Answer:
Empirical formula: Na3S4O9
Molecular formula: Na6S8O18
Explanation:
1) To find the empirical formula, which is the simplest whole number ratio of each element that makes up this unknown compound, we first divide the portion of each element by it's respective atomic mass.
Na= 23g/mol, S= 32g/mol, O=16g/mol
Na = 20.2/23 = 0.878mol
S = 37.6/32 = 1.175mol
O = 42.2/16 = 2.638mol
Next, we divide each number of moles by the smallest value (0.878mol)
Na = 0.878/0.878 = 1
S = 1.175/0.878 = 1.34
O = 2.638/0.878 = 3.004
Next, we multiply each decimal fraction by 3 to make it whole no:
Na = 3
S= 4.02 ~ 4
O= 9.012 ~ 9
The simplest ratio between Na, S and O is 3:4:9 hence, the empirical formula is Na3S4O9
2) To get the molecular formula, we use the molecular weight of each element in the empirical ratio, and the overall molar mass of the compound i.e.
Molar mass of compound= 682.8g/mol
molecular weight of Na3S9O4 = (3 x 23g/mol) + (4 x 32 g/mol) + (9 x 16 g/mol)
= 69 + 128 + 144
= 341 g/mol
Hence, (Na3S4O9)n = 682.8g/mol
= (341)n = 682.8
n = 682.8/341
n = 2.002
n~ 2
Hence, molecular formula = (Na3S4O9)2
= Na6S8O18
