Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Sis290025 on January 20, 2006, 12:52:30 PM
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A solution is prepared by dissolving 171 g of CdCl2 in enough water to make 250.0 mL of solution. If the density of the solution is 1.556 g/mL, what is the molarity of the solution?
a.0.440 M
b.3.73 M
c.0.933 M
d.0.684 M
Molarity = (mol solute)/(L solution)
Now my key question of this problem is about the given density. How do you use it (if you do use it)?
Normally, I would do so:
171 g CdCl2 * (1 mol CdCl2/183.311 g CdCl2) = 0.9328409 mol CdCl2
It is given that the solution volume = 250 mL = 0.250 L.
M = 0.9328409 mol CdCl2/0.250 L = 3.73 M
But the density is confusing me.
Please help soon.
Thank you.
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You don't need the density to calculate the molarity in this case!
c=n/V
n=m/M = 0.9328409 mol
V=0.25L
c=0.9328409 mol / 0.25L = 3.73 mol/L