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 find the amount of metal X deposited on the cathode, we can use the formula:

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

where:

• $Q$ = total charge (in coulombs)
• $F$ = Faraday's constant = $96500 \, C/mol$

First, we calculate the total charge $Q$:

• Current ($I$) = 1.50 A
• Time ($t$) = 30.0 min = 30.0 × 60 s = 1800 s

Substituting we find: $Q = I \times t = 1.50 \, A \times 1800 \, s = 2700 \, C$

Now using this charge: $n = \frac{2700}{96500} \approx 0.0279 \, mol$

From the mass of metal X produced (2.09 g) and the amount in moles calculated (0.0279 mol), we can find the molar mass ($M$) of metal X:

$M = \frac{\text{mass}}{n} = \frac{2.09 \, g}{0.0279 \, mol} \approx 75.0 \, g/mol$

Based on the calculated molar mass, metal X is likely to be chromium (Cr), which has an atomic mass around 51.8 g/mol, indicating it is likely a divalent ion.