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Molarity Calc II

Added Jan 29, 2015 •

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calculate the molarity of a solution prepared by dissolving 9.8 moles of solid NaOH that's sodium hydroxide in enough water to make 3.62 L of solution Define molarity moles of solute divided by liters of set a set or equation up here we have molarity equals moles of solute sodium hydroxide is the solute here cuz it's is Alton Water and we have 9.8 moles of that divided by liters of solution which is 3.62 leaders right here 9.8 divided by 3.62 round the answer to two significant should I have 9.8 up here and I get 2.7 what should the units be for this when you find molarity the final answer is in units of molar capital M since is 2.7 molar but what 2.7 molar really means is that there are 2.7 moles of NaOH of the solute for everyone liter of the solution of 2.7 molar but don't forget that means 2.7 moles for each one L of this solution up here you dissolve 152.5 grams of cucl2 that's copper chloride in water to make a solution with a final volume of 2.25 L what is its molarity  sulfur molarity is you know we want to take more solute divided by liters of solution cucl2 copper chloride in this case cuz 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 150 2.5 that number instead we have to convert this to moles and then we can plug it into the molarity equation animals the first thing we got to start with is the molar mass of copper chloride to find the molar mass of copper chloride we got to find Copper fluorine 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 63.55 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 35.44 but Abby's together I get 134.4 5 grams / 1 mol okay that's like the molar mass of it we're going to have to use this as a conversion actor to go between grams and moles 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 1Mobile for every 134.4 5G both of these are ways to express the ship between grams and moles for copper chloride now that I know how to go between grams and moles with this conversion factor 152.5 G and I can multiply it by one of these two conversion factors I don't want to use the one that gets rid of grams from the top of the equation up here  since Gramps on the top I'm going to choose this conversion factor with grams down here so now grams cancel. Cancel. I'm left with moles  turn on the radio 1 52.5 times 1 divided by 134.45 and that is going to give me 1.13 for moles I'm rounding to four figures here at one two three four significant figures and I don't worry about the one cuz the part of a definition so now I know that I have 1.13 for moles of can you see all 2 now I can go ahead and calculate the molarity so molarity is going to be moles of solute 1.13 for divided by liters of solution equals to .25 L and when I crank through that rounding it to three significant figures cuz I have sig figs there it's going to be 0.50 for more as I said before don't forget the wet that me is that there are 10.50 for moles of cucl2 for everyone Peter of this solution that we're making here A solution has a volume of 375 ml and contains 42.5 G NaCl sodium chloride what is its molarity  challenging question because they're two things we need to calculate molarity moles of volume in liters of solution either of these two things in the prop starting quite as a saw you so we can't use that right away will have to convert grams to moles and then instead of getting liters of solution we get milliliters of solution so before we can Mass equation we're going to have to convert milliliters of solution in 2 liters of solution let's go step by step show how we do these conversions and then how we can do them I already at the end of sodium chloride and turn it into moles of sodium chloride when the molar mass of sodium chloride will look at sodium and chlorine on the periodic table to get their masses and imma do 22.9. for sodium I only have one sodium and I only I only have one chlorine here so I'm just going to do 35.4 for here add those together and I'll get the molar mass which I'm going to be using as a conversion factor okay so I'm going to write this as 58.44 grams over one mole that's one way to write it or I can flip the conversion factor and I can write one mole divided by 80 658.44 grams conversion factors that all use for taking 42.5 grams of sodium chloride multiplying up by one of these it's going to be this one cuz I have grams up here grams down there so these cancel out 42.5 divided by 58.44 and that is going to put the and that is going to give me 0.727 moles sodium chloride moles of sodium chloride I have some halfway there the next thing that I have to do is have to take the volume which is 375 ml multiply that by a conversion factor so I can change it from milliliters into liters  so there are 100 1,000 ml in 1 L which means we can write these two conversion factors use a conversion factor that's going to turn milliliters into liters so since it's on the top here snuza version of the conversion factor that puts milliliters on the bottom here so I'll cancel this out cancel this app I'll be left with leaders and when I do that 375 / thousand and left with 0.375 leaders now I know my leaders to have my moles of sodium chloride and my liters of solution and I can finish this by saying molarity equals 0.727 moles divided by 0.375 liters and I mean .94 that's rounded to one to three significant figures  for my molarity one point 94 or the units and as before don't forget what this really means it means that for every leader of the solution there are 1.94 moles 1.94 moles per 1 liter of solution so sometimes you won't always be given moles you won't always be given and you'll probably have to convert from grams to moles or from milliliters into liters so just make sure you got your conversion factors set up straight in the video instead of having moles and liters in calculating molarity you'll be given Moe Larry and then you'll have to use that as a conversion factor to move between golden solution

Uploaded by Owen Jung.