Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral (The Remarkable Power)

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Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

Conceptual Understanding Based Questions

  1. MCQ: Litmus, a common acid-base indicator, is a natural substance extracted from which of the following organisms?
  1. Red roses
  2. Lichens
  3. Turmeric
  4. Onions

Assertion (A): Substances like sugar solution and salt solution are classified as neutral.

Reason (R): These substances do not change the colour of either red or blue litmus paper.

  1. Both A and R are factually correct, and R provides the precise logical explanation for A.
  2. A is true and R is also true, but R does not logically justify or clarify A.
  3. Assertion A holds true; however, the reason given in R is factually incorrect.
  4. Assertion A is not valid, but the statement in Reason R is accurate.
  1. Short Answer: Define an “acid-base indicator” based on its function in a laboratory setting.
  2. Short Answer: Which common household substances are acidic because they possess a sour taste?
  3. Long Answer: Explain the formation of lichens and describe the environmental conditions they require to grow.

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

Application Based Questions

  1. MCQ: If a gardener finds that their soil is too acidic and plants are not growing well, which substance should they add to neutralise it?
  1. Vinegar
  2. Organic manure
  3. Lime
  4. Amla juice

Assertion (A): Rubbing moist baking soda on an ant bite relieves stinging pain.

Reason (R): Baking soda is a base that neutralises the formic acid injected by the ant.

  1. Both A and R are factually correct, and R provides the precise logical explanation for A.
  2. A is true and R is also true, but R does not logically justify or clarify A.
  3. Assertion A holds true; however, the reason given in R is factually incorrect.
  4. Assertion A is not valid, but the statement in Reason R is accurate.
  1. Short Answer: Why does a yellow curry stain on a white shirt turn red when it is washed with soap?
  2. Short Answer: If you wanted to write a “secret message” on a paper coated with turmeric paste, what type of solution would you use to make the writing appear red?
  3. Long Answer: Describe how factory waste can affect a lake’s fish population and suggest a scientific method to prevent this damage.

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

Problem Solving & Reasoning Based Questions

  1. MCQ: A liquid sample does not change the colour of red litmus but turns blue litmus red. This liquid is:
  1. Basic
  2. Acidic
  3. Neutral
  4. A salt solution
  1. Short Answer: Three test tubes contain vinegar, baking soda solution, and sugar solution. If you only have turmeric paper, how can you identify the baking soda solution?
  2. Short Answer: When lemon juice (acid) is mixed with lime water (base) in sufficient quantity, the resulting liquid is neither acidic nor basic. What is this reaction called?
  3. Short Answer: If red rose extract turns a liquid green, what can you conclude about the nature of that liquid?
  4. Long Answer: Predict the result of adding excess amla juice to a solution that has already been turned green by red rose extract. Justify your reasoning.

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

Experimentation & Investigation Based Questions

  1. MCQ: To prepare “turmeric paper” strips for a science project, what is the correct first step?
  1. Boil turmeric in vinegar
  2. Mix turmeric with water to make a paste
  3. Dip blue litmus in turmeric powder
  4. Dry fresh turmeric in the sun for a week
  1. Short Answer: Outline the steps to prepare a red rose extract indicator without plucking fresh flowers.
  2. Short Answer: Describe how you can prepare lime water (calcium hydroxide solution) at home using “chuna”.
  3. Short Answer: How would you investigate if a specific flower from your garden can act as a natural indicator?
  4. Long Answer: Design an experiment using cotton cloth strips and chopped onions to identify whether a clear liquid is acidic or basic. Mention the name of this type of indicator.

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

Values & Awareness Based Questions

  1. MCQ: Why is it advised not to taste or touch unknown substances in the laboratory?
  1. a) They might be too salty
  2. b) They could be harmful or corrosive
  3. c) It will waste the chemical
  4. d) The teacher will get angry
  1. Short Answer: How does the work of Acharya Prafulla Chandra Ray inspire modern Indian students?
  2. Short Answer: Why did P.C. Ray advocate for using the mother tongue in education?
  3. Short Answer: In what way does using “fallen petals” for experiments (instead of plucking them) show a value for nature?
  4. Long Answer: Discuss the importance of “Neutralisation” in maintaining the balance of our environment, using the example of industrial waste.

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

Case Based Questions

  1. Case 1

At a science fair, Ashwin and Keerthi received a white paper sheet. A volunteer sprayed a liquid on it, and the words “Welcome to the Wonderful World of Science” appeared. Later, at a stall, they learned that some substances change colour when mixed with other substances. 

Question: What is the most likely reason for the hidden message appearing after spraying? 

  1. The paper was made from synthetic fibres 
  2. The spray contained a base and the paper had an acidic indicator 
  3. The spray was plain water and the paper had food colouring 
  4. The paper had turmeric paste and the spray was soap solution 
  1. Case 2

A student tested lemon juice, soap solution, and tap water using blue and red litmus papers. Lemon juice turned blue litmus red. Soap solution turned red litmus blue. Tap water did not change the colour of either litmus paper. 

Question: Which of the following correctly classifies the three substances? 

  1. Lemon juice – basic, Soap solution – acidic, Tap water – neutral 
  2. Lemon juice – acidic, Soap solution – basic, Tap water – neutral 
  3. Lemon juice – neutral, Soap solution – acidic, Tap water – basic 
  4. Lemon juice – acidic, Soap solution – neutral, Tap water – basic 
  1. Case 3

Keerthi prepared red rose extract by crushing petals in hot water and filtering. She added lemon juice to one test tube containing the extract and soap solution to another. The lemon juice turned the extract a shade of red, while the soap solution turned it green. 

Question: What can be concluded about red rose extract as an indicator? 

  1. It turns green in acids and red in bases 
  2. It shows no colour change in neutral solutions 
  3. It turns red in acids and green in bases 
  4. It can only detect bases, not acids 
  1. Case 4

While in the garden, Keerthi was bitten by a red ant. Her brother applied moist baking soda on the sting, and the pain reduced. The chapter explains that ant bites inject formic acid into the skin. 

Question: Why did applying moist baking soda relieve the pain? 

  1. Baking soda reduced the acid’s concentration.
  2. Baking soda reacted with the acid to form salt and water 
  3. Baking soda cooled the skin 
  4. Baking soda turned the acid into a gas 
  1. Case 5

Ashwin made a greeting card by applying turmeric paste on white paper and drying it. He wrote a hidden message using a solution from Table 2.4. The message became visible only when sprayed with another liquid. Turmeric paper turns red with bases but stays yellow with acids or neutrals. 

Question: Which pair of writing solution and spray liquid would reveal the message?  

  1. Writing with lemon juice, spraying with water 
  2. Writing with sugar solution, spraying with vinegar 
  3. Writing with soap solution, spraying with lime water
  4. Writing with baking soda solution, spraying with vinegar

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

Answer Key: Competency Based Worksheet

I. Conceptual:

  1. b
  2. a,
  3. Changes colour in acids/bases
  4. Lemon, Amla, Vinegar.
  5. Alga + Fungus association; needs rainfall/clean air.

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

II. Application:

  1. c
  2. a
  3. Soap is basic; Turmeric turns red in base
  4. Soap/Baking soda
  5. Acids kill fish; add basic substances to neutralise

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

III. Problem Solving:

  1. b
  2. Turmeric turns red only in base
  3. Neutralisation
  4. Basic
  5. Returns to red/neutral because amla is acidic

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

IV. Experimentation:

  1. b
  2. Crush petals, add hot water, filter
  3. Mix chuna in water, settle, filter
  4. Add extract to known acid/base
  5. Olfactory indicator; smell changes

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

V. Values:

  1. b
  2. Advancing research/pharmaceuticals
  3. Better understanding
  4. Preserving living plants
  5. Prevents pollution damage

Science Class 7 CBQ of Exploring Substances—Acidic, Basic, and Neutral

VI. Case Based:

  1. d) The paper had turmeric paste and the spray was soap solution (Turmeric turns red in basic solution; soap solution is basic)
  2. b) Lemon juice – acidic, Soap solution – basic, tap water – neutral (Acids turn blue litmus red; bases turn red litmus blue; neutrals affect neither)
  3. c) It turns red in acids and green in bases (From the PDF: “red rose extract seems to give red colour in an acidic solution and green colour in a basic solution”)
  4. b) Baking soda reacted with the acid to form salt and water (This is a neutralisation reaction: acid + base → salt + water + heat)
  5. d) Writing with baking soda solution (basic), spraying with vinegar (acidic)

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