April 21, 2014

Homework Help: Chemistry

Posted by Adam-- Dr Bob, Help! on Wednesday, September 26, 2012 at 5:34pm.

I Posted this question the other day:

A 1.00 g sample of enriched water, a mixture of H2O and D2O, reacted completely with Cl2 to give a mixture of HCl and DCl. The HCl and DCl were then dissolved in pure H2O to make a 1.00 L solution. A 25.00 mL sample of the 1.00 L solution was reacted with excess AgNO3 and 0.3800 g of an AgCl precipitate formed.
What was the mass % of D2O in the original sample of enriched water?

your reply was :

I have deleted the original response and replaced it with the following. Check my thinking.

Cl2 + H2O ==> HOCl + HCl
Cl2 + D2O ==> DOCl + DCl

let x = mass H2O
and y = mass D2O
x + y = 1.00
[x*(molar mass AgCl/molar mass H2O)] + [y*(molar mass AgCl/molar mass D2O)] = 0.3800 x 1000/25

Two equation in two unknowns. Solve for x and y and convert to percent. Check my thinking.


I understand your reasoning and I feel that this should work, but when I try to solve it I am confused. My two equations would be :

x + y = 1.00

15.2=7.96x + 7.16y

when I solve

x= 10.05 and y = -9.05

I'm not sure if this is wrong or if I just don't understand the concept. When I would calculate the % D2O it doesn't really make sense...

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