How can the vant Hoff factor be used for electrolytes? How is this problem done (step-by-step)? Thank you.

When 198. g of alanine (C3H7NO2) are dissolved in 1500. g of a certain mystery liquid X, the freezing point of the solution is 4.20 less than the freezing point of pure X Calculate the mass of iron(III) nitrate (Fe(NO3)3) that must be dissolved in the same mass of X to produce the same depression in freezing point. The van't Hoff factor i=3.40 for iron(III) nitrate in X. Be sure your answer has a unit symbol, if necessary, and is rounded to the correct number of significant digits