Answer is: mass of potassium is 172.04 grams
Balanced chemical reaction: 4K + O2 = 2K2O.
n(K2O) = 2.2 mol.
From chemical reaction: n(K2O) : n(K) = 2 : 4 ( 1 : 2).
n(K) = 4.4 mol.
m(K) = n(K) • M(K).
n(K) = 4.4 mol • 39.1 g/mol.
n(K) = 172.04 g.
n - amount of substance.
m - mass of substance.
M - molar mass.
