NCERT Solutions Curiosity Chapter 2 –13Section 2.1.2 — Activity 2.4: Let us find out

Book page 12 Updated on2026-09-05

Q1.

Add 20 – 30 drops of lemon juice in test tube A and 20 – 30 drops of soap solution in test tube B with the help of droppers. Observe and record any colour changes (Fig. 2.8) to the extract in Table 2.3.

Answer

The two test tubes end up looking completely different, exactly as in Fig. 2.8.

Test tube A (lemon juice): the extract turns a clear red.
Test tube B (soap solution): the extract turns green.

Repeating with the other samples of Activity 2.1 fills in Table 2.3.

S.No.	Name of the sample	The colour of the red rose extract after adding the sample	Nature of the substance
1.	Lemon juice	Red	Acidic
2.	Soap solution	Green	Basic
3.	Amla juice	Red	Acidic
4.	Tamarind water	Red	Acidic
5.	Vinegar	Red	Acidic
6.	Baking soda solution	Green	Basic
7.	Lime water	Green	Basic
8.	Tap water	No change	Neutral
9.	Washing powder solution	Green	Basic
10.	Sugar solution	No change	Neutral
11.	Salt solution	No change	Neutral

Tip: use the same number of drops of extract in every tube. If one tube has more extract than another, the shades cannot be compared fairly.

Q2.

Are the samples that change the colour of the flower extract to a shade of red the same as those that changed the colour of blue litmus paper to red? (Group A, Table 2.2)

Answer

Yes — exactly the same set: lemon juice, amla juice, tamarind water and vinegar, that is, all of Group A.

Why it happens: both dyes are reporting the same thing — the presence of an acid. Litmus reports it by going from blue to red; rose extract reports it by going red. Two different indicators, one and the same property.

Q3.

Are the samples that change the colour of the flower extract to a shade of green the same as those that changed the colour of red litmus paper to blue? (Group B, Table 2.2)

Answer

Yes — soap solution, baking soda solution, lime water and washing powder solution, that is, all of Group B.

Why it happens: these four contain bases. Red litmus answers "base" by turning blue; the rose extract answers "base" by turning green. The colours differ but the message is identical.

Q4.

Are the samples that do not change the colour of the flower extract the same as those that did not change the colour of red and blue litmus papers? (Group C, Table 2.2)

Answer

Yes — tap water, sugar solution and salt solution, that is, all of Group C.

Why it happens: these are neutral. Having neither acid nor base, they give an indicator nothing to respond to, so the rose extract keeps its original pink-red shade just as the litmus papers kept their original colours.

What the three answers together prove: an indicator is not magic tied to one particular dye. Any acid-base indicator sorts the same eleven samples into the same three groups — which is why the red rose extract is a genuine acid-base indicator.

Q5.

Can you now fill in the nature of the substances in Table 2.3?

Answer

Yes — read the colour and write the nature straight off it.

Red rose extract turns red → the substance is acidic
Red rose extract turns green → the substance is basic
Red rose extract shows no change → the substance is neutral

Applying the rule: lemon juice, amla juice, tamarind water and vinegar are acidic; soap solution, baking soda solution, lime water and washing powder solution are basic; tap water, sugar solution and salt solution are neutral. The completed column is shown in the table of Q1 above.

Why the red rose extract is better than turmeric here: it gives three distinguishable results, so it can separate all three natures. Turmeric paper, as you will see in Activity 2.5, gives only two and cannot tell an acid from a neutral substance.

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