Question

Electrolysis of water is carried out in Hoffman voltameter .Litmus is added to both cathodic and anodic compartments. What changes do you observe in the above process at the end of electrolysis? Justify.

Answer 1

Hint: Electrolysis is the process of breakdown of the compound into its ions and in the electrochemical cell, current flows from cathode to anode and electrons flow from anode to cathode and when litmus is added then, the region which is acidic in nature turns the litmus red and the region which is basic in nature, turns the litmus blue. Now identify that region and then, you can easily answer this statement.

Complete step by step answer:
First of all, let’s discuss what electrolysis is. By electrolysis we mean the process of breakdown of any substance into its ions.
Now coming next to the voltameter. Voltameter is a device which is used to determine the potential difference between the two points.
When we connect the two electrodes with a voltmeter, the proper measurements are obtained only if the positive terminal of the voltmeter is connected to the positive electrode and negative terminal of the voltmeter is connected to the negative electrode.
In the electrochemical cell, there is flow of current from positive terminal to negative i.e. from cathode to anode and the direction of flow of electrons is opposite to that of the direction of the current.
Now considering the statement;
Electrolysis of water results in the formation of the hydrogen ions and the hydroxyl ions. The hydrogen ions so formed are liberated in the form of the hydrogen gas from the positive electrode i.e. the cathode and some hydroxyl ions present in the cathodic region are basic in nature and turn red litmus blue.
On the other hand, the hydroxyl ions are liberated from the negative terminal of the battery i.e. the anode and the solution of the anodic region is acidic in nature and turns red litmus blue.
So, thus when the electrolysis of water is carried out in Hoffman voltameter and Litmus is added to both cathodic and anodic compartments, then the cathodic compartment turns red litmus blue and anodic compartment turns blue litmus red.

Note: If the connections in the voltameter are not correct, there will be no reading obtained in the voltameter and if the voltmeter gives proper reading , it indicates that the electrode is connected to the positive terminal of the voltmeter and is positive i.e. it acts as cathode and the electrode connected to the negative terminal of the voltmeter is negative i.e. it acts as anode.