NCERT Class VII Science Solutions: Chapter 5-Acids, Bases and Salts Part 2

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Question 4:

Is the distilled water acidic/basic/neutral? How would you verify it?

Answer:

Distilled water is neutral by nature. We can verify it by litmus test. Water does not change the colour of either red or blue litmus.

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Distilled Water Acid or Base How to Verify

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Question 5:

Describe the process of neutralization with the help of an example.

Answer:

When an acid solution and a base solution are mixed in suitable amounts, both the acidic nature of the acid and the basic nature of the base are destroyed. The resulting solution is neither acidic nor basic, it become neutral. This process is known as neutralization reaction.

Fill one fourth of a test tube with dilute hydrochloric acid and add few drop of litmus solution. Now the colour of the solutions become red. Now add to this acidic solution drops of sodium hydroxide solution gradually one by one with a dropper. Stir the tube gently. Continue adding the sodium hydroxide solution drop by drop while stirring till the colour just become green. Now the effect of hydrochloric acid is neutralized by the base sodium hydroxide.

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Describe the Process of Neutralisation

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Question 6:

Mark ‘T’ if the statement is true and ‘F’ if it is false:

  1. Nitric acid turn red litmus blue. (T/F)

  2. Sodium hydroxide turns blue litmus red. (T/F)

  3. Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)

  4. Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)

  5. Tooth decay is caused by the presence of a base. (T/F)

Answer:

  1. Nitric acid turn red litmus blue. (False)

  2. Sodium hydroxide turns blue litmus red. (False)

  3. Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (True)

  4. Indicator is a substance which shows different colours in acidic and basic solutions. (True)

  5. Tooth decay is caused by the presence of a base. (False)