Mole fraction= Moles of x/total moles correct?

Can someone explain to me why you use the value they give for the mole fraction as the moles of solute in the molality equation? I dont see how the mole fraction can be substituted as is.

Thanks in advance

anyone? please help

They give you the number of moles of solute which is the mole fraction = 2x10^-18. You are asked to find the molality which is moles of solute/kg of solvent. The solvent is water in this case and for some reason you assume its 1 mole of water = .018 kg.

i dont know if this helps but i tried.....
http://en.wikipedia.org/wiki/Mole_fraction

Mole fraction= Moles of x/total moles correct?

Can someone explain to me why you use the value they give for the mole fraction as the moles of solute in the molality equation? I dont see how the mole fraction can be substituted as is.

Thanks in advance

If you still need help can you post the entire problem?

Mole fraction= Moles of x/total moles correct?

Can someone explain to me why you use the value they give for the mole fraction as the moles of solute in the molality equation? I dont see how the mole fraction can be substituted as is.

Thanks in advance


same question...how do you figure that - why you use the value they give for the mole fraction as the moles of solute in the molality equation?

I understand what the equations are i just don't see why the mole fraction amount is getting used for moles of solute? does it have somethign to do with why we assume 1 mole?

Molality(m) = mole of solute/Kg of solvent

To solve this problem, we need to know the mole of solute(gas) and Kg of slovent(H2O) but what is given is only the mole fraction, 2x10^-18.

Mole fraction = Moles of solute/total moles of solute and solvent = Moles of gas/(Moles of gas + Moles of H2O)

From the Mole fraction given, let's say the solute gas is 2x10^-18 mole, then the total moles of solute and solvent should be 1 mole to make the mole fraction of 2x10^-18. However, the moles of gas is so small compared to H2O, we can approximate the total mole is equal to the mole of solvent H2O, i.e. mole fraction 2x10^-18 = 2x10^-18 mole gas/1 mole H2O

Now, we know the mole of solute = 2x10^-18 mole gas
then what's the Kg of solvent? => 1 mole H2O = 18g = 0.018Kg
Insert these numbers on the molality formula above. 2x10^-18 mole gas/0.018Kg = 1.11x10^-16m approximately 1x10^-16m.