Question

A chemist decomposes samples of several compounds; the masses of their constituent elements are listed. Calculate the empirical formula for each compound.

Express your answer as a chemical formula.

A. 0.2907 g F, 0.1224 g O

B. 0.205 g Al, 0.569 g As, 0.486 g O

C.1.443 g Se, 5.841 g Br

Answer 1

A)

1 mole of F = 19 gram

0.2907 g F = 0.0153 mole F

1 mole of O = 16 g

0.1224 g O = 0.00765 mole O

now 0.0153/0.00765 = 2

the empirical formula = F₂O

B)

1 mole of Al = 27 gram

0.205 g Al = 0.007592 mole Al

1 mole of As = 75 gram

0.569 g As = 0.0075866 mole As

1 mole of O = 16 g

0.486 g O = 0.030375 mole O

Al : As : O = 1 : 1 : 4

empirical formula = AlAsO₄

C)

1 mole of Se = 79 g

1.443 g Se = 0.018265 mole Se

1 mole of Br = 79.9 g

5.841 g Br = 0.0731 moles Br

Se : Br = 1 : 4

empirical formula = SeBr₄