Question

Hydrogen sulfide (H₂S) is a highly toxic gas. Assume the odor detection limit is approximately 4.7 x 10^-7 g H₂S per 1 g of air. The density of air is 0.0013 g/mL.

a) At this level, how many moles of H₂S are present in 1.0 L air?

b) How many H₂S molecules?

Answer 1

(a) Density of air = 0.0013 g/mL

volume of air = 1.0 L = 1000 mL

mass of air = (volume of air) * (density of air)

mass of air = (1000 mL) * (0.0013 g/mL)

mass of air = 1.3 g

concentration of H₂S = 4.7 x 10^-7 g / 1 g air

mass H₂S = (concentration of H₂S) * (mass of air)

mass H₂S = (4.7 x 10^-7 g / 1 g air) * (1.3 g air)

mass H₂S = 6.1 x 10^-7 g

moles H₂S = (mass H₂S) / (molar mass H₂S)

moles H₂S = (6.1 x 10^-7 g) / (34.08 g/mol)

moles H₂S = 1.8 x 10^-8 mol

(b) molecules of H₂S = (moles H₂S) * (Avogadro's number)

molecules of H₂S = (1.8 x 10^-8 mol) * (6.022 x 10²³ molecules / 1 mol)

molecules of H₂S = 1.1 x 10¹⁶ molecules