To Exploring Substances Acidic, Basic and Neutral

Acids · Bases · Indicators

Q1.

A solution turns red litmus paper blue. Which of the following will reverse the change?

• (i) Lime water
• (ii) Baking soda
• (iii) Vinegar
• (iv) Common salt solution

✅ Answer: (iii) Vinegar
Vinegar is an acid; it turns blue litmus back to red, so the solution is no longer basic.

Q2.

Three solutions A, B, and C are tested using indicators. Choose the correct option:

• A turns blue with red litmus.
• B turns red with turmeric.
• C turns green with rose extract.

• (i) Acidic, acidic, and acidic
• (ii) Neutral, basic, and basic
• (iii) Basic, basic, and acidic
• (iv) Basic, basic, and basic

✅ Answer: (iv) Basic, basic, and basic
A is basic (litmus → blue), B is basic (turmeric reddens in base), C is basic (rose extract turns green in base).

Q3.

Observe Figs. 2.13 – 2.15 and label the nature of each solution.

• Fig 2.13 → Green → Basic
• Fig 2.14 → No change → Neutral
• Fig 2.15 → Red → Acidic

Red-rose extract acts like pH paper: green = base, red = acid, no change = neutral.

Q4.

A liquid sample is tested with various indicators. Determine its nature.

Indicator	Red Litmus	Blue Litmus	Turmeric
Observation	No change	Turned red	No change

✅ Conclusion: Blue litmus turning red signals an acid. No change in other indicators confirms it.

Q5.

Manya is blindfolded and must classify two solutions. Which indicator should she use and why?

She should choose vanilla essence, an olfactory indicator.
• In an acidic solution the vanilla smell stays strong.
• In a basic solution the smell fades.
Since she cannot see colour changes, the scent guides her.

Q6.

Suggest materials for writing hidden messages and what could be in the spray bottle.

• Invisible inks: lemon juice, vinegar, or milk.
• Spray bottle: red-cabbage juice, iodine solution, or simply warm air/heat to reveal the writing.

Q7.

What happens if baking soda is added to a red grape-juice & rose-extract mix?

Baking soda (a base) neutralises the acids, shifting the reddish tint to green/blue.

Q8.

Keerthi wrote a secret note using orange juice. How can it be revealed?

Gently heat the paper. Sugars in orange juice caramelise and turn brown, making the message visible.

Q9.

How can natural indicators be prepared? Give one example.

Crush rose petals or purple-cabbage leaves in warm water, filter the coloured liquid, and use it as a natural pH indicator.

Q10.

You have vinegar, baking soda, and sugar solution. Explain how turmeric paper will identify them.

Turmeric paper turns red-brown only with baking soda (base).
No colour change with vinegar (acid) or sugar solution (neutral).

Q11.

Red-cabbage extract is added to liquid X and it turns green. Predict the nature of X and the effect of excess amla juice.

• Green means liquid X is basic.
• Adding amla juice (acid) neutralises it; the extract shifts back toward purple/red.

Q12.

Complete the flow chart for diagnosing soil health in a garden.

Garden Plants Showing Poor Health
Test Soil	Indicator Options	Turmeric, litmus, or red-cabbage extract
	Result → Soil Nature	Acidic → treat with lime / ash Basic → treat with organic compost / mild acid