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Calculate the molarity of a solution prepared by dissolving 9.8 moles of solid NaOH the sodium hydroxide in enough water to make three point six two liters of solution define molarity you take moles of solute and divide it by liters of solution so to set our equation up here we have molarity equals moles of solute sodium hydroxide is the solute here because it's getting dissolved in water and we have nine point eight moles of that divided by liters of solution which is three point six two liters right here so find molarity nine point eight divided by three point six two round the answer to two significant figures because I have nine point eight up here and I get two point seven one should the units be four this when you find molarity the final answer is in units of molar capital M so this two point seven molar but what two point seven molar really means is that there are two point seven moles of NaOH of the solute for every one litre of the solution so two point seven molar but don't forget that that means two point seven moles for each one liter of this solution up here you dissolve 152 point five grams of cucl two that's copper chloride in water to make a solution with a final volume of 2.25 liters what is its molarity so for molarity as you know we want to take moles of solute divided by liters of solution cucl two copper chloride is our solute in this case because it's getting dissolved in the water but the problem doesn't tell us how many moles of copper chloride we have it tells us how many grams of copper chloride we have so 150 two point five we can't use that number instead we have to convert this two moles and then we can plug it into the molarity equation so to convert this amount in grams into moles the first thing that we got to start with is the molar mass of copper chloride and so to find the molar mass of copper chloride we've got to find copper and chlorine on the periodic table and take a look at their atomic masses so copper there is one copper atom in copper chloride so I'll take the molar mass of copper 63 point five five and then there are two of these chlorines and copper chloride so I want to take two times the molar mass of chlorine which is thirty five point four four when I add these together I get one thirty four point four five grams per one mole okay that's like the molar mass of it now we're gonna have to use this as a conversion factor to go between grams and moles so remember that when we have conversion factors like this we can always write them in two ways we can write it like this or we can flip it and so we can say one mole for every one hundred and thirty-four point four five grams both of these are ways to express the relationship between grams and moles for copper chloride now that I know how to go between grams and moles with this conversion factor I can take one fifty two point five grams and I can multiply it by one of these two conversion factors I want to use the one that gets rid of grams from the top of the equation up here since grams on the top I'm going to choose this conversion factor with grams down here so now grams cancels out grams cancels out I'm left with moles and I'm gonna do 150 two point five times one divided by one thirty four point four five and that is gonna give me one point one three four moles I'm rounding to four significant figures here because I have one two three four significant figures and I don't worry about the one because it's part of a definition so now I know that I have one point one three four moles of C UCL two now I can go ahead and calculate the molarity so molarity is going to be moles of solute one point one three four moles divided by liters of solution equals two point two five liters and want to crank through that rounding it to three significant figures because I have three sig figs there it's going to be zero point five zero four molar and as I said before don't forget that what that means is that there are one zero point five zero four moles of C UCL two for every one liter of this solution that we're making here a solution has a volume of 375 milliliters and contains 42 point five grams of NaCl sodium chloride what is its molarity this is kind of a challenging question because there are two things we need to calculate molarity moles of solute and liters of solution we aren't given either of these two things in the problem okay instead of moles of solute we're given grams of solute sodium chloride is a solute so we can't use that right away we'll have to convert grams to moles and then instead of getting liters of solution we get milliliters of solution so before we can run this equation we're gonna have to convert milliliters of solution into liters of solution so let's go step by step to show how we do these conversions and then how we can do the molarity at the end the first thing that I'm going to do is I'm going to take this forty two point five grams of sodium chloride and turn it into moles of sodium chloride so I'm gonna need to start with a molar mass of sodium chloride look at sodium and chlorine on the periodic table to get their masses and I'm gonna do 20 2.99 for sodium I

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