Question

A 170 g sample of an unidentified compound contains 29.84 g Na, 67.49 g Cr, and 72.67 g O. What is the compounds empirical formula

Answer 1

To determine the empirical formula, divide the mass of each element by its atomic mass to find moles, then divide by the smallest mole value to get a whole number ratio. In this case, the empirical formula is Na2Cr2O7.

Step-by-step explanation:

To find the empirical formula of a compound from its mass composition, we divide the mass of each element by its atomic mass to find the relative number of moles of each element. Then, we divide by the smallest number of moles to get the simplest whole number ratio.

In this case, for sodium (Na), we have 29.84 g ÷ 22.99 g/mol = 1.297 moles.

For chromium (Cr), 67.49 g ÷ 51.996 g/mol = 1.298 moles.

For oxygen (O), 72.67 g ÷ 16.00 g/mol = 4.542 moles.

Dividing each by the smallest number, which is approximately 1.297, we get the empirical formula ratios as Na1Cr1O3.5.

Since we cannot have half an oxygen atom in the formula, we multiply each subscript by 2 to get whole numbers, resulting in Na2Cr2O7. Therefore, the empirical formula is Na2Cr2O7.