Question

Total number of different gases evolved during electrolysis of aqueous solution of sodium ethanoate is (A) 2 (B) 1 (C) 3 (D) 4

Short answer

The total number of different gases evolved during the electrolysis of an aqueous solution of sodium ethanoate is \(2\) (Option A). These gases are carbon dioxide (CO2) and hydrogen gas (H2).

Step-by-step solution

Analyze the aqueous solution of sodium ethanoate

An aqueous solution of sodium ethanoate contains the sodium ion (Na+) and the ethanoate ion (CH3COO-), along with water (H2O). This can be represented as: NaCH3COO + H2O → Na+ + CH3COO- + H2O

Electrolysis reactions at the anode and the cathode

During the electrolysis process, oxidation occurs at the anode, and reduction occurs at the cathode. The following reactions can occur: Anode: 1. Ethanoate ion can be oxidized into carbon dioxide (CO2) and water: 2CH3COO- → 2CO2 + 4e- + 2H2O 2. Water can be oxidized into oxygen (O2) and hydrogen ions (H+): 2H2O → O2 + 4e- + 4H+ Cathode: 1. Sodium ion can be reduced into sodium metal (Na): Na+ + e- → Na 2. Water can be reduced into hydrogen gas (H2) and hydroxide ions (OH-): 2H2O + 2e- → H2 + 2OH-

Determine which reactions take place

Now, we need to determine which reactions take place during the electrolysis process. Sodium is a highly reactive metal and does not easily get deposited as a metal, so the reduction of sodium ions is less likely to occur at the cathode. Therefore, the reduction of water into hydrogen gas and hydroxide ions is the probable reaction at the cathode. At the anode, since ethanoate ion is an organic ion, its oxidation will most likely occur in preference to water. Thus, the ethanoate ion will be oxidized into carbon dioxide and water.

Identify the gases evolved during the electrolysis process

From our analysis in steps 2 and 3, we identified that the following reactions occur during the electrolysis of the aqueous solution of sodium ethanoate: Anode: 2CH3COO- → 2CO2 + 4e- + 2H2O (formation of CO2 gas) Cathode: 2H2O + 2e- → H2 + 2OH- (formation of H2 gas) Thus, there are two different gases evolved during the electrolysis of the aqueous solution of sodium ethanoate: carbon dioxide and hydrogen gas. So, the correct answer is: (A) 2

Key concepts

Anode and Cathode Reactions

In the electrolysis of sodium ethanoate, we encounter complex reactions at both the anode and the cathode. Let's start with the anode, where oxidation takes place. At the anode, ethanoate ions (CH3COO-) lose electrons to form carbon dioxide (CO2) and water (H2O). This reaction can be represented as:

\( 2CH3COO^-\rightarrow 2CO2 + 4e^- + 2H2O \)

However, an alternative reaction is the oxidation of water itself, leading to the formation of oxygen gas and hydrogen ions:

\( 2H2O \rightarrow O2 + 4H^+ + 4e^- \)

The cathode is where reduction happens. In a less likely scenario, sodium ions (Na+) could gain electrons to form sodium metal:

\( Na^+ + e^- \rightarrow Na \)

More commonly though, water molecules are reduced to hydrogen gas (H2) and hydroxide ions (OH-):

\( 2H2O + 2e^- \rightarrow H2 + 2OH^- \)

In sodium ethanoate electrolysis, the more preferable reactions are the oxidation of ethanoate ions at the anode and the reduction of water at the cathode. This is due to the tendency of sodium to remain in solution due to its high reactivity and the organic nature of ethanoate ions favoring oxidation.

Gas Evolution in Electrolysis

The fascinating process of electrolysis involves not only the transformation of ions into new substances, but also the evolution of gases. These gases are tangible evidence of the chemical changes occurring during electrolysis. In the case of sodium ethanoate, the two primary gases evolved are carbon dioxide from the anode and hydrogen from the cathode.

At the anode, carbon dioxide is produced when ethanoate ions surrender their electrons:

\( 2CH3COO^- \rightarrow 2CO2 + 4e^- + 2H2O \)

Hydrogen gas, on the other hand, is liberated at the cathode through the reduction of water molecules:

\( 2H2O + 2e^- \rightarrow H2 + 2OH^- \)

This gas evolution is a critical aspect of electrolysis, as it often helps to identify the substances involved and the reactions taking place.

Oxidation and Reduction in Electrolysis

Understanding the core chemistry behind electrolysis lies in grasping the concepts of oxidation and reduction, often summarized by the mnemonic 'OIL RIG' which stands for 'Oxidation Is Loss, Reduction Is Gain' of electrons. During electrolysis, these two processes occur simultaneously at different electrodes.

Oxidation at the anode involves the loss of electrons. For example, as ethanoate ions are oxidized to carbon dioxide, they lose electrons:

\( 2CH3COO^- \rightarrow 2CO2 + 4e^- + 2H2O \)

At the cathode, reduction signifies the gain of electrons where water molecules are reduced to hydrogen gas:

\( 2H2O + 2e^- \rightarrow H2 + 2OH^- \)

Through these reactions, electrolysis represents a convenient method to effect chemical changes and to illustrate the fundamental principles of oxidation and reduction.