Tag: electrolysis and its applications

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Questions Related to electrolysis and its applications

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

During electrolysis of fused calcium hydride, the hydrogen is produced at:

  1. cathode

  2. anode

  3. hydrogen is not liberated at all
  4. $H _2$ produced reacts with oxygen to form water
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$CaH _2\, \xrightarrow {Electrolysis}\, Ca^{2+}\, +\, 2H^{-}$


At cathode (reduction) :
$Ca^{2+}\, +\, 2e^-\, \rightarrow\, Ca$

At anode (oxidation) :
$2H^{-}\, \rightarrow\, H _2\, +\, 2e^-$

At the anode, hydrogen is produced. 

Hence, option $B$ is correct.

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

Which of the following does not evolve oxygen at anode when the electrolysis is carried out of:

  1. Dilute $H _{2}SO _{4}$ with $Pt$ electrodes
  2. Fused sodium hydroxide with $Pt$ electrodes
  3. Acidic water with $Pt$ electrodes
  4. Dilute sulphuric acid using $Cu$ electrodes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$E^{\ominus} _{ox}$ of $Cu$ =$ - 0.34 $
Using copper electrodes, copper will oxidize : 
$Cu\, \rightarrow\, Cu^{2+}\, +\, 2e^{-}$
So oxygen is not evolved.

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.

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

In Hall's process, in the production of Al, carbon is used as the anode material. The reactions are:

  1. Anode: $Al^3+3e^-\, \rightarrow\, Al$

    Cathode: $C(s)+2O^{2-}\, \rightarrow\, CO _2(s)\, +\, 4e^-$
  2. Anode: $C(s)+2O^{2-}\, \rightarrow\, CO _2(s)\, +\, 4e^-$

    Cathode: $Al^3+3e^-\, \rightarrow\, Al$
  3. Anode: $Al\, \rightarrow\, Ae^{3+}\, +\, e^-$

    Cathode: $CO _2\, +\, 4e^-\, \rightarrow\, C(s)\, +\, 2O^2$

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

In the production of Al (in Hall's process), reactions are:
Cathode:
$Al^{3+}\, +\, 3e^-\, \rightarrow\, Al$
Anode:
$2O^{-2}\, \rightarrow\, O _2\, +\, 4e^-$
$C\, +\, O _2\, \rightarrow\, CO _2$