Question

6. Realgar is a deep red pigment used in painting. A 0.6817 g sample was found to contain 0.4774 g arsenic; the remainder was sulfur. The formula weight of this compound was measured to be 428, What are the empirical and molecular formulas of this compound?

Answer 1

answer and explanation

Total mass = 0.6817 g

Mass of arsenic = 0.4774 g

Mass of sulphur = 0.6817 – 0.4774 =0.2043 g

Then we must determine the mols for arsenic and sulphur

for Arsenic

mass = 0.4774 g

molar mass = 74.92 g/mol

mols = 0.4774g/74.92g/mol = 0.0064 mols

for sulphur

mass = 0.2043

molar mass = 32.06

mols = 0.2043/32.06 = 0.0064 mols

therefor the empirical formula is

As₁S ₁

and the empirical formula mass is

74.92+32.06 = 106.98 g/mol

therefor the molecular formula of the compound will be:

428/106.98 = 4.00

therefor the molecular formula is

As₄S₄