NCERT Class VII Science Solutions: Chapter 5-Acids, Bases and Salts Part 4

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Question 9:

Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.

Answer:

Turmeric is yellow in colour. When a base is added to it, the solution turns into pink colour. However turmeric remains yellow when an acid or neutral solution is added to it. We shall perform the following steps to identify the solution is base, acid or neutral.

  • Take few drops from each solution and test it with turmeric solution. If the solution turns into pink colour that solution is base i.e. Sodium Hydroxide. Mark that beaker (containing solution) as base.

  • Take a test tube and add few drops of base solution and second solution. Check if test tube becomes warm and then add turmeric solution to it. If the colour does not change, it means the solution added is acidic (HCl). The test tube becomes warm due to neutralization.

  • If the test tube of the above solution does not warm and it does show pink colour when turmeric is added, the second solution is neutral.

Question 10:

Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

Answer:

If a blue litmus paper when dipped in a solution, remains blue, it implies the solution is either basic or neutral.

As showing in images is a result for Blue litmus paper is di …

Blue Litmus Paper is Dipped in a Solution

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Question 11:

Consider the following statements:

  1. Both acids and bases change colour of all indicators.

  2. If an indicator gives a colour change with an acid, it does not give a change with a base.

  3. If an indicator changes colour with a base, it does not change colour with an acid.

  4. Change of colour in an acid and a base depends on the type of the indicator.

Which of these statements are correct?

  1. All four

  2. a and d

  3. b and c

  4. only d

Answer:

D. only d