Question

The molefraction of naphtlalene in n-heptane (MM=100) is 0.2 The molality of the solution is?

Answer 1

naphthalene is C10H8. and heptane C7H16. what are their molar masses?

Answer 2

C10H8 - 128

C7H16 - 100

Answer 3

how many moles in a 1kg of heptane?

Answer 4

1000/100 = 10

Answer 5

okay, now according to the mole fraction, how many moles of napthalene per 10 moles of heptane if mole fraction is 0.2

rememver mole fraction is no. of moles/total no. of moles.

Answer 6

*remember.

Answer 7

Did nt understand!

Answer 8

0.2 mole fraction means that there 0.2 moles of napthalene for every mole in the mixture,

Answer 9

ok!

Answer 10

we need to sind molality= No of moles of solute/ 1 kg solvent @apoorvk

Answer 11

yes i know that lo.

if there is 0.2 mole of napthalene in the mixture, that means, 0.8 mole is that of heptane. so

for every 4 moles of solvent, 1 moles is the solute.
how many moles of solute then for 10 moles aka 1 kg of this solvent?

Answer 12

2.5 mole??

Answer 13

@apoorvk r u there

Answer 14

yes. so what's the molality? try this yourself, we are almost there. actually there.

Answer 15

m=2.5 is it?

Answer 16

yes, right-o!!