Tag: chemistry

Questions Related to chemistry

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

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

  1. $O _2,\, H _2$

  2. $O _2,\, Na$

  3. $O _2,\, SO _2$

  4. $O _2,\, S _2O _8^{2-}$

Show answer
Correct Option: A
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.

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

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

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

  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 $2 : 1.$

Show answer
Correct Option: D
Explanation:

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

Hydrogen is liberated at cathode and ethane at anode.

Select the wrong statement.

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

  1. The electrolysis of molten $CaH _2$ liberates $H _2$ at cathode

  2. During the discharge of lead storage battery, sulphuric acid is consumed.

  3. Sulphur acts as a polymerizing agent in the vulcanization of rubber.

  4. Galvanization of iron denotes coating with Zn.

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Correct Option: A

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

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

  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

Show answer
Correct Option: B
Explanation:

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

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

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

  1. $1, 2, 3$

  2. $1, 2, 2$

  3. $2, 1, 3$

  4. $2, 1, 2$

Show answer
Correct Option: B
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 $2$

During electrolysis of an aqueous solution of CuSO$ 4$ using Pt electrodes, the product at the anode is ______. 

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

  1. Oxygen

  2. Copper

  3. Sulphur

  4. Hydrogen

Show answer
Correct Option: A
Explanation:

Upon electrolysis,
At anode:
$2OH^-$ $\rightarrow H _2O + \frac{1}{2}O _2 + 2e^- $
Hence option A is the right answer.

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

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

Show answer
Correct Option: C
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,$H _2 , Cl _2$.

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

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

  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

Show answer
Correct Option: A
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.

The product of electrolysis of concentrate solution of common salt is :

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

  1. $Na+Cl _2$

  2. $H _2+O _2$

  3. $NaOH+H _2+Cl _2$

  4. $Na+Cl _2+O _2$

Show answer
Correct Option: C
Explanation:

$Overall\quad reaction :\ { 2H } _{ 2 }O+{ 2Cl }^{ - }+{ 2Na }^{ + }\rightarrow { 2Na }^{ + }+{ 2OH }^{ - }+{ H } _{ 2 }+{ Cl } _{ 2 }$

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

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

  1. $Na$ and $Br _{2}$

  2. $Na$ and $O _{2}$

  3. $H _{2}, Br _{2}$ and $NaOH$

  4. $H _{2}$ and $O _{2}$

Show answer
Correct Option: C
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.