But molecular weight and molar mass mean the same thing. So we simply write molar mass and now we have this, we have Molarity and all we need is to find the Molar mass. Remember, the grams of compound was given initially 2 grams of unknown compound and we can check using our units that this makes sense, grams divided by grams per mole. The grams cancel moles goes on top and we're left with moles per kilogram. And that's exactly what molality is. Now, our third step.