Foundation Batch For Class 7

ACIDS, BASES, AND SALTS

LOREM IPSUM DOLOR SIT AMET

The Tale of the Three Chemists

Once upon a time in a magical kingdom called Chemia, three renowned chemists – Professor Acidic, Doctor Basic, and Engineer Neutral – were famous for their extraordinary potions. They each had a unique approach to their work, and the citizens relied on their expertise for solving everyday problems.

Chapter 1: Professor Acidic and the Sour Secrets

Introduction

Professor Acidic was known for his love of tangy fruits and sour flavors. His potions were sour to taste but incredibly powerful.

Characteristics of Acids

  1. Taste: Sour, like lemons and tamarinds.
  2. Litmus Test: Turn blue litmus red.
  3. Reaction with Metals: Produces hydrogen gas.

Examples of Acids

  • Natural Acids:
    • Citric Acid: Found in lemons and oranges.
    • Lactic Acid: Found in curd.
  • Mineral Acids:
    • Hydrochloric Acid (HCl): Found in stomach acid.
    • Sulphuric Acid (H2SO4​): Used in car batteries.

Professor’s Experiments:
One day, Professor Acidic demonstrated an experiment with zinc metal:

Zn+2HCl→ZnCl2+H2

The gas bubbles fizzing out amazed everyone. “That’s hydrogen gas,” he said.

Chapter 2: Doctor Basic and the Bitter Cure

Introduction

Doctor Basic, known for his bitterness, had a potion for every slippery situation. His remedies were effective but always tasted bitter.

Characteristics of Bases

  1. Taste: Bitter, like baking soda.
  2. Litmus Test: Turn red litmus blue.
  3. Touch: Soapy and slippery.

Examples of Bases

  • Strong Bases:
    • Sodium Hydroxide (NaOH): Found in soaps.
    • Potassium Hydroxide (KOH): Used in fertilizers.
  • Weak Bases:
    • Magnesium Hydroxide (Mg(OH)2​): Used as antacids.

Doctor’s Experiment:
Doctor Basic once mixed his potion with vinegar. A white froth appeared as he explained the reaction:

CH3COOH+NaOH→CH3COONa+H2O

“See how my base neutralizes acid!” he smiled.

Chapter 3: Engineer Neutral and the Salt Factory

Introduction

Engineer Neutral was a mediator. Whenever Professor Acidic and Doctor Basic fought, he would mix their potions to form salts.

What are Salts?
Salts are neutral substances formed when acids and bases react.

Examples of Salts

  • Sodium Chloride (NaCl): Table salt.
  • Calcium Carbonate (CaCO3​): Found in chalk.
  • Potassium Nitrate (KNO3​): Used in fireworks.

Engineer’s Neutralization Formula:

Acid+Base→Salt+Water

For example:

HCl+NaOH→NaCl+H2O

Daily Life Connection:
Engineer Neutral explained how:

  • Antacids neutralize stomach acid.
  • Lime (a base) is used to treat acidic soil.

Chapter 4: The pH Festival

The citizens of Chemia celebrated their knowledge at the pH Festival. They used the pH Scale to measure the strength of acids and bases.

The pH Scale

  • Acids: pH < 7.
  • Neutral: pH = 7.
  • Bases: pH > 7.

Activities at the Festival

  1. Testing the pH of lemon juice, soap, and milk.
  2. Using turmeric and litmus paper as indicators.
  3. Observing the color changes with phenolphthalein.

Applications in Real Life

  • Acids:
    • Vinegar in cooking.
    • Citric acid in soft drinks.
  • Bases:
    • Baking soda for cleaning.
    • Ammonia in fertilizers.
  • Salts:
    • Sodium chloride for preserving food.
    • Plaster of Paris for molds.

Practice Questions

Fill in the Blanks

  1. Acids turn blue litmus ______.
  2. The pH of a neutral solution is ______.

Match the Following

Column A

Column B

Hydrochloric Acid

Stomach Acid

Sodium Hydroxide

Soap-Making

Sodium Chloride

Table Salt

Competitive Exam Question

  1. Write the reaction between hydrochloric acid and sodium hydroxide.
  2. What is the role of pH in agriculture?

Bonus Activity: Kitchen Chemistry

Experiment:

  • Collect substances like lemon juice, soap, and sugar.
  • Test their pH using litmus paper.
  • Discuss: Why does milk have a pH closer to neutral?

Summary Table for Competitive Exams

Category

Acids

Bases

Salts

Definition

Produce H+ ions

Produce OH− ions

Neutral compounds

Examples

HCl,H2​SO4​

NaOH,KOH

NaCl,CaCO3

Litmus Test

Blue to Red

Red to Blue

Neutral (No effect)

Story Takeaway:
Through the lives of Professor Acidic, Doctor Basic, and Engineer Neutral, students can now appreciate the fascinating world of Acids, Bases, and Salts. Whether it’s the tangy taste of lemons or the soapy touch of a detergent, chemistry is all around us!

 

Basic Understanding

  1. Acids are substances that produce:
    A) OH⁻ ions
    B) H⁺ ions
    C) O₂ gas
    D) CO₂ gas
  2. Bases are substances that produce:
    A) H⁺ ions
    B) O₂ ions
    C) OH⁻ ions
    D) H₂ gas
  3. What is the taste of acids?
    A) Bitter
    B) Sweet
    C) Sour
    D) Salty
  4. What is the taste of bases?
    A) Sour
    B) Bitter
    C) Sweet
    D) Salty
  5. Acids turn blue litmus:
    A) Green
    B) Red
    C) Yellow
    D) No change
  6. Bases turn red litmus:
    A) Blue
    B) Red
    C) Yellow
    D) Green
  7. Which of the following is a natural acid?
    A) NaOH
    B) Citric acid
    C) KOH
    D) CaO
  8. Which is a strong base?
    A) NaOH
    B) CH₃COOH
    C) HCl
    D) H₂SO₄
  9. The pH of a neutral solution is:
    A) 0
    B) 7
    C) 14
    D) 10
  10. Which of the following is a salt?
    A) HCl
    B) NaOH
    C) NaCl
    D) H₂SO₄

11–25: Conceptual Questions

  1. Which acid is present in lemon?
    A) Lactic acid
    B) Citric acid
    C) Acetic acid
    D) Formic acid
  2. Which acid is present in curd?
    A) Citric acid
    B) Lactic acid
    C) Hydrochloric acid
    D) Nitric acid
  3. Hydrochloric acid is found in:
    A) Blood
    B) Stomach
    C) Milk
    D) Plants
  4. Which gas is produced when acids react with metals?
    A) Oxygen
    B) Hydrogen
    C) Nitrogen
    D) Carbon dioxide
  5. Which property is shown by bases?
    A) Sour taste
    B) Slippery feel
    C) No reaction
    D) Acidic nature
  6. What is formed when acid reacts with base?
    A) Acid
    B) Base
    C) Salt and water
    D) Gas only
  7. Which of the following is a weak base?
    A) NaOH
    B) KOH
    C) Mg(OH)₂
    D) CaO
  8. Which indicator turns pink in basic solution?
    A) Litmus
    B) Turmeric
    C) Phenolphthalein
    D) Methyl orange
  9. Which indicator turns red in acidic solution?
    A) Litmus
    B) Phenolphthalein
    C) Turmeric
    D) None
  10. The pH value less than 7 indicates:
    A) Base
    B) Neutral
    C) Acid
    D) Salt
  11. The pH value more than 7 indicates:
    A) Acid
    B) Base
    C) Neutral
    D) Salt
  12. Which of the following is neutral?
    A) Lemon juice
    B) Soap solution
    C) Pure water
    D) Vinegar
  13. Which salt is used in cooking?
    A) CaCO₃
    B) NaCl
    C) KNO₃
    D) NaOH
  14. Which substance is used as antacid?
    A) HCl
    B) NaOH
    C) Mg(OH)₂
    D) H₂SO₄
  15. Which acid is present in vinegar?
    A) Citric acid
    B) Acetic acid
    C) Lactic acid
    D) Formic acid

26–40: Application-Based Questions

  1. Why should acids be diluted before use?
    A) To increase strength
    B) To reduce harmful effects
    C) To change color
    D) To produce gas
  2. Why does soap feel slippery?
    A) Acidic nature
    B) Basic nature
    C) Neutral nature
    D) Salty nature
  3. Why are antacids used?
    A) Increase acidity
    B) Neutralize stomach acid
    C) Produce acid
    D) Stop digestion
  4. Why is lime added to acidic soil?
    A) Increase acidity
    B) Neutralize acidity
    C) Add water
    D) Reduce salts
  5. Why does turmeric change color in base?
    A) Indicator property
    B) Chemical reaction
    C) Physical change
    D) Heating effect
  6. Which substance will turn red litmus blue?
    A) Lemon juice
    B) Vinegar
    C) Soap solution
    D) Milk
  7. Which of the following has pH close to 7?
    A) Milk
    B) Lemon juice
    C) Soap
    D) Vinegar
  8. Why should we not touch strong acids?
    A) They are cold
    B) They are corrosive
    C) They are heavy
    D) They are neutral
  9. Which of the following is used in fertilizers?
    A) KOH
    B) NaCl
    C) HCl
    D) CO₂
  10. Why is baking soda used in cooking?
    A) Acidic nature
    B) Basic nature
    C) Neutral nature
    D) Salty taste
  11. Why do acids conduct electricity?
    A) Presence of ions
    B) Presence of gas
    C) Presence of heat
    D) Presence of solids
  12. Which substance is used in car batteries?
    A) HCl
    B) H₂SO₄
    C) NaOH
    D) KOH
  13. Why does milk turn sour?
    A) Formation of acid
    B) Formation of base
    C) Evaporation
    D) Cooling
  14. Which salt is used in chalk?
    A) NaCl
    B) CaCO₃
    C) KNO₃
    D) NaOH
  15. Why is plaster of Paris used?
    A) Acidic nature
    B) Quick setting property
    C) Bitter taste
    D) Slippery feel

41–50: Higher Thinking Questions

  1. Which of the following is strongest acid?
    A) CH₃COOH
    B) HCl
    C) H₂O
    D) NaCl
  2. Which of the following is strongest base?
    A) Mg(OH)₂
    B) NaOH
    C) NH₄OH
    D) H₂O
  3. What happens when acid reacts with metal carbonate?
    A) Salt + Water
    B) Salt + CO₂ + Water
    C) Gas only
    D) No reaction
  4. Which of the following has highest pH?
    A) HCl
    B) Water
    C) NaOH
    D) Vinegar
  5. Which indicator shows no change in neutral solution?
    A) Litmus
    B) Phenolphthalein
    C) Turmeric
    D) All
  6. Why do strong acids have low pH?
    A) Less ions
    B) More H⁺ ions
    C) Less water
    D) More OH⁻ ions
  7. Which substance neutralizes acid spill?
    A) Vinegar
    B) Baking soda
    C) Lemon juice
    D) HCl
  8. Why do bases taste bitter?
    A) Chemical property
    B) Physical property
    C) Neutral property
    D) Thermal property
  9. Which is an example of neutralization?
    A) HCl + NaOH
    B) HCl + Zn
    C) NaOH + CO₂
    D) HCl + H₂O
  10. Which factor determines strength of acid/base?
    A) Color
    B) pH value
    C) Taste
    D) Shape

Answer Key (1–50)

1-B, 2-C, 3-C, 4-B, 5-B, 6-A, 7-B, 8-A, 9-B, 10-C
11-B, 12-B, 13-B, 14-B, 15-B, 16-C, 17-C, 18-C, 19-A, 20-C
21-B, 22-C, 23-B, 24-C, 25-B
26-B, 27-B, 28-B, 29-B, 30-A, 31-C, 32-A, 33-B, 34-A, 35-B
36-A, 37-B, 38-A, 39-B, 40-B
41-B, 42-B, 43-B, 44-C, 45-D, 46-B, 47-B, 48-A, 49-A, 50-B