How much powder do I weigh out for a solution at this concentration?

Make up a solution

Getting from a target molarity and volume to a mass on the balance.

Mass equals concentration times volume times molar mass, and the only thing that makes it difficult is the molar mass. Take it from the formula on the bottle you are actually holding, not from the compound name: the hydrate matters. Copper sulfate pentahydrate is 249.7 g/mol against 159.6 for the anhydrous salt, so weighing by the wrong one leaves you 36% short and nothing about the solution will look wrong.

The same goes for salts of acids and bases. Sodium acetate and sodium acetate trihydrate are different powders. If the protocol does not say which, the safest reading is whichever one your stockroom carries, and it is worth writing down which you used.

Dissolve in most of the final volume and only then make up to the mark. Solids take up space: dissolving into the full volume gives you a solution more dilute than intended, and the error grows with concentration.

Purity and water content on a certificate of analysis are not decoration. A reagent quoted at 95% needs proportionally more mass, and hygroscopic powders weighed on a humid day carry water you did not intend to add.

What to use