a Q on boiling point

[gomawum]

Advertisement - Members don't see this ad

in the kaplan book, the change of BP = Kb * m
but the other book says that change of BP = Kb * m * I
and I is the van't hoff factor,

and the question was
what is the BP of a 2m solution of NaCl in water? (Kb = 0.5)

which one should I use?

 

[gomawum]

one more thing , do I have to know all the solubility rule? such as SO4 2- is soluble in water except Ag, Pb, etc

 

[uvaGirL07]

in the kaplan book, the change of BP = Kb * m
but the other book says that change of BP = Kb * m * I
and I is the van't hoff factor,

and the question was
what is the BP of a 2m solution of NaCl in water? (Kb = 0.5)

which one should I use?

Use the second equation. You need to consider the dissociation if it occurs. I think Kaplan just assumed nonelectrolytes (where i = 1)... so I think they just left out the "i"... but if you're dealing with electrolytes, you definitely need to know that "i" is a part of that equation.

And YES, you should know the general solubility rules.

Hope that helps.

by the way...

NaCl dissociates into Na+ and Cl-, so your i = 2 in that case.

 

[sads786]

yeah i had the kaplan book too and they dont realize how important the i factore is because they assume its one in most probs...for NaCl, the i is 2 because as stated above NaCl breaks up into ions of Na+ and Cl-