Molarity Example 2

Jules Bruno
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in this example question. It says how many grams of sodium phosphate, which has a molecular mass off 1 63.94 g per mole, are present in 300 mL of a 3000. Mueller sodium phosphate solution. All right, so in this question, they're asking us to discover grams. Now, before we start plugging in numbers and doing calculations, let's talk about what the sentence is saying and how we need to be on the lookout when we see it written in such a way. Now here we have a number, and here we have another number and they are connected together by the word off. Just remember, when off is in between, two values off is really telling us to multiply them together. Now we have more clarity here, which remember Mole Arat e equals moles over leaders and realize this that if I were to multiply both sides by leaders, then we would see that moles equals leaders times more clarity. Leaders times more clarity. Look at this. This is Miller leaders. If I were to convert those into leaders and then multiplied by the mole Arat E, that would give me moles of sodium phosphate. And we know if we have moles of a compound, we can use its molecular mass or Mueller wait to help us determine the grams of that compound. So that's the key. So just remember here when we have volume of polarity, that's really just telling us. Hey, you have moles there. All right, So we're gonna first take the 300 mL, and I'm going to convert it into leaders. Remember, this is a metric prefix conversion, so middle leaders go on the bottom leaders go on top. Remember that the metric prefix is on the same side with one. So one millie is 10 to the minus three milliliters. Cancel out. Now, I have leaders also remember that morality is a conversion factor. So that 0.550 Moeller is really saying that a half 0. moles off that compound over one leader. So I need leaders to cancel out. So I'll put the one leader here. And then we have 550 moles off sodium phosphate. Here leaders cancel out and look, I have moles of sodium phosphate. Finally, I convert those moles into Gramps, so one more of sodium phosphate. We're told that the molecular weight is 1 63. g. So plug that in so moles cancel out and I'll be left with grams at the end. So initially, what I'll get is 27.501 g of sodium phosphate. Looking at the question, 300.0 has 46 figs, 460.550 has three sig figs, and this number here has 56 things. We go with the least number of significant figures, So this comes out to be 27.1 g of sodium phosphate, so this would be the grams of our compound. So just remember, when they're giving us volume of morality, they're telling us what the moles are here. In this case, we just have to find grams. So take those molds that you've isolated and convert them into grams and you have your final answer