The gram formula mass of a compound is nothing but the molar mass.
The molar mass of K2CO3 (Potassium Carbonate) is given by
Atomic weights of individual elements are
K (Potassium) = 39 g
C (Carbon) = 12 g
O (Oxygen) = 16 g
Hence, that of K2CO3 = 39(2) + 12 + 16(3)
= 78 + 12 + 48
= 138.
