Finding volume using Molarity + Equation

[ballinbob]

Homework Statement

In the photographic process silver bromide is dissolved by adding sodium thiosulfate. Determine the volume in mL of 0.0138 M Na2S2O3 should be added to dissolve 0.250 g of AgBr.

Homework Equations

The equation is : AgBr (s) + Na2S2O3 (aq) → Na3Ag(S2O3)2 (aq) + NaBr (aq)

The Attempt at a Solution

I know your supposed to use the definition of molarity and do some conversions, but it would never turn out right. The answer sheet says the answer is 194 mL.

Thanks everyone

 

[Borek]

Show how you are doing it. I got 193 mL - most likely because of the slightly different molar masses used.