the reacting equation of the reaction is as follows
AgBr (S) + 2 Na2S2O3 ----> Na3Ag(S2O3) + NaBr
the moles of Na2S203= 0.350 x 1l= 0.350moles
by use of reacting ratio AgBr to Na2S2O3 which is 1:2
therefore the moles of AgBr = 0.350/2=0.175moles
mass is hence= moles x molar mass of AgBr
0.175 x187.8=32.865g
