Question

How many grams of HCl are needed in order to make 0.500 liters of a 0.100 M HCl solution?

1.82 g

18.2 g

0.500 g

Answer 1

In a liter you have .1 mol of HCl
.1 * (35.5 + 1) = 3.65 grams/liter
so in half a liter you have 1.825 grams of HCl

Answer 2

There is nothing wrong with Damon's response but I do these slightly differently. Chemistry thinks in mols. So we ask ourselves "How many mols do I need?" That's
mols = M x L = 0.1 x 0.500 = 0.05
Then mols = grams/molar mass
0.05 = g/36.5 and solve for g = 36.5 x 0.05 = 1.825. If your chem prof is picky about significant figures s/he will tell you that's too many and you should round that number to 1.82.