Question

A compound contains arsenic and oxygen as its only elements. A 1.626 g sample of the compound contains 1.060 g of arsenic. What is the empirical formula for this compound?

Answer 1

Our sample has 1.626 g, and 1.060 g is As.

Amount of Oxygen = 1.626 - 1.060 = 0.566 g O

Part 1) We must calculate the number of moles of each element:

Please, get the atomic masses of As and O from the periodic table.

For As) 1.060 g As x (1 mole As/74.92 g) = 0.01415 moles As

For O) 0.566 g O x (1 mole O/16.00 g) = 0.03537 moles O

Part 2) We need to calculate the subindexes we put in the empirical formula:

Let's divide the number of moles by the smallest one of them

For As) 0.01415 moles As/0.01415 moles As = 1

For O) 0.03537 moles O/0.01415 moles As = 2.5

We convert these 2 values into whole numbers, multiplying by 2:

1 x 2 = 2

2.5 x 2 = 5

The empirical formula: As2O5