Tag: chemical changes

Questions Related to chemical changes

Which of the following reaction takes place at the cathode during electroplating of metal with silver using sodium argentocyanide as an electrolyte?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. ${ Ag }^{ + }+{ e }^{ \ _ }\longrightarrow Ag$

  2. $Ag \longrightarrow { Ag }^{ \ _ } + { e }^{ \ _ }$

  3. $2{ Ag }^{ + }+{ e }^{ \ _ }\longrightarrow Ag$

  4. $Ag^+\longrightarrow { Ag }^{ \ _ } +{ e }^{ \ _ }$

Show answer
Correct Option: A
Explanation:

In electroplating with silver,
reaction at cathode:
$Ag^+ +e^-\rightarrow Ag$.

During electroplating of an article with nickel, the reduction reaction of the electrolysis occurs at:

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. cathode

  2. anode

  3. both $A$ and $B$

  4. none of these

Show answer
Correct Option: A
Explanation:

No matter what, reduction always occurs at cathode. 

In the electroplating of silver, $AgNO _3$ solution is usually used as:

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. oxidant

  2. reductant

  3. electrode

  4. electrolyte

Show answer
Correct Option: D
Explanation:

The process of depositing a thin layer of silver electrolytically on the metal surface is called silver plating. The article to be silver-plated is used as cathode while anode consists of pure silver. 


The bath contains a solution of potassium argentocyanide ($AgNO _3$ + excess of KCN). The complex ion is very stable and ionisation is very small at a time with the result slow and uniform deposition of silver takes place. 

$[Ag(CN) _2]^2 \rightleftharpoons Ag^+ + 2CN^-$


Hence, option D is correct.

The metal which is deposited at the cathode during the electrolysis of the solution of silver chloride 

is:  

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. Ag

  2. H

  3. Cl

  4. Na

Show answer
Correct Option: A
Explanation:

Reactions:
At cathode:
$Ag^+ +e^-\rightarrow Ag$
At anode:
$2 H _2O \rightarrow O _2 + 4H^+ + 4 e^-$

Galvanization of iron denotes coating with:

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. copper

  2. aluminium

  3. silver

  4. none of the above

Show answer
Correct Option: D
Explanation:

Galvanization is the process of applying a protective zinc coating to steel or iron, to prevent rusting. Galvanization of Iron meaning coating with zinc.


It forms a coating of corrosion-resistant zinc which prevents corrosive substances from reaching the more delicate part of the metal. The zinc serves as a sacrificial anode so that even if the coating is scratched, the exposed iron will still be protected by the remaining zinc.

Which of the following is not an electrochemical process?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. Transmission of nerve impulses in human body

  2. Rusting of iron

  3. Lightning

  4. None of the above

Show answer
Correct Option: C
Explanation:

Both transmission of nerve impulse and  rusting of iron are results of electrochemical reactions.In transmission of nerve impulse numerous small molecules function as neurotransmitters at various chemical synapses.Rust is an iron oxide, usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Lightning is a sudden electrostatic discharge during an electrical storm between electrically charged regions of a cloud. 

Galvanized iron sheets are coated with :

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. copper

  2. nickel

  3. zinc

  4. carbon

Show answer
Correct Option: C
Explanation:

Galvanization is the process of applying a protective zinc coating to steel or iron in order to prevent it from rusting.

Electro refining which is based on phenomenon of Electrolysis where:

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. impure metal is made anode and pure metal is cathode

  2. impure metal is cathode and pure metal is anode

  3. pure metal makes both anode and cathode

  4. none of the above

Show answer
Correct Option: A
Explanation:

This method is based upon the phenomenon of electrolysis. The crude metal is made anode whereas the thin sheet of a pure metal is made cathode. The electrolyte is the solution of the soluble salt of the same metal, preferably a double salt on passing electricity the metal from anode goes into solutions as ions due to oxidation while the pure metal gets deposited at the cathode due to the reduction of metal ions the impurities settle down below the anode as Anode Mud.

State True or False:
Rusting of iron is a physical change.

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. True

  2. False

Show answer
Correct Option: B

Which of the following is the preferred electrolyte for silver plating?

chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

  1. $AgCl+HCl$

  2. $Ag{NO} _{3}+H{NO} _{3}$

  3. ${Ag} _{2}{SO} _{4}$

  4. $AgCN+NaCN$

Show answer
Correct Option: D
Explanation:

Silver plating is an electroplating process utilizing an electrolyte containing silver cyanide solution and some free cyanide ions and operating at pH value not less than $8$. Free cyanide prevents precipitation of silver cyanide salt from the solution, provides electrical conductivity of the electrolyte and helps in the dissolution of silver anodes.