Questions & Answers

During electrolysis of fused calcium hydride, the hydrogen is produced at:
A. cathode
B. anode
C. hydrogen is not liberated at all
D. ${{\text{H}}_{2}}$ produced reacts with oxygen to form water

Answer Verified Verified
Hint: Initially the ionic compound $\left( \text{Ca}{{\text{H}}_{2}} \right)$ will ionise as the solution is aqueous. Then, see the charges that made them move towards their opposite sites respectively. Then, by reduction or oxidation form the products that will be obtained on the electrodes.

Complete answer:
Let us see the solution of this question step by step:

Step (1)- In aqueous solution, the ionic compound which is calcium hydride or $\text{Ca}{{\text{H}}_{2}}$ will ionise. The ionization of this ionic compound will lead to the formation of $\text{C}{{\text{a}}^{+2}}$ (calcium ions) and $\text{2}{{\text{H}}^{-}}$(hydride ions) ions. The reaction is $\text{Ca}{{\text{H}}_{2}}\to \text{C}{{\text{a}}^{+2}}+\text{2}{{\text{H}}^{-}}$.

Step (2)- As calcium ions have positive charge, it will move towards the negative electrode (cathode for reduction). Whereas, hydride ions formed will move towards the positive electrode as it is negatively charged. The positive electrode is anode. Anode will cause the hydride ions to oxidise.

Step (3)- The reduction and oxidation will occur at cathode and anode respectively, as,
$\text{C}{{\text{a}}^{+2}}+2{{\text{e}}^{-}}\to \text{Ca}$ (this is reduction of calcium ions to form element calcium after gaining two electrons). This is reduction because the oxidation state of calcium changes from +2 to 0, which is decreasing.
Similarly, the oxidation process is $\text{2}{{\text{H}}^{-}}\to {{\text{H}}_{2}}+2{{\text{e}}^{-}}$ (After losing two electrons, hydrogen gas is produced at anode). The oxidation state is increasing from -2 to 0, thus, it is oxidation.
The correct answer to this question is the electrolysis products of fused calcium hydride are hydrogen gas and calcium and hydrogen gas is produced at anode,
So, the correct answer is “Option B”.

Additional Information:
Uses of calcium hydride:
(1)- It is highly used for the production of hydrogen gas.
(2)- It is a reducing agent, which produces metal from the metal oxides of Ti, V and Nb.
(3)- It reacts vigorously with water to produce hydrogen gas. Thus, it is used as a drying agent or mild desiccant also. It is also used to dry alcohol.

Note: The answer to this question can be achieved directly, as gases are generally produced or obtained at anode. Because their respective ions are negatively charged, they undergo oxidation which occurs at anode.

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