Tag: chemical changes

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Questions Related to chemical changes

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

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

  1. ${ Ag }^{ + }+{ e }^{ \ _ }\longrightarrow Ag$
  2. $Ag \longrightarrow { Ag }^{ \ _ } + { e }^{ \ _ }$
  3. $2{ Ag }^{ + }+{ e }^{ \ _ }\longrightarrow Ag$
  4. $Ag^+\longrightarrow { Ag }^{ \ _ } +{ e }^{ \ _ }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

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

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

  1. oxidant

  2. reductant

  3. electrode

  4. electrolyte
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

Galvanization of iron denotes coating with:

  1. copper

  2. aluminium

  3. silver

  4. none of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

Which of the following is not an electrochemical process?

  1. Transmission of nerve impulses in human body

  2. Rusting of iron

  3. Lightning

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
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. 

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

Electro refining which is based on phenomenon of Electrolysis where:

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. $AgCl+HCl$
  2. $Ag{NO} _{3}+H{NO} _{3}$
  3. ${Ag} _{2}{SO} _{4}$
  4. $AgCN+NaCN$
Reveal answer Fill a bubble to check yourself
D Correct answer
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.