At Bodhiclasses, we believe that learning is not just about acquiring information—it’s about awakening the mind. Rooted in the values of curiosity, clarity, and connection, Bodhiclasses is more than an educational platform; it’s a space where knowledge is nurtured with care and presented with purpose. This chapter introduces students to the concept of Exploring Substances – acids, bases, and neutral substances, along with the use of indicators to test their nature. It includes real-life applications of neutralisation reactions in everyday scenarios such as soil treatment, ant bites, and industrial waste management. This post deals with some sample practice questions that the students can practice for greater clarity.
Practice Questions
Subject: Science | Chapter: 2 | Board: NCERT | Grade: 7
Category: Important Questions | Sample Paper | Worksheet | Practice Questions
Multiple Choice Questions (MCQs): Exploring Substances
1. Which substance turns blue litmus paper red?
A) Baking soda
B) Vinegar
C) Soap solution
D) Lime water
Answer: B) Vinegar
2. Red litmus paper turns blue in the presence of a:
A) Neutral solution
B) Basic solution
C) Acidic solution
D) Salt solution
Answer: B) Basic solution
3. Turmeric turns red when mixed with:
A) Acid
B) Neutral substance
C) Base
D) Water
Answer: C) Base
4. What is formed in a neutralisation reaction?
A) Salt and water
B) Acid only
C) Base only
D) Only heat
Answer: A) Salt and water
5. Which of the following is a natural indicator?
A) Phenolphthalein
B) Methyl orange
C) Litmus
D) Hydrochloric acid
Answer: C) Litmus
6. Onion acts as a/an:
A) Olfactory indicator
B) Synthetic indicator
C) Basic solution
D) Neutraliser
Answer: A) Olfactory indicator
7. Which of the following is acidic in nature?
A) Soap solution
B) Lemon juice
C) Salt solution
D) Lime water
Answer: B) Lemon juice
8. Baking soda is:
A) Neutral
B) Acidic
C) Basic
D) Neither
Answer: C) Basic
9. Which indicator gives green colour in a basic solution?
A) Turmeric
B) Blue litmus
C) Red rose extract
D) Sugar solution
Answer: C) Red rose extract
10. The neutralisation of factory waste before releasing into rivers is an example of:
A) Experiment
B) Natural process
C) Pollution
D) Application of neutralisation
Answer: D) Application of neutralisation
One Mark Questions (Very Short Answer Type): Exploring Substances
1. What colour does turmeric paper turn in basic solution?
Answer: Reddish-brown
2. Name one natural indicator.
Answer: Litmus
3. What is the taste of acidic substances?
Answer: Sour
4. What is the nature of soap solution?
Answer: Basic
5. Which part of red rose is used for preparing an indicator?
Answer: Petals
6. What is formed when an acid reacts with a base?
Answer: Salt and water
7. Name a base used to neutralise acidic soil.
Answer: Lime (calcium oxide)
8. What does a neutral substance do to litmus paper?
Answer: It causes no colour change.
9. What type of indicator is onion?
Answer: Olfactory indicator
10. Name a substance that remains yellow with turmeric.
Answer: Vinegar (acidic)
Two Marks Questions (Short Answer Type): Exploring Substances
1. Define neutralisation reaction with an example.
Answer: A neutralisation reaction is the chemical reaction between an acid and a base to form salt and water with the release of heat.
Example: Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water
2. What is the function of indicators in chemistry?
Answer: Indicators help determine whether a substance is acidic, basic, or neutral by changing their colour based on the chemical nature of the substance.
3. Write two uses of neutralisation reactions in daily life.
Answer:
- Treating ant bites using baking soda.
- Neutralising acidic soil with lime for better crop growth.
4. Why should turmeric not be used to test acids?
Answer: Turmeric does not change colour in acidic or neutral solutions, so it cannot differentiate them.
5. Give two differences between acids and bases.
Answer:
- Acids taste sour, bases taste bitter.
- Acids turn blue litmus red; bases turn red litmus blue.
6. How is turmeric paper prepared?
Answer: Turmeric paste is applied on filter paper, dried, and cut into strips to make turmeric paper.
7. Mention the nature of vinegar and baking soda.
Answer: Vinegar is acidic; baking soda is basic.
8. Why is neutralisation called an exothermic reaction?
Answer: Because it releases heat along with salt and water.
9. What happens when an acid is added to lime water?
Answer: The basic nature of lime water is neutralised, and the solution becomes less alkaline.
10. What is the colour of red rose extract in acidic and basic media?
Answer: Red in acidic solution; green in basic solution.
Higher Order Thinking Skills (HOTS) Questions
1. A farmer’s field shows poor growth due to acidic soil. Suggest a method to test and treat it.
Answer: Use red cabbage extract or litmus to test the soil’s pH. If acidic, treat with lime (a base) to neutralise the soil and improve fertility.
2. Ashwin spilled curry on his shirt, and the stain turned reddish-brown when washed with soap. Explain the reason.
Answer: Turmeric in curry acts as a natural indicator. When soap (a base) is applied, the turmeric turns red due to the basic reaction.
3. How can you test an unknown liquid using only turmeric paper and red rose extract?
Answer:
- If turmeric paper turns red → Basic
- If red rose extract turns green → Basic
- If no change in turmeric, but red rose extract turns red → Acidic
- No change in either → Neutral
4. Why are factory wastes neutralised before discharge into water bodies?
Answer: Because acidic waste can kill aquatic life and pollute the environment. Neutralisation with basic substances helps reduce environmental harm.
5. Devise a science fair experiment to demonstrate invisible ink using acid-base indicators.
Answer:
- Write on white paper using soap solution (basic).
- Spray turmeric solution.
- The message will appear red due to the base-indicator reaction.
This demonstrates neutralisation and indicator use in a creative way.
