Let's solve the worksheet step by step and explain each answer.
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I. Fill in the blanks:
1)
Acids are _______ in taste and ______ in nature.
✔ Answer: *Sour, acidic*
Explanation: Acids have a sour taste (e.g., lemon juice) and are acidic in nature.
2)
The most commonly used natural indicator is _______.
✔ Answer: *Litmus*
Explanation: Litmus is a natural dye extracted from lichens and is widely used to test acidity or basicity. It turns red in acids and blue in bases.
3)
Aqueous solution of baking soda is bitter in taste and feels soapy on touching because it contains _______.
✔ Answer: *Base* (or *basic substance*)
Explanation: Baking soda (sodium bicarbonate) is a base. Bases are bitter in taste and feel slippery or soapy.
4)
China rose indicator turns acidic solution to _______ and basic solution to _______.
✔ Answer: *Dark pink / magenta, green*
Explanation: China rose (Hibiscus flower) extract acts as a natural indicator. It turns
dark pink/magenta in acidic solutions and
green in basic solutions.
5)
_______ are used to test whether a substance is acidic or basic in nature.
✔ Answer: *Indicators*
Explanation: Indicators are substances that change color depending on the pH of the solution — they help determine if a substance is acidic or basic.
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II. Choose the correct answer:
1)
What is the color change observed when phenolphthalein indicator is added to acidic solution?
a) pink
b) green
c) red
d) colorless
✔
✔ Correct Answer: d) colorless
Explanation: Phenolphthalein is a common acid-base indicator. It remains
colorless in acidic solutions and turns
pink in basic solutions.
2)
Neutralization reaction is a _________.
a) physical and reversible change
b) physical and irreversible change
c) chemical and reversible change
d) chemical and irreversible change
✔
✔ Correct Answer: d) chemical and irreversible change
Explanation: A neutralization reaction occurs when an acid reacts with a base to form salt and water. This is a
chemical change because new substances are formed. It is generally
irreversible under normal conditions.
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✔ Final Answers Summary:
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I. Fill in the blanks:
1) Sour, acidic
2) Litmus
3) Base
4) Dark pink / magenta, green
5) Indicators
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II. Choose the correct answer:
1) d) colorless
2) d) chemical and irreversible change
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This worksheet tests foundational knowledge about acids, bases, indicators, and neutralization reactions — key concepts in Grade 7 science. Let me know if you'd like a printable version or explanation in simpler terms!
Parent Tip: Review the logic above to help your child master the concept of acids bases and salts worksheets.
