Chapter 5 Acids, bases and salts

Worksheet for class 7 Science Chapter 5 Acids, bases and salts

This page consists of MCQ-based questions with detailed solutions for Chapter 5 Acids, bases and salts of class 7 science prepared by HT experts. Check out all the worksheets for class 7 science. Do solve NCERT textbook with the help of NCERT solutions for class 7 science. 

Questions and answers for CBSE class 7 science Chapter 5 Acids, bases and salts Set-1

1. The waste released from the factories is mainly harmful for 

a) aerial organism.

b) aquatic organisms.

c) arboreal organism.

d) terrestrial organism.

Ans. (b)

Explanation: The wastes of many factories contain acids. If they are allowed to

flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances.  

2.. The container meant for storage of strong acids should be made up of 

a) metals.

b) plastics.

c) ceramics.

d) rubber.

Ans. (c)

Explanation: All the mineral acids (except carbonic acid) react with metals. So the acids are not stored in metal containers. Vessels made up of glass and ceramics are considered to be safe for storing acids.

3.. The common name of sodium carbonate is

a) baking soda.

b) washing soda.

c) caustic soda.

d) slaked lime.

Ans. (b)

Explanation: It is used as a cleaning agent in homes and industries. 

4. The nature of ammonia, found in many household products, such as window cleaners, is 

a) basic.

b) acidic.

c) neutral.

d) amphoteric.

Ans. (a)

Explanation: Being basic, it turns red litmus solution into the blue.

5. The hydrated salt among the following is 

a) common salt

b) Bleaching powder.

c) Washing soda.

d) Table salt.

Ans. (a)

Explanation: Washing soda (Na2CO3.10H2O) contains ten molecules of water.

6.  A substance ‘X’ changes the red litmus solution into blue. ‘X’ is

a) citric acid.

b) oxalic acid.

c) sodium hydroxide.

d) hydrochloric acid.

Ans. (c)

Explanation: Sodium hydroxide is basic. Basic solutions change the colour of red litmus solution into blue.

7. The substance that shows different colours in acidic and basic solutions is

a) indicators.

b) lacto metre

c) lux metre.

d) ammeter.

Ans. (a)

Explanation: Special types of substances are used to test whether a substance is acidic or basic. These substances are known as indicators. The indicators change their colour when added to a solution containing an acidic or a basic substance. 

8.  Tooth decay starts when the pH of the mouth is lower than

a) 5.5

b) 6.5

c) 7.5

d) 8.5

Ans.  (a)

Explanation: Tooth enamel made up of calcium phosphate (Ca3PO4) is the hardest material in our body. When we eat food containing sugar, then the bacteria present in our mouth break down the sugar to form acid (lactic acid). This acid lowers the pH in the mouth and it is strong enough to attack the enamel of our teeth and corrode it. 

9.   The solution of base turns phenolphthalein solution into

a) yellow.

b) pink.

c) orange.

d) colourless.

Ans. (b)

Explanation: Phenolphthalein is used as an indicator. The phenolphthalein molecule is colourless. However, the phenolphthalein ion is pink. When a base is added to the phenolphthalein, ionization as H+ ions is reduced which led to the pink colour in the solution. 

10. An indicator which changes from blue to red in acids is a

a) litmus solution.

b) methyl orange.

c) phenolphthalein.                                

d) turmeric powder.

Ans. (a)

Explanation: The litmus is a natural indicator. It is extracted from lichens. It has a mauve (purple) colour in distilled water. When it is added to an acidic solution, it turns red.

11. An acid found in grapes and mangoes is 

a) lactic acid.

b) oxalic acid.

c) tartaric acid.

d) citric acid.

Ans. (c)

Explanation:  Tartaric acid is a white crystalline organic acid.  It occurs naturally in many plants, particularly grapes, unripe mangoes, and tamarinds.  It is added to other foods to give a sour taste and is used as an antioxidant.

12. A blue crystalline salt, used as a fungicide in agriculture is

a) blue vitriol.

b) green vitriol.

c) limestone.

d) quick lime.

Ans. (a)

Explanation:  Copper sulphate pentahydrate is a fungicide, when mixed with lime it is called Bordeaux and used to control fungus on grapes, melons, and other berries. A dilute solution of copper sulphate is used to treat aquarium fish for various parasitic infections.

13. When we add the china rose indicator to the sodium hydroxide solution, the colour of the solution changes into 

a) pink.

b) blue.

c) orange.

d) green.

 Ans. (d)  

Explanation: Sodium hydroxide solution is basic.

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