Question

What mass of `Na_(2)SO_(4).7H_(2)O` contains exactly `6.023 xx 10^(22)` atoms of oxygen ? .

Answer 1

Molar mass of `Na_(2) SO_(4).7H_(2)O = 275 gm`
`1` mole `Na_(2)SO_(4).7H_(2)O` has `11` mol `O` atoms
`rArr 11N_(A) O- "atoms are in" 275 g Na_(2)SO_(4).7H_(2)O`
`rArr 6.023 xx 10^(22) O -"atoms are in" =(275)/(11 xx 6.023 xx 10^(23)) xx 6.023 xx 10^(22) g = 2.5g` .