Question

A solution of `Na_(2)S_(2)O_(3)` is standardised iodometrically against 3.34 g of pure `KBrO_(3)` (converted to `Br^(-)`), requiring 40 mL `Na_(2)S_(2)O_(3)` solution. What is the molarity of `Na_(2)S_(2)O_(3)` solution ? (Molar mass of `KBrO_(3)=167 g "mol"^(-1)`)

Answer 1

Correct Answer - 3
Necessary equations :
`KBrO_(3)+KIrarrI_(2)Br^(-)`
`I_(2)+Na_(2)S_(2)O_(3)rarrNa_(2)S_(4)O_(6)+`Nal
equivalent of `I_(2)` = equivalent of `KBrO_(3)=12xx10^(-2)`
equivalent of `Na_(2)S_(2)O_(3)=`equivalent of `KBrO_(3)=12xx10^(-2)`
equivalent of `Na_(2)S_(2)O_(3)`=equivalent of `I_(2)`
`Mxx1xx(40)/(1000)=12xx10^(-2)`
so molarity = 3M.