The first step is to find the empirical formula by dividing the percent composition by the respective atomic/molecular masses and finding the smallest whole-number ratio of the elements. The molar ratios will give the subscripts of the empirical formula.
For carbon:
75.95 g C / 12.011 g/mol C = 6.324 mol C
For nitrogen:
17.72 g N / 14.007 g/mol N = 1.262 mol N
For hydrogen:
6.33 g H / 1.008 g/mol H = 6.286 mol H
The smallest whole-number ratio of these molar ratios is approximately 1:1:1. Therefore, the empirical formula is C1H1N1, which can be simplified to just "CHN".
Next, we need to find the molecular formula by determining how many empirical formula units are in the molecule. To do this, we divide the molar mass of the compound by the empirical formula mass.
Empirical formula mass = 12.011 + 1.008 + 14.007 = 27.026 g/mol
Molecule formula units = 240 g/mol / 27.026 g/mol = 8.88
The molecular formula is then obtained by multiplying the subscripts in the empirical formula by 8.88:
C8.88H8.88N8.88
Simplifying (dividing by 8.88 and rounding to the nearest whole number), we get:
C1H1N1
Therefore, the molecular formula is the same as the empirical formula: CHN.
An unknown compound has a percent composition of 75.95% C, 17.72% N, and 6.33% H by mass with a molar mass of about 240 g/mol. Determine the molecular formula of the dye. (Atomic mass of C-12.011 g/mol; N =14.007 g/mol; H- 1.008 g/mol).
C10H15N3
C15H10N3
C15H15N3
C15H12N3
1 answer