In a dry cell (battery), which of the following are used as electrolytes ?

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Q: 20 (IAS/2009)
In a dry cell (battery), which of the following are used as electrolytes ?

question_subject: 

Science

question_exam: 

IAS

stats: 

0,37,49,37,18,23,8

keywords: 

{'electrolytes': [0, 0, 1, 0], 'dry cell': [0, 0, 1, 1], 'zinc chloride': [0, 0, 2, 0], 'sodium chloride': [1, 0, 0, 1], 'ammonium chloride': [0, 1, 2, 0], 'magnesium chloride': [0, 0, 2, 0], 'calcium chloride': [0, 0, 1, 1], 'battery': [0, 0, 1, 3]}

In a dry cell, the electrolyte is the substance that allows the flow of ions between the cathode and anode, thus facilitating the chemical reactions that generate the electrical energy. Out of the given options, the most commonly used electrolyte in a dry cell is Ammonium chloride (NH4Cl) in combination with Zinc chloride (ZnCl2). Therefore, option 1: Ammonium chloride and Zinc chloride is the correct answer.

The choice of Ammonium chloride and Zinc chloride as the electrolytes in a dry cell has several reasons:

1. Conductivity: Ammonium chloride is highly soluble in water, and it dissociates into ammonium ions (NH4+) and chloride ions (Cl-) when dissolved. Similarly, Zinc chloride dissociates into zinc ions (Zn2+) and chloride ions (Cl-) in water. These ions facilitate the flow of electric current within the cell by acting as charge carriers.

2. Electrochemical reactions: In a dry cell, the anode is typically made of zinc (Zn), which undergoes an oxidation reaction, releasing electrons according to the equation: Zn -> Zn2+ + 2e-. The chloride ions from the electrolyte help balance the charge generated during this process.

3. Reduction reaction: In the cathode, a reduction reaction takes place, which involves the reduction of manganese dioxide (MnO2). The ammonium ions from the electrolyte play a role in this reaction by reacting with the manganese dioxide according to the equation: 2NH4+ + 2MnO2 + 2e- -> Mn2O3 + 2H2O + 2NH3. This reaction helps maintain the overall charge balance in the cell.

It is important to note that the other options (2: Sodium chloride and Calcium chloride, 3: Magnesium chloride and Zinc chloride, and 4: Ammonium chloride and Calcium chloride) do not match the commonly used electrolyte combination in a dry cell. Sodium chloride and Calcium chloride, for example, are not typically used as electrolytes in dry cells due to their lower solubility and less efficient electrochemical reactions compared to Ammonium chloride and Zinc chloride.

In summary, option 1: Ammonium chloride and Zinc chloride is the correct answer because it aligns with the commonly used electrolytes in a dry cell and supports the necessary electrochemical reactions for the cell to function efficiently.