Class 7 Science Chapter 2 Test Paper (40 Marks) – Acidic, Basic and Neutral Substances | USP

Class 7 Science Chapter 2 Test Paper – Exploring Substances: Acidic, Basic and Neutral | USP Indore

This is a competency-based test paper for Class 7 Science Chapter 2 – Exploring Substances: Acidic, Basic and Neutral, prepared by Unique Study Point (USP), Indore. The paper carries 40 marks with a time limit of 1.5 hours, and is based on the NCERT Curiosity textbook (Session 2026-27). All questions are application-based and scenario-driven, testing real understanding of acids, bases, and neutral substances.

Test Paper Structure — At a Glance

• 📘 Section A – MCQ: 10 Questions × 1 Mark = 10 Marks
• 📗 Section B – Short Answer (2 Marks): 4 Questions × 2 Marks = 8 Marks
• 📙 Section C – Short Answer (3 Marks): 3 Questions × 3 Marks = 9 Marks
• 📕 Section D – Long Answer: 1 Question × 5 Marks = 5 Marks
• 📓 Section E – Case Study: 2 Case Studies × 4 Marks = 8 Marks
• ⏱️ Total: 40 Marks | Time: 1.5 Hours

Topics Covered in This Test Paper

• Acids, Bases, and Neutral Substances – properties and examples
• Natural Indicators – Litmus, Turmeric, Red Rose Extract, Red Hibiscus, Purple Cabbage, Onion (olfactory indicator)
• Litmus Test – Blue litmus paper, Red litmus paper; colour changes in acidic and basic solutions
• Turmeric as an indicator – yellow in acid/neutral, red in base
• Red Rose Extract – red in acidic, green in basic solution
• Neutralisation Reaction – Acid + Base → Salt + Water + Heat
• Real-life applications: Bee sting, Ant bite, Soil treatment, Factory waste treatment
• Hydrangea flower colour change (blue in acidic soil, pink in basic soil)
• Secret Message Activity using turmeric paper
• Acid-Base reaction with marble (calcium carbonate + vinegar → CO₂)
• Antacids and stomach acidity (HCl + base → neutralisation)
• Soil pH management for farming – acidic soil vs basic soil treatment

Section-wise Question Summary

Section A – MCQ Questions (Scenario-Based)

Q1. Lemon juice on blue litmus paper — colour change observed.
Q2. Soapy, slippery feeling of water — nature of the substance.
Q3. Turmeric paste turning red with detergent — what does it indicate?
Q4. Hydrangea flowers — acidic vs basic soil treatment to change flower colour.
Q5. Purple cabbage extract colour with unknown liquid — identifying acidic/basic.
Q6. Neutralisation reaction equation — Acid + Base → ?
Q7. Bee sting relief — which substance to apply and why.
Q8. Turmeric paper colour change with unknown solution — nature of solution.
Q9. Which is NOT a natural acid-base indicator?
Q10. Litmus test on four liquids P, Q, R, S — identifying the basic liquids.

Section B – Short Answer Questions (2 Marks Each)

Q11. Why is a base used to treat both ant bite and bee sting? Are both the same type of acid?
Q12. Predict the colour of red rose extract with tap water — justify with reasoning.
Q13. Acidic soil vs basic soil — what should each farmer add to restore healthy soil?
Q14. Identifying vinegar vs baking soda solution using onion strips (olfactory indicator) — blindfolded test.

Section C – Short Answer Questions (3 Marks Each)

Q15. Three liquids (lemon, washing powder, tap water) — identifying all using only litmus paper and turmeric paper; can turmeric alone identify all three?
Q16. Lake polluted by acidic factory waste — method to treat water, type of reaction, general equation.
Q17. Lemon juice + blue litmus → colour change; lime water added drop by drop → neutralisation observed; one extra drop of lemon juice added at end — predict and explain all colour changes.

Section D – Long Answer Question (5 Marks)

Q18. Secret Message activity using turmeric-coated paper — which writing solutions make messages visible; why some messages appear and others don\'t; effect of spraying lemon juice instead of water; two alternative natural indicators; can turmeric alone distinguish acidic, basic, and neutral substances?

Section E – Case Study Questions (4 Marks Each)

Case Study 1 (Aman – Marble and Vinegar):
Q19a. Nature of vinegar and soap solution based on reaction with marble.
Q19b. Antacid neutralising stomach HCl — type of reaction and general equation.
Q19c. Baking soda added to lemon juice before marble — why no bubbles?
Q19d. Harm of acidic factory waste in rivers — treatment process and substance used.

Case Study 2 (Nandini – Hydrangea and Soil Testing):
Q20a. Nature of garden soil based on red rose extract (green) and turmeric paper (red) results.
Q20b. Effect of adding lime to soil — type of reaction; colour of hydrangea after treatment.
Q20c. Growing tea plants (need acidic soil) — lime or manure? Why?
Q20d. Nandini tests four soil samples with turmeric — is her conclusion about all being basic correct?

Key Concepts Tested in This Paper

• Acid: Tastes sour, turns blue litmus red, turns red rose extract red, no effect on turmeric. Examples: Lemon juice, vinegar, tamarind water, formic acid (ant sting).
• Base: Feels slippery, turns red litmus blue, turns turmeric red, turns red rose extract green. Examples: Baking soda, soap solution, lime water, washing powder.
• Neutral: No change in litmus, turmeric stays yellow. Examples: Tap water, salt solution, sugar solution.
• Neutralisation: Acid + Base → Salt + Water + Heat. Used in ant/bee sting treatment, antacids, soil correction, and factory waste treatment.
• Turmeric limitation: Cannot distinguish between acidic and neutral substances — both keep turmeric yellow. Only litmus or other indicators can make this distinction.
• Olfactory Indicator: Onion — smell changes in acidic and basic conditions.

Important FAQs – Class 7 Science Chapter 2

Q. What is an indicator in chemistry?
Ans. An indicator is a substance that changes colour in the presence of an acid or a base, helping us identify the nature of a solution. Common indicators include litmus, turmeric, red rose extract, and red hibiscus extract.

Q. What happens when turmeric paper is dipped in a basic solution?
Ans. Turmeric paper turns red when it comes in contact with a basic solution (like baking soda or soap solution). It stays yellow with acidic and neutral solutions. This is why turmeric alone cannot distinguish between acidic and neutral substances.

Q. Why is baking soda applied on a bee sting?
Ans. A bee sting introduces an acid (called melittin) into the skin. Baking soda is a mild base (sodium bicarbonate) that neutralises the acid, providing relief from pain and swelling. This is a practical example of a neutralisation reaction.

Q. What is the general equation for neutralisation?
Ans. Acid + Base → Salt + Water + Heat. This reaction results in the formation of a neutral solution (or near-neutral). It is used in antacids, soil treatment, and industrial waste neutralisation.

Q. Why do hydrangea flowers change colour based on soil type?
Ans. Hydrangea flowers turn blue in acidic soil and pink or red in basic soil. This happens because the soil\'s nature affects how the plant absorbs certain minerals, which in turn changes the pigment colour of the flowers.

Q. Can turmeric distinguish between all three types of substances?
Ans. No. Turmeric turns red only in basic solutions. It stays yellow for both acidic and neutral solutions. Therefore, turmeric alone cannot distinguish between acidic and neutral substances. Litmus paper is needed for complete identification.

About Unique Study Point (USP), Indore

Unique Study Point (USP) is a trusted coaching institute in Amitesh Nagar, Indore, Madhya Pradesh, offering quality education for Classes VI to X in Mathematics, Science, and Social Science. All study materials are prepared by experienced educators and strictly follow the latest CBSE-NCERT Curiosity syllabus 2026-27.

📍 Amitesh Nagar, Indore, M.P.  |  📞 8103405051  |  🌐 uniquestudyonline.com