How much Ca is present in the total amount of Ca(NO3)2 that contains 20 g of nitrogen?
One molecule of Ca(NO3)2 contains 2 atoms of N.
Mass of nitrogen in one mole Ca(NO3)2 molecule = 28 g ( 2 x molar mass of nitrogen)
28g N = one mole molecule of Ca(NO3)2.
20 g N = 1x 20 /28 = 0.71 mole of Ca(NO3)2.
One molecule of Ca(NO3)2 contains 2 atoms of N.
1 mole Ca(NO3)2 = 40 g Ca
0.71 mole Ca(NO3)2 = 40 x 0.71 = 28.4 g Ca.