Exploring Substances Acidic Basic and Neutral Class 7 Extra Questions and Answers Science Chapter 2

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Class 7 Science Chapter 2 Exploring Substances Acidic Basic and Neutral Extra Questions

Class 7 Science Chapter 2 Extra Questions on Exploring Substances Acidic Basic and Neutral

Exploring Substances Acidic Basic and Neutral Class 7 Very Short Question Answer

Question 1.
Name two natural indicators.
Answer:
Turmeric and red cabbage extract.

Question 2.
What is the nature of lemon juice?
Answer:
Acidic.

Question 3.
Which acid is present in vinegar?
Answer:
Acetic acid.

Question 4.
What colour does turmeric turn in base?
Answer:
Reddish-brown.

Question 5.
Give one example of neutral substance.
Answer:
Distilled water.

Question 6.
What colour is turmeric paper?
Answer:
Yellow.

Question 7.
Name a flower used as an indicator.
Answer:
China rose (Hibiscus).

Exploring Substances Acidic Basic and Neutral Class 7 Short Question Answer

Question 1.
How do you make lime water?
Answer:
By dissolving a small amount of quick lime (chuna, calcium oxide) in water, leaving the mixture to settle and filtering the liquid in another container; the clear solution is lime water.

Question 2.
What is the difference between acidic, basic, and neutral solutions?
Answer:

• Acidic solutions have sour taste and turn blue litmus paper red. Examples: Vinegar, Lemon juice.
• Basic solutions are soapy to touch, bitter in taste and turn red litmus paper blue. Examples: Baking soda solution, lime water.
• Neutral solutions: They are neither acidic nor basic and do not change the colour of litmus paper. Example: Water.

Question 3.
Why does red litmus paper turn blue when put in lime water solution?
Answer:
Red litmus paper turns blue in a basic solution. This shows that lime water is basic in nature.

Question 4.
What is the role of turmeric paper in identifying basic solutions?
Answer:
Turmeric paper is a natural plant indicator and turns from yellow to reddish-brown in the presence of basic solutions. It helps to identify basic substances.

Question 5.
How does the extract of red rose help in determining whether a solution is acidic or basic?
Answer:
Red rose extract acts as a natural indicator. It turns green in basic * solutions and remains pink or red in acidic solutions, helps us to identify the nature of the solution.

Question 6.
Explain the process of neutralisation with an example.
Answer:
Neutralisation is the reaction between an acid and a base to form salt and water. For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), it forms water (H20) and sodium chloride (NaCl). Hence we cannot identify vinegar is acidic or neutral with turmeric paper.

Question 7.
Why is vinegar considered acidic and how can you identify it with turmeric paper?
Answer:
Vinegar contains acetic acid, making it acidic. When turmeric paper is dipped in vinegar, it will not change colour because turmeric paper doesn’t change colour in acids. It remains yellow.

Question 8.
What is the significance of using natural indicators in the laboratory?
Answer:
Natural indicators, such as turmeric and red cabbage extract, help us to identify acidic, basic, and neutral substances without needing synthetic chemicals. They are cost effective and safe to use.

Question 9.
What will happen if a few drops of amla juice are added to a basic solution?
Answer:
Neutralisation reaction will take place. Amla juice, being acidic, will neutralise the basic solution.

Question 10.
How can the nature of soil be tested using a Hydrangea plant?
Answer:
Hydrangea plant can test soil nature by its flower colour.

• Blue flowers show acidic soil.
• Pink flowers show basic soil.

Question 11.
If a solution turns turmeric paper from yellow to red, what does it indicate?
Answer:
If turmeric paper turns red, it indicates the presence of a basic solution because turmeric paper turns red in bases.

Exploring Substances Acidic Basic and Neutral Class 7 Long Question Answer

Question 1.
Explain the process of neutralisation with an example.
Answer:
Neutralisation is a chemical reaction between an acid and a base that results in the formation of salt and water. Example: Ant bites produces formic acid that causes pain and irritation. It is treated by rubbing baking soda as it is basic so effect of acid is neutralised by base.

Question 2.
Describe the various types of indicators and their role in identifying acidic and basic solutions.
Answer:
Indicators are substances that change colour in acidic and basic solutions. There are two main types of indicators:
1. Natural Indicators: These are plant-based substances, found in nature that change colour in acidic and basic solutions.

• Turmeric: It turns yellow in neutral and acidic solutions but turns red in basic solutions.
• Red Cabbage Extract: It turns red or pink in acidic solutions, purple in neutral solutions, and green or blue in basic solutions.
• Red Rose Extract: It remains red in acidic solutions and turns green in basic solutions.
• Litmus Paper: Blue litmus paper turns red in acidic solutions, and red litmus paper turns blue in basic solutions.

2. Olfactory Indicators: These substances have different odour (smell) in acids and bases.
Example: Onion juice has a characteristic smell in acidic solutions and loses its smell in basic solution.
Role of Indicators: Indicators are essential for determining whether a solution is acidic, neutral, or basic.

Question 3.
How can we prepare a natural indicator from red cabbage and how does it help in determining the nature of a solution?
Answer:
Preparation of Red Cabbage Indicator:

1. Take a few leaves of red cabbage and chop them into small pieces.
2. Boil the pieces of red cabbage in water for about 10-15 minutes.
3. Strain the solution to obtain the coloured liquid, which will be purple in colour.

How It Works: Red cabbage extract is used as an indicator that changes colour depending on the nature of the solution.

• In acidic solutions, the extract will turn red or pink.
• In neutral solutions, the extract will remain purple.
• In basic solutions, the extract will turn green or blue.

Thus, by adding red cabbage extract to a solution, we can easily determine whether the solution is acidic, neutral, or basic.

Question 4.
What happens when acidic substances mix with basic substances? Explain with the help of an activity.
Answer:
When acidic substances are mixed with basic substances they form salt and water (neutral substances) which are neither acidic nor basic. Such reactions are called as neutralisation reactions.

Neutralisation:
Acid + Base → Salt + Water + Heat.

Question 5.
Identify acids, bases, and neutral substances from the following: lemon juice, soap water, distilled water, vinegar, baking soda solution.
Answer:

• Acids: Lemon juice, vinegar
• Bases: Soap water, baking soda solution
• Neutral: Distilled water

Question 6.
Predict what happens when these indicators are added to solutions:
Answer:
(a) Turmeric in soap water→ Turns red
(b) Red litmus in vinegar → Remains red
(c) Blue litmus in baking soda → No change
(d) China rose extract in lemon juice → Turns bright pink

Exploring Substances Acidic Basic and Neutral Class 7 Case Based Questions

I. In chemistry lab, Amit tested three samples A, B, C using litmus paper.

• Sample A turned blue litmus red.
• Sample B turned red litmus blue.
• Sample C showed no change with either paper.

Answer the following questions:

Question 1.
Name the acidic sample.
Answer:
Sample A is acidic because it turned blue litmus red, which is the reaction shown by acids.

Question 2.
Which sample is basic?
Answer:
Sample B is basic because it turned red litmus blue, which is the characteristic reaction of a base.

Question 3.
What is the nature of Sample C?
Answer:
Sample C is neutral, as it showed no change with either red or blue litmus paper.

Question 4.
Name one natural indicator.
Answer:
Red rose extract or turmeric can be used as a natural indicator.

Question 5.
What colour change is observed when red rose extract is put in acidic solution and basic solution respectively?
Answer:
Red rose extract gives red colour in an acidic solution and green colour in a basic solution.

Question 6.
A farmer’s soil became acidic due to excess fertiliser. What is the remedy?
Answer:
Excessive use of chemical fertlisers makes the soil acidic. When the soil is too acidic the plants cannot grow well. So, the farmer should treat the soil with a base like slaked lime (calcium hydroxide) or quick lime (calcium oxide) to neutralize the excess acidity of soil.

Exploring Substances Acidic Basic and Neutral Extra Questions for Practice

Very Short Answer Type Questions

Question 1.
Name an acid present in milk.

Question 2.
What is the colour of turmeric in a basic solution?

Question 3.
Name any two natural indicators.

Question 4.
What type of solution turns red litmus paper blue?

Question 5.
Write the formula of quick lime (chuna).

Short Answer Type Questions

Question 1.
Why do we use indicators?

Question 2.
What is neutralisation reaction?

Question 3.
What is an acid base indicator? Give an example.

Question 4.
Why should factory waste be neutralised?

Question 5.
Which substances are formed when acids react with bases?

Long Answer Type Questions

Question 1.
Explain how you would test the presence of acids and bases in household substances.

Question 2.
Describe how a turmeric paper is prepared and used.

Question 3.
How does neutralisation help in real life? Give three examples.

Case/ Source Based Questions

I. The Rani was conducting an experiment with three solutions: lemon juice, soap solution, and saltwater. She tested each solution with red and blue litmus papers. Lemon juice turned blue litmus red, soap solution turned red litmus blue, and saltwater showed no change.

Answer the following questions:

Question 1.
Which solution is acidic?

Question 2.
Which one is basic?

Question 3.
What is the nature of saltwater?*

Question 4.
Which indicators could Rani use apart from litmus?

II. A group of class 7 students visited a nearby agricultural farm. They observed that some crops were not growing well. The science teacher gave them red rose extract to test the soil. In one part of the farm, the extract turned pink, while in another it turned green.

Answer the following questions:

Question 1.
What is the nature of the soil where extract turned pink?

Question 2.
What does the green colour indicate about the second soil sample?

Question 3.
What can the farmer do to improve acidic soil?

Question 4.
Which natural indicator was used in this activity?

Question 5.
Why is it important to know the nature of soil in farming?

Multiple Choice Questions (MCQs)

Choose the correct option in the following questions:

Question 1.
Which of the following turns turmeric paper red?
(a) Lemon juice
(b) Vinegar
(c) Soap solution
(d) Sugar solution

Question 2.
Which natural indicator turns green in basic solutions?
(a) Turmeric
(d) Red cabbage
(c) Red rose extract
(d) Litmus

Question 3.
Which of the following is a neutral substance?
(a) Baking soda
(b) Lemon juice
(c) Common salt solution
(d) Vinegar

Question 4.
Which solution can be used to treat acidic soil?
(a) Vinegar
(b) Lime water
(c) Soap water
(d) Orange juice

Question 5.
Which indicator shows different colours in acid and base but remains unchanged in neutral solutions?
(a) Turmeric
(b) China rose
(c) Litmus
(d) Red cabbage extract

Assertion-Reason Questions

Directions: Each of the questions (i) and (ii) contain two statements – first Assertion’ and second ‘Reason’. Select the correct answer to these questions from the codes (a), (b), (c) or (d) as given below:
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true and Reason is NOT the correct explanation of Assertion.
(c) Assertion is true and Reason is false.
(d) Assertion is false and Reason is true.

(i) Assertion (A): Baking soda is used to treat insect stings.
Reason (R): Insect stings are acidic in nature.

(ii) Assertion (A): Red cabbage is not a natural indicator.
Reason (R): It gives different colours with acids and bases.

Fill in the Blanks

(i) _______ is an indicator that turns yellow in acid and red in base.
(ii) Acids have a _______ taste.
(iii) The solution formed after neutralisation is called _______.
(iv) Blue litmus paper turns _______ in an acidic solution.
(v) _______ is a base used to treat acidity in stomach .

True or False:

State whether the statements given below are True or False:
(i) Lemon juice turns red litmus blue.
(ii) Baking soda is an acid.
(in) Acids and bases react to form salt, water and heat.
(iv) Turmeric can be used as an indicator.
(v) Base turns blue litmus blue.

Match the following:

Question 1.
(a) Match the following items given in Column A with that in Column B:

Column A	Column B
1. Vinegar	(a) Neutral
2. Soap water	(b) Acidic
3. Salt solution	(c) Basic
4. Turmeric paper	(d) Natural Indicator

(b) Match the following items given in Column A with that in Column B:

Column A	Column B
1. Acidic Soil	(a) Baking soda
2. Acidity in Stomach	(b) Organic Matter (Mature)
3. Basic Soil	(c) Anta acid
4. Ant Bite	(d) Quick Lime