Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: ozzlomo on May 04, 2009, 10:06:18 PM
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Sodium Fluoride has a solubility of 4.22g per 100g of water at 18 degrees C. Express this solute in terms of mole fraction, mass percent, and molality.
Sodium Fluoride (NaF) moles : 4.22g / 41.99 g/mol = .101 moles
H2O moles: 100g / (18.02 g/mol) = 5.55 moles
NaF Mole Fraction : .101 moles / 5.651 moles =
NaF Mass Percent : 4.22g / 104.22g X 100 = 4.05 %
Molality: 0.101 moles / 0.1 kg = 1.01 m
What are the mole fractions of ethanol (C2H5OH) and water in a solution prepared by mixing 60.0 ml of ethanol with 40.0 ml of water at 25 degrees C? The densities of ethanol and water at this temperature are 0.789 g/mol and 1.00 g/ml respectively.
Volume of ethanol is 60.0 ml.
60.0 ml X 7.89g/1ml = 473.4g
473.4g / 46.08 g/mol = 10.27 moles Ethanol
Volume of H2O is 40.0 ml.
40.0ml X 1.00g/1ml = 40.0g
40.0g / 18.02 g/mol = 2.22 moles H2O
Ethanol Mole Fraction: 0.178
H2O Mole Fraction: 0.822
Are my answers, units, and sig. figs correct?
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The first one is correct.
In the task you wrote:
0.789 g/mol
And then you counted:
60.0 ml X 7.89g/1ml = 473.4g
You also mixed up unit.