Calculating Mole Fraction from Molality: Sodium Nitrate Solution Example

[Qube]

Homework Statement

The molality of an aqueous sodium nitrate solution is 2.14 m. What is the mole fraction of sodium nitrate?

Homework Equations

Molality = moles of solute / kg of solvent.

Mole fraction of A = moles of A / total number of moles (in this case, moles of solute + moles of solution).

The Attempt at a Solution

Assuming we have 1 kg of solvent, we can assume we have 2.14 moles of NaNO3.

Mole fraction of NaNO3 is therefore 2.14 / [(1000/18) + 2.14] = 0.0370.

1000/18 because 1000 grams of water is present and there are 18 grams per mole of water. The grams cancel out and yield moles of water.

 

[Borek]

Looks OK. You will get slightly better result by using more accurate molar mass of water.

 

[Qube]

I appreciate your consideration and helpfulness!