9th class Chemistry Notes Chapter 7 - MCQs,Questions and Practicals

Here are the Matric 9th Chemistry Notes Chapter 7 Electrochemistry - MCQs,Questions and Practicals. It Includes short questions, Long question and Practical Questions.

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Define Corrosion. What is its chemical nature?

 Give examples.

 Ans.

 Corrosion:

 "Corrosion is slow and continuous eating away of a metal by the surrounding medium.

 Chemical Nature of Corrosion: Corrosion is chemically a redox chemical reaction (oxidation-reduction reaction) that takes place by the action of air and moisture with the metals.

 Examples:

 Rusting of iron and other metals are the most common examples of corrosion.(i)

 Fe

 O3. nH2O ()+4H(a)

 (iv) What is meant by electroplating? What are its objectives?

 Ans. Electroplating:

 "Electroplating is depositing of one metal over the other by means of electrolyses."

 Objectives of Electroplating: The objectives of electroplating are as under:(1) (2) It is used to improve the appearance of metals 

 (3) It is used to protect metals against corrosion 

How electroplating of silver is carried out?

 Electroplating of Silver:

 Principle:

 The electroplating of silver is carried out by establishing an electrolytic cell.

 Method:

 The pure piece of silver strip acts as anode that is dipped in silver nitrate solution.

 The cathode is the metallic object to be coated such as Silver spoon.

 When the current is passed through the cell, the Anions dissolve at the anode, and migrate towards the cathode where they discharge and deposit on the object spoon.

(vi) How electroplating of zinc is carried out?

 Ans. Electroplating of Zinc:

 (1) The target metal is cleaned in alkaline detergent type solution, and it is treated with acid, in order to remove any rust or surface scales.

 (2) Next, the zinc is deposited on the metal by immersing it in a chemical bath containing electrolyte zinc sulphate.

 (3) A current is applied, which results in zinc being deposited on the target metal i.e. cathode.

 (vii) Discuss, why galvanizing is considered better than that of tin plating?

 Ans. Advantaging of Galvanizing over Tin Coating: The tin protects the iron only as long as its protective layer remains intact. Once it is broken and the iron is exposed to the air and water, a galvanic cell is established and iron rusts rapidly.

 On the other hand, galvanizing protects the iron against corrosion even after the coating surface is broken.

 That is why galvanizing is better than tin coating.

 (viii) How electroplating of chromium is carried out?

 Ans.

 Procedure of Electroplating of Chromium 

(1) The electroplating of chromium is carried out by establishing an electrolytic cell.

(2) The object to be electroplated acts as cathode while anode is made of antimonial-lead.

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