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:
Answer: b. Remove the layer of magnesium oxide from the ribbon surface
Reasoning: Magnesium ribbon is cleaned with sandpaper to remove the oxide layer that may have formed on its surface. This oxide layer can prevent or slow down the burning of magnesium when it reacts with oxygen in the air.
Q2. In a chemical reaction between sulphuric acid and barium chloride solution the white precipitates formed are of:
Answer: b. Barium sulphate
Reasoning: Barium sulphate is formed as a white precipitate when sulphuric acid reacts with barium chloride. The reaction is a double displacement reaction where the ions exchange partners.
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:
Answer: a. Exothermic process
Reasoning: Respiration is an exothermic process because it releases energy. During respiration, glucose combines with oxygen to produce carbon dioxide, water, and energy.
Q4. A chemical reaction does not involve:
Answer: d. Changing of the atoms of one element into those of another element to form new products
Reasoning: Chemical reactions involve the rearrangement of atoms to form new substances, but they do not change one type of atom into another. Such changes are characteristic of nuclear reactions, not chemical reactions.
Q5. It is necessary to balance a chemical equation in order to satisfy the law of:
Answer: d. Conservation of mass
Reasoning: The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. Balancing a chemical equation ensures that the same number of atoms of each element are present on both sides of the equation.
Q6. You are given the following chemical reaction:
Answer: b. Redox reaction as well as displacement reaction
Reasoning: This reaction involves the transfer of electrons between substances, which is characteristic of redox (reduction-oxidation) reactions. Additionally, it is a displacement reaction where one element displaces another in a compound.
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:
Answer: c. Green to brown
Reasoning: Ferrous sulphate crystals are green in color. Upon heating, they decompose to form ferric oxide, which is brown in color, along with the release of sulphur dioxide and sulphur trioxide gases.
Q8. Following is given a diagram showing an experimental set-up:
Answer: c. Electrolysis of water
Reasoning: The given set-up is typically used for the electrolysis of water, where water is decomposed into hydrogen and oxygen gases by passing an electric current through it.
Q9. The neutralization reaction between an acid and a base is a type of:
Answer: a. Double displacement reaction
Reasoning: In a neutralization reaction, the hydrogen ions (H+) from the acid react with the hydroxide ions (OH−) from the base to form water. This is a double displacement reaction because the ions exchange partners.
Q10. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is:
Answer: b. 2:1
Reasoning: Water (H2O) decomposes into hydrogen (H2) and oxygen (O2) gases during electrolysis. The balanced chemical equation for this reaction is:
\(2\text{H}_2\text{O} \rightarrow 2\text{H}_2 + \text{O}_2\)
This shows that two moles of hydrogen gas are produced for every one mole of oxygen gas.
Q11. Select the oxidising agent for the following reaction:
\( \text{H}_2\text{S} + \text{I}_2 \rightarrow 2\text{HI} + \text{S} \)
Answer: a. \( \text{I}_2 \)
Reasoning: In this reaction, iodine (I2) is reduced to hydrogen iodide (HI) by gaining electrons from hydrogen sulphide (H2S). Therefore, iodine acts as the oxidising agent because it gains electrons.
Q12. We store silver chloride in a dark coloured bottle because it is:
Answer: c. to avoid action by sunlight
Reasoning: Silver chloride is photosensitive, meaning it can decompose when exposed to light, forming silver and chlorine gas. Storing it in a dark-colored bottle helps to prevent this decomposition by blocking light.
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: \( \text{Ca} + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2 \)
Reasoning: Calcium reacts with water to form calcium hydroxide and hydrogen gas. Balancing the equation ensures that the same number of each type of atom appears on both sides of the equation.
(b) \( \text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3 \)
Balanced equation: \( \text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3 \)
Reasoning: Nitrogen and hydrogen gases react to form ammonia. The balanced equation shows that one mole of nitrogen reacts with three moles of hydrogen to produce two moles of ammonia, ensuring the conservation of atoms.
(c) \( \text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2 \)
Balanced equation: \( \text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2 \)
Reasoning: Zinc reacts with sulfuric acid to produce zinc sulfate and hydrogen gas. The equation is already balanced, showing one mole of zinc reacting with one mole of sulfuric acid to produce one mole of zinc sulfate and one mole of hydrogen gas.
(d) \( \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \)
Balanced equation: \( \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \)
Reasoning: Calcium carbonate decomposes into calcium oxide and carbon dioxide upon heating. The balanced equation reflects the conservation of mass, showing that one mole of calcium carbonate decomposes to form one mole of calcium oxide and one mole of carbon dioxide.
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
Reasoning: Reduction is the gain of hydrogen or electrons by a substance. When hydrogen is added to a substance, it is reduced.
2. In a ___________ reaction two or more substances combine to form a new single substance.
Answer: combination
Reasoning: A combination reaction occurs when two or more substances react to form a single new substance.
3. Unbalanced reactions are also known as ___________.
Answer: skeletal reactions
Reasoning: Unbalanced reactions, where the number of atoms for each element is not the same on both sides of the equation, are referred to as skeletal reactions.
4. Reactions in which heat is given out along with the products are called ___________ reactions.
Answer: exothermic
Reasoning: Exothermic reactions release heat into the surroundings as the reaction progresses.
5. Reactions in which energy is absorbed are known as ___________ reactions.
Answer: endothermic
Reasoning: Endothermic reactions absorb energy from the surroundings, usually in the form of heat.
6. When an element displaces another element from its compound, a ___________ reaction occurs.
Answer: displacement
Reasoning: In a displacement reaction, one element replaces another element in a compound.
7. Those reactions, in which two compounds react by an exchange of ions to form two new compounds, are called ___________ reactions.
Answer: double displacement
Reasoning: Double displacement reactions involve the exchange of ions between two compounds to form new compounds.
8. Precipitation reactions produce ___________ salts.
Answer: insoluble
Reasoning: Precipitation reactions result in the formation of an insoluble salt that precipitates out of the solution.
9. Reduction is the ___________ of oxygen or gain of hydrogen.
Answer: loss
Reasoning: Reduction is defined as the loss of oxygen or the gain of hydrogen or electrons.
10. The digestion of food in the body is an example of ___________ reaction.
Answer: decomposition
Reasoning: Digestion involves the breakdown of complex food molecules into simpler substances, which is characteristic of decomposition reactions.
11. The addition of oxygen to a substance is called ___________.
Answer: oxidation
Reasoning: Oxidation is defined as the addition of oxygen to a substance or the loss of hydrogen or electrons.
12. When calcium carbonate is heated, it decomposes to give ___________ and ___________.
Answer: calcium oxide, carbon dioxide
Reasoning: When heated, calcium carbonate decomposes to form calcium oxide and carbon dioxide gas.
13. Chemical equations are balanced to satisfy the law of ___________.
Answer: conservation of mass
Reasoning: Balancing chemical equations ensures that the law of conservation of mass is obeyed, meaning that the mass of the reactants equals the mass of the products.
14. A solution made in water is known as an ___________ solution and indicated by the symbol ___________.
Answer: aqueous, (aq)
Reasoning: A solution made in water is called an aqueous solution and is represented by the symbol (aq) in chemical equations.
Assignment 4. True/False
1. The number of atoms of each element is conserved in any chemical reaction.
Answer: True
Reasoning: The law of conservation of mass states that atoms cannot be created or destroyed in a chemical reaction, so the number of atoms of each element remains the same.
2. Oxidation is the loss of electrons from a substance.
Answer: True
Reasoning: Oxidation involves the loss of electrons from a substance, which can also be accompanied by the addition of oxygen or the loss of hydrogen.
3. Reduction is the gain of electrons by a substance.
Answer: True
Reasoning: Reduction involves the gain of electrons by a substance, which can also be accompanied by the loss of oxygen or the gain of hydrogen.
4. A complete chemical equation represents the reactants, products and their physical states symbolically.
Answer: True
Reasoning: A complete chemical equation shows the reactants and products along with their physical states (solid, liquid, gas, or aqueous).
5. A magnesium ribbon burns with a dazzling flame in air (oxygen) and changes into a white substance, magnesium oxide.
Answer: True
Reasoning: When magnesium burns in air, it reacts with oxygen to form magnesium oxide, which is a white powder. The reaction releases a lot of energy, producing a dazzling flame.
6. Rusting is a double decomposition reaction.
Answer: False
Reasoning: Rusting is a redox reaction where iron reacts with oxygen and water to form hydrated iron(III) oxide, commonly known as rust. It is not a double decomposition reaction.
7. The reaction between nitrogen and hydrogen to give ammonia is an example of a combination reaction.
Answer: True
Reasoning: The reaction between nitrogen and hydrogen to form ammonia is a combination reaction because two or more reactants combine to form a single product.
8. Action of heat on ferrous sulphate is an example of decomposition reaction.
Answer: True
Reasoning: When ferrous sulphate is heated, it decomposes into ferric oxide, sulfur dioxide, and sulfur trioxide. This is a decomposition reaction because a single compound breaks down into multiple products.
9. The formation of \( \text{Na}^+ \) and \( \text{Cl}^- \) ions from sodium and chlorine is an example of a redox reaction.
Answer: True
Reasoning: The reaction between sodium and chlorine to form sodium chloride involves the transfer of electrons. Sodium loses an electron (oxidation) and chlorine gains an electron (reduction), making it a redox reaction.
10. During the decomposition of lead nitrate the brown fumes of sulphur dioxide are formed.
Answer: False (The brown fumes are nitrogen dioxide)
Reasoning: When lead nitrate decomposes, it forms lead oxide, nitrogen dioxide, and oxygen. The brown fumes observed are due to nitrogen dioxide, not sulfur 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: \( 2\text{ZnS} + 3\text{O}_2 \rightarrow 2\text{ZnO} + 2\text{SO}_2 \)
Reasoning: Zinc sulphide reacts with oxygen to form zinc oxide and sulfur dioxide. Balancing the equation ensures that the same number of atoms of each element are present on both sides of the equation.
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: \( \text{AgNO}_3 (aq) + \text{NaCl} (aq) \rightarrow \text{AgCl} (s) + \text{NaNO}_3 (aq) \)
Reasoning: Silver nitrate reacts with sodium chloride to form silver chloride and sodium nitrate. Silver chloride precipitates out of the solution as a solid, while sodium nitrate remains in solution.
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: \( \text{S} + 6\text{HNO}_3 \rightarrow \text{H}_2\text{SO}_4 + 6\text{NO}_2 + 2\text{H}_2\text{O} \)
Reasoning: Sulphur reacts with concentrated nitric acid to form sulphuric acid, nitrogen dioxide, and water. Balancing the equation ensures the conservation of mass.
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: \( \text{BaCl}_2 (aq) + \text{K}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + 2\text{KCl} (aq) \)
Reasoning: Barium chloride reacts with potassium sulphate to form barium sulphate and potassium chloride. Barium sulphate precipitates out of the solution as a solid.
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: \( 2\text{AgNO}_3 \rightarrow 2\text{Ag} + 2\text{NO}_2 + \text{O}_2 \)
Reasoning: Upon heating, silver nitrate decomposes to form silver metal, nitrogen dioxide, and oxygen gas. The balanced equation ensures that the same number of atoms are present on both sides.
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: \( \text{Al(OH)}_3 + 3\text{HNO}_3 \rightarrow \text{Al(NO}_3)_3 + 3\text{H}_2\text{O} \)
Reasoning: Aluminium hydroxide reacts with nitric acid to form aluminium nitrate and water. The balanced equation reflects the conservation of mass.
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:
- Action of water on quick lime
- Action of heat on ferrous sulphate crystals
- Iron nails kept in copper sulphate solution
- 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.
Reactions
-
Action of water on quick lime:
CaO + H2O → Ca(OH)2
Reasoning: When quick lime (calcium oxide) reacts with water, it forms calcium hydroxide. This reaction is exothermic and releases heat.
-
Action of heat on ferrous sulphate crystals:
2FeSO4 → Fe2O3 + SO2 + SO3
Reasoning: Heating ferrous sulphate crystals results in decomposition to form ferric oxide, sulphur dioxide, and sulphur trioxide. This reaction involves the breakdown of ferrous sulphate into simpler substances.
-
Iron nails kept in copper sulphate solution:
Fe + CuSO4 → FeSO4 + Cu
Reasoning: When iron nails are placed in copper sulphate solution, iron displaces copper from copper sulphate due to its higher reactivity, forming iron sulphate and copper metal.
-
Reaction between sodium sulphate and barium chloride solutions:
Na2SO4 + BaCl2 → BaSO4 + 2NaCl
Reasoning: Sodium sulphate reacts with barium chloride to form barium sulphate, which precipitates out of the solution, and sodium chloride remains in solution. This is a double displacement reaction.
Experiment No 3
Aim:
- To prepare a temporary mount of a peel to show stomata.
- 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.