Acids, Bases and Salts Class 7 Science Notes - Chapter 5

Substances that taste sour in water solutions are called acids. For example, mineral acids, phosphoric acids, etc. Some properties of acids are as follows –

  • They change the color of a few indicators. The blue litmus paper turns red
  • They liberate hydrogen on reacting with some metals such as iron
  • They form salts on reacting with bases
  • Acid catalysis – they encourage definite chemical reactions

Substances that taste bitter in water solution are called bases. These substances produce hydroxide ions. For example, hydroxides of alkali and alkaline earth metals, ammonia water solutions, etc. Some properties of bases are as follows –

  • Slippery to touch
  • They can change the color of a few indicators. The red litmus paper turns blue
  • Formation of salts when reacted with acids
  • Base catalysis – enhances chemical reactions

Acids Bases And Salts Class 7 Questions

  1. Distinguish between bases and salts.
  2. Distilled water is ______________ (basic/acidic/neutral)
  3. When blue litmus paper is dipped in a solution and still remains blue, then can you tell the nature of solution? Explain in detail.
  4. Which tablet is taken to stop suffering from acidity? Why?
  5. How to verify if the distilled water is neutral or acidic or basic?
  6. Which solution is applied to the skin when there is an ant bite? Why?
  7. Answer the following saying true or false-
    • Nitric acid does not turn red litmus paper blue.
    • Presence of base causes tooth decay.

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