7th Standard CBSE Science Unit 5 Acids, Bases and Salts Sample Question Paper | QB365

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7th Standard CBSE Science Unit 5 Acids, Bases and Salts Sample Question Paper

Published on: 31/07/2019

Acids, Bases and Salts

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Questions:

Generic 3

3 x 3 = 9

Write three differences between an organic acid and a mineral acid.

Describe the process of neutralisation with the help of an example.

Is the distilled water acidic/basic/neutral? How would you verify it?

True or False

5 x 1 = 5

Common salt dissolved in water turns blue litmus red.

(a)

True

(b)

False

Lime water turns red litmus blue.

(a)

False

(b)

True

A compound if acidic will turn all indicators red.

(a)

True

(b)

False

Sodium hydroxide turns blue litmus to red.

(a)

True

(b)

False

Nitric acid turns red litmus to blue.

(a)

True

(b)

False

Generic 2

4 x 2 = 8

Which part of our body contains hydrochloric acid?

10.

Which acid does each cell in our body contains?

11.

Name the reaction when an acid is mixed with base.

12.

Is lime water an acidic or basic solution?

Generic 5

2 x 5 = 10

13.

Nitesh was playing with his friends in the garden. Suddenly, Nitesh was stung by a honeybee and was in great pain. Immediately, his friends call his mother. She applied baking soda solution on the affected area and then took him to the doctor.
Read the above passage and answer the following questions:
(a) What could be the reason for this burning pain?
(b) Why did his mother applied baking soda solution on the affected area?
(c) What values are shown by Nitesh's friends?

14.

Boojho, Paheli and their friend Golu were provided with a test, each containing China rose solution which was pink in colour. Boojho added 2 drops of solution 'A' in his test tube and got dark pink colour. Paheli added 2 drops of solution '8'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.

Multiple Choice Question

5 x 1 = 5

15.

Raw mango is sour in taste due to presence of

(a)

Tartaric acid

(b)

Citric acid

(c)

Formic acid

(d)

Oxalic acid

16.

Stomach secretes:

(a)

HCl

(b)

H₂SO₄

(c)

CH₃COOH

(d)

NaOH

17.

Sting of an ant contains

(a)

Vinegar

(b)

Common salt

(c)

Formic acid

(d)

Milk of magnesia

18.

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

19.

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

Fill up / 1 Marks

5 x 1 = 5

20.

Ammonium chloride is an example of _____________salt

21.

_____________is used to remove acidity of solids

22.

When an acid mixed with a base, a __________ reaction takes place.

23.

Acid + Base \(\longrightarrow\) _____________ + Water

24.

The substances which show different colours in acidic, basic and neutral solutions are called __________

Match the following

5 x 1 = 5

25.

Fertilizer

26.

Curd

27.

Turmeric

28.

Milk of magnesia

29.

Sodium chloride

1 Marks

3 x 1 = 3

30.

How is salt formed?

31.

What is the chemical name of vitamin C?

32.

What are neutral substances/solutions?

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Answers Key:

Generic 3

3 x 3 = 9

Organic acid	Mineral acid
These acids are naturally occurring acids and are found in plants and animals. These contain- COOH as functional group as reactive part. These acids are week. Examples: Lactic acid, acetic acid, citric.acid.	These are derived from the mineral of the earth These contain H⁺ ions as reactive part. These acids are strong. Examples: Hydrochloric acid, sulphuric acid, nitric acid.

The reaction between an acid and a base is known as neutralisation reaction. In this reaction, both acid and base cancel each other's effect. Neutralisation reaction results in the formation of salt and water. During this reaction, energy in the form of heat is evolved.
Acid + Base \(\longrightarrow\) Salt + Water + Heat \(\uparrow\)
e.g. when sodium hydroxide (NaOH) is added to hydrochloric acid (HCI), sodium chloride (NaCl) and water (H₂O) are obtained.
NaOH + HCI \(\longrightarrow\) NaCI + H₂O + Heat \(\uparrow\)
Sodium Hydrochloric Sodium Water
hydroxide Acid Chloride

Distilled water is neither acidic nor basic. When we test its nature through litmus paper strips, we have found neither red nor blue changes in colour which verifies its neutral nature.

True or False

5 x 1 = 5

(b)
False

(a)
False

(b)
False

(b)
False

(b)
False

Generic 2

4 x 2 = 8

Stomach contains hydrochloric acid

10.

Each cell of our body contains deoxyribonucleic acid (DNA).

11.

Neutralisation reaction.

12.

Lime water (calcium hydroxide) is a basic solution.

Generic 5

2 x 5 = 10

13.

(a) The reason for this burning pain is honeybee sting which causes pain and irritation. This is due to the acidic liquid (formic acid) injected into the skin by the honeybee.
(b) The effect of acid can be neutralised by rubbing the affected area by baking soda solution which is a mild base.
(c) Nitesh's friends are caring, supportive and helpful.

14.

China rose (gudhal) is an acid-base indicator.
China rose solution in different medium shows following changes:
China rose + acid \(\longrightarrow\) Give dark pink colour, hence A is an acidic solution.
China rose + base \(\longrightarrow\) give green colour, hence B is a basic solution.
China rose + neutral \(\longrightarrow\) No change in colour, hence C is a neutral solution.

Multiple Choice Question

5 x 1 = 5

15.