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Electrochemistry: Solved Exercise and Think-Tank

 Electrochemistry: Solved Exercise and Think-Tank 

Question 2: Give short answers.

I. What is Oxidation State?

Ans. Oxidation state or oxidation number may be define as

The number of charge that an element has in a molecule or compound.

ii. What is the oxidation number of Cr in chromic acid (H2CrO4)?

Answer.

Oxidation state of H = +1

Oxidation state of O = -2

Oxidation state of Cr = X

Since, the algebraic sum of oxidation state of all atoms in a neutral molecule or formula unit is zero. So,

2(Oxidation state of H) + (Oxidation state of Cr) + 4(Oxidation state of O) = 0

2(+1) + (Oxidation state of Cr)+ 4(-2) = 0

+2 +2 (X) -8 =0

2 (X) -6 =0

2 (X) =+6

X = +3

Oxidation state of Cr = +3

iii. Identify reducing agent in the following reaction.

CuO    +   H2       ------------> Cu         +        H2O

Answer. 

Let us calculate oxidation state of each element in the reaction.

+2(-2)        0                         0                    2(+1)(-2)

 CuO   +    H2   ------------> Cu         +          H2O 

As oxidation number of Cu is being reduced so it is an oxidizing agent. In the same way oxidation number of Cu H is being increased, so it is reducing agent.

iv.Write chemical reactions that occur in Nelson cell.

Answer 

At cathode 

2H+    +   2e-      -------------------->   H2

At anode 

2Cl-       --------------->  Cl2       +     2e-

Na+       +       OH-     ----------->  NaOH

v. Why tin plated steel is used to make food cane?

Answer. 

Tin plated steel is used to make food canes because components of food beverage ☕️ and preservatives contain organic acids or their salts. These acids and salts are corresive. They may mat react with iron snd may form toxic substances.  However tin plating is non-poionous and prevents corrosion.

vi. Explane one example from daily life which involve oxidation reduction reaction.

Answer. Daily life example of redox reaction is photography 📸. A photographic film is a simple plastic sheet coated with gelatin containing salt of AgBr in emulsion form. When photographic film is exposed to sunlight, AgBr crystals 🔮 become activated. This activation depends upon intensity of light. When exposed film  🎥 is placed in hydroquinone solution that is mild reducing agent, activated silver Ag+ is reduced to black metallic silver.This reduced silver forms image. 

Ag+    e-    ---------> Ag

Inactive AgBr is removed from the film by a  solvent such thiosulphate called fixer. Thus photography involves redox reaction.

Question 3: define oxidation and reduction in terms of laws are gain of oxygen are hydrogen.

Question 4: define oxidation and reduction in terms of laws are gain of electron.

Question 5: List the possible uses of electrolytic cell.

Answer.

Following are possible uses of electrolytic cell.

1. Down silence used for the commercial preparation of sodium metal. It produces chlorine gas as a by product.

2. Nelson cell is used for the commercial preparation of sodium hydroxide. It also produces chlorine and Arjun gas as a by product.

3. Electrolytic cells are used for the commercial preparation of calcium and magnesium metals.

4. Electrolytic cells are also used for preparation of aluminium metal commercially.

5. Electrolytic cells are also use for purification of copper.

6. Electrolytic cells are also used to to electroplate metal such as thin silver Nickel on steel.

7. Electrolytic cells can also be used to prepare anodized aluminium anodized aluminium can be absorb dies dying of anodiz aluminium can produce metallic rod metallic blue or other metallic colour on the metal surface

Question 6: Sketch or Daniel cell labelling the cathode anode and the direction of flow of the electron.

Question 7: Describe how a battery produces electrical energy.

Answer. A battery 🔋 is a galvanic cell or a group of galvanic cells joined in a series. It produces electrical energy by redox reaction. When this battery is connected to an external circuit, electrons start to move from anode to cathode through external circuit. Its anode undergoes oxidation reaction while cathode undergo reduction reaction. 

Question 8: Describe the methods of recovering metal from its ores.

Question 9: explain electrolytic refining of copper.

Question 10: compare the effects of al2o3 and fe2o3 formation on their parent metal and side example from daily life.

Answer.

When aluminium is exposed to air, a layer of aluminium oxide (Al2O3) is formed on its surface. This layer is tough and firmly adhers to the metal surface. So it serves to protect the underlying aluminium layer from the further corrosion. 


On the other hand, when iron is exposed to air it forms insoluble layer of rust Fe2O3.xH2O that forms on the surface of iron. This layer is porous and cannot protect the protect the underlying layer from further corrosion. As a result, this layer flakes away and exposes metal for further corrosion. 


Question 11: explain how food and beverage industry deals with corrosion. 

Question 12 explain how Chemistry interacts with photography.

Question 13: electrolysis has a major role in electrochemical industries.

a. Catch a and electrolytic cell label the anode and cathode and indicates the direction of electron transfer.

  b. Describe the nature of electrochemical process.

  c. Distinguish between electrolytic and volte cell.

Question 14: state the substance which are oxides are used give reason for your answer.

a.      N2    +        3H2        ------------------->    2NH3

b.      CO2   +      2Mg     ---------------------->   2MgO   +   C

c. 

  

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