The concentration of the alkane in a particular sample of rainwater is 0.2 ppb. assume that the density of rainwater is close to 1.00 g/ml and find the molar concentration of

Ppb stands for parts per billion 10⁻⁹.

M (C₂₀H₄₂, alkane) = 282,55 g/mol.

V (C₂₀H₄₂) = 1000 ml = 1 dm³.

m (C₂₀H₄₂) = 2·10⁻⁷ g.

n (C₂₀H₄₂) = m (C₂₀H₄₂) : M (C₂₀H₄₂).

n (C₂₀H₄₂) = 2·10⁻⁷ g : 282,55 g/mol.

n (C₂₀H₄₂) = 7,07·10⁻¹⁰ mol.

c (C₂₀H₄₂) = n (C₂₀H₄₂) : V (C₂₀H₄₂).

c (C₂₀H₄₂) = 7,07·10⁻¹⁰ mol/dm³.