Q29 of 79 Page 3

State reasons for the following observations:

(a) The shining surface of some metals becomes dull when exposed to air for a long time.


(b) Zinc fails to evolve hydrogen gas on reacting with dilute nitric acid.


(c) metal sulphides occur mainly in rocks but metal halides occur mostly in sea and lake waters.

(a) Metals react with the things like moisture, oxygen, carbon dioxide to form a layer of substance like rust in iron which hides their shiny surface. This is what we call corrosion.

(b) Nitric acid is a strong oxidising agent and Zinc is not a very reactive metal according to the reactivity series. Hence the nitric acid oxidises the hydrogen gas which is produced may be in the first step if reaction between acid or metal had taken place. So the hydrogen gas does not evolve.


(c) Metal sulphides are insoluble in water and halides are soluble so they get washed away in spite of getting deposited over the crust.

More from this chapter

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27

Define the terms: (i) mineral (ii) ore, and (iii) gangue. .

 28

Samples of four metals A, B, C and D were taken and added to the solutions given in the following table, one by one. The results obtained are as follows:


Metal

Iron (II) sulphate

Copper (II) sulphate

Zinc sulphate

Silver nitrate

A

No reaction

Displacement

    

B

Displacement

  

No reaction

  

C

No reaction

No reaction

No reaction

Displace

D

No reaction

No reaction

No reaction

No reaction

Use the above table to answer the following questions about metals A, B, C and D:


(i) Which is the most reactive metal?


(ii) What would you observe when metal B is added to a solution of copper (II) sulphate?


(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.

 30

Four metal A, B, C and D are added to the following aqueous solutions one by one. The observations made are tabulated below:


Answer the following questions based on the above observations:


(a) Which is the most active metal and why?


(b) What would be observed if B is added to a solution of copper (II) sulphate and why?


(c) Arrange the metal A, B, C and D in order of increasing reactivity.


(d) The container of which metal can be used to store both zinc sulphate solution and silver nitrate solution?


(e) Which of the above solutions can be easily stored in a container made up of any of these metals?

 31

(a) What is meant by corrosion? Name any two methods used for the prevention of corrosion.

(b) Suppose you have to extract metal M from its enriched sulphide ore. If M is in the middle of the reactivity series, write various steps used in extracting this metal.