Exploring Substances: Acidic, Basic, and Neutral teaches students how to test common substances using indicators. Lemon juice, soap solution, turmeric, red rose extract, litmus paper and baking soda become tools for identifying acids, bases and neutral substances.
Important Questions Class 7 Science Chapter 2 help students revise indicators, colour changes, neutralisation reactions and daily-life applications. The chapter is based on experiments, so strong answers must explain both the observation and the reason behind it.
Class 7 Science Chapter 2 begins at a science fair, where hidden words appear on a white sheet after a liquid is sprayed. This scene introduces the main idea of the chapter: some substances change colour when they react with acidic or basic substances.
Students learn how litmus, red rose extract, turmeric paper and onion strips help identify substances. The chapter also explains why ant bites sting, how acidic soil can affect plants, and why factory waste must be treated before release. These questions prepare students for activity-based, reasoning-based and application-based answers in school exams.
Key Takeaways from Class 7 Science Chapter 2
| Detail |
Information |
| Chapter Name |
Exploring Substances: Acidic, Basic, and Neutral |
| Class |
7 |
| Subject |
Science |
| Main Concept |
Testing substances as acidic, basic or neutral |
| Important Indicators |
Litmus, red rose extract, turmeric, onion |
| Main Reaction |
Acid + Base → Salt + Water + Heat |
| Daily-Life Uses |
Ant bite relief, soil treatment, factory waste treatment |
| Question Types |
MCQs, short answers, long answers, activity-based questions |
Important Questions Class 7 Science Chapter 2 with Answers
These questions cover the most important concepts from the chapter. Focus on colour changes, examples and the reason behind each observation.
Important Questions Class 7 Science Chapter 2: Acidic, Basic and Neutral Substances
Q1. What are acidic, basic and neutral substances?
Acidic substances turn blue litmus paper red. They usually taste sour when they are edible. Lemon juice, amla juice, tamarind water and vinegar are acidic substances.
Basic substances turn red litmus paper blue. They usually feel slippery to touch. Soap solution, baking soda solution, lime water and washing powder solution are basic substances.
Neutral substances do not change red or blue litmus paper. Tap water, sugar solution and salt solution are common examples.
Q2. What is an acid-base indicator?
An acid-base indicator is a substance that shows different colours in acidic and basic solutions.
Litmus is an acid-base indicator. It turns red in acidic solutions and blue in basic solutions. Red rose extract, turmeric and some natural substances also act as indicators.
Q3. What is litmus?
Litmus is a natural substance obtained from lichens. It is available as a solution and as paper strips.
Blue litmus paper turns red in acidic substances. Red litmus paper turns blue in basic substances. Litmus helps students identify whether a substance is acidic or basic.
Q4. Why is lemon juice acidic in nature?
Lemon juice is acidic because it contains acids such as citric acid. It turns blue litmus paper red.
Students should not identify acids only by taste. The safer method is to use indicators like litmus paper.
Q5. Why does baking soda solution feel slippery?
Baking soda solution feels slippery because it is basic in nature. Many bases feel soapy or slippery to touch.
Students should not taste or touch unknown substances during experiments. They should use indicators for testing.
Class 7 Science Chapter 2 Question Answer on Litmus Test
Litmus test questions are common because this is the first major experiment in the chapter. Students must remember the colour change clearly.
Litmus Test Class 7 Science Questions
Q1. What happens when blue litmus paper is dipped in lemon juice?
Blue litmus paper turns red in lemon juice. This shows that lemon juice is acidic in nature.
Lemon juice contains citric acid. That is why it gives a sour taste and changes blue litmus to red.
Q2. What happens when red litmus paper is dipped in soap solution?
Red litmus paper turns blue in soap solution. This shows that soap solution is basic in nature.
Soap solution also feels slippery. This is another common property of basic substances.
Q3. What happens when litmus paper is dipped in sugar solution?
Sugar solution does not change red or blue litmus paper. This shows that sugar solution is neutral.
Neutral substances are neither acidic nor basic. Salt solution and tap water also fall in this group.
Q4. How can you group substances using litmus paper?
Substances can be grouped into three categories using litmus paper.
Substances that turn blue litmus red are acidic. Substances that turn red litmus blue are basic. Substances that do not affect either paper are neutral.
Q5. Why is litmus called an acid-base indicator class 7?
Litmus is called an acid-base indicator because it shows different colours in acids and bases.
It turns red in acidic solutions and blue in basic solutions. This colour change helps students identify the nature of a substance.
Natural Indicators Class 7 Science: Red Rose, Turmeric and Onion
Natural indicators are important because the chapter shows how students can prepare and use them at home or in class. These questions test activity-based understanding.
Turmeric as Indicator Class 7 and Other Natural Indicators
Q1. How can red rose extract be used as an indicator?
Red rose extract can test whether a substance is acidic or basic. It gives a shade of red in acidic solutions and green in basic solutions.
Students prepare it by crushing red rose petals, soaking them in hot water, filtering the coloured liquid and using the extract for testing.
Q2. What colour does red rose extract show in lemon juice and soap solution?
Red rose extract gives a red shade in lemon juice. This shows that lemon juice is acidic.
It gives a green shade in soap solution. This shows that soap solution is basic.
Q3. How does turmeric paper act as an indicator?
Turmeric paper helps identify basic substances. It turns red when a basic substance is added to it.
Turmeric paper does not show a clear colour difference between acidic and neutral substances. This is why it cannot identify all three groups completely.
Q4. Why did a curry stain change colour after soap was applied?
A curry stain contains turmeric. Turmeric turns red in the presence of basic substances.
Soap is basic in nature. So, when soap touches a turmeric stain, the yellow stain changes colour.
Q5. What are olfactory indicators?
Olfactory indicators are substances whose smell changes in acidic or basic media.
Onion can act as an olfactory indicator. A blindfolded student can use such an indicator because it depends on smell, not colour.
Class 7 Science Chapter 2 MCQ with Answers
Class 7 Science Chapter 2 MCQ questions often test indicator colours, examples and daily-life neutralisation. Read each option carefully because acids, bases and neutral substances can look similar in daily life.
Q1. A substance turns blue litmus paper red. The substance is:
(a) Basic
(b) Acidic
(c) Neutral
(d) Metallic
Answer: (b) Acidic
Acids turn blue litmus paper red.
Q2. A substance turns red litmus paper blue. The substance is:
(a) Acidic
(b) Neutral
(c) Basic
(d) Salty
Answer: (c) Basic
Bases turn red litmus paper blue.
Q3. Which of the following is neutral?
(a) Lemon juice
(b) Vinegar
(c) Soap solution
(d) Sugar solution
Answer: (d) Sugar solution
Sugar solution does not change red or blue litmus paper.
Q4. Turmeric paper turns red in:
(a) Basic solution
(b) Acidic solution
(c) Neutral solution
(d) Pure water
Answer: (a) Basic solution
Turmeric changes from yellow to red in basic substances.
Q5. Red rose extract gives green colour in:
(a) Lemon juice
(b) Amla juice
(c) Soap solution
(d) Vinegar
Answer: (c) Soap solution
Soap solution is basic, so red rose extract gives a green colour.
Q6. Litmus is obtained from:
(a) Rose petals
(b) Lichens
(c) Turmeric
(d) Onion
Answer: (b) Lichens
Litmus is a natural indicator obtained from lichens.
Q7. Which substance can help reduce pain from an ant bite?
(a) Vinegar
(b) Lemon juice
(c) Moist baking soda
(d) Tamarind water
Answer: (c) Moist baking soda
Ant bite contains formic acid. Baking soda is basic and neutralises the acid.
Q8. Acid and base react to form:
(a) Salt and water
(b) Sugar and water
(c) Acid and heat only
(d) Base and salt only
Answer: (a) Salt and water
Neutralisation forms salt and water with the release of heat.
Class 7 Science Chapter 2 Extra Questions and Answers
Class 7 Science Chapter 2 extra questions and answers help students prepare for application-based tests. They also cover the textbook activity questions.
Q1. Why did the words appear on the white sheet at the science fair?
The words appeared because the sheet likely had a message written with a basic substance such as soap solution. The spray may have contained turmeric solution.
Turmeric turns red in basic substances. So, when turmeric solution touched the soap-written message, the hidden words became visible.
Q2. Which solution can Ashwin use to write on turmeric paper?
Ashwin can use soap solution or baking soda solution. Both are basic in nature.
Turmeric turns red when it comes in contact with a base. So, a message written with a basic solution becomes visible on turmeric paper.
Q3. Can turmeric paper identify vinegar, baking soda solution and sugar solution separately?
Turmeric paper can identify baking soda solution because it turns red with bases.
However, it cannot clearly separate vinegar and sugar solution. Vinegar is acidic and sugar solution is neutral, but both do not produce the same clear basic colour change on turmeric paper.
Q4. Why should students not taste unknown substances during acid-base testing?
Students should not taste unknown substances because some acids and bases can harm the mouth, skin and body.
Safe testing uses indicators. Litmus, red rose extract and turmeric paper help identify substances without tasting them.
Q5. What happens when excess amla juice is added to a basic liquid tested with red rose extract?
Amla juice is acidic. If excess amla juice is added to a basic liquid, it can neutralise the base and may make the solution acidic.
The red rose extract colour may shift away from green. With enough acid, it can show a reddish shade.
Neutralisation Class 7 Science Important Questions
Neutralisation is one of the highest-value ideas in this chapter. Students should remember the word equation and daily-life examples.
Neutralisation Class 7 Science Questions
Q1. What is neutralisation?
Neutralisation is the reaction in which an acid and a base cancel each other’s effect.
The products are salt and water. Heat also gets released during the reaction.
Acid + Base → Salt + Water + Heat
Q2. What happens when lime water is added to lemon juice containing blue litmus solution?
Blue litmus first turns red because lemon juice is acidic. When lime water is added, it neutralises the acid.
After enough lime water is added, the solution may turn blue. This shows that the acidic effect has ended and the basic effect has become stronger.
Q3. Why does moist baking soda relieve pain from an ant bite?
An ant bite injects formic acid into the skin. This acid causes stinging pain and redness.
Baking soda is basic. It neutralises the acid and reduces the effect of the bite.
Q4. How can acidic soil be treated?
Acidic soil can be treated with lime. Lime is basic and neutralises the acidic nature of the soil.
Poor plant growth may also happen due to nutrient deficiency. Soil testing helps identify the correct cause.
Q5. How can basic soil be treated?
Basic soil can be treated by adding organic matter such as manure or composted leaves.
Organic matter releases acids slowly. These acids help neutralise the basic nature of the soil.
Q6. Why should factory waste be neutralised before release into water bodies?
Factory waste may be acidic or basic. If released untreated, it can harm fish and other aquatic life.
Acidic waste can be neutralised by adding basic substances. This makes the waste less harmful before release.
Activity-Based Questions from Exploring Substances Acidic Basic and Neutral Class 7
Activity-based questions test observation and reasoning. Students should write what happened and what it proves.
Q1. A liquid shows no change with red litmus but turns blue litmus red. Identify its nature.
The liquid is acidic. Acids do not change red litmus because it is already red.
They turn blue litmus red. So, the observation confirms acidic nature.
Q2. A liquid turns turmeric paper red. What is its nature?
The liquid is basic. Turmeric turns red in the presence of basic substances.
Examples may include soap solution, baking soda solution, lime water or washing powder solution.
Q3. A solution turns red rose extract green. What does this show?
The solution is basic in nature. Red rose extract gives green colour in basic solutions.
If an acidic substance is added in excess, the basic nature may reduce due to neutralisation.
Q4. Manya is blindfolded. Which indicator should she use to test acids and bases?
Manya should use an olfactory indicator such as onion. Olfactory indicators show changes through smell.
This helps a blindfolded student test substances without depending on colour changes.
Q5. Vinegar produces bubbles with eggshell or marble, but soap solution does not. Why?
Vinegar is acidic and reacts with eggshell or marble. Eggshell and marble contain calcium carbonate.
The reaction produces carbon dioxide gas, which appears as bubbles. Soap solution is basic, so it does not produce the same bubbling reaction.
Long Answer Questions from Class 7 Science Chapter 2
Long answers should explain the concept with examples from the chapter. Add the observation, reason and conclusion.
Q1. Explain how litmus helps classify substances as acidic, basic and neutral.
Litmus is a natural acid-base indicator obtained from lichens. It is available as red and blue litmus paper.
When blue litmus paper turns red, the substance is acidic. Lemon juice, vinegar, amla juice and tamarind water show this change.
When red litmus paper turns blue, the substance is basic. Soap solution, baking soda solution, lime water and washing powder solution show this change.
If neither red nor blue litmus changes colour, the substance is neutral. Tap water, sugar solution and salt solution are examples.
This classification helps students test substances safely without tasting them.
Q2. Describe how natural indicators are prepared and used.
Natural indicators can be prepared from flowers, vegetables or spices. Red rose petals, turmeric, purple cabbage, beetroot and hibiscus can act as indicators.
To prepare red rose extract, fallen red rose petals are washed and crushed. Hot water is added, and the mixture is covered for a few minutes.
The coloured liquid is filtered and used as an indicator. It gives red colour in acidic solutions and green colour in basic solutions.
Turmeric paper is prepared by dipping paper in turmeric paste and drying it. It turns red in basic solutions.
Natural indicators make science practical because students can test substances from daily life.
Q3. Explain neutralisation with three daily-life examples.
Neutralisation occurs when an acid reacts with a base. The reaction forms salt and water with the release of heat.
In an ant bite, formic acid enters the skin. Moist baking soda, which is basic, neutralises the acid and reduces pain.
In soil treatment, acidic soil can harm plant growth. Farmers add lime because it is basic and can neutralise acidic soil.
In water bodies, acidic factory waste can harm fish. Basic substances can neutralise acidic waste before release.
These examples show that neutralisation solves real-life problems.
Q4. How is turmeric used to reveal secret messages?
Turmeric is yellow in normal conditions. It turns red when it comes in contact with a basic substance.
A secret message can be written on white paper using soap solution or baking soda solution. After drying, the message may not appear clearly.
When turmeric solution is sprayed on the paper, the part with the basic substance turns red. The hidden message becomes visible.
This experiment shows how an indicator reacts with a basic substance.
Q5. Why is Class 7 Science Chapter 2 important for later chemistry?
This chapter builds the foundation for acids, bases and salts. Students first learn how to identify substances through indicators.
Later, they study stronger ideas such as pH, chemical reactions, salts and laboratory indicators. This chapter makes those topics easier.
It also trains students to observe colour changes carefully. That skill matters in chemistry experiments.
The chapter connects science with daily life through food, soap, soil, ant bites, stains and water pollution.
Common Mistakes Students Make in Class 7 Science Chapter 2
Students often know the answer but lose marks because of small concept errors. Avoid these mistakes while revising.
- Do not write that all bitter substances are basic. Bitter gourd is bitter but not basic.
- Do not say turmeric identifies acids clearly. Turmeric mainly helps test bases.
- Do not confuse lime water with lemon juice. Lime water is calcium hydroxide solution.
- Do not write only “colour changed” in activity answers. Mention the indicator and colour.
- Do not taste unknown substances to test acids or bases.
- Do not forget heat in the neutralisation reaction.
Quick Revision Points for Class 7 Science Chapter 2
Use these points before a class test.
- Acids turn blue litmus red.
- Bases turn red litmus blue.
- Neutral substances do not change red or blue litmus.
- Litmus comes from lichens.
- Red rose extract turns red in acids and green in bases.
- Turmeric turns red in basic substances.
- Turmeric cannot clearly separate acidic and neutral substances.
- Onion acts as an olfactory indicator.
- Neutralisation forms salt, water and heat.
- Baking soda helps reduce ant bite pain.
- Lime treats acidic soil.
- Organic matter treats basic soil.
- Factory waste should be neutralised before release.