Question

If 0.125 L of aqueous solution with a density of 0.810 g/mL contains 13.7 µl of ethanol, epress the concentration of ethanol in ppm, ppb, molarity, molality, and vol%. Pure ethanol has a density of 0.789 g/mL

Answer 1

Molarity = number of moles of solute/per L of solution

=> 2.498 *10^(-4)/0.125 = 1.9984 * 10^(-3) M

Molality = number of moles of solute/per Kg of solvent

Mass of solvent = 810 gm/L * 0.125L = 101.25 gms

Mass of ethanol = 789 gm/L * 13.7 * 10^(-6) L = 0.0108093 gms

molar mass of ethanol = 46 gm/mol

number of moles of ethanol = 0.0108093/46 = 2.498 * 10^(-4) moles

molality = 2.498 * 10^(-4)/(101.25/1000) = 0.00232 m

Volume Percentage = 13.7 * 10^(-6)/0.125 * 100 = 1.0960 * 10^(-2)%

ppm = mg/L = 10.8093/0.125 = 86.4744 ppm

ppb = mg/uL = 86474.4 ppb