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determining an unknown solid using freezing point?
Suppose it is found that the actual molecular mass of your unknown solid is exactly two times larger than that which you determined experimentally. What could you conclude about the nature of your unknown solid and the assumptions you made in your calculations?
1 Answer
- NikhileshLv 77 years agoFavorite Answer
Answer
Depression of freezing point is expressed by
ΔTf = molality * Kf * i
Molality = moles of solute / kg solvent ,[ Mass of solute /Molar mass of solute]/kg solvent
Kf = freezing point constant
i = Van't Hoff factor
Depression of freezing point is a product of molality, freezing point depression constant and Vant Hoff factor
When Vant factor is halved molality has to double , in a given condition, with everything constant, this is only possible if molar mass is halved
Relation between molar mass and Vant Hoff factor:
ΔTf = moles of solute / kg solvent * Kf * i
moles of solute = [ ΔTf * kg solvent] / kf * i
Mass of solute / molar mass of solute = [ ΔTf * kg solvent] / kf * i
Molar mass of solute = Mass of solute*kf* i/ [ ΔTf * kg solvent]
In a given situation with all being constant , Molar mass is directly influenced by Vant Hoff factor
Coming to the question - Where the assumptions would have gone wrong
1. It must have been assumed that the solid is a non electrolyte, with Vant Hoff factor = 1
2. Actually the unknown compound is an ionic compound with Vant Hoff factor = 2
