Ace Your Exams: Top Questions for Class 10 Science Chapter 2 - Acids, Bases, and Salts

 

Ace Your Exams: Top Questions for Class 10 Science Chapter 2 - Acids, Bases, and Salts

Meta Description: Preparing for your Class 10 Science exam? This comprehensive guide provides a curated list of important questions, key topics, and expert tips for Chapter 2: Acids, Bases, and Salts. Boost your confidence and score high with our SEO-friendly blog post.

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Master Class 10 Science Chapter 2: The Ultimate Guide to Important Exam Questions

As the board exams approach, it's crucial to focus your preparation on the topics and questions that matter most. Chapter 2 of your Class 10 Science syllabus, "Acids, Bases, and Salts," is a fundamental chapter with a significant weightage in the examination. To help you excel, we've compiled a comprehensive list of important questions, ranging from multiple-choice to long-answer types, based on previous year papers and key concepts.

This guide will walk you through the essential questions and topics, ensuring you have a solid understanding and are well-prepared to tackle any question thrown your way.

Cracking the Concepts: Key Topics to Revise

Before diving into the questions, ensure you have a strong grasp of these core concepts from the chapter:

• Properties of Acids and Bases: Understand their physical and chemical properties, including their reaction with metals, metal carbonates, and each other (neutralization).

• The pH Scale: Know the significance of the pH scale, how to interpret pH values, and its application in daily life (e.g., in soil, our digestive system).

• Indicators: Be familiar with different types of indicators (litmus, phenolphthalein, methyl orange, and olfactory indicators) and their color changes in acidic and basic mediums.

• Important Salts: Learn the common names, chemical formulas, preparation, and uses of key salts like:

  • Sodium Chloride (NaCl)

  • Sodium Hydroxide (NaOH) - Chlor-alkali process

  • Bleaching Powder (CaOCl₂)

  • Baking Soda (NaHCO₃)

  • Washing Soda (Na₂CO₃.10H₂O)

  • Plaster of Paris (CaSO₄.½H₂O)

• Water of Crystallization: Understand what it is and be able to give examples of hydrated salts.

Multiple-Choice Questions (MCQs - 1 Mark)

1. What happens when a solution of an acid is mixed with a solution of a base in a test tube? (a) The temperature of the solution increases. (b) The temperature of the solution decreases. (c) The temperature of the solution remains the same. (d) Salt formation takes place. Answer: (d) Salt formation takes place. (A neutralization reaction also releases heat, so the temperature would increase).

2. Which of the following salts does not contain water of crystallization? (a) Blue vitriol (b) Baking soda (c) Washing soda (d) Gypsum Answer: (b) Baking soda

3. A solution turns red litmus blue. Its pH is likely to be: (a) 1 (b) 4 (c) 5 (d) 10 Answer: (d) 10

4. The chemical formula for Plaster of Paris is: (a) CaSO₄.2H₂O (b) CaSO₄.½H₂O (c) CaSO₄ (d) CaSO₄.H₂O Answer: (b) CaSO₄.½H₂O

Short Answer Questions (SAQs - 2-3 Marks)

1. Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character? Answer: HCl and HNO₃ are ionic compounds that ionize in water to produce hydrogen ions (H⁺), which are responsible for their acidic character. Alcohol and glucose are covalent compounds and do not dissociate in water to produce H⁺ ions.

2. A milkman adds a very small amount of baking soda to fresh milk. (a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline? (b) Why does this milk take a long time to set as curd? Answer: (a) The milkman shifts the pH to slightly alkaline to prevent the milk from turning sour quickly due to the production of lactic acid. (b) The lactic acid produced has to first neutralize the alkali before the pH can drop to the level required for the milk to set as curd, hence it takes longer.

3. What is the water of crystallization? Give an example of salts with water of crystallization and their chemical formulas. Answer: The water of crystallization is the fixed number of water molecules present in one formula unit of a salt. For example, hydrated copper sulfate (Blue Vitriol) has the chemical formula CuSO₄.5H₂O, indicating five water molecules of crystallization.

4. What is a neutralization reaction? Give two examples. Answer: A neutralization reaction is a chemical reaction in which an acid and a base react quantitatively with each other to form a salt and water. For example:

   • HCl + NaOH → NaCl + H₂O

   • H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O

Long Answer Questions (LAQs - 5 Marks)

1. (a) What is the Chlor-alkali process? (b) Write the chemical equation for the reaction involved. (c) Name the products obtained and write one use of each. Answer: (a) The Chlor-alkali process is the electrolysis of an aqueous solution of sodium chloride (brine). (b) 2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g) (c) Products and their uses:

   • Sodium Hydroxide (NaOH): Used in the manufacture of soaps and detergents, paper making, and artificial fibers.

   • Chlorine (Cl₂): Used for water treatment, production of PVC, and as a disinfectant.

   • Hydrogen (H₂): Used as a fuel, in the hydrogenation of oils to make margarine, and in the production of ammonia for fertilizers.

2. (a) How is Plaster of Paris prepared? (b) What is its chemical name and formula? (c) Why should Plaster of Paris be stored in a moisture-proof container? (d) Write two of its important uses. Answer: (a) Plaster of Paris is prepared by heating gypsum (CaSO₄.2H₂O) at a carefully controlled temperature of 373 K (100°C). CaSO₄.2H₂O(s) → CaSO₄.½H₂O(s) + 1½H₂O(g) (b) Its chemical name is Calcium Sulphate Hemihydrate, and its formula is CaSO₄.½H₂O. (c) It should be stored in a moisture-proof container because it readily absorbs moisture from the air and sets into a hard mass (gypsum), losing its plastering property. (d) Uses:

• Used by doctors for setting fractured bones.

• Used for making toys, decorative materials, and for smoothening surfaces.

3. . A milkman adds a very small amount of baking soda to fresh milk. (a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline? (b) Why does this milk take a longer time to set as curd? Answer: (a) He makes the milk slightly alkaline to prevent it from turning sour quickly. The natural fermentation of milk produces lactic acid, which lowers the pH and makes it sour. The alkaline baking soda neutralizes this acid. (b) For milk to turn into curd, the pH needs to become acidic. Since the milkman has made the milk slightly alkaline, the lactic acid produced during fermentation first has to neutralize the alkali before the pH can drop enough for the curd to set. This process takes a longer time.

4.  What is the chemical name and formula for Plaster of Paris? Why should it be stored in a moisture-proof container? Answer:

• Chemical Name: Calcium Sulphate Hemihydrate

• Chemical Formula: CaSO₄·½H₂O

• Reason for Storage: Plaster of Paris should be stored in a moisture-proof container because it readily absorbs water (moisture) from the atmosphere and gets converted into a hard, solid mass called gypsum (CaSO₄·2H₂O). This reaction is irreversible and makes the Plaster of Paris useless for its intended purpose.

• CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O

5. . Why do HCl and HNO₃ show acidic characters in aqueous solutions, while solutions of compounds like alcohol and glucose do not? Answer: The acidic character of a substance is due to the presence of hydrogen ions (H⁺). When HCl or HNO₃ are dissolved in water, they dissociate to produce H⁺ ions. However, compounds like alcohol and glucose, although they contain hydrogen atoms, are covalent compounds and do not dissociate in water to produce H⁺ ions. Therefore, they do not show acidic character.
6. What happens when an acid or a base is mixed with water? Why is it recommended that the acid should be added to water and not water to the acid? Answer: When an acid or a base is mixed with water, the concentration of ions (H₃O⁺ for acids, OH⁻ for bases) per unit volume decreases. This process is called dilution. The process is highly exothermic (releases a lot of heat). It is recommended to add acid slowly to water with constant stirring because if water is added to a concentrated acid, the heat generated is so large that the mixture can splash out and cause severe burns. The glass container may also break due to excessive local heating.

7. Write the chemical formula and two important uses of (a) Washing Soda and (b) Baking Soda. Answer: (a) Washing Soda:

   • Formula: Na₂CO₃·10H₂O (Sodium Carbonate Decahydrate)

   • Uses:

     1. Used in the glass, soap, and paper industries.

     2. Used for removing the permanent hardness of water.

   (b) Baking Soda:

• Formula: NaHCO₃ (Sodium Hydrogen Carbonate)

• Uses:

1. Used as an antacid to relieve indigestion.

2. Used in soda-acid fire extinguishers.

8. What is the "water of crystallization"? Give an example. Answer: The water of crystallization is the fixed number of water molecules that are chemically bonded to the crystal structure of a salt. These water molecules are responsible for the geometric shape and sometimes the color of the crystals.

• Example: Copper Sulphate crystals (CuSO₄·5H₂O) are blue because they contain five molecules of water of crystallization. When heated, they lose this water and turn into a white amorphous powder.

9.  What gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas? Answer:

• Gas Liberated: Hydrogen gas (H₂).

• Example: When zinc metal reacts with dilute sulphuric acid, hydrogen gas is evolved.

  • Equation: Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

• Test for Hydrogen Gas: To test for hydrogen gas, bring a burning candle or a matchstick near the mouth of the test tube where the gas is being evolved. The gas will burn with a characteristic "pop" sound, which confirms the presence of hydrogen.

10.  What is bleaching powder? Write its chemical formula and one of its uses. Answer:

    • Description: Bleaching powder is a pale yellowish powder with a strong smell of chlorine. Its chemical name is Calcium Oxychloride.

    • Chemical Formula: CaOCl₂

    • Use: It is used for bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories, and as a disinfectant for drinking water to make it free of germs.

Final Exam Tips

• Practice Diagrams: Be sure to practice the diagram for the Chlor-alkali process and the experimental setup for the reaction of acids with metals.

• Memorize Formulas and Equations: Create a chart of all the important chemical formulas and balanced equations from this chapter for quick revision.

• Solve Previous Year Papers: This will help you understand the pattern of questions and manage your time effectively during the exam.

• Clear Your Doubts: Don't hesitate to ask your teachers for clarification on any topic you find difficult.

By thoroughly preparing these important questions and understanding the core concepts, you can confidently aim for a top score in your Science exam. Good luck!