Unit Test: Exploring Substances: Acidic, Basic, and Neutral | Science (Curiosity) Class 7 - New NCERT PDF Download

Maximum Marks: 30
Attempt all questions

• Question numbers 1 to 7 carry 1 mark each.
• Question numbers 8 to 12 carry 2 marks each.
• Question numbers 13 to 15 carry 3 marks each.
• Question numbers 16 carry  4 marks each.

Q1. Which of the following substances turns blue litmus paper to red?  (1 Mark)
(i) Soap solution
(ii) Lemon juice
(iii) Sugar solution
(iv) Salt solution

​Q2. The yellow colour of turmeric paper changes to ______ in a basic solution. (1 Mark)

Q3. Which of the following is a natural acid-base indicator? (1 Mark)
(i) Vinegar
(ii) Red rose extract
(iii) Baking soda
(iv) Tap water

​Q4. What is the result of a neutralisation reaction? (1 Mark)

​Q5. Which indicator can be used to identify basic substances but not acidic ones? (1 Mark)
(i) Blue litmus
(ii) Red litmus
(iii) Turmeric paper
(iv) Red rose extract

​Q6. Substances that do not change the colour of litmus paper are called ______. (1 Mark)

​Q7. Why is moist baking soda used to relieve an ant bite? (1 Mark)
(i) It neutralises the acidic liquid
(ii) It cools the skin
(iii) It prevents infection
(iv) It reduces swelling

​Q8. Explain how red rose extract acts as an acid-base indicator. (2 Mark)

​Q9. Why is litmus considered an acid-base indicator? (2 Mark)

​Q10. How does neutralisation help in treating acidic soil? (2 Mark)

​Q11. Describe the feel and taste of basic substances. (2 Mark)

​Q12. What are olfactory indicators, and give one example? (2 Mark)

​Q13. Explain the process of preparing turmeric paper and its use as an indicator. (3 Mark)

​Q14. What is Neutralisation Reaction? Describe how neutralisation reactions are applied in daily life with two examples. (3 Mark)

​Q15. How can you identify whether a substance is acidic, basic, or neutral using indicators? (3 Mark)

Q16. Read the passage below and answer the questions that follow. (4 Mark)

Aarav and Kaira attended a science fair on National Science Day. At the entrance, they were given a white paper, which remained blank until a volunteer sprayed a liquid on it, revealing the message: "Welcome to the Wonderful World of Science." This sparked their curiosity. Later at the ‘Colourful World of Substances’ stall, they discovered natural indicators like turmeric, red rose extract, and litmus paper being used to test substances such as lemon juice, baking soda, and soap solution.
They decided to recreate the magic message at home. Aarav coated a card with turmeric paste and let it dry. Kaira used a cotton bud dipped in a solution to write on it. When they sprayed another solution over the card, the message turned dark red!
Answer the following:
(a) Name the two solutions likely used for writing the message and for spraying the card.
(b) Why did the message turn red only after spraying?
(c) What does this activity demonstrate about turmeric?
(d) Is turmeric a suitable indicator for all substances? Explain briefly.

You can access the solutions to this Unit Test here.