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Find the empirical formula of a compound containing 40% sulfur and 60% oxygen, by mass. - Leaving Cert Chemistry - Question g - 2014

Question g

Find the empirical formula of a compound containing 40% sulfur and 60% oxygen, by mass.

Worked Solution & Example Answer:Find the empirical formula of a compound containing 40% sulfur and 60% oxygen, by mass. - Leaving Cert Chemistry - Question g - 2014

Step 1

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Answer

To find the moles of sulfur (S), we use the formula:

$\text{Moles of S} = \frac{\text{Mass of S}}{\text{Molar mass of S}}$

Given that the compound contains 40% sulfur by mass, and assuming 100 g of the compound:

Mass of S = 40 g.

The molar mass of sulfur (S) is approximately 32 g/mol:

$\text{Moles of S} = \frac{40 \text{ g}}{32 \text{ g/mol}} = 1.25 \text{ moles}$

Step 2

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Answer

Next, we calculate the moles of oxygen (O):

$\text{Moles of O} = \frac{\text{Mass of O}}{\text{Molar mass of O}}$

Given that the compound contains 60% oxygen by mass:

Mass of O = 60 g.

The molar mass of oxygen (O) is approximately 16 g/mol:

$\text{Moles of O} = \frac{60 \text{ g}}{16 \text{ g/mol}} = 3.75 \text{ moles}$

Step 3

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Answer

Now, we find the simplest whole number ratio of the moles of sulfur to oxygen:

$\text{Ratio of S to O} = \frac{1.25}{1.25} : \frac{3.75}{1.25} = 1 : 3$

Thus, the empirical formula of the compound is:

SO₃

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