Calculate the mass of the copper deposited during electrolysis when a current of 4A passes through a copper salt for 2 hours. [Ece of Copper z=3.3x10-7kgC-1]

Analysis

To solve this problem, we need to use Faraday’s First Law of Electrolysis, which states that the mass of a substance deposited during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.

Concept

The formula for calculating the mass ($m$) deposited is:

Where:

• $m$ = mass deposited (in kg)
• $z$ = electrochemical equivalent (Ece) of the substance (in kg/C)
• $I$ = current (in Amperes, A)
• $t$ = time (in seconds, s)

Step-by-Step Solution

1. Identify the given values:

• Current ($I$) = $4\text{ A}$
• Time ($t$) = $2\text{ hours}$
• Electrochemical equivalent ($z$) = $3.3 \times 10^{-7}\text{ kg/C}$

2. Convert time to SI units (seconds): Since there are 3,600 seconds in an hour:

3. Substitute the values into the formula:

4. Perform the calculation:

• First, multiply the current and time: $4 \times 7200 = 28,800\text{ C}$
• Now, multiply by the Ece: $m = 3.3 \times 10^{-7} \times 28,800$
• $m = 3.3 \times 10^{-7} \times 2.88 \times 10^4$
• $m = (3.3 \times 2.88) \times 10^{-7+4}$
• $m = 9.504 \times 10^{-3}\text{ kg}$

Rounding to two significant figures, we get $9.5 \times 10^{-3}\text{ kg}$.

Conclusion

Comparing our result to the given options, it matches option C.

Exam Tip

Always remember to convert time from hours or minutes to seconds before plugging it into the formula. Many students lose marks because they forget this conversion! Also, keep an eye on the units of the Ece provided in the question—if it is given in $\text{kg/C}$, your final answer will be in $\text{kg}$.