- #1

antonisz

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## Homework Statement

Calculate the molarity of a solution made by adding 35.5 mL of concentrated ammonia (28.0 % by mass, density 0.880 g/mL) to some water in a volumetric flask, then adding water to the mark to make exactly 250 mL of solution. (It is important to add concentrated acid or base to water, rather than the other way, to minimize splashing and maximize safety.)

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## Homework Equations

Molarity = mol / liter

Mass % = (grams of solute / grams of solution) * 100

Density = mass / volume

## The Attempt at a Solution

a) I used the ml of NH

_{3}to find the number of grams of NH

_{3}- 35.5 ml * 0.88 g/ml = 31.24 g

b) I then used that amount to find the number of mole - (31.24 g / 17.03) = 1.8344 mol of NH

_{3}

This is where I am stuck. I used the % mass formula to find that the total grams of solution is 111.57 (0.28 = 31.24 / x and cross multiply), but I have no idea where to go from here.

I know that if I compute the molarity using (1.8344 mol / .250 L) I'll get the moles of NH

_{3}at concentration 100%, would I need to multiply the number of moles by 0.28 to get the 28% concentration?

*Edit* Yes, it turns out that that would make sense, too much chemistry for the last 2 hours! I haven't taken Gen Chem in a couple years and getting thrown into Analytical, I should have reviewed some of these concepts. [/B]