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Electrolysis of Water – Equation, Diagram and Experiment

Electrolysis of Water

Electrolysis of water is the process of converting water (H2O) into hydrogen (H+) and hydroxide (OH-) ions by passing an electric current through it. Ions move to the opposing electrodes, releasing pure hydrogen (H2) and oxygen (O2) gases. Electrolysis of water is an oxidation-reduction reaction that does not occur spontaneously. Since the heat in the form of electricity is supplied to the electrolytic cell in the electrolysis of water,  the reaction is endothermic.

Applications of Electrolysis of Water

  • Water electrolysis is used to generate oxygen for the International Space Station.
  • Hydrogen produced as a byproduct of the chlor alkali process is used to make specialty chemicals and other small-scale applications.
  • The hydrogen gas produced in this manner can be used as hydrogen fuel or mixed with oxygen to produce oxyhydrogen gas, which is used in welding and other applications.
  • Heavy water is created by electrolysis of water.
  • Electrolysis produces about 5% of the hydrogen gas produced worldwide.

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Electrolysis of Water Equation

Electrolysis of water takes place in an electrolytic cell, which consists of a positively charged anode and a negatively charged cathode, both of which are typically made of platinum. The chemical reaction for water electrolysis can be divided into two halves that take place at the cathode and anode. Electrolysis of water equation can be written as:

At the cathode, hydrogen ions acquire electrons and are converted into hydrogen gas in a reduction reaction. The following is a half-reaction:

2 H+ (aq.) + 2 e → H2 (g)

An oxidation reaction occurs when water molecules transfer electrons to the anode and release oxygen gas. The half-reaction is depicted below.

2 H2O (l) → O2 (g) + 4 H+ (aq.) + 4 e

Overall, the Electrolysis of water equation is

2 H2O (l) + electrical energy → 2 H2 (g) + O2 (g)

As a result of the electrolysis of water reaction, hydrogen and oxygen are separated from the water.

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Electrolysis of Water Diagram

Electrolysis of water diagram is given below:

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Electrolysis of Water Reaction

The electrolysis of water reaction produces hydrogen and oxygen gases. The electrolytic cell is made up of a pair of platinum electrodes immersed in water with a small amount of an electrolyte such as H2SO4. The electrolyte is required because pure water cannot carry enough charge due to a lack of ions. Water is oxidized to oxygen gas and hydrogen ions at the anode. Water is reduced to hydrogen gas and hydroxide ions at the cathode.

oxidation (anode):       2H2O(l)O2(g)+4H+(aq)+4e−        E0=1.23V

reduction (cathode):    2H2O(l)+2eH2(g)+2OH(aq)     E0=0.83V


overall reaction:          2H2O(l)O2(g)+2H2(g)                    E0cell=2.06V

In order to obtain the overall electrolysis of the water reaction, the reduction half-reaction was multiplied by two to equalize the electrons. The hydrogen ion and hydroxide ions produced in each reaction combine to form water. The H2SO4 is not used up in the reaction.

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Electrolysis of Water Experiment

To better understand the decomposition process (a single reactant (water) breaks down to give simpler products) (hydrogen and oxygen) we will perform the Electrolysis of water experiment:

Materials required:
  • Plastic mug
  • Rubber stopper
  • Carbon electrodes (anode & cathode)
  • Battery
  • Water
  • Dilute sulphuric acid and
  • Test tube
Experimental procedure:
  • Drill two holes in the bottom of the plastic mug.
  • Insert the two rubber stoppers into the corresponding holes.
  • Insert the anode and cathode carbon electrodes into the rubber stoppers.
  • Connect a 6-volt battery to these carbon electrodes.
  • Fill the plastic mug halfway with water so that the carbon electrodes are submerged.
  • To this water, add a few drops of sulphuric acid.
  • Fill two test tubes with water, then invert the test tubes onto the carbon electrodes.
  • Turn on the current from the 6-volt battery.
  • Allow the apparatus to rest for a while.

There will be bubble formation at both electrodes in the test tubes (which means gas is forming or liberating from water)

Water begins to move in the test tube as a result of the formation of bubbles.

  • Carefully remove the test tubes from the mug once they have been filled with the gases.
  • Place a lit candle near the mouth of the test tubes to determine which gas is present.

Result:

  • When we place a lit candle near the mouth of one of the test tubes, the gas ignites and burns with a pop sound, indicating the presence of hydrogen in the test tube.
  • When we place a burning candle near the mouth of another test tube, the candle begins to burn brightly, indicating that the test tube contains oxygen.
  • The negative gas collected at the anode is oxygen, and the positive gas collected at the cathode is hydrogen.
Decomposition reaction:
 
2H2O(l) −→Electricity—-2H2(g) + O2(g)
 (Water)                            (Hydrogen) + (Oxygen)

Conclusion:

A decomposition reaction occurs when a single reactant breaks down to give simpler products in this electrolysis of water experiment. Under the right conditions, water decomposes to form hydrogen and oxygen. In this case, electricity is the appropriate condition for water decomposition.

 

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Electrolysis of water is a Decomposition Reaction

The electrolysis of water is a decomposition reaction. This is because water splits into its constituent elements, hydrogen, and oxygen, under the effect of an electric current. The mole ratio of hydrogen and oxygen gases liberated during the electrolysis of water is 2:1.

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Electrolysis of Water – FAQs

Q1. Which electrodes are used in the electrolysis of water?
Ans.
Platinum electrodes are used in the electrolysis of water.

Q2. Which type of chemical reaction is the electrolysis of water?
Ans.
Electrolysis of water is a decomposition reaction as water splits into its constituent elements, hydrogen, and oxygen, under the effect of an electric current.

Q3. What happens during the electrolysis of water?
Ans. During the electrolysis of water, water decomposes into oxygen gas and hydrogen gas. An electric current is passed through the solution to accomplish this. The cathode generates hydrogen gas, while the anode generates oxygen gas.

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