Chemistry · Physics

Electrochemistry and Current Electricity

272 Questions

Review fundamental concepts of electrochemistry and current electricity through these practice questions. The set includes numerical problems on electrolysis, drift velocity, and electrode potentials. These topics frequently appear in engineering, CSIR NET, and state PSC prelims examinations for thorough preparation.

Electrolysis calculationsElectrode potentialNernst equationDrift velocityFuel cellsMolar conductivity

Electrochemistry and Current Electricity Questions

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

Electrolysis of a solution of $ MnSO _{4}$ in aqueous sulphuric acid is a method for the preparation of $ MnO _{2}$ as per the reaction: $ Mn^{2+}(aq)+2H _{2}O\rightarrow MnO _{2}(s)+2H^{+}(aq)+H _{2}(g).$ Passing a current of 19.3 A for 2 h gives only 52.2 g of $MNO _{2}.$ The current efficiency is (Mn = 55)

  1. 8.33 %

  2. 83.33 %

  3. 41.67 %

  4. 100 %
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Calculate theoretical yield using Faraday's laws: Q = I * t = 19.3 * 7200 = 138960 C. Moles of electrons = Q / F = 138960 / 96500 = 1.44 mol. Reaction: Mn2+ + 2H2O -> MnO2 + 4H+ + 2e-. Moles of MnO2 = 1.44 / 2 = 0.72 mol. Mass = 0.72 * 87 = 62.64 g. Efficiency = (52.2 / 62.64) * 100 = 83.33%.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

If mercury is used as cathode in the electrolysis of aqueous NaCl solution, the ions discharged at cathode are:

  1. H$^+$
  2. Na$^+$
  3. OH$^-$
  4. Cl$^-$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In presence of Hg electrode, sodium ions are discharged in the form of a mercury sodium amalgam and chloride ions are converted to chlorine. 
So, $Na^+$ ions discharged at cathode.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

State True or False.
The ratio of gases liberated at cathode and anode during electrolysis of CH$ _3$COONa(aq) is 1 : 3.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The given statement is True.
 The ratio of gases liberated at cathode and anode during electrolysis of $\displaystyle CH _3COONa$ (aq) is $\displaystyle 1:3$
$\displaystyle 2CH _3COONa \rightarrow CH _3-CH _3 \uparrow + 2CO _2  \uparrow+2NaOH+H _2 \uparrow$
hydrogen gas is liberated at cathode and ethane and carbon dioxide gases are liberated at anode.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

In the electrolysis of $Na _{2}SO _{4}$ solution using inert electrode

a) the anodic reaction is

$2H _{2}O\rightarrow O _{2}(g)+4e^{-}+4H^{+}$

b)$H _{2}(g)$ and $O _{2}(g)$ is produced in a molar ratio of 2:1

c) 23 grams of sodium is produced at the cathode

d) the cathode reaction is $Na^{+}+e^{-}\rightarrow Na$

  1. a and b are correct

  2. c,d are correct

  3. only c is correct

  4. all are correct
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The discharge potential of $ { H }^{ + } $ ions is lower than $ { Na }^{ + } $ ions. Hence $ { H }^{ + } $ ions will be liberated at cathode in preference to $ { Na }^{ + } $ ions.
The discharge potential of $ { OH }^{ - } $ ions is lower than $ { SO } _{ 4 }^{ 2- } $ ions. Hence $ { OH }^{ - } $ ions will be liberated at anode (in the form of $ { O } _{ 2 } $ molecule) in preference to $ { SO } _{ 4 }^{ 2- } $ ions. This is the electrolysis of water. Hence $ { H } _{ 2 } $ and $ { O } _{ 2 } $ are produced in the molar ratio of 2:1 which is same as that present in water molecule.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

A gas which does not conduct electricity in the liquid state but conducts electricity when dissolved in water is :

  1. $HCl$.
  2. $H _2$.
  3. $SO _2$.
  4. $Cl _2$.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
It is HCl having a unique property which does not conduct electricity when it is in gas phase since the gas phase of HCl is in the form of molecules and not in ionic form, the anhydrous HCl gas does not conduct electricity.
             But HCl solution or Aquous $HCl$ conducts electricity since HCl completely dissociates in solution to form hydronium $H _3O^+$ and $Cl^-$ ions which are getting transported into opposite direction when potential electric junction is created by applying differential voltage, thus migration of these ions in opposite directions to each other allows electricity and thus becomes conductor of electricity.
Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

During electrolysis of aqueous $CuBr _{2}$ using Pt electrode:

  1. $Br _{2}(g)$ is evolved at anode.

  2. Cu(s) is deposited at cathode
  3. $Br _{2}(g)$ is evolved at anode and $H _{2}(g)$ at cathode
  4. $H _{2}(g)$ is evolved at anode
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Explanation

Aqueous $CuBr _{2}$ :
At cathode:

$Cu^{2+}\, +\, 2e^{-}\, \rightarrow\, Cu$;  
At anode :
$2Br^{\ominus}\, \rightarrow\, Br _{2}\, +\, 2e^{-}$

$Br _{2}(g)$ is evolved at anode and Cu(s) is deposited at cathode.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

Which of the following statements is/are correct ?

  1. The electrolysis of concentrated $H _{2}SO _{4}$ at $0 - 5^{\circ}C$ using a Pt electrode produces $H _{2}S _{2}O _{8}$
  2. The electrolysis of a brie solution produces $NaClO _{3}$ and NaClO.
  3. The electrolysis of a $CuSO _{4}$ solution using Pt electrodes causes the liberation of $O _{2}$ at anode and the deposition of copper at cathode.

  4. All electrolytic reactions are redox reactions.
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer
Explanation

Electrolysis of concentrated $H _{2}SO _{4}$ at $0 - 5^{\circ}C$ using Pt electrode produces $H _{2}S _{2}O _{8}$.

At anode : $2H _{2}SO _{4}\, \rightarrow\, H _{2}S _{2}O _{8}\, +\, 2H^{\oplus}\, +\, 2e^{-}$

Statement (b) is wrong. Electrolysis of brine (aq. NaCl) gives $H _{2}(g)$ at cathode and $Cl _{2}(g)$ at anode.

Statements (c) and (d) are factual statements.

Hence, A, B and D are correct options.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

When an aqueous solution of $CaCl _{2}$ is electrolyzed using inert electrodes, which of the following is(are) true ?

  1. Calcium deposits on cathode

  2. Calcium deposits an anode

  3. Chlorine is liberated on anode

  4. Calcium hydroxide precipitates near cathode on prolonged hydrolysis.
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation

During electrolysis of aqueous $CaCl _2$

We have,
At anode: $2Cl^- \rightarrow Cl _2 + 2e^-$
At anode: $2H^+ + 2e^- \rightarrow H _2$
Electrolyte = $Ca^{2+} + OH^-$

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

A dilute aqueous solution of sodium fluoride is electrolyzed, the products at the anode and cathode are:

  1. $O _{2},\, H _{2}$
  2. $F _{2},\, Na$
  3. $O _{2},\, Na$
  4. $F _{2},\, H _{2}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Ion with higher potential will go to corresponding electrode and discharge.
So,
$NaF$:
Cathode : $2H^{\oplus}\, +\, 2e^{-}\, \rightarrow\, H _{2}$
Anode : $4\overset{\ominus}{O}H\, \rightarrow\, O _{2}\, +\, 2H _{2}O\, +\, 4e^{-}$

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

A solution of sodium sulphate was electrolyzed using some inert electrode. The products at the electrodes are:

  1. $O _2,\, H _2$
  2. $O _2,\, Na$
  3. $O _2,\, SO _2$
  4. $O _2,\, S _2O _8^{2-}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since the reduction potential of $H _2O$ is greater than reduction potential of $Na^{\oplus}\, so\, H _2O$ undergoes reduction to give
$H _2(g)$ at cathode.

$\displaystyle H _2O\, +\, e^-\, \rightarrow\, \overset {\ominus}O H +\, \frac{1}{2} H _2(g)$

Similarly, the oxidation potential of $H _2O$ is greater than the oxidation potential of $SO _4^{2-}$ ion. So, $H _2O$ undergoes oxidation to give $O _2(g)$ at anode.

$\displaystyle H _2O\, \rightarrow\, 2H^{\oplus}\, +\, 2e^-\, +\, \frac{1}{2} O _2(g)$

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

Which one is wrong if electrolysis of $CH _3COONa (aq)$ is made using $Pt$ electrodes?

  1. $pH$ of solution increases
  2. Molar ratio of gases at anode and cathode is $ 3 : 1.$
  3. $[CH _3COO^{\ominus}]$ in solution decreases.
  4. The molar ration of gases at anode and cathode is $2 : 1.$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Sodium acetate undergoes electrolysis to form ethane gas, carbondioxide and hydrogen gas.

Hydrogen is liberated at cathode and ethane at anode.