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

Aug 18, 2017

%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?