![]() ![]() So they already give us the molar mass of potassium chloride, but it'll be useful for us to know the molar mass of potassium itself. You might need a periodic table, so I'll give you one right over there. See if you can figure that on your own, and I will give you a hint. Potassium chloride are in the potassium supplement? So pause this video and Which has a molar mass of 74.55 grams per mole. The potassium is present in the supplement as potassium chloride, Told that a 0.450 gram potassium supplement containsĢ2% potassium by mass. Dimensional analysis is used quite widely in chemistry and physics as a quick conversion tool. So Sal converts grams of K to moles of K, then moles of K to moles of KCl, then moles of KCl to grams of KCl. ![]() But he doesn't multiply simply by 39.10 g/mol as the periodic table gave him, he takes the reciprocal of the molar mass so that the unit grams of K cross cancel and his answer will have units of moles of K.Įssentially he is doing a conversion at each step until he arrives at an answer with the correct units. So for example he fist multiples the mass of potassium in grams (0.099g of K) by the molar mass of potassium. Every time Sal multiplies two numbers together he also cross cancels the same unit along the diagonal so that each time his answer has a new unit. Now the type of fraction (whether you want one fraction or its reciprocal) is what matters here to get the correct answer. This involves multiplying an initial number by a series of fractions to get your answer. So Sal is using something called dimensional analysis to solve this problem. ![]()
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