The amount of sodium hypochlorite in a bleach solution can be determined by
using a given volume of bleach to oxidize excess iodide ion to iodine;
\(\mathrm{ClO}^{-}\) is reduced to \(\mathrm{Cl}^{-}\). The amount of iodine
produced by the redox reaction is determined by titration with sodium
thiosulfate, \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3} ; \mathrm{I}_{2}\)
is reduced to \(\mathrm{I}^{-}\). The sodium thiosulfate is oxidized to sodium
tetrathionate, \(\mathrm{Na}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}\). In this
analysis, potassium iodide was added in excess to \(5.00 \mathrm{~mL}\) of
bleach \(\left(d=1.00 \mathrm{~g} / \mathrm{cm}^{3}\right)\). If \(25.00
\mathrm{~mL}\) of \(0.0700 \mathrm{M} \mathrm{Na}_{2} \mathrm{~S}_{2}
\mathrm{O}_{3}\) was required
to reduce all the iodine produced by the bleach back to iodide, what is the
mass percent of \(\mathrm{NaClO}\) in the bleach?