[LolaGoesLala]

A1g 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 L solution was reacted with excess AgNO3 and 0.3800g of an AgCl precipitate formed. What was the mass % of D2O in the original sample of enriched water?

Atomic masses: (g/mol): H = 1 , D: 2 , O = 16 , Cl = 35.5 , Ag = 107.9

[Arkcon]

You could start to try to solve this problem with a series of balanced equations.  It will be useful, even for later problems.   Thing is, I don't see how this problem is solvable as stated, as both HCl and DCl will react with silver nitrate the same.  A little slower maybe, but the end product is the same.

[LolaGoesLala]

i did start actually:

H20 + CL2 -> 2HCL + 1/2O2
D20 + CL2 -> 2DCL + 1/2O2

H20 MASS = X
D20 MASS = 1-X

18x x 2(36.5) = H20 and HCL
20(1-x) x 2(37.5) = D20 and DCL

but then i don't know how to inclue 25 mL and 0.38 g of AgCL in there...

[Arkcon]

Write out that reaction, and you'll see what I'm talking about

[LolaGoesLala]

I just talked to one of the tutors.. this is what they said..

mass of AgCL =  total moles of HCL and DCL
0.00265 = (50x/10000) + ((30-30x)/20000)

[Borek]

You have two unknowns - amount of H and amount of D in the 1 g sample of water. Make it number of moles. Express mass of the water in terms of n_H and n_D (it will require molar masses), and express number of moles of AgCl in terms of n_H and n_D. Then solve.