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Q1 (Medium): A solution turns the red litmus paper to blue. Excess addition of which of the following solution would reverse the change? (i) Lime water (ii) Baking soda (iii) Vinegar (iv) Common salt solution
Answer:
We have studied that
basic substances
turn
red litmus blue
and
acidic substances
turn
blue litmus red
. This is why we need an acidic solution to reverse the change.
- Solution is basic - turns red litmus blue
- Need acidic substance to reverse the change
- Vinegar is acidic - will turn blue back to red
- Other options are basic or neutral substances
Q3 (Easy): Observe and analyse Figs. 2.13, 2.14, and 2.15, in which red rose extract paper strips are used. Label the nature of solutions present in each of the containers.
Answer:
We have studied that
red rose extract
gives
red colour
in
acidic solutions
and
green colour
in
basic solutions
. Based on the science:
- Red colour indicates acidic solution
- Green colour indicates basic solution
- No colour change indicates neutral solution
Q5 (Medium): Manya is blindfolded. She is given two unknown solutions to test and determine whether they are acidic or basic. Which indicator should Manya use to test the solutions and why?
Answer:
We have studied that
olfactory indicators
change
odour
in
acidic
or
basic
medium. This is why Manya should use smell-based indicators.
- Onion strips change odour in different solutions
- Can smell the difference without seeing
- Acidic solutions give different odour than basic
- Litmus paper needs vision to see colour
Q8 (Medium): Keerthi wrote a secret message to her grandmother on her birthday using orange juice. Can you assist her grandmother in revealing the message? Which indicator would you use to make it visible?
Answer:
We have studied that
acidic substances
like
orange juice
are
invisible
on paper but
react
with
basic indicators
. This is why we need a basic indicator spray.
- Orange juice is acidic - invisible on paper
- Spray baking soda solution (basic indicator)
- Acid-base reaction makes writing visible
- Colour change reveals the secret message
Q9 (Easy): How can natural indicators be prepared? Explain by giving an example.
Answer:
We have studied that
natural substances
like
flowers
and
vegetables
can act as
acid-base indicators
. This is why we can prepare them at home.
- Crush flower petals or vegetable pieces
- Add hot water and let it soak
- Filter the coloured liquid extract
- Test with acids and bases
Q10 (Medium): Three liquids are given to you. One is vinegar, another is a baking soda solution, and the third is a sugar solution. Can you identify them only using turmeric paper? Explain.
Answer:
We have studied that
turmeric paper
turns
red
in
basic solutions
but shows
no change
in
acidic
and
neutral
solutions. This is why we cannot identify all three.
- Baking soda (basic) - turns turmeric red
- Vinegar (acidic) - no colour change
- Sugar solution (neutral) - no colour change
- Cannot distinguish between vinegar and sugar
