9th chemistry chapter 7 solved exercise short questions
Solved Exercise Short Questions :
Q#1 : Define oxidation in terms of electros . Give an example .
“Oxidation is the loss of electrons by an atom or ion “
Q#2 : Define reduction in terms of loss or gain of oxygen or hydrogen . Give an example .
“The addition of hydrogen or removal of oxygen during a chemical reaction is called reduction .”
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 .
- 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 ?
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 .
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 .