[sundrops]

Ok I"m having a little trouble. I know this question is pretty textbook but i can't get it right and i dont know why...

Calculate the freezing point of a solution of 3.20 g of naphthalene (C10H8) in 16.95 g of benzene.
The freezing point of pure benzene is 5.5°C.
Kf = 5.12°C kg/mol.

[3.2g C10H8 / 128.2 g/mol C10H8 ] = 0.025 mol C10H8

[0.025 mol C10H8 / 0.00698kg benzene ] = 3.59 mol/kg

M(solute) * Kf = delta T
3.59 mol/kg * 5.12 = 18.39

delta T = Tf - Ti
18.39 = 5.5 - T1
T1 - -13

i also inputted +13, +18
and I've already used up 8 tries - please *delete me*  

[elaineiiv]

 I believe your mistake is very basic. you simply misread something 16.98g is not equal to .00698kg(which gives you 3.58) but to .01698kg wich gives you a value of 1.47. big difference.

also, in your last calculations, I'm not sure how you get Ti to equal -13. check wether you're not making an error with the negative signs

hope that helps