Washing soda has the formula `Na_(2) CO_(2).10H_(2)O`. What is mass of anhydrous sodium carbonate left when all the water of crystallisation is expelled by heating 57.2 g of washing soda?

Explanation

`Na_(2)CO_(3).10H_(2)Ooverset("Heat")toNa_(2)CO_(3)+10H_(2)O`
Molecular weight of `Na_(2)CO_(3).10H_(2)O`
`= 2 xx 23 + 12 + 3 xx 16 + 10 [1 xx 2 + 16] `
=46+ 12+48+ 180=286
Molecular weight of `Na_(2)CO_(3) = 2 xx 23 + 12 + 3 xx 16 `
`=46+12+48=106`
286 g of `Na_(2)CO_(3).10H_(2)O` leaves `Na_(2)CO_(3) = 106 g `
`therefore57.2g` of `Na_(2)CO_(3).10H_(2)O` leaves `Na_(2)CO_(3)`
`=106/286xx57.2=21.2`g