Question

Thyroxine, the hormone has given below structure

The percentage of iodine in thyroxine is ____%. (nearest integer)

(Given molar mass in g mol$^{-1}$ C:12, H:1, O:16, N:14, I:127)

Answer 1

65%

Answer 2

1. Determine the molecular formula:
   The structure described is thyroxine, which has the formula

   $$\ce{C_{15}H_{11}I_4NO_4}$$

2. Calculate the molar mass:

   $$\begin{aligned} M &= 15\times12 \; (\text{C}) + 11\times1 \; (\text{H}) + 4\times127 \; (\text{I}) + 1\times14 \; (\text{N}) + 4\times16 \; (\text{O})\\[1mm] &= 180 + 11 + 508 + 14 + 64 = 777\, \text{g/mol} \end{aligned}$$

3. Find the percentage of iodine:
   Mass of iodine = $4\times127 = 508\,\text{g}$

   $$\%\,I = \left(\frac{508}{777}\right) \times 100 \approx 65.3\%$$

   Rounding to the nearest integer gives 65%.

Thyroxine’s molecular formula is $\ce{C15H11I4NO4}$. Its molar mass is calculated as 777 g/mol; iodine contributes 508 g. Thus, percentage iodine is $(508/777)\times100\approx65\%$.