A teacher demonstrated the process of electrolysis of a molten salt using an unknown metal salt, XBr₂ - VCE - SSCE Chemistry - Question 9 - 2012 - Paper 1

To determine the amount of metal X deposited at the cathode, we first calculate the total charge (Q) passed through the circuit using the formula:

$Q = I \times t$

where:

• I = current in amperes = 1.50 A
• t = time in seconds = 30.0 minutes = 30.0 \times 60 = 1800 s

Calculating Q: $Q = 1.50 \times 1800 = 2700 \text{ C}$

Next, we apply Faraday's law to find the number of moles of metal X deposited:

$n = \frac{Q}{F \times z}$

where:

• F = Faraday's constant = 96485 C/mol
• z = charge number of metal ion (assumed to be 2 for this case)

Substituting the values: $n = \frac{2700}{96485 \times 2} = 0.0140 \text{ mol}$

To identify metal X, we can use the mass of the metal produced and its molar mass. The molar mass of metal X is calculated as:

$M(X) = \frac{\text{mass}}{n} = \frac{2.09}{0.0140} \approx 149.29 \text{ g/mol}$

Looking at the periodic table, the metal whose molar mass is closest to 149.29 g/mol is likely to be Rhodium (Rh), which has a molar mass of approximately 102.91 g/mol. Therefore, metal X can be identified as Rhodium.