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Lactose, C12H22O11, is a naturally occurring sugar found in mammalian milk. A 0.335M solution of lactose in water has a density of 1.0432 g/mL at 20∘C. What is the concentration of this solution in the following units?

a)Mole fraction: I got the anwser it is 6.46*10-3

b) Mass parcent: Got the answer it is 11.0 %


C)Molality: Got this one wrong twice, i dont know why, i used the equation  moles of sulute over mass of solvent, but keep getting it wrong.

Maybe you confused molarity with molality? But that's not very possible, because molarity is already given.
Here is my attempt:
Molality is: b=n/msolvent
msolvent is the mass of the solvent. Since the mass percentage of lactose is 11%, the solvent should be the rest 89%. This means that the solvent is: 0,89*m
Also, we know that c=n/V. And density is ρ=m/V <=> V=m/ρ=m/1,0432
So, we go back to c=n/V and replace: c=n/(m/1,0432) <=>c=1,0432*n/m <=> n=c*m/1,0432

Now, we can calculate molality: b=n/msolvent=(c*m/1,0432)/(0,89*m)=0,035/(0,89*1,0432)=0,0377mol/g (=30,77mol/kg if it's wanted in SI)

What did you find?

this is what i found 0.361, I dont know how that answer came to be, maybe theres rounding involved or two step process of converting molarity to molality

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I wish i knew that lol the 0.361 is correct, But i used 0.355, sadly it was my third and final attempt, but i thanks for showing me How to do it.

thanks