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Acids, Bases and Salts – CBSE NCERT Study Resources

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Acids, Bases and Salts

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10th

10th - Science

Acids, Bases and Salts

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Overview of the Chapter: Acids, Bases and Salts

This chapter introduces students to the fundamental concepts of acids, bases, and salts, which are essential in both daily life and industrial applications. The chapter covers their properties, reactions, and uses, along with pH scale and indicators.

1. Understanding Acids and Bases

Acids: Substances that release hydrogen ions (H⁺) in aqueous solutions, taste sour, and turn blue litmus red.

Bases: Substances that release hydroxide ions (OH⁻) in aqueous solutions, taste bitter, feel soapy, and turn red litmus blue.

Examples of acids include hydrochloric acid (HCl) and citric acid, while examples of bases include sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)₂).

2. Chemical Properties of Acids and Bases

Acids and bases react with metals, metal carbonates, and each other to form salts and water. Key reactions include:

  • Acid + Metal → Salt + Hydrogen gas
  • Acid + Metal Carbonate → Salt + Water + Carbon dioxide
  • Acid + Base → Salt + Water (Neutralization Reaction)

3. pH Scale and Indicators

pH Scale: A scale ranging from 0 to 14 that measures the acidity or alkalinity of a solution. pH 7 is neutral, below 7 is acidic, and above 7 is basic.

Common indicators like litmus, phenolphthalein, and methyl orange are used to determine the pH of substances.

4. Salts and Their Preparation

Salts: Ionic compounds formed by the neutralization reaction between an acid and a base.

Examples include sodium chloride (NaCl) and copper sulfate (CuSO₄). Salts can be acidic, basic, or neutral depending on their parent compounds.

5. Importance in Daily Life

Acids, bases, and salts have numerous applications, such as in food preservation, medicine, agriculture, and cleaning agents.

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
What is the chemical formula of hydrochloric acid?
Answer:

HCl

Question 2:
Name the gas evolved when dilute HCl reacts with metal carbonate.
Answer:

Carbon dioxide (CO2)

Question 3:
What is the pH range of acidic solutions?
Answer:

0 to less than 7

Question 4:
Which indicator turns pink in basic solutions?
Answer:

Phenolphthalein

Question 5:
What is the common name of sodium hydroxide?
Answer:

Caustic soda

Question 6:
Name the salt formed when NaOH reacts with HCl.
Answer:

Sodium chloride (NaCl)

Question 7:
Which acid is present in vinegar?
Answer:

Acetic acid (CH3COOH)

Question 8:
What is the nature of litmus in neutral solutions?
Answer:

Purple

Question 9:
Name the base used in antacids.
Answer:

Magnesium hydroxide (Mg(OH)2)

Question 10:
What is the pH of pure water?
Answer:

7

Question 11:
Which gas is released when acids react with metals?
Answer:

Hydrogen (H2)

Question 12:
What is the chemical name of washing soda?
Answer:

Sodium carbonate (Na2CO3)

Question 13:
Which salt is used in fire extinguishers?
Answer:

Sodium bicarbonate (NaHCO3)

Question 14:
What is the color of methyl orange in acidic solutions?
Answer:

Red

Question 15:
What is the pH range of acidic solutions?
Answer:

The pH range of acidic solutions is 0 to 6.9. A pH less than 7 indicates acidity, with lower values being more acidic.

Question 16:
Name the gas evolved when a metal reacts with a dilute acid.
Answer:

Hydrogen gas (H₂) is evolved when a metal reacts with a dilute acid. This is a characteristic property of acid-metal reactions.

Question 17:
What is the chemical formula of baking soda?
Answer:

The chemical formula of baking soda is NaHCO₃ (Sodium Hydrogen Carbonate). It is a mild base used in cooking and antacids.

Question 18:
Why does turmeric stain turn red when washed with soap?
Answer:

Turmeric contains a natural indicator that turns red in basic solutions. Since soap is basic, the stain changes color.

Question 19:
What is the common name of CaOCl₂?
Answer:

The common name of CaOCl₂ is bleaching powder. It is used for disinfecting water and bleaching clothes.

Question 20:
Which acid is present in vinegar?
Answer:

Acetic acid (CH₃COOH) is present in vinegar. It gives vinegar its sour taste and is a weak organic acid.

Question 21:
What happens when blue litmus paper is dipped in a basic solution?
Answer:

Blue litmus paper remains blue in a basic solution. Litmus is a natural indicator that turns red in acids and blue in bases.

Question 22:
Name the salt formed when hydrochloric acid reacts with sodium hydroxide.
Answer:

The salt formed is sodium chloride (NaCl), commonly known as table salt. This is a neutralization reaction.

Question 23:
What is the nature of rainwater?
Answer:

Rainwater is slightly acidic (pH ≈ 5.6) due to the dissolution of carbon dioxide (CO₂) from the air, forming carbonic acid.

Question 24:
Which gas is released when an acid reacts with a carbonate?
Answer:

Carbon dioxide (CO₂) gas is released when an acid reacts with a carbonate. This reaction also produces water and a salt.

Question 25:
What is the pH value of a neutral solution?
Answer:

The pH value of a neutral solution is 7. Pure water is an example of a neutral substance.

Question 26:
Why is distilled water a poor conductor of electricity?
Answer:

Distilled water lacks ions, which are necessary for conducting electricity. It is pure H₂O with no dissolved salts or minerals.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
What is the chemical formula of washing soda?
Answer:

The chemical formula of washing soda is Na₂CO₃·10H₂O (Sodium carbonate decahydrate). It is commonly used as a water softener and cleaning agent.

Question 2:
Why does dry HCl gas not change the color of dry litmus paper?
Answer:

Dry HCl gas does not change the color of dry litmus paper because acidity is exhibited only in the presence of water (H₂O), which ionizes HCl to release H⁺ ions.

Question 3:
What is the nature of aqueous solutions of salts of strong acids and strong bases?
Answer:

Aqueous solutions of salts formed from strong acids and strong bases are neutral (pH = 7). Examples include NaCl (from HCl and NaOH).

Question 4:
Name the acid present in ant sting and give its chemical formula.
Answer:

The acid present in an ant sting is methanoic acid (formic acid), with the chemical formula HCOOH. It causes irritation and pain.

Question 5:
Define a universal indicator and its purpose.
Answer:

A universal indicator is a mixture of several indicators that shows a range of colors to indicate the pH value of a solution. It helps in identifying the strength of acids and bases.

Question 6:
Why is Plaster of Paris stored in moisture-proof containers?
Answer:

Plaster of Paris (CaSO₄·½H₂O) absorbs moisture from the air and hardens into gypsum (CaSO₄·2H₂O). Moisture-proof containers prevent this reaction.

Question 7:
What is the common name of sodium bicarbonate? Mention one use.
Answer:

The common name of sodium bicarbonate (NaHCO₃) is baking soda. It is used as a leavening agent in baking to make cakes and bread fluffy.

Question 8:
How does the concentration of hydronium ions (H₃O⁺) change when a solution becomes more acidic?
Answer:

As a solution becomes more acidic, the concentration of hydronium ions (H₃O⁺) increases. Lower pH values correspond to higher H₃O⁺ concentrations.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Explain why dilute hydrochloric acid is a stronger acid than dilute acetic acid even though both are acids.
Answer:

Hydrochloric acid (HCl) is a strong acid because it completely dissociates in water to release H+ ions, making it highly conductive and reactive.

On the other hand, acetic acid (CH3COOH) is a weak acid as it only partially dissociates, releasing fewer H+ ions.

Thus, even in dilute form, HCl shows stronger acidic properties than acetic acid due to higher ionization.

Question 2:
How does the pH value change when a solution of a base is diluted with water? Justify your answer.
Answer:

When a base is diluted with water, its pH decreases but remains greater than 7.

This happens because dilution reduces the concentration of OH- ions per unit volume, making the solution less alkaline.

However, since it is still a base, the pH does not drop below 7.

Question 3:
Why is sodium hydrogen carbonate used as an antacid? Write the chemical reaction involved.
Answer:

Sodium hydrogen carbonate (NaHCO3) acts as an antacid because it is a mild base that neutralizes excess stomach acid (HCl).

The reaction is:
NaHCO3 + HCl → NaCl + H2O + CO2

The released CO2 provides relief from acidity and bloating.

Question 4:
Differentiate between mineral acids and organic acids with one example of each.
Answer:
  • Mineral acids are inorganic, highly corrosive, and derived from minerals. Example: Sulphuric acid (H2SO4).
  • Organic acids are naturally occurring, weaker, and contain carbon. Example: Citric acid (C6H8O7) found in citrus fruits.
Question 5:
What happens when blue litmus paper is dipped in a solution of sodium hydroxide? Explain.
Answer:

When blue litmus paper is dipped in sodium hydroxide (NaOH), it remains blue.

This is because NaOH is a strong base, and blue litmus does not change color in basic or neutral solutions—it only turns red in acidic conditions.

Question 6:
Describe the process of neutralization with an example and its application in daily life.
Answer:

Neutralization is a reaction where an acid and a base react to form salt and water.

Example: HCl + NaOH → NaCl + H2O

Application: Antacids like milk of magnesia neutralize excess stomach acid to relieve indigestion.

Question 7:
Explain the process of neutralization with an example.
Answer:

Neutralization is a chemical reaction where an acid reacts with a base to form salt and water. This reaction releases heat, making it exothermic.


Example: When hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), it forms sodium chloride (NaCl) and water.
HCl + NaOH → NaCl + H2O
Question 8:
Why do acids not show acidic behavior in the absence of water?
Answer:

Acids show acidic behavior only in the presence of water because water helps in the dissociation of acids into H+ ions, which are responsible for their acidic properties. In the absence of water, acids remain in molecular form and cannot release H+ ions.

Question 9:
Differentiate between a strong acid and a weak acid with examples.
Answer:
  • Strong Acid: Completely dissociates in water to release H+ ions. Example: Hydrochloric acid (HCl).

  • Weak Acid: Partially dissociates in water, releasing fewer H+ ions. Example: Acetic acid (CH3COOH).
Question 10:
What is the pH range of acidic, basic, and neutral solutions?
Answer:
  • Acidic solutions: pH < 7
  • Neutral solutions: pH = 7
  • Basic solutions: pH > 7

The pH scale ranges from 0 (highly acidic) to 14 (highly basic).

Question 11:
How is the concentration of hydroxide ions (OH-) related to the pH of a solution?
Answer:

The concentration of hydroxide ions (OH-) increases as the pH of a solution increases. Higher pH means more OH- ions, indicating a basic solution. Conversely, lower pH means fewer OH- ions, indicating an acidic solution.

Question 12:
Describe the preparation of washing soda (Na2CO3.10H2O) from sodium chloride.
Answer:

Washing soda is prepared through the Solvay process:


1. Sodium chloride (NaCl) reacts with ammonia (NH3) and carbon dioxide (CO2) to form sodium hydrogen carbonate (NaHCO3).
NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl

2. NaHCO3 is heated to form sodium carbonate (Na2CO3).
2NaHCO3 → Na2CO3 + CO2 + H2O

3. Crystallization with water gives washing soda (Na2CO3.10H2O).

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the neutralization reaction with an example from daily life and a chemical equation.
Answer:
Concept Overview

A neutralization reaction occurs when an acid reacts with a base to form salt and water.

Process Explanation

Our textbook shows the reaction between HCl (acid) and NaOH (base) forming NaCl and H2O: HCl + NaOH → NaCl + H2O.

Real-world Application

In daily life, we use antacids (bases) to neutralize excess stomach acid (HCl) for relief from acidity.

Question 2:
How do acids and bases conduct electricity? Explain with an example.
Answer:
Concept Overview

Acids and bases conduct electricity due to the presence of ions (H+ and OH-) in their aqueous solutions.

Process Explanation

We studied that HCl dissociates into H+ and Cl- ions, allowing current flow. Similarly, NaOH releases Na+ and OH- ions.

Real-world Application

Car batteries use sulfuric acid (H2SO4) for ion conduction to generate electricity.

Question 3:
Describe the preparation of washing soda (Na2CO3.10H2O) from sodium chloride with equations.
Answer:
Concept Overview

Washing soda is prepared via the Solvay process using NaCl, NH3, and CO2.

Process Explanation

Our textbook shows these steps:

  • NH3 + CO2 + H2O → NH4HCO3
  • NH4HCO3 + NaCl → NaHCO3 + NH4Cl
  • Heating NaHCO3 gives Na2CO3.

Real-world Application

It is used in detergents and glass manufacturing.

Question 4:
Why is pH important in soil for agriculture? Give an example of a pH indicator.
Answer:
Concept Overview

Soil pH affects nutrient availability and microbial activity. Ideal pH for most crops is 6-7.

Process Explanation

We studied that acidic soil (pH < 6) can be treated with lime (CaO), while alkaline soil (pH > 7) uses gypsum.

Real-world Application

Litmus, a natural indicator, turns red in acidic and blue in basic soil. Farmers test soil pH before planting crops like wheat.

Question 5:
Compare the properties of mineral acids and organic acids with examples.
Answer:
Concept Overview

Mineral acids are inorganic (e.g., HCl), while organic acids contain carbon (e.g., citric acid).

Process Explanation

Our textbook shows:

  • Mineral acids are strong and corrosive (H2SO4).
  • Organic acids are weak and found in food (acetic acid in vinegar).

Real-world Application

HCl is used in industries, whereas lactic acid (organic) is in curd.

Question 6:
Explain the neutralization reaction with an example from daily life and a reaction from NCERT.
Answer:
Concept Overview

A neutralization reaction occurs when an acid reacts with a base to form salt and water.

Process Explanation

We studied that HCl (acid) + NaOH (base) → NaCl (salt) + H2O. This is an NCERT example.

Real-world Application

In daily life, antacids like milk of magnesia (Mg(OH)2) neutralize stomach acid (HCl) to relieve acidity.

Question 7:
Describe how pH affects soil quality and crop growth with NCERT and real-life examples.
Answer:
Concept Overview

pH measures acidity/basicity. Soil pH impacts nutrient availability.

Process Explanation

Our textbook shows acidic soil (pH < 7) harms crops like wheat. Lime (CaO) is added to neutralize it.

Real-world Application

Farmers test soil pH before planting. Blue litmus turns red in acidic soil, as per NCERT experiments.

Question 8:
Explain the preparation of washing soda (Na2CO3.10H2O) using Solvay process with NCERT reference.
Answer:
Concept Overview

Washing soda is a sodium salt prepared via Solvay process.

Process Explanation

NCERT states: NaCl + NH3 + CO2 + H2O → NaHCO3 (heated) → Na2CO3.

Real-world Application

It is used to soften water and make detergents, as mentioned in Chapter 2.

Question 9:
Compare strong acids and weak acids with one NCERT example and a daily-life instance.
Answer:
Concept Overview

Strong acids ionize completely (e.g., HCl), while weak acids partially ionize (e.g., CH3COOH).

Process Explanation

NCERT shows HCl dissociates fully in water, whereas acetic acid (vinegar) shows partial dissociation.

Real-world Application

Lemon juice (weak acid) is safer for cooking than concentrated sulfuric acid (strong acid).

Question 10:
Explain the formation of acidic rain and its effects using NCERT and real-world cases.
Answer:
Concept Overview

Acid rain forms when SO2/NOx dissolve in rainwater, lowering pH.

Process Explanation

NCERT explains: SO2 + H2O → H2SO3 (sulfurous acid).

Real-world Application

It corrodes Taj Mahal's marble (CaCO3), as studied in our textbook.

Question 11:
Explain the process of neutralization reaction with an example. How is this reaction useful in everyday life?
Answer:

The neutralization reaction is a chemical reaction where an acid and a base react to form salt and water. This reaction occurs when the H+ ions from the acid combine with the OH- ions from the base to form water, while the remaining ions form a salt.


Example: When hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the reaction is as follows:
HCl + NaOH → NaCl + H2O
Here, sodium chloride (NaCl) is the salt formed, and water is produced.


Applications in everyday life:

  • Antacid tablets: Used to neutralize excess stomach acid (HCl) to relieve indigestion.
  • Soil treatment: Farmers add slaked lime (base) to acidic soil to neutralize it for better crop growth.
  • Bee stings and ant bites: Baking soda (base) is applied to neutralize formic acid injected by insects.
  • Factory waste treatment: Acidic industrial waste is neutralized before disposal to prevent environmental harm.


Neutralization reactions are crucial in maintaining balance in biological systems and industrial processes, making them highly relevant in daily life.

Question 12:
Describe the preparation, properties, and uses of bleaching powder. Include its chemical equation.
Answer:

Bleaching powder (chemically known as calcium oxychloride) is prepared by the action of chlorine gas on dry slaked lime (calcium hydroxide). The chemical equation for its preparation is:

Ca(OH)2 + Cl2 → CaOCl2 + H2O

Properties of bleaching powder:

  • It is a white powder with a strong smell of chlorine.
  • It is soluble in water but forms a suspension due to impurities.
  • It reacts with dilute acids to release chlorine gas, which acts as a bleaching agent.

Uses of bleaching powder:

  • Bleaching: Used to bleach cotton, linen, and wood pulp in the textile and paper industries.
  • Disinfection: Acts as a disinfectant for drinking water and swimming pools.
  • Oxidizing agent: Used in chemical industries for oxidation reactions.

Bleaching powder is a versatile compound with wide applications due to its strong oxidizing and disinfecting properties.

Question 13:
Describe the preparation, properties, and uses of bleaching powder. Include the chemical equation for its formation.
Answer:

Bleaching powder, chemically known as calcium oxychloride (CaOCl2), is prepared by the action of chlorine gas on dry slaked lime (calcium hydroxide, Ca(OH)2). The chemical equation for its formation is:

Ca(OH)2 + Cl2 → CaOCl2 + H2O

Properties of bleaching powder:

  • It is a white powder with a strong smell of chlorine.
  • It is soluble in water but forms a suspension due to impurities.
  • It reacts with dilute acids to release chlorine gas, which acts as a bleaching agent.

Uses of bleaching powder:

  • Bleaching: Used to bleach cotton, linen, and wood pulp in the textile and paper industries.
  • Disinfection: Acts as a disinfectant for drinking water and swimming pools.
  • Oxidizing agent: Used in chemical industries for oxidation reactions.

Bleaching powder is a versatile compound with significant industrial and domestic applications due to its oxidizing and disinfecting properties.

Question 14:
Explain the process of neutralization with an example. How is this reaction useful in everyday life?
Answer:

The process of neutralization is a chemical reaction where an acid and a base react to form salt and water. This reaction is exothermic, meaning it releases heat. The general equation for neutralization is:


Acid + Base → Salt + Water

For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), they form sodium chloride (NaCl) and water:


HCl + NaOH → NaCl + H2O

In everyday life, neutralization reactions are highly useful:

  • Indigestion Relief: Antacids like magnesium hydroxide (Mg(OH)2) neutralize excess stomach acid (HCl).
  • Soil Treatment: Farmers add slaked lime (Ca(OH)2) to acidic soil to neutralize it for better crop growth.
  • Bee Sting Treatment: A mild base like baking soda (NaHCO3) neutralizes the formic acid injected by a bee sting.

Thus, neutralization plays a vital role in balancing chemical properties in daily applications.

Question 15:
Describe the preparation, properties, and uses of Plaster of Paris. Include a labeled diagram of its setting process.
Answer:

Preparation: Plaster of Paris (POP) is prepared by heating gypsum (CaSO4·2H2O) at 373 K. The reaction is:
CaSO4·2H2O → CaSO4·½H2O + 1½H2O


Properties:

  • It is a white powder.
  • When mixed with water, it forms a hard solid mass (setting process).
  • The setting reaction is exothermic.


Uses:

  • Making casts for broken bones.
  • Making decorative items and ceiling designs.
  • Fireproofing material.


Diagram (Setting Process):
[Diagram: Labeled steps showing POP powder + water → paste → hard solid mass with heat release]

Question 16:
Explain the process of neutralization with the help of an example. How is this reaction useful in everyday life?
Answer:

Neutralization is a chemical reaction where an acid and a base react to form salt and water, resulting in the cancellation of their acidic and basic properties. The general equation for neutralization is:

Acid + Base → Salt + Water

For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), they form sodium chloride (NaCl) and water:

HCl + NaOH → NaCl + H2O

This reaction is highly useful in everyday life:

  • Indigestion Relief: Antacids like magnesium hydroxide (Milk of Magnesia) neutralize excess stomach acid.
  • Soil Treatment: Farmers add slaked lime (Ca(OH)2) to acidic soil to neutralize it for better crop growth.
  • Bee Sting Treatment: A mild base like baking soda is applied to neutralize the acidic venom from bee stings.

Neutralization is also used in industries to treat acidic waste before disposal, preventing environmental harm.

Question 17:
Explain the process of neutralization with the help of an example. Also, mention its importance in everyday life.
Answer:

The process of neutralization is a chemical reaction where an acid and a base react to form salt and water, resulting in the cancellation of their acidic and basic properties. This reaction is exothermic, meaning it releases heat.


Example: When hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), they neutralize each other to form sodium chloride (NaCl) and water (H2O). The chemical equation is:


HCl + NaOH → NaCl + H2O


Importance in everyday life:

  • Indigestion relief: Antacids like milk of magnesia (a base) neutralize excess stomach acid (HCl) to relieve acidity.
  • Soil treatment: Farmers add slaked lime (a base) to acidic soil to neutralize it for better crop growth.
  • Bee stings: Applying baking soda (a base) neutralizes the formic acid injected by a bee sting.
  • Wastewater treatment: Neutralization is used to balance the pH of industrial waste before disposal.

This reaction is crucial as it helps maintain balance in biological and environmental systems, ensuring safety and efficiency in various applications.

Question 18:
Explain the process of neutralization with a suitable example. How is this reaction useful in everyday life?
Answer:

Neutralization is a chemical reaction where an acid and a base react to form salt and water, resulting in the cancellation of their acidic and basic properties. The general equation is:

Acid + Base → Salt + Water

For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), they form sodium chloride (NaCl) and water:

HCl + NaOH → NaCl + H2O

In everyday life, neutralization is highly useful:

  • Indigestion Relief: Antacids (like magnesium hydroxide) neutralize excess stomach acid.
  • Soil Treatment: Farmers add slaked lime (Ca(OH)2) to acidic soil to neutralize it.
  • Wasp/Bee Stings: Bee stings (acidic) are treated with baking soda (base), while wasp stings (basic) are treated with vinegar (acid).

This reaction ensures balance in chemical systems and practical applications in health and agriculture.

Question 19:
Describe the preparation, properties, and uses of Plaster of Paris. Include a labeled diagram of its setting process.
Answer:

Plaster of Paris (POP) is chemically calcium sulphate hemihydrate (CaSO4·½H2O). It is prepared by heating gypsum (CaSO4·2H2O) at 373K:

CaSO4·2H2O → CaSO4·½H2O + 1½H2O

Properties:

  • White powder that forms a hard solid when mixed with water.
  • Releases heat during setting (exothermic reaction).
  • Expands slightly while hardening, filling molds precisely.

Uses:

  • Making casts for fractured bones.
  • Decorative ceiling designs and wall coatings.
  • Fireproofing material and in surgical bandages.

Setting Process (Diagram Description):
When water is added, POP rehydrates to form gypsum crystals, interlocking to form a solid mass.
CaSO4·½H2O + 1½H2O → CaSO4·2H2O
(Diagram would show powder → paste → crystalline structure formation.)

Question 20:
Explain the process of neutralization reaction with an example. How is this reaction useful in everyday life? Provide a detailed explanation with a balanced chemical equation.
Answer:

The neutralization reaction is a chemical reaction where an acid and a base react to form salt and water, resulting in the cancellation of their acidic and basic properties. This reaction is exothermic, meaning it releases heat.


Example: When hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), sodium chloride (NaCl) and water (H2O) are formed.


Balanced Chemical Equation:
HCl + NaOH → NaCl + H2O


Applications in Everyday Life:

  • Antacid tablets: Used to neutralize excess stomach acid (HCl) with bases like magnesium hydroxide (Mg(OH)2).
  • Soil treatment: Farmers add slaked lime (Ca(OH)2) to neutralize acidic soil.
  • Bee stings: Baking soda (a base) is applied to neutralize formic acid from bee stings.

Question 21:
Describe the preparation, properties, and uses of bleaching powder. Include its chemical formula and a labeled diagram showing its industrial preparation.
Answer:

Preparation of Bleaching Powder:
Bleaching powder (chemically known as calcium oxychloride) is prepared by passing chlorine gas over dry slaked lime (calcium hydroxide).


Chemical Equation:
Ca(OH)2 + Cl2 → CaOCl2 + H2O


Properties:

  • It is a white powder with a strong smell of chlorine.
  • It is soluble in water but forms a suspension due to impurities.
  • It acts as an oxidizing agent and releases chlorine when treated with dilute acids.


Uses:

  • Disinfectant: Used to purify water and sanitize surfaces.
  • Bleaching agent: Used in the textile and paper industries.
  • Oxidizing agent: Used in chemical reactions.


Diagram (Industrial Preparation):
[A labeled diagram would show a chamber where dry slaked lime is exposed to chlorine gas, with arrows indicating the flow of reactants and products.]

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A farmer tested soil pH and found it highly acidic. Our textbook mentions slaked lime as a remedy.
Case Summary: Soil pH = 4.5, crops show stunted growth.
Q1: Why is acidic soil harmful? Q2: How does slaked lime neutralize it?
Answer:
Case Summary: Acidic soil (pH < 7) harms plant nutrient absorption.
Scientific Principle: We studied that acids release H⁺ ions, damaging roots. Slaked lime (Ca(OH)₂) is a base.
Solution Approach:
  • Q1: Low pH dissolves toxic metals like Al³⁺ (NCERT Example 2.3).
  • Q2: Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O (neutralization). Farmers use this to raise pH.
Question 2:
A student mixed dilute HCl with NaOH and observed no visible change.
Case Summary: Solution became warm.
Q1: Name the reaction type. Q2: How can we confirm salt formation?
Answer:
Case Summary: Neutralization reaction produces salt and water.
Scientific Principle: Our textbook shows HCl + NaOH → NaCl + H₂O (Ex 2.6).
Solution Approach:
  • Q1: Exothermic neutralization (heat released).
  • Q2: Evaporate water to get NaCl crystals or test pH (≈7). Real-world use: Antacid tablets work similarly.
Question 3:
A soap solution has pH 9.
Case Summary: It turns red litmus blue but doesn’t harm skin.
Q1: Why is soap basic? Q2: How is its mildness useful?
Answer:
Case Summary: Soap is a mild base from saponification (NCERT Ex 2.12).
Scientific Principle: Bases contain OH⁻ ions; soap’s pH (8–10) is skin-safe.
Solution Approach:
  • Q1: Fatty acids + NaOH → soap (basic salt).
  • Q2: Mildness avoids irritation while cleaning oils (real-world application).
Question 4:
Vinegar (pH=3) and baking soda (pH=9) were mixed, releasing gas.
Case Summary: Gas turns limewater milky.
Q1: Identify the gas. Q2: Write the reaction.
Answer:
Case Summary: Acid (CH₃COOH) + base (NaHCO₃) → CO₂ gas.
Scientific Principle: We studied carbonates react with acids (NCERT Ex 2.5).
Solution Approach:
  • Q1: CO₂ (confirmed by limewater test).
  • Q2: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂↑. Used in baking (real-world).
Question 5:
A student observed effervescence when adding baking soda to vinegar.
Case Summary: Reaction produced gas turning limewater milky.
Q1: Identify the gas. Q2: Write the reaction and a real-world use.
Answer:
Case Summary: Vinegar (acetic acid) reacts with baking soda (NaHCO3).
Scientific Principle: We studied carbon dioxide (CO2) turns limewater milky.
Solution Approach: Reaction: CH3COOH + NaHCO3 → CH3COONa + H2O + CO2. Real-world use: Fire extinguishers utilize this reaction.
Question 6:
A soap solution has pH 9.
Case Summary: It feels slippery and turns red litmus blue.
Q1: Classify the solution. Q2: Explain litmus test with a NCERT example.
Answer:
Case Summary: Soap solution (pH 9) shows basic properties.
Scientific Principle: Bases turn red litmus blue, as in our textbook’s NaOH example.
Solution Approach: Slippery feel confirms base. Litmus test works because bases accept H+ ions, changing litmus color. NCERT example: Lime water test.
Question 7:
Laboratory data shows:
SubstancepH
Lemon juice2.2
Baking soda8.4

Q1: Which is stronger acid/base? Q2: How does pH affect tooth decay?
Answer:
Case Summary: Lemon juice (pH 2.2) is acidic, baking soda (pH 8.4) is basic.
Scientific Principle: Lower pH = stronger acid (lemon juice). Higher pH = stronger base (baking soda).
Solution Approach: Acidic pH erodes tooth enamel (NCERT example: Bacteria produce acids from sugar). Baking soda neutralizes mouth acids.
Question 8:
A farmer tested soil pH and found it acidic. Our textbook mentions slaked lime as a remedy.
Case Summary: Soil pH = 5.2, crops show stunted growth.
Q1: Why is acidic soil harmful? Q2: How does slaked lime neutralize it?
Answer:
Case Summary: Acidic soil (pH 5.2) affects crop growth.
Scientific Principle: Acidic soil releases excess H⁺ ions, blocking nutrient absorption (NCERT Example: Tea gardens).
Solution Approach:
  • Slaked lime (Ca(OH)₂) is a base that reacts: Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O.
  • Neutralizes acidity, improves soil fertility (Real-world: Farmers in Assam use this).
Question 9:
A student mixed dilute HCl with NaOH and observed no visible change.
Case Summary: Reaction mixture remains colorless.
Q1: What is this reaction called? Q2: How can we confirm neutralization occurred?
Answer:
Case Summary: HCl + NaOH → No color change.
Scientific Principle: This is a neutralization reaction (NCERT Example: NaOH + HCl → NaCl + H₂O).
Solution Approach:
  • Use pH paper to check if pH = 7.
  • Add phenolphthalein (turns pink in base, colorless at neutral pH). Real-world: Lab tests for antacid effectiveness.
Question 10:
A chef used baking soda (NaHCO₃) to make fluffy pancakes.
Case Summary: Dough rises with gas bubbles.
Q1: Which gas is released? Q2: Why is NaHCO₃ called a mild base?
Answer:
Case Summary: NaHCO₃ releases gas in dough.
Scientific Principle: Heating NaHCO₃ produces CO₂ (NCERT Example: Baking soda in fire extinguishers).
Solution Approach:
  • Reaction: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂↑.
  • It’s mild as it doesn’t harm skin (Real-world: Used in toothpaste).
Question 11:
A doctor prescribed Mg(OH)₂ for acidity.
Case Summary: Patient complained of stomach pain after eating spicy food.
Q1: How does Mg(OH)₂ relieve acidity? Q2: Why is it preferred over NaOH?
Answer:
Case Summary: Mg(OH)₂ treats stomach acidity.
Scientific Principle: It neutralizes excess HCl (NCERT Example: Milk of Magnesia).
Solution Approach:
  • Reaction: Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O.
  • NaOH is too strong and can damage tissues (Real-world: Antacids use mild bases).
Question 12:
A farmer tested the soil of his field and found it to be highly acidic. He was advised to add a substance to neutralize the acidity.

(a) Name the substance he should add and justify your choice based on its properties.
(b) Write the chemical reaction involved in this process.
Answer:

(a) The farmer should add calcium hydroxide (slaked lime) or calcium oxide (quicklime) to neutralize the acidic soil. These substances are basic in nature and react with acids to form neutral salts and water, thereby reducing soil acidity. They are also cost-effective and easily available for agricultural use.

(b) The chemical reaction is:
Ca(OH)2 + H2SO4 → CaSO4 + 2H2O
(Calcium hydroxide reacts with sulfuric acid in the soil to form calcium sulfate and water.)

Question 13:
A student observed that a solution turns red litmus blue but has no effect on blue litmus.

(a) What inference can be drawn about the nature of the solution?
(b) Name one household substance that exhibits this property and write its chemical formula.
Answer:

(a) The solution is basic in nature because it turns red litmus blue, which is a characteristic property of bases. Bases do not affect blue litmus.

(b) A common household substance with this property is sodium hydroxide (caustic soda), used in cleaning agents. Its chemical formula is NaOH.

Question 14:
During a lab activity, a student added dilute hydrochloric acid to a test tube containing sodium carbonate.

(a) What observation would the student make?
(b) Write the balanced chemical equation for this reaction.
Answer:

(a) The student would observe effervescence (bubbling) due to the release of carbon dioxide gas. The gas can be tested by passing it through lime water, which turns milky.

(b) The balanced chemical equation is:
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
(Sodium carbonate reacts with hydrochloric acid to form sodium chloride, water, and carbon dioxide.)

Question 15:
A doctor prescribed an antacid tablet to a patient suffering from acidity.

(a) Explain how the antacid provides relief.
(b) Name the active ingredient present in most antacids and write its chemical formula.
Answer:

(a) Antacids are basic substances that neutralize excess hydrochloric acid in the stomach, relieving acidity. They raise the pH of the stomach contents, reducing irritation and pain.

(b) The active ingredient in most antacids is magnesium hydroxide. Its chemical formula is Mg(OH)2.

Question 16:
A student tested two solutions, P and Q, with universal indicator. Solution P turned the indicator red, while solution Q turned it blue.

Based on this observation, answer the following:

  • Identify the nature of solutions P and Q.
  • Give one example each of such solutions from everyday life.
  • Explain how these solutions react with litmus paper.
Answer:

Solution P is an acid because it turns universal indicator red (pH < 7). An example is lemon juice.

Solution Q is a base because it turns universal indicator blue (pH > 7). An example is baking soda solution.

Reaction with litmus paper:
1. Acidic solution (P) turns blue litmus red but has no effect on red litmus.
2. Basic solution (Q) turns red litmus blue but has no effect on blue litmus.

Question 17:
A farmer observed that the soil in his field was too acidic, affecting crop growth. He was advised to add slaked lime to the soil.

Answer the following:

  • What is the chemical name of slaked lime?
  • Explain how it helps neutralize acidic soil.
  • Write the chemical reaction involved in this process.
Answer:

The chemical name of slaked lime is calcium hydroxide (Ca(OH)2).

Neutralization process:
Slaked lime is a base that reacts with the acids present in the soil, forming water and a salt. This reduces soil acidity, improving crop growth conditions.

Chemical reaction:
Ca(OH)2 + H2SO4 (acid in soil) → CaSO4 + 2H2O
(Calcium hydroxide reacts with sulfuric acid to form calcium sulfate and water.)

Question 18:
A student tested two solutions, P and Q, with universal indicator. Solution P turned the indicator red, while solution Q turned it blue.

(a) Identify the nature of solutions P and Q.

(b) What happens when a few drops of solution P are added to a solution of Q? Explain with a balanced chemical equation if applicable.

Answer:

(a) Solution P turned the universal indicator red, indicating it is an acidic solution (pH < 7). Solution Q turned the indicator blue, indicating it is a basic solution (pH > 7).

(b) When a few drops of P (acid) are added to Q (base), a neutralization reaction occurs, forming salt and water.
Example (assuming HCl as acid and NaOH as base):
HCl + NaOH → NaCl + H2O
The pH of the resulting solution moves closer to 7 (neutral) depending on the quantities mixed.

Question 19:
A farmer observed that the soil in his field was too acidic, affecting crop growth. He was advised to add slaked lime to the soil.

(a) Why is slaked lime recommended for acidic soil?

(b) Write the chemical name and formula of slaked lime. What precaution should the farmer take while applying it?

Answer:

(a) Slaked lime (a base) neutralizes the excess acidity in the soil by reacting with H+ ions, raising the pH to a level suitable for plant growth.

(b) Chemical name: Calcium hydroxide
Formula: Ca(OH)2
Precaution: The farmer should wear gloves and avoid direct contact, as slaked lime is caustic. It should be evenly spread and mixed with soil to prevent localized high pH spots.

Question 20:
A student conducted an experiment to test the pH of various household substances using a universal indicator. The results were recorded as follows:
Lemon juice - pH 2, Baking soda solution - pH 9, Vinegar - pH 3, Milk of magnesia - pH 10.
Based on the data, answer the following:
(i) Which substance is the strongest acid and which is the strongest base?
(ii) What happens to the pH of lemon juice if water is added to it? Justify your answer.
Answer:

(i) The strongest acid among the given substances is lemon juice (pH 2) because it has the lowest pH value, indicating higher acidity. The strongest base is milk of magnesia (pH 10) as it has the highest pH value, indicating higher alkalinity.


(ii) When water is added to lemon juice, its pH increases (becomes less acidic). This happens because dilution reduces the concentration of hydrogen ions (H⁺) in the solution. Since pH is inversely proportional to H⁺ concentration, the pH rises. However, the solution remains acidic as water is neutral (pH 7) and does not neutralize the acid completely.

Question 21:
A farmer observed that the soil in his field was too acidic, which affected crop growth. He was advised to add slaked lime (calcium hydroxide) to the soil.
(i) Why is slaked lime added to acidic soil?
(ii) Write the chemical reaction involved in this process.
(iii) What precaution should the farmer take while applying slaked lime?
Answer:

(i) Slaked lime (calcium hydroxide) is added to acidic soil because it is a base that neutralizes the excess acidity (H⁺ ions) in the soil. This improves soil fertility and promotes healthy crop growth.


(ii) The chemical reaction is:
Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O
Here, calcium hydroxide reacts with hydrogen ions to form calcium ions and water, neutralizing the acid.


(iii) The farmer should avoid over-application of slaked lime, as excessive alkalinity can harm crops. He should also wear protective gloves and goggles since slaked lime is corrosive and can cause skin or eye irritation.

Question 22:
A student tested two solutions, X and Y, with universal indicator. Solution X turned orange, while solution Y turned blue.

Based on this observation, answer the following:

  • Identify the nature (acidic/basic) of solutions X and Y.
  • What is the approximate pH range of each solution?
  • Give one example of a household substance that could match each solution.
Answer:

Solution X turned orange with universal indicator, indicating it is acidic. The approximate pH range for orange is 3-6. A common household substance matching this could be lemon juice (pH ~2-3).


Solution Y turned blue, indicating it is basic. The approximate pH range for blue is 8-11. A common household substance matching this could be baking soda solution (pH ~9).


Universal indicator changes color based on pH: red (strong acid) to purple (strong base). This helps classify substances as acidic or basic.

Question 23:
A farmer observed that the soil in his field was too acidic, affecting crop growth. He was advised to add slaked lime to the soil.

Answer the following:

  • Why is acidic soil harmful to plants?
  • How does slaked lime help neutralize the soil?
  • Write the chemical name and formula of slaked lime.
Answer:

Acidic soil (pH < 7) harms plants because:

  • It reduces nutrient availability (e.g., nitrogen, phosphorus).
  • It increases toxicity of metals like aluminum, damaging roots.

Slaked lime (chemically calcium hydroxide, formula: Ca(OH)2) neutralizes acidity by reacting with hydrogen ions (H+) in the soil:
Ca(OH)2 + 2H+ → Ca2+ + 2H2O.
This raises the pH, making the soil more neutral.


Farmers also use organic matter (compost) or crushed eggshells (calcium carbonate) as alternatives.

Question 24:
A student tested two solutions, P and Q, with universal indicator. Solution P turned the indicator red, while solution Q turned it blue.

Identify the nature of solutions P and Q and explain how their pH values differ. Also, suggest one natural source for each solution.

Answer:

Solution P is acidic as it turns universal indicator red, indicating a pH below 7. Solution Q is basic as it turns the indicator blue, indicating a pH above 7.


Natural sources:

  • Solution P: Lemon juice (contains citric acid)
  • Solution Q: Baking soda solution (contains sodium bicarbonate, a mild base)

Question 25:
A farmer observed that the soil in his field was too acidic, affecting crop growth. He was advised to add slaked lime to the soil.

Explain why slaked lime is used and write the chemical reaction involved. Also, mention one alternative substance that can be used for the same purpose.

Answer:

Slaked lime (calcium hydroxide) is a base that neutralizes soil acidity by reacting with excess hydrogen ions (H⁺).

Chemical reaction:
Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O

Alternative substance: Powdered limestone (calcium carbonate) can also be used to reduce soil acidity gradually.

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