Problem regarding failure of equivalence concept


> 
> Chile salt peter, a source of $\ce{NaNO3}$ also contains $\ce{NaIO3}$. The $\ce{NaIO3}$ can be used as a source of iodine, produced in the following reactions.
> 
> 
> \begin{align}
> \ce{IO3- + 3 HSO3- &-> I- + 3 H+ + 3 SO4^2-} \tag{i}\\
> \ce{5 I- + IO3- + 6 H+ &-> 3 I2 (s) + 3 H2O} \tag{ii}
> \end{align}
> 
> 
> One litre of chile salt peter solution containing $\pu{5.80 g}$ $\ce{NaIO3}$ is treated with stoichiometric quantity of $\ce{NaHSO3}$. Now an additional amount of same solution is added to the reaction mixture to bring about the second reaction. How many grams of $\ce{NaHSO3}$ are required in step (i) and what additional volume of chile salt peter must be added in step (ii) to bring in complete conversion of $\ce{I-}$ to $\ce{I2}$?
> 
> 
> 


My working out using Mole concept:
[![enter image description here](https://i.stack.imgur.com/XhRjp.jpg)](https://i.stack.imgur.com/XhRjp.jpg)


My working out using equivalence:
[![enter image description here](https://i.stack.imgur.com/j2Uiq.jpg)](https://i.stack.imgur.com/j2Uiq.jpg)


Why does the equivalence concept not work?
Please tell me what is wrong and what is the correct method to use equivalence.


