Q1(b). Nanomolar concentration to ppb

Answer in brief

Approximately 2.29 ppb by mass, assuming water density 1.00 kg/L.

Key points

• Molar mass is 29(12.011)+60(1.008)=408.799 g/mol.
• Mass concentration is 5.6×10⁻⁹(408.799)=2.2893×10⁻⁶ g/L, or 2.2893 μg/L.
• In dilute water of density about 1 kg/L, 1 μg/L≈1 μg/kg=1 ppb.
• Hence the concentration is about 2.3 ppb to the precision of the input.