Question

What is the mass percentage composition of potassium in saltpeter, `KNO_3`?

Answer 1

`%K` by mass in `KNO_3="Mass of metal"/"Mass of compound"xx100%`

Explanation:

And thus...............we interrogate the molar masses of the compound, and of potassium.....

`K%=(39.1*g*mol^-1)/(101.1*g*mol^-1)xx100%~=39%`

How did I know the atomic mass of potassium?