Question

Question #29ef3

Answer 1

The empirical formula is `K_2O`

Explanation:

21.7 g of potassium is 0.555 mol (`21.7g -:39.1 g/"mol"`)

4.44 g of oxygen is 0.2775 mol (`4.44g-:16.0 g/"mol"`)

This change to moles is necessary, because we need to compare quantities using a unit that refers to a number of atoms rather than a total mass.

Now, look for a whole-number ratio between these two values. If it is not obvious, try dividing both by the smaller. This will give you a ratio in which one term is a one, and should be easier to recognize.

Oxygen: `0.2775-:0.2775 = 1.0`

Potassium: `0.555-:0.2775 = 2.0`

So, the ratio in the compound is 2 atoms of K for each 1 atom of O, giving a formula `K_2O`

Answer 2

`K_2O` is the `"empirical formula"`.

Explanation:

The empirical formula is the simplest whole number ratio that represents constituent atoms in a species. Given masses of constituent atoms, we simply divide thru by the atomic mass:

`"Moles of potassium"=(21.7*g)/(39.10*g*mol^-1)=0.555*mol`

`"Moles of oxygen"=(4.44*g)/(15.999*g*mol^-1)=0.278*mol`

And if I divide thru by `0.278*mol`, clearly I get `K_2O`. Capisce?