Homework Help: Chemistry

Posted by ALISON on Wednesday, December 14, 2011 at 1:04am.

An 8.00 mass % aqueous solution of ammonia has a density of 0.9651g/ml. Calculate the molality, molarity, and mole fraction of NH3.

This question seems simple but I cannot seem to remember how to do this. Help please?

Chemistry - Dr Russ, Wednesday, December 14, 2011 at 3:30am
I'll get you started....

8.00 mass percent means that 100 g of the solution as 8.00 g of ammonia and 94.00 g of water.

The 100 g of solution will have a volume of

100 g / 0.9651 g/ml

=103.61 ml

Thus (based on NH3) the 8.00 g represents 8.00 g /17 g mol
=0.4706 mol

so concentration is

0.4706 mol / 103.61 ml
=0.004542 mol/ml
or molarity = 4.542 mol/L

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