NCERT Exemplar solutions for Science [English] Class 7 chapter 5 - Acids, Bases and Salts [Latest edition]

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

Products of a neutralisation reaction are always

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

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

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

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

A neutralisation reaction is a

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

Which of the following set of substances contain acids?

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

Which of the following is an acid-base indicator?

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).

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

All substances are either acidic or basic.

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

A compound if acidic will turn all indicators red.

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

Lime water turns red litmus blue.

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

Common salt dissolved in water turns blue litmus red.

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

Phenolphthalein is a natural indicator.

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

Calamine can be used to treat ant stings.

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

Lemon water is basic in nature.

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

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? The nature of the solutions is given in the table for your help.

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

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

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

Lemon juice and vinegar taste ___________ because they contain ___________.

Turmeric and litmus are _________ acid-base indicators.

Phenolphthalein gives _________ colour with lime water.

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

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.

Fill in the crossword given in 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 to the basic solution.

(5) Nature of ant’s sting.

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

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 to the farmer to neutralise the soil?

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

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

1. a piece of blue litmus paper in each test tube.
2. a piece of red litmus paper in each test tube.
3. a few drops of phenolphthalein solution to each test tube.

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.

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

Explain two neutralisation reactions related to daily life situations.