Study electrolysis of water

# Objective

Study electrolysis of water

# The Theory

Water electrolysis is the breakdown of water into oxygen and hydrogen gas due to an electric current passing through it. The reaction has a standard potential of -1.23 V, implying that a potential difference of 1.23 volts is required to split water.

The process by which ionic chemicals are broken into simpler substances when an electric current is delivered through them is known as electrolysis. The chemical reaction in which hydrogen and oxygen gases are decomposed by transmitting an electric current is known as water electrolysis. Water electrolysis is mainly used to produce clean hydrogen and oxygen gases. It involves putting an electric current over water, which causes the water to decompose into hydrogen and oxygen.

## Equation of electrolysis of water

Half reactions in the electrolysis of pure water at pH=7, and 25°Care

At cathode: 2H2O(l) + 2e– → H2(g) + 2OH–   E° = -0.42 V

At anode: 2H2O → O2(g) + 4H+ + 4e–    E° = +0.82 V

The net reaction of electrolysis of water is given as follows;

2H2O + Electrical energy → O2 + 2H2      E° = -1.24 V

The cell potential of pure water electrolysis is negative, making it thermodynamically unfavourable. Because of the low ion concentration and the surfaces to be traversed, an additional voltage (overvoltage) of around 0.6V is required at each electrode. Continuous electrolysis of clean water is only achievable at an external voltage of 2.4V. Because pure water electrolysis is thermodynamically infeasible, techniques to make it kinetically viable are being researched. One way is to enhance conductivity by increasing the number of ions accessible by adding acid, base, or non-reacting salts.

A battery is connected to the electrodes, and current is sent through them until the test tubes are filled with the required gas. The gas in the cathode sideburns with a popping sound when the extinguished splint is brought near the mouth of the test tube. Because hydrogen gas has this feature, the gas within the test tube is shown to be hydrogen. The anode side flame splint burns brighter, indicating that the gas is oxygen. This experiment proves that water is composed of hydrogen and oxygen.

2H2O → H2 (g)+ O2 (g)

The ratio of hydrogen to oxygen is 2:1. As a result, for every two volumes of hydrogen collected at the cathode, one volume of oxygen is collected at the anode.

Distilled water conducts no current, whereas tap water conducts a tiny current. The baking soda solution will facilitate a significant degree of electrolysis. The solution, including table salt, will best assist electrolysis.

Table salt, known as sodium chloride (NaCl), is an excellent electrolyte supplement. Salt breaks into Na+ and Cl- ions in water, which are excellent conductors of current or the movement of electric charges. The gases formed in the water-salt solution include hydrogen, oxygen, and chlorine (Cl2).

## Factors Affecting the Efficiency of Electrolysis

• The total number of cations and anions in the solution.
• The ion mobility rate to the electrode.
• Activation energy required for electron transport from the electrode to electrolyte ions.
• The influence of the gas bubble around the electrode on subsequent electrotransfer,  and so on.

## Electrolytes and Non-Electrolytes

Chemical compounds are classified into two types based on their capacity to transmit electricity through aqueous solutions. Electrolytes and nonelectrolytes are the two groups. Electrolytes are chemicals that may dissolve in water and generate ions. These ions can transmit electricity through the solution. Nonelectrolytes are chemical substances that do not conduct electricity when dissolved in water. This is because they do not create ions when dissolved in water. The primary distinction between electrolytes and nonelectrolytes is that electrolytes may be ionised when dissolved in water, but nonelectrolytes cannot.

# Learning Outcomes

The students will be able to

•  Identify the cations and anions in an aqueous solution.
•  Describe the electrolysis of an aqueous solution.
•  Predict the products of electrolysis of an aqueous solution.