# chemistry

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The molecular mass of a substance was determined by the freezing point depression technique. The minimum data required for the determination are

a. delta Tf and Kf only.
b. delta Tf , Kf and mass of solute.
c. delta Tf , Kf , mass of solute and mass of solvent.
d. delta Tf , Kf , mass of solute, mass of solvent and identity of solvent.
e. delta Tf , Kf , mass of solute, mass of solvent and identity of solvent and solute

?

• chemistry -

delta T = dT = i*Kf*m
m = mols/kg solvent
moles solute = g solute/molar mass solute

Working backwards, this is what we must have.
moles = g solute/molar mass solute.
If we are to solve for molar mass solute, we must have g solute in order to know moles.

Next we have m = moles/kg solvent
We have moles now, so to solve for m we must have kg solvent.

Next we have delta T = Kf*m
We now have m, we must have
Kf and delta T

I have typed in bold those that we must have. In addition, we must know i in dT = i*Kf*m. If we know the identity of the solvent and identity of the solvent, we usually know i, the van't Hoff factor.

• chemistry -

so its e?

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