Electrochemistry

Step 1: Write the electrode reaction for aluminium.
In molten , aluminium ion is reduced at the cathode as follows:
This shows that 1 mole of aluminium requires 3 moles of electrons, that is, 3 Faradays of electricity.
Step 2: Calculate the number of moles of aluminium.
Molar mass of aluminium
Given mass of aluminium
Step 3: Calculate Faradays required.
Since mole of Al requires F,
Step 4: Conclusion.
Therefore, the amount of electricity required to produce g of aluminium is 4.44 F.
Final Answer:4.44 F.

Step 1: Use the relation between and equilibrium constant.
At , the standard cell potential and equilibrium constant are related by the formula:
where is the number of electrons transferred in the balanced redox reaction.
Step 2: Find the value of .
From the reaction, copper is oxidised as:
and silver ions are reduced as:
Hence, the number of electrons transferred is:
Step 3: Substitute the given values.
Given,
Using the formula,
So,
Step 4: Calculate .
Step 5: Conclusion.
Therefore, the equilibrium constant of the given reaction is . Hence, the correct option is .
Final Answer: .

Step 1: Understand what a fuel cell is.
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel directly into electrical energy. In the hydrogen-oxygen fuel cell, hydrogen acts as fuel and oxygen acts as oxidizing agent. The overall reaction produces water.
Step 2: Identify the characteristics of fuel cells.
Fuel cells are known for high efficiency because they convert chemical energy directly into electrical energy without combustion. In the hydrogen-oxygen fuel cell, the reaction is:
Because the main product is water, such cells are considered environmentally clean or nearly pollution free.
Step 3: Analyze the options.

• (A) True. Fuel cells convert chemical energy directly into electrical energy.
• (B) Not true. The water formed in hydrogen-oxygen fuel cells is generally considered pure enough and has even been used for drinking in space applications after proper handling.
• (C) True. Hydrogen reacts with oxygen to form water in the fuel cell.
• (D) True. Fuel cells are considered pollution free because they mainly produce water.

Step 4: Conclusion.
Hence, the statement which is not true for a fuel cell is that the water produced during the reaction cannot be used for drinking.
Final Answer:Water produced during reaction, can not be used for drinking.

Step 1: Recall the meaning of reducing agent.
A reducing agent is a substance that loses electrons and causes reduction of another species. The stronger the tendency of a metal to lose electrons, the stronger is its reducing character. On the other hand, a metal that does not lose electrons easily behaves as a weak reducing agent.
Step 2: Use standard reduction potentials.
The tendency of a metal to act as a reducing agent can be understood from its standard reduction potential . A more negative reduction potential means the metal more readily undergoes oxidation, so it is a stronger reducing agent. A more positive reduction potential means the metal resists oxidation and is therefore a weaker reducing agent.
From the given values:
Step 3: Compare the metals.

• Li: Very negative , so it is a very strong reducing agent.
• Mg: Also has negative , so it is a strong reducing agent.
• Ag: Positive , so it is weaker than Li and Mg as a reducing agent.
• Au: Has the highest positive value, so it has the least tendency to lose electrons and is therefore the weakest reducing agent.

Step 4: Conclusion.
Since gold has the highest positive standard reduction potential among the given metals, it behaves as the weakest reducing agent.
Final Answer:Au.