IN the analysis of `0.5 g` sample of feldspar, a mixture of chlorides of sodium and potassium is obtained which weighs `0.1180 g`. Subsequent treatment of the mixed chlorides with silver nitrate gives `0.2451 g` of silver chloride. What is the percentage of sodium oxide and potassium oxide in the sample ?

Answer

(i) `0.0179g`, (ii) `10.6 %`

Explanation

Oxides of sodium and potassium are converted into chlorides according to following reactions:
`Na_(2)O+2HCl rarr 2NaCl +H_(2)O`
`K_(2)O+2HCl rarr 2KCl+H_(2)O`
Finally all the chlorides of `NaCl` and `KCl` are converted into `AgCl`, hence
moles of `(NaCl+KCl)=` moles of `AgCl`
(one mole of either `NaCl` or `KCl` gives one mole of `AgCl`)
Now, let the chloride mixture contain `x` g `NaCl`.
`implies x/58.5+(0.118-x)/74.5=0.2451/143.5`
Solving for `x` gives `x=0.0338 h` (mass of `NaCl`)
`implies` Mass of `KCl=0.118-0.0338`
`=0.0842 g`
Also, moles of `Na_(2)O=1/2 xx` moles of `NaCl`
`implies` Mass of `Na_(2)O=1/2xx0.0338/58.5xx62=0.0179g`
Similarly, mass of `K_(2)O=1/2xx0.0842/74.5xx94=0.053 g`
`implies` Mass `%` of `Na_(2)O=0.0179/0.5xx100=3.58%`
Mass `%` of `K_(2)O=0.053/0.5xx100=10.6%`