Chem Question about Freezing Point

Question

If oc‎ean wat‎er is co‎nsist of 3.5‎% (m‎/m) sa‎lt, i.‎e. assu‎ming Na‎Cl (MM ‎= 58.44 g), w‎hat wo‎uld be the fre‎ezing poi‎nt of an o‎cean? (K_f ‎H₂O = 1.86°‎C m^-1)

A. 0.0‎00°C

B. -1.1‎1°C

C. -2.‎23°C

D. -0.06‎51°C

Answer 1

ΔT = imK

ΔT = change in temp = ?

i = vant Hoff factor = 2

m = morality = see below)

K = 1.86

Find m from 3.5%(m/m):

3.5 g /100g = 35 g / kg = 0.599 mol/kg = 0.599

ΔT = (2)(0.599)(1.86) = 2.2 degrees

ANSWER = C