Question

Calculate the mass of anhydrous sodium carbonate Na2Co3 required to prepare 2.5 litres of 0.50M aqueous solution.(Na=23,C=12,O=16)

Answer 1

How many mols do you want? That's mols = M x L = ?
How many grams is that. grams = mols x molar mass = ?

Answer 2

Moles=concentration x Volume (n=cv)
0.5 x 250 divided by 1000
0.5/1 x 250/1000= 0.125
Calculate the Molar MAss of anhydrous Calcium Carbonate
Na2 = (2 x 22.98) + C (1 x 12.01) + O3 (3 x 15.99) = 105.987 g/Mol
m (MASS)= 0.125 x 105.987 = 13.248 g
:)