Let’s go step by step to solve each question.
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I. Fill in the blanks:
1)
Acids are _______ in taste and _______ in nature.
→ Acids taste sour (like lemon or vinegar). They turn blue litmus red — that means they are acidic in nature.
✔ Answer: *sour, acidic*
2)
The most commonly used natural indicator is _______.
→ Natural indicators come from plants. The most common one taught in school is litmus (from lichens), but sometimes turmeric or china rose are also mentioned. However, “litmus” is the most standard answer for this level.
✔ Answer: *litmus*
3)
Aqueous solution of baking soda is bitter in taste and feels soapy on touching because it contains _______.
→ Baking soda is sodium bicarbonate. When dissolved in water, it forms a basic solution. Bases feel soapy and taste bitter. So, it contains *base* or more specifically, *hydroxide ions* — but at Grade 7 level, we say it contains *base*.
✔ Answer: *base*
4)
China rose indicator turns acidic solution to _______ and basic solution to _______.
→ China rose (hibiscus) juice is a natural indicator. In acid → dark pink/magenta. In base → green.
✔ Answer: *dark pink, green*
5)
_______ are used to test whether a substance is acidic or basic in nature.
→ These are called indicators — like litmus, phenolphthalein, etc.
✔ Answer: *Indicators*
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II. Choose the correct answer:
1)
What is the color change observed when phenolphthalein indicator is added to acidic solution?
→ Phenolphthalein is colorless in acid and pink in base. So in acidic solution, it stays colorless.
Options:
a) pink → no, that’s in base
b) green → not related
c) red → no
d) colorless → YES
✔ Correct answer: *d) colorless*
2)
Neutralization reaction is a ________.
→ Neutralization is when acid + base → salt + water. It’s a chemical reaction (new substances formed) and it cannot be easily reversed — so irreversible.
Options:
a) physical and reversible → no
b) physical and irreversible → no, it’s chemical
c) chemical and reversible → no, not reversible
d) chemical and irreversible → YES
✔ Correct answer: *d) chemical and irreversible change*
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Final Answer:
I. Fill in the blanks:
1) sour, acidic
2) litmus
3) base
4) dark pink, green
5) Indicators
II. Choose the correct answer:
1) d) colorless
2) d) chemical and irreversible change
Parent Tip: Review the logic above to help your child master the concept of acids bases and salts worksheet.
