Chapter 5: Acids, Bases and Salts

  Science

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  Chapter 5: Acids, Bases and Salts

  Class: VII

 

  Multiple Choice Questions

 

Question 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.

 

Answer 1

(b)

 

Question 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.

Answer 2

(c)

Question 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.

Answer 3

(b)

 

Question 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

Answer 4

(d)

Question 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

Answer 5

(a)

Question 6

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

(a) China rose (Gudhal)

(b) Beetroot

(c) Lichen

(d) Blue berries (Jamun)

Answer 6

(c)

 

Question 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.

Answer 7

(d)

Question 8

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

(a) basic

(b) acidic

(c) neutral

(d) either neutral or acidic

Answer 8

(a)

Question 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

Answer 9

(d)

Question 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

Answer 10

(c)

Question 11

Which of the following is an acid-base indicator?

(a) Vinegar

(b) Lime water

(c) Turmeric

(d) Baking soda

Answer 11

(c)

 

Very Short Answer Questions

 

Question 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).

Answer 12

Hint: Evaporation

Question 13

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

(a) All substances are either acidic or basic.

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

(c) Lime water turns red litmus blue.

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

(e) Phenolphthalein is a natural indicator.

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

(g) Lemon water is basic in nature.

Answer 13

(a) False. Substances can be neutral as well.

(b) False. Acids do not turn all indicators red.

(c) True

(d) False. It does not change the colour of litmus at all.

(e) False. It is a man-made indicator.

(f) True

(g) False. It is acidic in nature.

 

Question 14

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

Answer 14

No, because orange juice is acidic in nature.

 

Short Answer Questions

 

 

Question 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.

 

Answer 15

 

Question 16

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

Answer 16

Wasp sting inject a liquid in the skin which is acidic in nature.

Hence, baking soda is the appropriate remedy, as it is basic in

nature and neutralises the acid.

 

Question 17

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

Answer 17

The effect of an ant bite can be neutralised by rubbing moist

baking soda.

 

Question 18

 

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

Answer 18

(a) (iii); (b) (v); (c) (iv); (d) (i); (e) (ii)

 

Question 19

Fill the blanks in the following sentences

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

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

(c) Phenolphthalein gives _________ colour with lime water.

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

(a) Tartaric acid (i) soap

(b) Calcium hydroxide (ii) curd

(c) Formic acid (iii) unripe mangoes

(d) Sodium hydroxide (iv) ant's sting

(e) Lactic acid (v) lime water

Column I Column II

Answer 19

. (a) sour, acids (b) natural (c) pink (d) neutralise, salt

 

Long Answer Questions

 

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.

Answer 20

‘A’ is an acidic solution.

‘B’ is a basic solution.

‘C’ is a neutral solution.

 

Question 21

 

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

Fig. 5.2

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.

Answer 21

 

Question 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?

Answer 22

Hint: If the soil is too acidic, it is treated with bases such as

quick lime (calcium oxide) or slaked lime (calcium hydroxide).

If the soil is too basic, organic matter is added to it. Organic

matter releases acids which neutralises the basic nature of the

soil.

 

Question 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.

Answer 23

. Hint: Use both red and blue litmus solutions and predict the

colours in each case.

 

Question 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.

Fig 5.3

Answer 24

 

Question 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.

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

neutralised?

Answer 25

Hint:

(a) Since factory waste may contain acids or bases, it can

kill the fish.

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

neutralised by adding basic substances.

 

Question 26

Explain two neutralisation reactions related to daily life situation.

Answer 26

Hint:

1. Indigestion
2. Ant sting