The formula for sodium dihydorgen phosphate heptahydrate is:
NaH2PO4.7H2O
To determine the mass % of sodium you first need to find the total mass:
1 Na = 1 x 22.990 = 22.990
16 H = 16 x 1.0079 = 16.1264
1 P = 1 x 30.97 = 30.97
11 0 = 11 x 15.9994 = 175.9934
Total = 246.084 g
For the mass % of Sodium:
(22.99 g Na/246.084 g total)x 100% = 9.34%
