# Given the reaction:Na2S2O3(aq) + 4Cl2(g) + 5H2O(aq) --> 2NaHSO4(aq) + 8HCl(aq), how many moles of Na2S2O3 are needed to react with 0.12mol of Cl2?

0.03 mol $N {a}_{2} {S}_{2} {O}_{3}$
We can use the mole ratio to solve this problem. We will assume that we have excess ${H}_{2} O$ and it won't effect our ratio. We are told that we will react 0.12 mol of $C {l}_{2}$ so we will start there.
$0.012 m o l C {l}_{2}$ X $\frac{1 m o l N {a}_{2} {S}_{2} {O}_{3}}{4 m o l C {l}_{2}}$= $0.03 m o l N {a}_{2} {S}_{2} {O}_{3}$