of electrons from a substance.
Answer: True

3. Reduction is the gain of electrons by a substance.
Answer: True

4. A complete chemical equation represents the reactants, products and their physical states symbolically.
Answer: True

5. A magnesium ribbon burns with a dazzling flame in air (oxygen) and changes into a white substance, magnesium oxide.
Answer: True

6. Rusting is a double decomposition reaction.
Answer: False

7. The reaction between nitrogen and hydrogen to give ammonia is an example of a combination reaction.
Answer: True

8. Action of heat on ferrous sulphate is an example of decomposition reaction.
Answer: True

9. The formation of \( \text{Na}^+ \) and \( \text{Cl}^- \) ions from sodium and chlorine is an example of a redox reaction.
Answer: True

10. During the decomposition of lead nitrate the brown fumes of sulphur dioxide are formed.
Answer: False (The brown fumes are nitrogen dioxide)

Assignment 5. Given below are word equations. Convert them into chemical equations using symbols and valencies. Balance the equations. Use appropriate signs for gases and precipitates in the reaction.

i) Zinc Sulphide + Oxygen gas → Zinc oxide solid + Sulphur dioxide gas

Word Equation: \( \text{ZnS} + \text{O}_2 \rightarrow \text{ZnO} + \text{SO}_2 \)
Balanced Equation: \( 2\text{ZnS} + 3\text{O}_2 \rightarrow 2\text{ZnO} + 2\text{SO}_2 \)

ii) Silver nitrate solution + Sodium chloride solution → Silver chloride precipitate + Sodium nitrate solution

Word Equation: \( \text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} + \text{NaNO}_3 \)
Balanced Equation: \( \text{AgNO}_3 (aq) + \text{NaCl} (aq) \rightarrow \text{AgCl} (s) + \text{NaNO}_3 (aq) \)

iii) Sulphur solid + Concentrated nitric acid → Sulphuric acid + Nitrogen dioxide gas + Water

Word Equation: \( \text{S} + \text{HNO}_3 \rightarrow \text{H}_2\text{SO}_4 + \text{NO}_2 + \text{H}_2\text{O} \)
Balanced Equation: \( \text{S} + 6\text{HNO}_3 \rightarrow \text{H}_2\text{SO}_4 + 6\text{NO}_2 + 2\text{H}_2\text{O} \)

iv) Barium chloride solution + Potassium sulphate solution → Barium sulphate precipitate + Potassium chloride solution

Word Equation: \( \text{BaCl}_2 + \text{K}_2\text{SO}_4 \rightarrow \text{BaSO}_4 + \text{KCl} \)
Balanced Equation: \( \text{BaCl}_2 (aq) + \text{K}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + 2\text{KCl} (aq) \)

v) Silver nitrate on heating → silver metal + nitrogen dioxide gas + Oxygen gas

Word Equation: \( \text{AgNO}_3 \rightarrow \text{Ag} + \text{NO}_2 + \text{O}_2 \)
Balanced Equation: \( 2\text{AgNO}_3 \rightarrow 2\text{Ag} + 2\text{NO}_2 + \text{O}_2 \)

vi) Aluminium hydroxide + Nitric acid → Aluminium nitrate + Water

Word Equation: \( \text{Al(OH)}_3 + \text{HNO}_3 \rightarrow \text{Al(NO}_3)_3 + \text{H}_2\text{O} \)
Balanced Equation: \( \text{Al(OH)}_3 + 3\text{HNO}_3 \rightarrow \text{Al(NO}_3)_3 + 3\text{H}_2\text{O} \)

Subject Enrichment Activity

Write the following experiments in your lab file. All the experiments are given in the Science Lab Skills (Practical Book).

Experiment No 1

Aim:

To observe the action of Zn, Fe, Cu, and Al metals on the following salt solutions:

• \(\text{ZnSO}_4 (\text{aq.})\)
• \(\text{FeSO}_4 (\text{aq.})\)
• \(\text{CuSO}_4 (\text{aq.})\)
• \(\text{Al}_2(\text{SO}_4)_3 (\text{aq.})\)

Arrange Zn, Fe, Cu and Al metals in the decreasing order of reactivity based on the above result.

Experiment No 2

Aim:

To perform and observe the following reactions and classify them into:

• Combination reaction
• Decomposition reaction
• Displacement reaction
• Double displacement reaction

Reactions:

1. Action of water on quick lime
2. Action of heat on ferrous sulphate crystals
3. Iron nails kept in copper sulphate solution
4. Reaction between sodium sulphate and barium chloride solutions

Note: Draw the diagram on the blank page with a pencil. Must write Aim, Material required, Basic Principles, Procedure, Observation, Inference, and Precautions on the ruled side.

Experiment No 3

Aim:

1. To prepare a temporary mount of a peel to show stomata.
2. To show experimentally that light is necessary for photosynthesis.

Note: Draw the diagram on the blank page with a pencil. Must write Aim, Material required, Basic Principles, Procedure, Observation, Inference, and Precautions on the ruled side.