Question

Measurements show that unknown compound X has the following composition: element mass % chromium 68.4% oxygen 31.5% Write the empirical chemical formula of X.

Answer 1

Answer: The empirical formula of X is
`Cr_2O_3`

Step-by-step explanation:

If percentage are given then we are taking total mass is 100 grams.

So, the mass of each element is equal to the percentage given.

Mass of Cr = 68.4 g

Mass of O = 31.5 g

Step 1 : convert given masses into moles.

Moles of Cr =
`\frac{\text{ given mass of Cr}}{\text{ molar mass of Cr}}= (68.4g)/(52g/mole)=1.31moles`

Moles of O =
`\frac{\text{ given mass of O}}{\text{ molar mass of O}}= (31.5g)/(16g/mole)=1.97moles`

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For Cr =
`(1.31)/(1.31)=1`

For O =
`(1.97)/(1.31)=1.5`

The simple whole number ratio of Cr : O= 2: 3

Hence the empirical formula is
`Cr_2O_3`