Class 10 Science Chapter 1 Question Answers - Chemical Reactions and Equations

Q1: Write the balanced chemical equation for the reaction between calcium carbonate (CaCO₃) and hydrochloric acid (HCl). Describe the type of chemical reaction taking place, and identify the products formed.
Ans: Balanced Chemical Equation:
CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O
Type of Reaction:
This is a double displacement reaction. Calcium carbonate reacts with hydrochloric acid to form calcium chloride, carbon dioxide, and water.
Explanation: In this reaction, calcium carbonate (CaCO₃) reacts with hydrochloric acid (HCl) to produce calcium chloride (CaCl₂), carbon dioxide (CO₂), and water (H₂O). The balanced equation indicates that one molecule of calcium carbonate reacts with two molecules of hydrochloric acid. Calcium chloride is a soluble salt, carbon dioxide is a gas that evolves and can be observed as bubbles, and water is also formed. This reaction is commonly used to demonstrate the formation of gas and the characteristic effervescence in chemistry experiments.

Q2: A piece of iron (Fe) is left exposed to humid air, leading to the formation of a reddish-brown flaky substance. Write the balanced chemical equation for this reaction. Identify the compounds involved and explain the process of rusting of iron.
Ans: Balanced Chemical Equation:
4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃
Compounds Involved:
Iron (Fe), oxygen (O₂), water (H₂O), iron(III) hydroxide (Fe(OH)₃)
Explanation: The given reaction represents the process of rusting of iron. When iron is exposed to humid air, it reacts with oxygen and water to form iron(III) hydroxide, which is a reddish-brown flaky substance. The balanced equation indicates that four atoms of iron react with three molecules of oxygen and six molecules of water to produce four molecules of iron(III) hydroxide. Rusting is an example of a chemical change where iron undergoes oxidation, combining with oxygen in the presence of moisture. The reddish-brown rust layer gradually forms on the iron surface, leading to its corrosion.

Q3: A metal X is found to be a good conductor of electricity and is used in electrical wires. When metal X reacts with dilute hydrochloric acid (HCl), it produces a gas Y that catches fire if a burning splinter is brought near it. Write the balanced chemical equation for this reaction, identify gas Y, and explain the reaction taking place.
Ans: Balanced Chemical Equation:
2X + 6HCl → 2XCl₃ + 3H₂
Gas Y:
Gas Y is hydrogen gas (H₂).
Explanation: In the given reaction, metal X reacts with dilute hydrochloric acid (HCl) to produce metal chloride (XCl₃) and hydrogen gas (H₂). The balanced equation indicates that two atoms of metal X react with six molecules of hydrochloric acid, producing two molecules of metal chloride and three molecules of hydrogen gas. The gas produced, hydrogen, is highly flammable and burns with a pop sound when a burning splinter is brought near it. Metal X is likely to be a reactive metal, and this reaction is a typical example of a single displacement reaction, where the metal displaces hydrogen from the acid.

Q4: A white compound P is used in agriculture as a fertilizer. When compound P is heated, it decomposes to give off a brown gas Q with a pungent smell. Write the balanced chemical equation for the decomposition of compound P, identify gas Q, and explain the process of decomposition.
Ans: Balanced Chemical Equation:
2NH₄NO₃ → 4H₂O + 2NO₂ + O₂
Gas Q:
Gas Q is nitrogen dioxide (NO₂).
Explanation: The provided equation represents the decomposition of compound P, which is ammonium nitrate (NH₄NO₃). When heated, ammonium nitrate decomposes into water (H₂O), nitrogen dioxide gas (NO₂), and oxygen gas (O₂). The balanced equation shows that two molecules of ammonium nitrate decompose to yield four molecules of water, two molecules of nitrogen dioxide, and one molecule of oxygen. The brown gas Q, nitrogen dioxide, has a pungent smell and is often released during the decomposition process. Ammonium nitrate is commonly used as a fertilizer in agriculture due to its nitrogen content.

Q5: Magnesium (Mg) reacts with oxygen (O₂) to form a white compound R which has a combination of magnesium oxide and magnesium nitride. Write the balanced chemical equation for this reaction, explain the formation of compound R, and state any one use of magnesium oxide.
Ans: Balanced Chemical Equation:
3Mg + N₂ → Mg₃N₂
2Mg + O₂ → 2MgO
Mg₃N₂ + 6H₂O → 3Mg(OH)₂ + 2NH₃
Formation of Compound R: Compound R is a combination of magnesium oxide (MgO) and magnesium nitride (Mg₃N₂). Magnesium first reacts with nitrogen gas (N₂) to form magnesium nitride, as shown in the first equation. Then, magnesium reacts with oxygen gas (O₂) to produce magnesium oxide, as shown in the second equation. Compound R is formed from magnesium oxide and magnesium nitride when it reacts with water, yielding magnesium hydroxide (Mg(OH)₂) and ammonia gas (NH₃).
Use of Magnesium Oxide: Magnesium oxide is commonly used as a refractory material in the construction of furnace linings due to its high melting point and resistance to high temperatures. It is also used in the manufacture of electrical insulators and as an antacid to neutralize excess stomach acid.
In this series of reactions, magnesium undergoes oxidation by reacting with both oxygen and nitrogen, resulting in the formation of magnesium oxide and magnesium nitride, respectively. The subsequent reaction with water leads to the formation of magnesium hydroxide and ammonia gas.

Q6: When a piece of blue copper sulfate pentahydrate (CuSO₄·5H₂O) crystals is heated, it undergoes a series of changes. Write the balanced chemical equation for the decomposition of copper sulfate pentahydrate, identify the compounds formed during each step of its decomposition, and explain the color changes observed.
Ans: Balanced Chemical Equation:
CuSO₄·5H₂O → CuSO₄ + 5H₂O
Compounds Formed: 
Copper sulfate pentahydrate (CuSO₄·5H₂O) decomposes into anhydrous copper sulfate (CuSO₄) and water (H₂O).
Explanation: During the heating of blue copper sulfate pentahydrate crystals, they lose their water molecules, leading to the formation of anhydrous copper sulfate. The balanced equation shows that one molecule of copper sulfate pentahydrate decomposes into one molecule of anhydrous copper sulfate and five molecules of water. The color changes observed during this process are due to the loss of water molecules. Initially, the blue crystals of copper sulfate pentahydrate lose their water content, resulting in the formation of white anhydrous copper sulfate. The overall color change is from blue to white.

Q7: Hydrogen gas is an important industrial raw material. Describe the method of preparation of hydrogen gas using granulated zinc and dilute hydrochloric acid. Write the balanced chemical equation for the reaction, identify the products formed, and explain how hydrogen gas is collected.
Ans: Method of Preparation:
Hydrogen gas can be prepared by reacting granulated zinc with dilute hydrochloric acid.
Balanced Chemical Equation:
Zn + 2HCl → ZnCl₂ + H₂
Products Formed:
Granulated zinc (Zn) reacts with dilute hydrochloric acid (HCl) to produce zinc chloride (ZnCl₂) and hydrogen gas (H₂).
Explanation: In this reaction, granulated zinc reacts with dilute hydrochloric acid to produce zinc chloride and hydrogen gas. The balanced equation indicates that one atom of zinc reacts with two molecules of hydrochloric acid to yield one molecule of zinc chloride and one molecule of hydrogen gas. The hydrogen gas is collected over water using the displacement of water method. A delivery tube is connected to the reaction flask, and the other end of the tube is placed in an inverted gas jar filled with water. As the hydrogen gas is produced, it displaces the water in the gas jar, and the collected gas can be identified by its characteristic properties, such as its flammability and the popping sound it makes when ignited.

Q8: Sodium metal (Na) reacts vigorously with water (H₂O) to produce a compound X and a gas Y. Write the balanced chemical equation for this reaction, identify compound X and gas Y, and explain the observations made during the reaction.
Ans: Balanced Chemical Equation:
2Na + 2H₂O → 2NaOH + H₂
Compound X:
Compound X is sodium hydroxide (NaOH).
Gas Y:
Gas Y is hydrogen gas (H₂).
Explanation: Sodium metal reacts with water to produce sodium hydroxide and hydrogen gas. The balanced equation indicates that two atoms of sodium react with two molecules of water to yield two molecules of sodium hydroxide and one molecule of hydrogen gas. During the reaction, sodium metal reacts vigorously with water, producing hydrogen gas as bubbles, which is released with effervescence. The solution becomes hot due to the exothermic nature of the reaction. Sodium hydroxide, a strong base, is formed and dissolves in the water, giving the solution a slippery feel and a characteristic soapy touch.

Q9: During the process of respiration, glucose (C₆H₁₂O₆) is oxidized in cells to release energy. Write the balanced chemical equation for the complete combustion of glucose, identify the products formed, and explain how this energy is utilized by cells.
Ans: Balanced Chemical Equation:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
Products Formed:
Glucose (C₆H₁₂O₆) undergoes complete combustion to produce carbon dioxide (CO₂) and water (H₂O).
Explanation: During the process of respiration, glucose is oxidized in cells to release energy. The balanced equation represents the complete combustion of glucose in the presence of oxygen. One molecule of glucose reacts with six molecules of oxygen to produce six molecules of carbon dioxide and six molecules of water. This reaction releases a significant amount of energy in the form of heat and light. In cells, this energy is utilized through a series of biochemical reactions to produce adenosine triphosphate (ATP), which serves as the primary energy currency for various cellular processes, such as muscle contraction, active transport, and synthesis of biomolecules.

Q10: Sulfur dioxide (SO₂) is a harmful gas released during the combustion of fossil fuels. Write the balanced chemical equation for the formation of sulfur dioxide during the combustion of sulfur (S), identify the oxidizing agent involved, and explain the environmental impact of sulfur dioxide emissions.
Ans: Balanced Chemical Equation:
S + O₂ → SO₂
Oxidizing Agent:
The oxidizing agent involved in the combustion of sulfur to form sulfur dioxide is oxygen (O₂).
Environmental Impact: Sulfur dioxide (SO₂) emissions contribute to air pollution and have several negative environmental impacts. When released into the atmosphere, sulfur dioxide can react with water vapor to form sulfuric acid (H₂SO₄), a major component of acid rain. Acid rain can lead to the acidification of soil and bodies of water, harming aquatic ecosystems and affecting plant growth. Sulfur dioxide can also contribute to the formation of particulate matter, which can have adverse effects on respiratory health and air quality. Additionally, sulfur dioxide emissions can contribute to the formation of smog, which can further deteriorate air quality and have harmful effects on human health.