Asked by write2khin

An aqueous solution of Na2SO4 has a molal concentration of 0.293 mol kg-1. Its density is 1.0350 g mL-1.

Calculate the molar concentration of Na2SO4.
----- mol L-1

Calculate the mass percent of Na2SO4 in the solution.
------- %

What is the mole fraction of Na2SO4 in the solution?
-----
How to work out , i cant figure it out




Answers

Answered by DrBob222
0.293 m = 0.293 moles/kg solvent.
Take enough to have 0.293 mole which will have 1 kg solvent.
0.293 moles x molar mass Na2SO4 = about 41 g (but you need to do it exactly). The solution thus has a mass of 1000 + 41 = 1041. Use the density to convert to mL, then to L and moles/L = M
Answered by DrBob222
0.293 m = 0.293 moles Na2SO4/1000 g solvent.
0.293 x 142.043 = about 42 grams solute (you need to do it accurately). The solution has a mass of 41+1000 = about 1041 grams. mass percent = (mass solute/g soln)*100 = (41/1041)*100 = ??
Answered by DrBob222
0.293 m = 0.293 moles/kg solvent.
Take enough solution to have 0.293 moles which will be 1 kg solvent.
0.293 moles Na2SO4.
moles H2O = 1000/18.015 = about 55.
Total moles = 55+0.293.
mole fraction Na2SO4 = (moles Na2SO4/total moles)
Answered by chrustek
thanks dr bob... this really helped :) but in question 1 & 2, why did u add 41 to 1000? where did u get the 1000 from?! thanks :)
Answered by mel<3
does anyone know how to convert to Ml in question one using the density?? im really confused :/
Answered by mel<3
sorry i mean mL woops :)
Answered by Dr. Chem
Question one answer, extended explanation :
divide 1041 g by the density (1.0350) to get volume- 1,006.382609mL
then use formula c = n/v
c = 41.606 / (142 x 1,006.382609)
= 0.000291141 mol/mL x 1000
= 0.291141756 mol/L
Answered by rita
DrBob's solution for the molar fraction is wrong. I did what he said moles Na2SO4/ total moles: 0.293/55.802.... to get 0.00250679 and in my online quiz it was wrong.
Answered by rita
woops i meant 0.005250707, still wrong.
Answered by Beth
I don't understand how we can know the total moles of solution if the question doesn't specify what the aqueous solution is. Do we always assume its water??
There are no AI answers yet. The ability to request AI answers is coming soon!

Related Questions