Question

Calculate the freezing point of a sample of seawater having a salinity of 3.8 % . Use a van’t Hoff factor of 1.9 in your calculation. Assume the sample contains water as the solvent and NaCl as the solute. Express the temperature in degrees Celsius to one decimal place.

Answer 1

suppose mass = 1 kg or 1000 grams

mass of NaCl = mass percentage * mass of solution / 100

= 3.8 * 1000 / 100

= 38 grams

moles of NaCl = mass / molar mass

= 38 / 58.5

= 0.65

molality = moles / mass of solvent ( in kg)

= 0.65 / 1

= 0.65 m

delta T = i*Kf*molality

Kf = 1.86 C/m

= 1.9*1.86 * 0.65

= 2.30

freezing point of pure water = 0 C

T(solution) = Pure water temperature - delta T

= 0 - 2.30

= -2.3 C

any query please comment

if satisfiesd please rate it thanks