A 2.0 g sample of a mixture containing
`Na _(2) CO _(3), Na HCO _(3)` and is gently `Na _(2) SO _(4)`
heated till the evolution of `CO_(2)` stops. The evolved `CO_(2) `has volume of 123.9 mL measured at 50 mm Hg pressure and 298 K.
1.5 g of the same sample is completely neutralised by 150 mL of 0.1M HCl. The percentage composition of `Na_(2) SO_(4)` in the original mixture is:

Answer

32

Explanation

In 2g sample `toCO _(2)` Liberated
Moles of `CO _(2)`
`= (( 750)/( 760) xx (123. 9 )/(1000) xx (1)/( 0. 082) xx (1)/( 298)) = 5xx 10 ^(-3) = 5 xx 10 ^(-3)`
moles `= 5 m M -= 10 m M ` of `Na HCO _(3)` in mixture
Moles of `Na HCO _(3)` in 2 g sample `= 2 xx 5 xx ` 10 m M
1.5 g sample `-= 150 xx (1)/(10) = 15 mM ` of HCl
`2.0g` sample `-= 15 xx (2)/(1.5) = 20 ` mM.
20 mM HCl will be utilised by
10 mM `NaHCO _(3)`
`+ 5 mM Na _(2) CO _(3)` present in 2 g sample
`Na HCO _(3) = 10 mM = 10 xx 10 ^(-3) xx 84 = 0.84g (42 %)`
`Na _(2) CO _(3) = 5 mM = 5 xx 10 ^(-3) xx 104`
`= 0. 52 g = ( 26%)`
`Na _(2) SO _(4) = ` (By difference) `= 0. 64 g (32%)`