Final answer:
To convert mass composition to an empirical formula, calculate the number of moles of each element, establish a molar ratio, and adjust the ratio to get the smallest whole numbers for each element, yielding the empirical formula.
Step-by-step explanation:
Converting Mass Composition to Empirical Formula
To derive an empirical formula from mass composition, follow these steps: First, calculate the number of moles of each element based on the mass given. Use the atomic weights to convert grams to moles. Then, divide the molar amounts by the smallest molar amount obtained to establish a tentative molar ratio. Finally, if the resulting numbers are not whole numbers, multiply all molar ratios by the smallest common factor to obtain the smallest whole-number empirical formula.
Example:
Suppose a substance contains 1.71 g of Carbon (C) and 0.287 g of Hydrogen (H). The molar mass of C is 12.01 g/mol, and for H, it is 1.01 g/mol. To determine the moles, divide the mass of each by its molar mass:
1.71 g C ÷ 12.01 g/mol = 0.142 moles of C
0.287 g H ÷ 1.01 g/mol = 0.284 moles of H
Now divide each by the smaller molar amount, which is 0.142 moles:
0.142 moles C ÷ 0.142 moles = 1
0.284 moles H ÷ 0.142 moles = 2
The simplest whole-number ratio is 1:2, so the empirical formula is CH2.