a) To prepare 500 cm^3 of standard sodium carbonate solution of about 0.1 M, what mass of anhydrous sodium carbonate is needed?

0.1 times 0.5 times 82 = 4.1g

b) If the mass of anhydrous sodium carbonate actually used for (a) is 5.125g, what would be the molarity of the solution prepared?

5.125 divided by 82 divided by 0.5 = 0.125

c)Is the solution prepared in (b) a standard solution? Explain.

Now my book says that standard solution is a solution of known molarity. And since I worked out that the molarity is 0.125, so the molarity is known. So it should be a standard solution. But I think that it isnt and there is more to it. So is it a standard solution or not? and why?