`0.56 g` of lime stone was treated with oxalic acid to give `CaC_(2)O_(4)`. The precipitate decolorized `45 ml` of `0.2N KMnO_(4)` in acid medium. Calculate `%` of `CaO` in lime stone.

Explanation

`underset(CaCO_(3))("Limestone")overset("Oxalic acid")rarrCaC_(2)O_(4)overset(KMnO_(4))rarr"decolorizes"`
`therefore` Redox changes:
For `CaC_(2)O_(4), C_(2)^(3+)rarr2C^(4+)+2e`
For `KMnO_(4), 5e+Mn^(7+)rarrMn^(2+)`
`therefore` Meq.of `CaCO_(3)=` Meq.of `CaC_(2)O_(4)=` meq.of `KMnO_(4)`
`because` Meq.of `CaCO_(3)=` Meq.of `CaO` ( since `CaO` is present in `CaCO_(3)`)
`therefore` Meq.of `CaO=` Meq.of `KMnO_(4)`
`(w)/(56//2)xx1000=45xx0.2`
Wt.of `CaO=0.252g`
`therefore %` of `CaO` in limestone `=(0.252)/(0.56)xx100=45%`