NCERT Exemplar Solutions, for Class 7, Science Chapter 5, Acids, Bases and Salts Solutions

Multiple Choice Questions

1. The correct way of making a solution of acid in water is to 

(a) add water to acid

(b) add acid to water 

(c) mix acid and water simultaneously 

(d) add water to acid in a shallow container

Ans: The correct answer is option (b). When we add water to acid, it releases some energy. We can feel this energy by touching the surface of the test tube. Sometimes, released heat is too huge. Because of this glasses of test tube may prove wrong and acid can split over. So, in practice, you have to take an excessive amount of water and mix acid drop by drop. In order that heat generated can be cooled down by this water and mistakes can be prevented.

2. Products of a neutralisation reaction are always 

(a) An acid and a base

(b) An acid and a salt 

(c) A salt and water 

(d) A salt and a base

Ans: The correct answer is option (c). Bases and acids cancel each other’s qualities and properties. They make water and salt as products.

3. Turmeric is a natural indicator. On adding its paste to acid and base separately, which colours would be observed 

(a) Yellow in both acid and base

(b) Yellow in acid and red in base 

(c) Pink in acid and yellow in base 

(d) Red in acid and blue in base

Ans: The correct answer is option (b), Yellow in acid and red in base.

4. Phenolphthalein is a synthetic indicator and its colours in acidic and basic solutions, respectively are 

(a) Red and blue

(b) Blue and red

(c) Pink and colourless 

(d) Colourless and pink

Ans: The correct answer is option (d), Colourless and pink.

5. When the soil is too basic, plants do not grow well in it. To improve its quality what must be added to the soil?

(a) Organic matter 

(b) Quick lime 

(c) Slaked lime 

(d) Calamine solution

Ans: The correct answer is option (a). To improve its quality organic matter must be added to the soil.

6. ‘Litmus’, a natural dye is an extract of which of the following? 

(a) China rose (Gudhal) 

(b) Beetroot 

(c) Lichen 

(d) Blueberries (Jamun)

Ans: The correct answer is option (c).

7. Neutralisation reaction is a 

(a) Physical and reversible change 

(b) Physical change that cannot be reversed

(c) Chemical and reversible change 

(d) Chemical change that cannot be reversed

Ans: The correct answer is option (d). A chemical reaction where base and acid reacts with each other quantitatively, known as a neutralization reaction. It is a permanent process.

8. A solution changes the colour of the turmeric indicator from yellow to red. The solution is 

(a) basic 

(b) acidic 

(c) neutral 

(d) either neutral or acidic

Ans: The correct answer is option (a).

9. Which of the following set of substances contain acids? 

(a) Grapes, lime water 

(b) Vinegar, soap 

(c) Curd, milk of magnesia 

(d) Curd, vinegar

Ans: The correct answer is option (d). Curd contains ‘lactic acid’ and vinegar contains ‘acetic acid’.

10. On adding phenolphthalein indicator to a colourless solution, no change is observed. What is the nature of this solution? 

(a) Basic 

(b) Either acidic or basic 

(c) Either acidic or neutral 

(d) Either basic or neutral

Ans: The correct answer is option (c). With acidic/ neutral solutions, the colour of the phenolphthalein indicator will not change.

11. Which of the following is an acid-base indicator? 

(a) Vinegar 

(b) Lime water 

(c) Turmeric 

(d) Baking soda

Ans: The correct answer is option (c). In acidic solution colour of turmeric is yellow but in a basic solution, it gives red colour.

Very Short Answer Questions

12. Look at the given reaction. 

Hydrochloric acid + Sodium hydroxide (base) → Sodium chloride (salt) + Water 

Sodium chloride formed in this reaction remains in solution form. Can we get solid sodium chloride from this solution? Suggest a method (if any).

Ans: In water ‘sodium chloride’ is soluble and it gives a solution of common salt. By ‘evaporation procedure’ we can get ‘solid sodium chloride’.

13. State whether the following statements are true or false. Correct the false statements. 

(a) All substances are either acidic or basic.

Ans: The given statement is false. In nature, all substances can be ‘acidic’, ‘basic’ or ‘neutral’. 

(b) A compound if acidic will turn all indicators red. 

Ans: The given statement is false. Acids do not turn all indicators red.

(c) Lime water turns red litmus blue. 

Ans: The given statement is true. 

(d) Common salt dissolved in water turns blue litmus red. 

Ans: The given statement is false. The colour of litmus paper will not change. 

(e) Phenolphthalein is a natural indicator. 

Ans: The given statement is false. A man-made indicator is Phenolphthalein. 

(f) Calamine can be used to treat an ant’s sting. 

Ans: The given statement is true. 

(g) Lemon water is basic in nature.

Ans: The given statement is false. The nature of ‘Lemon water’ is acidic.

14. Paheli is suffering from indigestion due to acidity. Is it advisable to give her orange juice in this situation and why?

Ans: Orange juice is acidic. So, it is not advisable to take orange juice in her situation.

Short Answer Questions

15. Look at Figure 5.1 which shows solutions taken in test tubes A, B, C and D. What colour is expected when a piece of red litmus paper is dropped in each test tube? Nature of the solutions is given in the table for your help.

Ans: According to the given condition:

16. While playing in a park, a child was stung by a wasp. Some elders suggested applying paste of baking soda and lemon juice as a remedy. Which remedy do you think is appropriate and why?

Ans: Bicarbonate of soda has a basic nature, whereas juice has an acidic tendency. Because wasp stings emit methanoic acid into the string region, which causes irritation, applying baking soda paste is a better cure than applying lemon juice paste. Baking soda has a very basic nature.

17. Form a sentence using the following words – baking soda, ant bite, moist, effect, neutralised, and rubbing.

Ans: The arranged form of given words: 

“The effect of ant bite can be neutralized by rubbing moist baking soda on the affected area”.

18. Match the substances in Column I with those in Column II.

Ans: The correct table is given below:

19. Fill the blanks in the following sentences 

(a) Lemon juice and vinegar taste ___________ because they contain ___________. 

Ans: sour, acids. 

(b) Turmeric and litmus are _________ acid-base indicators. 

Ans: natural

(c) Phenolphthalein gives _________ colour with lime water. 

Ans: pink

(d) When an acidic solution is mixed with a basic solution, they _________ each other forming _________ and water.

Ans: neutralize, salt

Long Answer Question

20. Boojho, Paheli and their friend Golu were provided with a test tube each containing China rose solution which was pink in colour. Boojho added two drops of solution ‘A’ in his test tube and got dark pink colour. Paheli added 2 drops of solution ‘B’ to her test tube and got green colour. Golu added 2 drops of solution ‘C’ but could not get any change in colour. Suggest the possible cause for the variation in their results.

Ans: The 'China rose' is a natural indication that transforms the colour of acid to pink, the colour of base to green, and the colour of neutral solutions remains unchanged. As a result, solution A is acidic. The solution B serves as a foundation. Solution C is a non-reactive solution.

21. Fill in the cross word given as Figure 5.2 with the help of the clues provided.

Across 

(2) The solution which does not change the colour of either red or blue litmus. 

(4) Phenolphthalein gives pink colour in this type of solution. 

(7) Colour of blue litmus in lemon juice. 

Down 

(1) It is used to test whether a substance is acidic or basic. 

(3) It is a natural indicator and gives pink colour in basic solution. 

(5) Nature of ant’s sting. 

(6) It is responsible for increase in temperature during a neutralisation reaction.

Ans: Across

(2) Neutral

(4) Base

(7) Red

Down

(1) Indicator

(3) Turmeric

(5) Acidic

(6) Heat

22. A farmer was unhappy because of his low crop yield. He discussed the problem with an agricultural scientist and realised that the soil of his field was either too acidic or too basic. What remedy would you suggest the farmer to neutralise the soil?

Ans: When the soil in his field becomes too acidic, 'bases' such as slaked lime (calcium hydroxide)' or 'quicklime (calcium oxide)' are used to treat it. If his field's soil is too basic, organic matter is put to it. Organic matter produces acids, which neutralise the soil's natural (basic) character.

23. You are provided with four test tubes containing sugar solution, baking soda solution, tamarind solution, salt solution. Write down an activity to find the nature (acidic/basic/neutral) of each solution.

Ans: We can determine the nature of each solution (acidic/basic/neutral) by tasting the solution in the test tube.

Sugar solution: The sugar solution will have a sweet flavour. It has neither a sour nor a bitter flavour. As a result, it is classified as a neutral solution.

Baking soda solution: The baking soda solution has a bitter taste. As a result, it falls within the category of a fundamental solution.

Tamarind solution: The tamarind solution will have a sour flavour. As a result, it falls under the acidic solution category.

Salt solution: The salt solution will have a salty flavour. It has neither a sour nor a bitter flavour. As a result, it is classified as a neutral solution.

24. You are provided with three test tubes A, B and C as shown in Figure 5.3 with different liquids. What will you observe when you put 

(a) a piece of blue litmus paper in each test tube. 

(b) A piece of red litmus paper in each test tube. 

(c) A few drops of phenolphthalein solution to each test tube.

Ans: You will observe:

25. Paheli observed that most of the fish in the pond of her village were gradually dying. She also observed that the waste of a factory in their village is flowing into the pond which probably caused the fish to die. 

(a) Explain why the fish were dying. 

Ans: Factory wastes may include a significant proportion of basic or acidic substances. These pollutants make it harder to live in the water.

(b) If the factory waste is acidic in nature, how can it be neutralised?

Ans: The acids will be neutralised by the base. We can make water less dangerous and neutral by adding the base (limestone, lime, etc.) to it.

26. Explain two neutralisation reactions related to daily life situation.

Ans: The following are two neutralisation reactions that occur in everyday situations:

a) Digestive disorders: Hyperacidity occurs when the stomach produces too much 'hydrochloric acid.' Digestive problems develop as a result of this. Basic ingredients such as milk of magnesia' or 'baking soda' can be used to treat the acid.

b) Ant-bite: The sting of an ant causes the body to produce 'methanoic acid' or 'formic acid.' These acids induce discomfort and a burning feeling. Because moist baking soda is basic in nature, rubbing it on the problem solves it.

Importance of the NCERT Exemplar solutions for the Class 7, Chapter 5, Acid, Bases and Salts.

The solutions for the Class 7 NCERT Exemplar, Chapter 5, Acid, Bases and Salts, help the students in the following manner.

• In comparing their answers with the one provided in the solutions, and therefore making sure that they are on the right path.

• Solutions provide the students with the best way to answer the questions.

Considering these points, Vedantu has brought the solutions for the Class 7 NCERT Exemplar, Science subject, Chapter 5, Acid, Bases and Salts, completely free of cost for all the students to download.

Also, if you are looking for the solutions to the other subjects of NCERT Class 7 you can find it here: NCERT Solutions for Class 7 (2024-25 Session) Maths, Science, SST, English and Hindi (vedantu.com).