Electrochemistry

9th chemistry chapter 7 solved exercise short questions

Solved Exercise Short Questions :

Q#1 : Define oxidation in terms of electros . Give an example .

Oxidation:

“Oxidation is the loss of electrons by an atom or ion “

Example :

Q#2 : Define reduction in terms of loss or gain of oxygen or hydrogen . Give an example .

Reduction:

“The addition of hydrogen or removal of oxygen during a chemical reaction is called reduction .”

Example :

Q#3 : What is difference between valency and oxidation state ?

Q#4 : Differentiate between oxidizing and reducing agents .

Q#5 : Differentiate between strong and weak electrolytes.

Q#6 : How is electroplating of tin on steel carried out ?

Electroplating of tin :

Tin is usually electroplated on steel into a container containing a solution of tin salt .

• The steel is connected to an electrical circuit , acting as cathode .
• while the other electrode made of tin metal acts as anode .
• When an electrical current passes through the circuit , tin metal ions present in the solution deposit on steel .

Q#7 : Why is steel plated with nickel before the electroplating chromium .

Steel is plated with nickel before the electroplating of chromium .

Reason :

Because;

• chromium do not adhere well on the steel surface and
• chromium allows moisture to pass through it and metal is stripped off.

That’s why , before chromium plating , nickel is plated first on steel .

Q#8 : How can you explain that following reaction is oxidation in terms of increase of oxidation number ?

“The loss of electrons is called oxidation .”

In above equation ;

Al⁰ with zero oxidation state changes to Al⁺³ by loss of 3 electrons .

So, oxidation reaction takes place .

Q#9 : How can you prove with an example that conversion of an ion to an atom is an oxidation process ?

Example :

In this equation ; loss of electrons take place .

• Chlorine ion (anion) converts into chlorine molecule by losing electrons .
• So, oxidation takes place .

Q#10 : Why does the anode carry negative charge in galvanic cell but positive charge in electrolytic cell ? Justify with comments .

• In case of Galvanic Cell , electrons are lost by the atoms at anode plate and make it electron rich .

So, anode carry negative charge .

• In case of Electrolytic Cell , the anode is attached to the positive terminal of the battery ,

That’s why it carry positive charge .

Q#11 : Where do the electrons flow from Zn electrode in Daniel’s cell ?

In Daniel’s cell , the electrons flow from Zn electrode (anode) towards the cathode made up of copper .

Q#12 : Why do electrodes get their names ‘anode’ and ‘cathode’ in galvanic cell ?

In Galvanic Cell ,

• where oxidation takes place is referred as anode .
• while where reduction takes place is referred as cathode .

Q#13 : What happens at the cathode in a galvanic cell ?

In galvanic cell , reduction of Cu⁺² ions takes place at cathode .

The electrons are gained by “Cu” ions of solution and “Cu” atoms are deposited at cathode .

Q#14 : Which solution is used as an electrolyte in Nelson’s cell ?

In Nelson’s cell , Brine (saturated solution of NaCl) is used as an electrolyte .

Q#15 : Name the by-products produced in Nelson’s cell ?

By-products produced in Nelson’s cell are :

• Hydrogen gas (H2)
• Chlorine gas (Cl2)

Q#16 : Why galvanizing is done ?

Galvanizing is done to protect the iron against corrosion . It protects iron even after damage to zinc layer .

“The process of coating a thin layer of zinc or iron is galvanizing “

Q#17 : Why is an iron grill painted frequently ?

Iron grill is painted frequently .

Reason :

Because , due to presence of oxygen and water in air , it may corrode .

Iron is painted to prevent from rusting.

Q#18 : Why is O2 necessary for rusting ?

Oxygen acts as an oxidizing agent in rusting and oxidizes iron by gaining electrons from it in presence of H⁺ ions .

Q#19 : In electroplating of chromium, which salt is used as an electrolyte ?

Chromium Sulphate Cr2(SO4)3 with few drops of H₂SO₄ acts as an electrolyte in electroplating of chromium .

Q#20 : Write the redox reaction taking place during the electroplating of chromium ?

Q#21 : In electroplating of silver , from where do Ag⁺ ions come and where do they deposit ?

In electroplating of silver , Ag⁺ ions come from anode made up of pure silver and they deposit at cathode .

At Anode :

Q#22 : What is the nature of electrode used in electroplating of chromium .

• Anode is made up of anti-monial lead while ,
• Cathode is the object to be electroplated .