`1.5 g` sample of `P_(2)O_(3)` and some impurity was dissolved in water and warmed gentally till `P_(2)O_(3)` disproportionated quantitatively to `PH_(3)` and `H_(3)PO_(4)`. The solutions was then boiled to get rid off `PH_(3(g))` and then cooled finally to room temperature and diluted to `100 mL`. `10 mL` of this solution was mixed with `20 mL` of `0.3M NaOH`. Now `10 mL` of this solution required `3.6 mL` of `0.05 M H_(2)SO_(4)` for back titration. Determine `%` by weight of `P_(2)O_(3)` in sample.

Answer

`80%`;