Acompound is found to contain 6.360 % silicon, 36.18 % bromine, and 57.46 % iodine by mass. what is the molecular formula for this compound?

The empirical formula is SiBr₂I₂.

Explanation:

We can’t calculate the molecular formula, because we don’t know the molar mass of the compound.

Assume that you have 100 g of the compound.  

Then you have 6.360 g Si, 36.18 g Br, and 57.46 g I.  

1. Calculate the moles of each element.

Moles of Si  = 6.360× 1/28.08  = 0.2265 mol Si

Moles of Br = 36.18 × 1/79.90   = 0.4528 mol Br

Moles of I   = 57.46 × 1/126.90 = 0.4449 mol I

2. Calculate the molar ratios.  

Divide all values by the smallest number.

Si:  0.2265/0.2265  = 1

Br: 0.4528/0.2265   = 2.000

I:    0.4449/0.2265   = 1.964

3. Determine the empirical formula

Round off all numbers to the closest integer.  

Si:  1

Br: 2

I:    2

The empirical formula is SiBr₂I₂.