In the process of developing a photographic film, silver bromide is dissolved by adding a solution of sodium thiosulphate: AgBr(s)+2NaS2O3=Na3Ag(S2O3)2(aq)+NaBr(aq)

If you want to dissolve0.250g of AgBr (fw 187.8), how many milliliters of 0.0139 M Na2S2O3 should you add?

Question

In the process of developing a photographic film, silver bromide is dissolved by adding a solution of sodium thiosulphate: AgBr(s)+2NaS2O3=Na3Ag(S2O3)2(aq)+NaBr(aq)

If you want to dissolve0.250g of AgBr (fw 187.8), how many milliliters of 0.0139 M Na2S2O3 should you add?

anonymous · Answer

I know the right answer is 163mL. I just can't figure out how to get that answer. I'm not even getting close to the right answer.

anonymous · Answer

Sorry that is 193mL NOT 163mL

aaronq · Answer

since everything stoichiometrically reacts in ratios of moles, convert all the units into moles

aaronq · Answer

for every mole of AgBr you need 2 of NaS...

then once you know the amount of moles

molarity=moles/L of solvent

anonymous · Answer

Yes but I'm not getting to 193mL. Im getting really small decimal amounts

aaronq · Answer

did you convert from L to millilitres?

anonymous · Answer

ok I got  it thank you. Its 0.250g(1/187.8g)=1.00133molAgBr x (2/1)=0.00266molNa2S2O3
0.0138M=0.0138mol/L x(1L/1000mL)=0.0000138mol/mL
0.00266/0.0000138=193mL Na2S2O3