Acids, Bases, and Salts form one of the most important topics in Class 7 Science. Understanding these substances is not only useful for examinations but also helps in daily life. This page provides easy notes and a complete set of questions and answers including MCQs, very short, short, and long answer types, all designed in a simple way. You can directly jump to notes or questions using the buttons given above.

Acids, Bases and Salts - Class 7 Science Notes

Introduction

Every substance around us can be classified into different groups. Among them, acids, bases, and salts are very important in chemistry. We find them in fruits, vegetables, medicines, cleaning products, fertilizers, and many other things.

Acids

  • Acids are substances that have a sour taste.
  • They turn blue litmus paper into red.
  • Acids can be natural (from plants and fruits) or synthetic (made in laboratories).

Examples of Natural Acids: Citric acid (lemon, orange), Lactic acid (curd), Tartaric acid (tamarind), Malic acid (apple).

Examples of Mineral Acids: Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3).

Bases

  • Bases have a bitter taste and a soapy feel.
  • They turn red litmus paper into blue.
  • Strong bases are also called alkalies if they are soluble in water.

Examples of Bases: Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Calcium hydroxide (lime water).

Indicators

Indicators are special substances that change their colour when added to acids or bases.

  • Litmus: Natural indicator obtained from lichens.
  • Turmeric: Turns red with bases but remains yellow with acids.
  • China rose (Hibiscus): Gives pink colour in acids and green in bases.

Neutralization Reaction

When an acid reacts with a base, both lose their properties and form a neutral product called salt and water. This process is called neutralization.

Equation: Acid + Base → Salt + Water

Salts

  • Salts are formed when acids react with bases.
  • They can be neutral, acidic, or basic in nature.
  • Common salt (NaCl) is the most widely used salt in daily life.

Uses of Acids

  • Citric acid is used in food preservation.
  • Sulphuric acid is used in car batteries.
  • Hydrochloric acid helps in digestion in our stomach.

Uses of Bases

  • Sodium hydroxide is used in making soaps.
  • Calcium hydroxide is used in whitewashing walls.
  • Magnesium hydroxide is used in medicines to reduce acidity.

Uses of Salts

  • Common salt is used in food.
  • Sodium carbonate is used in washing powder.
  • Potassium nitrate is used in fertilizers.

Daily Life Examples

  • Toothpaste is basic in nature, it neutralizes excess acid in our mouth.
  • Antacids like milk of magnesia are bases used to cure acidity.
  • Vinegar (acetic acid) is used in pickles and cooking.

Thus, acids, bases, and salts are not only important for chemistry but also for health, environment, and industries.

Acids, Bases and Salts - Questions and Answers

Multiple Choice Questions (MCQ)

  1. Lemon contains which acid?
    a) Hydrochloric acid
    b) Citric acid
    c) Nitric acid
    d) Sulphuric acid
    Answer: b) Citric acid
  2. Which indicator is obtained from lichens?
    a) Turmeric
    b) Litmus
    c) Phenolphthalein
    d) Methyl orange
    Answer: b) Litmus
  3. Which of the following is a base?
    a) NaOH
    b) HCl
    c) HNO3
    d) CH3COOH
    Answer: a) NaOH
  4. Neutralization produces:
    a) Acid only
    b) Base only
    c) Salt and water
    d) Gas
    Answer: c) Salt and water
  5. Which of these is used in whitewashing walls?
    a) NaOH
    b) Ca(OH)2
    c) KOH
    d) H2SO4
    Answer: b) Ca(OH)2
  6. Milk of magnesia is:
    a) Acid
    b) Base
    c) Salt
    d) Indicator
    Answer: b) Base
  7. Which acid is present in vinegar?
    a) Acetic acid
    b) Citric acid
    c) Lactic acid
    d) Malic acid
    Answer: a) Acetic acid

Very Short Answer Questions

  1. Name one acid found in curd.
    Answer: Lactic acid
  2. Which indicator turns red in acid?
    Answer: Blue litmus
  3. What is the taste of bases?
    Answer: Bitter
  4. Give an example of natural indicator.
    Answer: Turmeric
  5. Which acid is present in our stomach?
    Answer: Hydrochloric acid
  6. What is the chemical name of common salt?
    Answer: Sodium chloride (NaCl)
  7. Name one base used in medicine.
    Answer: Magnesium hydroxide

Short Answer Questions

  1. Define acids with two examples.
    Answer: Acids are sour-tasting substances that turn blue litmus red. Examples: Citric acid in lemon, Hydrochloric acid.
  2. What are bases? Give examples.
    Answer: Bases are bitter and soapy substances that turn red litmus blue. Example: NaOH, KOH.
  3. Explain neutralization with an equation.
    Answer: When acid reacts with base, they form salt and water. Example: HCl + NaOH → NaCl + H2O.
  4. What is an indicator? Give two examples.
    Answer: Substances that show colour change in acids or bases. Examples: Litmus, Turmeric.
  5. Why does toothpaste contain a base?
    Answer: To neutralize acids formed by bacteria in the mouth.
  6. Name two uses of salts in daily life.
    Answer: Common salt for cooking, Sodium carbonate for washing powder.
  7. Why is vinegar used in food preservation?
    Answer: Because it contains acetic acid which prevents microbial growth.

Long Answer Questions

  1. Explain the difference between acids and bases with examples.
    Answer: Acids are sour, turn blue litmus red, e.g., citric acid, HCl. Bases are bitter, soapy, and turn red litmus blue, e.g., NaOH, KOH. Both are chemically opposite in nature.
  2. What are indicators? Explain natural and synthetic indicators with examples.
    Answer: Indicators are substances used to identify acids and bases. Natural indicators: Litmus, turmeric. Synthetic indicators: Phenolphthalein, methyl orange.
  3. Explain neutralization reaction with daily life examples.
    Answer: Acid + Base → Salt + Water. Example: Antacid tablet neutralizes excess HCl in stomach. Toothpaste neutralizes acids in mouth. Lime reacts with soil acids to improve fertility.
  4. Write uses of acids, bases, and salts in detail.
    Answer: Acids: Preservatives, car batteries, digestion. Bases: Soap making, medicines, whitewashing. Salts: Cooking (NaCl), washing powder (Na2CO3), fertilizers (KNO3).
  5. Why are acids, bases, and salts important in our daily life?
    Answer: They are used in cooking, cleaning, medicine, agriculture, industry, and even in biological processes like digestion. Their correct use makes life comfortable and healthy.
  6. Describe the role of hydrochloric acid in our stomach.
    Answer: HCl helps digest food, kills harmful germs, and activates enzymes. Excess acid causes discomfort, so bases like antacids are used to neutralize it.
  7. Explain with examples how natural indicators are used at home.
    Answer: Turmeric changes red with bases, used to test soap solutions. China rose petals change pink in acids and green in bases. Such natural indicators help in simple experiments at home.