Question

How do you solve empirical formula calculations?

Answer 1

The explanation is given below.

Explanation:

Step 1 : Assume percentages as masses contained in a total of 100 grams.

Step 2 : Use `n = m /M` formula to calculate the number of moles in each atom.
`n` = number of moles
`m` = mass of substance
`M` = molar mass

Step 3 : Divide all number of moles by the smallest.

Step 4 : Round them to nearest whole numbers and assign as subscripts.

Example question: Calculate empirical formula of a compound that has `11%` hydrogen and `89%` oxygen.

Assume that 100 grams contains `11` `g` of `H` and `89` `g` of `O`.

To move on to step 2, you also need to know the molar mass of `H` and `O`. In that case, the molar mass of `H` is `1.0` `g`/`mol` and the molar mass of `O` is `16.0` `g`/`mol`.

Now you can find the number of moles for each atom.
`n(H)` = `11/1.0` = `11` moles
`n (O)` = `89/16.0` = `5.6` moles

Step 3, multiply the number of moles by the smallest.
`H` = `11 / 5.6 = 2.00`
`O = 5.6 /5.6= 1.00`
*Has been rounded to nearest whole number

Step 4, assign them as subscripts.
Since there is 2 Hydrogen and and 1 Oxygen, you know that the empirical formula is `H_2O`.