How would you prepare 500cm3 of a solution of 0.1 Molar NA2CO3

Answer 1

How many moles do you want? That's M x L = 0.1 M x 0.500 L = 0.05 moles.
How many grams in 0.05 moles? That's grams = mols x molar mass = 0.05 x 106 g Na2CO3/mol Na2CO3 = 53 g.
Weigh out 53 g Na2CO3, place in a 500 cc volumetric flask, add some distilled water, swirl until the solid is dissolved, add distilled water to the mark on the volumeric flask, stopper, mix thoroughly, label. done.