Question

Arrange the following aqueous solutions in order of decreasing freezing points (lowest to highest temperature): 0.10 m Na3PO4, 0.35 m NaCl, 0.20 m MgCl, 0.15 m C6H12O6 and 0.15 m CH3COOH.

Answer 1

delta T = i*Kf*m

i is the van't Hoff factor which is 4 for Na3PO4, 2 for NaCl, 3 for MgCl2(you made a typo here), 1 for C6H12O6 and 1 for CH3COOH.

Example for Na3PO4.
delta T = 4*1.86*0.1 = ?

For NaCl:
delta T = 2*1.86*0.35 = ?

Then freezing point = 0 - delta T = ?

So which has the lower freezing point.
Calculate all of them then arrange in order.

Answer 2

C6H12O6>CH3COOH>Na3PO4>MgCl2>NaCl