chp 9 question below

Question

How many milliliters of 0.0210 MM Na2S2O3Na2S2O3 solution are needed to dissolve 0.640 gg of AgBrAgBr?

AgBr(s)+2Na2S2O3(aq)→Na3Ag(S2O3)2(aq)+NaBr(aq)

Answer 1

How many milliliters of 0.0210 M Na₂SO₃ solution are needed to dissolve 0.640 g of AgBr?

AgBr(s) + 2Na₂SO₃(aq) ==> Na₃Ag(S₂O₃)₂ (aq) + NaBr(aq) .. balanced equation

mols AgBr present = 0.640 g AgBr x 1 mol AgBr / 187.8 g = 3.41x10^-3 mols AgBr

mols Na₂SO₃ needed = 3.41x10^-3 mol AgBr x 2 mol Na₂SO₃ / mol AgBr = 6.82x10^-3 mol Na₂SO₃

Volume (mls) Na₂SO₃ needed = 6.82x10^-3 mol x 1 L / 0.0210 mol x 1000 ml / L = 325 mls Na₂SO₃ needed