How would you prepare 50ml of
0.2M HCL
You want how many mols? That's M x L = 0.2 M x 0.050 L = 0.01 mols.
mols = grams/molar mass so
grams HCl = mols HCl x molarmass HCl.
That's approx 36.5 x 0.01 = about 0.365 g. Place that many grams HCl in a 50 mL volumetric flask, add DI water to the mark on the flask, mix thoroughly, stopper. Done.