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NCERT Solutions Curiosity Chapter 2 –19Section 2.3 Neutralisation in Daily Life, and Let us wrap up! — In-text Questions

Book page 18 Updated on2026-09-05

Q1.
Situation 1: Keerthi was observing a butterfly in the garden with her hand resting on a tree trunk. Suddenly, a red ant bit her, leaving her skin red with stinging pain (Fig. 2.11). Her brother helped her by applying moist baking soda to the affected area, which relieved the pain. What do you think might be the reason for this?
Answer

The ant bite injects an acid, and the baking soda is a base that neutralises it.

Ant bite → injects formic acid into the skin → burning, stinging pain
Moist baking soda (a base) rubbed on
→ neutralisation → acid destroyed → pain relieved
Why it must be moist baking soda: dry powder just sits on the skin. Water lets the baking soda spread into the bitten spot and actually reach the acid. This is the same neutralisation reaction as Activity 2.7 — only here the acid is under your skin instead of in a test tube.
Tip: wash the spot with plenty of water first. Do not scratch it — scratching pushes the acid deeper and can cause an infection.
Q2.
What remedies do people use to treat ant bites in your region?
Answer

Most traditional remedies turn out to be either a base that neutralises the acid or something that soothes the swelling.

Common remedyWhat it isHow it helps
Moist baking soda pasteBasicNeutralises the formic acid
Lime (chuna) pasteBasicNeutralises the acid; used in many villages
ToothpasteMildly basicNeutralises and cools
Calamine lotionContains zinc carbonate, a baseNeutralises and soothes
Ice or cold waterNeutralDoes not neutralise, but numbs the pain and reduces swelling

Sample answer: "In my area people rub moist baking soda or a little chuna on an ant bite, and elders sometimes press a crushed tulsi leaf on it."

Why acids are not used: lemon juice or vinegar on an ant bite would add more acid to the acid already there and make the sting worse. The remedy must be the opposite of the problem.
Q3.
Situation 2: On the Farmer’s Portal (an online platform from the Department of Agriculture, Cooperation and Farmers Welfare), a query from a farmer states, “My plants are not growing well lately”. After a detailed discussion, it was found that the excessive use of chemical fertilisers (substances added to soil to help plants grow better) made the soil acidic. What remedy might be provided to him?
Answer

Treat the field with lime, which is a base (Fig. 2.12). The lime neutralises the excess acid and brings the soil back towards neutral, after which the plants grow well again.

Excess chemical fertilisers → soil becomes acidic → poor plant growth
Add lime (a base) → neutralisation → soil fit for plants again

The chapter also gives the opposite case: if the soil is basic, organic matter such as manure and composted leaves is added — organic matter releases acids that neutralise the basic nature of the soil.

Why acidic soil hurts plants: roots can only take up nutrients from the soil water within a certain range of conditions. Too much acid locks the nutrients up, so the plant starves even though the food is right there in the soil.
Did you know? The chapter adds a third possibility — the soil may be perfectly neutral and the plants still unhealthy. That points to a deficiency of nutrients, not to acid or base at all. Always test before you treat.
Q4.
Situation 3: Ashwin’s friend Gurbir stays near an industrial area. He shared with him that the fish population in his neighbourhood lake was declining day by day! What do you think might be the causes for this?
Answer

The most likely cause is factory waste being released into the lake.

  • If the waste is acidic or basic, it changes the nature of the lake water. Fish can survive only in water that is close to neutral.
  • The waste may also make the water dirty and cut down the oxygen dissolved in it.
  • Other everyday causes worth mentioning: sewage from houses, and fertiliser washed off nearby fields into the lake.
Why fish are the first to suffer: a fish lives with the water constantly passing over its gills. Anything harmful in the lake reaches its blood within minutes — it cannot walk away from a polluted patch as a land animal can.
Q5.
If the factory waste is acidic in nature, what could be done to save the fish in the lake?
Answer

Neutralise the waste before it is released. Basic substances are added to the acidic factory waste in a treatment tank, and only after it has become neutral is it allowed into the lake.

Acidic factory waste
+ basic substance (for example lime)
→ neutralisation → waste becomes neutral
→ only then released into the lake
Why treat it at the factory and not in the lake: the waste is concentrated and small in volume at the outlet pipe, so a manageable amount of base can fix it. Once it has spread through a whole lake, no practical quantity of base could reach every part of it — and the fish would already be dead. Treating pollution at its source is always cheaper and kinder than cleaning it up afterwards.
Q6.
Let us wrap up! Now, can you explain why the words ‘Welcome to the Wonderful World of Science’ appeared on Ashwin and Keerthi’s paper sheets when the liquid was sprayed on them? Do you think that one possibility could be using a turmeric solution for the spraying liquid and a soap solution for writing on the paper?
Answer

Yes — that is exactly how the trick works, and it is nothing but the turmeric indicator used cleverly.

  1. The message was written on the white sheet beforehand with a soap solution (basic) and allowed to dry. Dry soap solution on white paper is practically invisible.
  2. At the gate the volunteer sprayed a turmeric solution on the sheet. The whole sheet turned pale yellow.
  3. Wherever the turmeric met the dried base, it turned red. So the letters appeared in red on a yellow background.
Invisible writing = soap solution (base), dried
Spray = turmeric solution (indicator)
Turmeric + base → red
→ the message appears
Why the writing is invisible before spraying: a colourless liquid dried on white paper reflects light almost exactly like the paper itself. Nothing coloured is on the sheet until the indicator arrives and creates the colour on the spot.
Try This: swap the two around — write with turmeric solution and spray with soap solution. The message still appears in red, because it is the meeting of base and turmeric that makes the colour, not the order in which they arrive.
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