The freezing-point depression of a .100m MgSO4 solution is 0.225C. Determine the experimental van't hoff factor of MgSO4 at this concentration. Please help! I have no idea what to do.

Question

The freezing-point depression  of a .100m MgSO4 solution is 0.225C. Determine the experimental van't hoff factor of MgSO4 at this concentration. Please help! I have no idea what to do.

aaronq · Answer

use the freezing-point depression formula, plug in and solve

anonymous · Answer

ok, but what are the values? I know the formula is $$\Delta T _{f}=K _{f}m$$. I know the molarity but is the .225 the change in freezing point or the constant??

aaronq · Answer

you're mission the constant in the equation 

$$DeltaT=iK _{f}m$$

aaronq · Answer

i= van't hoff constant

anonymous · Answer

wouldn't I be missing two variables if I use that formula? I think that's why my book says to use the normal formula and then use the i =(actual number of particles in solution after dissociation /number of formula units initially dissolved in solution)

aaronq · Answer

you look Kf up in a table?

how would you know the amount of dissoluted particles?

anonymous · Answer

it's not mentioned in my book.

aaronq · Answer

sorry i've been looking for it can't find it on the internet. are you sure it's not in the book?

preetha · Answer

You need to look up Kf.  Kf is the same for a given solvent at a given temp.  You have Kf, you have m, DeltaT.  Solve for i.  I is the number of particles or vanthoff actor.  For MgSO4 it should be 2.  Each MgSO4 will dissolve and give you 2 particles so the depression in FP is twice as much as say the same concentration of glucose solute.

anonymous · Answer

The answer is i=1.21 so..how can I calculate that?