Question

A 20.38 gram sample of cobalt is heated in the presence of excess sulfur. A metal sulfide is formed with a mass of 31.47 g. Determine the empirical formula of the metal sulfide.

Answer 1

Answer: The empirical formula of the metal sulfide is $CoBr_{2}$.

Explanation:

Given: Mass of metal = 20.38 g

Mass of metal sulfide = 31.47 g

Moles is the mass of a substance divided by its molar mass.

So, moles of cobalt (molar mass = 59 g/mol) are as follows.

$Moles = \frac{mass}{molarmass}\\= \frac{20.38 g}{59 g/mol}\\= 0.345 mol$

Moles of bromine (molar mass = 80 g/mol) are as follows.

$Moles = \frac{(31.47 - 20.38) g}{80 g/mol}\\= \frac{11.09 g}{80 g/mol}\\= 0.138 mol$

Now, the ratio of number of moles of cobalt and number of moles of bromine are as follows.

Moles of Co : Moles of Br = 1 : 2

Hence, the empirical formula is $CoBr_{2}$.

Thus, we can conclude that the empirical formula of the metal sulfide is $CoBr_{2}$.