Tag: chemistry

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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:
$2O^{-2}\, \rightarrow\, O _2\, +\, 4e^-$
$C\, +\, O _2\, \rightarrow\, CO _2$

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

During the electrolysis of an aqueous solution of $HCOOK$, the number of gases obtained at cathode, anode, and a total number of gases are:

  1. $1, 2, 3$
  2. $1, 2, 2$
  3. $2, 1, 3$
  4. $2, 1, 2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

At cathode:
$\displaystyle H _2O\, +\, e^-\, \rightarrow\, \overset{\ominus}O H\, +\, \frac{1}{2} H _2\, (one)$
At anode:
$2HCOO^{\ominus}\, \rightarrow\, 2CO _2\, +\, H _2\, (two)$
$H _2\, and\, CO _2$ at anode and $H _2$ at cathode

With the total number of gases $2$

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

Name the process from which chlorine is obtained as by product. What will happen if an aqueous solution of NaCl is subjected to electrolysis.

  1. Haber process, $NaOH, H _2, Cl _2$
  2. Down cell process, Na metal and $Cl _2$ gas are obtained
  3. Down cell process, $NaOH, H _2, Cl _2$

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Haber process is used for producing ammonia from nitrogen and hydrogen.
Down's Process. Molten NaCl upon electrolysis will give Na metal and $Cl _2$ gas. Aqueous NaCl will form NaOH,$H _2 , Cl _2$.

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

If aq. NaCl is electrolysed using graphite as anode and Hg as cathode than products are:

  1. $\displaystyle Cl _{2}$ gas at anode and Na at cathode
  2. $\displaystyle Cl _{2}$ gas at anode and $\displaystyle H _{2}$ gas at cathode
  3. $\displaystyle O _{2}$ gas at anode and $\displaystyle H _{2}$ gas at cathode
  4. $\displaystyle Cl _{2}$ gas at anode and $\displaystyle O _{2}$ gas at cathode
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If aq. $NaCl$ is electrolyzed using graphite as anode and $Hg$ as cathode then products are $Cl _2$ gas at anode and $Na$ at the cathode.

In the presence  of Hg electrode the over voltage of $H _2$ is very high and reduction of $H _2O$ is possible.

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

The products formed when an aqueous solution of $NaBr$ is electrolysed in a cell having inert electrodes are :

  1. $Na$ and $Br _{2}$
  2. $Na$ and $O _{2}$
  3. $H _{2}, Br _{2}$ and $NaOH$
  4. $H _{2}$ and $O _{2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$NaBr\rightleftharpoons Na^{+} + Br^{-}$
$2H _{2}O + 2e\rightarrow H _{2} + 2OH^{-}$
$Na^{+} + OH^{-} \rightarrow NaOH$ At cathode
$Br^{-}\rightarrow Br + e^{-}$
$Br + Br \rightarrow Br _{2}$ At anode
So the products are $H _{2}$ and $NaOH$ (at cathode) and $Br _{2}$ (at anode).

Hence, option C is correct option.