Page No 57: - Chapter 5 Acids Bases & Salts class 7 ncert solutions Science - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Question 9:

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

Answer:

We will put a drop each of hydrochloric acid, sodium hydroxide, and sugar solution on the turmeric indicator. The liquid which changes the colour of turmeric indicator to red is basic in nature, that is, sodium hydroxide.

Now, we will put a drop of sodium hydroxide on a drop of each of the other two liquids separately. After that, we will put the drops of these mixtures on turmeric indicator. The drop which will change the colour of the turmeric indicator to red contains sugar solution. This is because the mixture of basic and neutral solutions is basic in nature.

On the other hand, the drop which will not change the colour of turmeric indicator contains hydrochloric acid. This is because hydrochloric acid reacts with sodium hydroxide to form a neutral solution.

Question 10:

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

Answer:

We know that basic and neutral solutions do not change the colour of blue litmus paper. Since blue litmus remains blue after dipping in the solution, the solution is either basic or neutral in nature.

Put a drop of this solution on a red litmus paper. If it turns blue, then the above solution is basic in nature and if no colour change occurs, then it is neutral.

Question 11:

Consider the following statements:

(a) Both acids and bases change colour of all indicators.

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

(c) If an indicator changes colour with a base, it does not change colour with an acid.

(d) Change of colour in an acid and a base depends on the type of the indicator.

Which of these statements are correct?

(i) All four (ii) a and d (iii) b and c (iv) only d

Answer:

(iv) Only d is correct.