Molarity (video) | Solutions and mixtures | Khan Academy

Video transcript

– [ teacher ] indium this video recording, we ‘re gon sodium lecture about one of the about coarse room to measure solute concentration inch ampere solution. And that exist molarity. And molarity be define a the number of mole of solute, the thing that we be dissolve in a solvent, that separate aside the liter of solution. so let ‘s good do associate in nursing model and see if we can calculate the molarity of adenine solution. indeed let ‘s allege that one have, this constitute deoxyadenosine monophosphate container here. And one ‘m go to dissolve some sodium sulfate indiana water. so sodium sulfate be the solute and urine be the solvent. together, they give uracil this solution. And lease ‘s state we own adenine sum, the sum book of solution equal 250 milliliter of solution. And that solution be make up of fair to give ourselves deoxyadenosine monophosphate bit of deoxyadenosine monophosphate refresher course. We own the solution, which be water, information technology be water inch this position. And you might read, bash we have 250 milliliter of water ? And the answer would equal not quite because the 250 milliliter that ‘s the bulk of the body of water summation the sodium sulfate. And thus we ‘re gon sodium have approximately sodium sulfate indium here. And let ‘s state we know that we give birth 35.5 gram of sodium sulfate. That be the formula for sodium sulfate. And indeed give this information, how perform we digit out molarity ? well, the first thing you might say exist okay, iodine know the number of gram of sodium sulfate. iodine necessitate to figure out the number of counterspy. And to name out the act of counterspy, you ‘d have to look at the molar mass. You could visualize that away from vitamin a periodic table of elements. merely merely to speed uracil along, one will aid you out angstrom little piece hera. The molar mass sodium sulfate, molar multitude be 142.04 gram per breakwater. so grant everything iodine ‘ve immediately assure you, witness if you displace hesitate this video recording and design out the molarity of this solution. What ‘s the molarity of the sodium sulfate in this solution ? all correctly, nowadays get ‘s make through this together. so first, we wan sodium figure out the number of gram molecule of solute. so we can begin with the multitude of solute that we give birth right over here. so we induce 35.5 gram of sodium sulfate. And now if we pale sodium number out the number of mole, learn i ‘m gon sodium multiply this prison term something that would cancel out the gram. And sol one do n’t lack gram per counterspy. iodine lack gram molecule per gram. And so iodine could write this. one could multiply this time for every one gram molecule of sodium sulfate, NA2SO4, we have 142.04. iodine ‘ll write this way, gram of sodium sulfate. And you can see very clearly that that bequeath cancel with that and we ‘re leave with breakwater of sodium sulfate. so we ‘ll experience angstrom calculator out indium vitamin a second and equitable take 35.5 and divide that aside 142.04. And then to figure out molarity, we pale sodium divide by the liter of solution. sol up here we take ampere calculation for count of counterspy and then the liter take solution, 250 milliliter be the same thing vitamin a 0.250 liter of our solution. And now we can merely use our calculator to figure out what this be. 35.5 divide by 142.04 equal that, and then we divide that aside 0.25. one could merely throw a zero indium there. And then that scram uracil that properly over there. And then we can think about how many significant design we own. so we induce trey over here. We rich person one, two, trey, four, five over here. We suffer three over here. so, i would pronounce that we receive three meaning name. And sol we would orotund this right most operating room this nine right over here. well, if we orotund that up, we have 1.00, if we be to travel to trey significant figure. so that get uracil 1.00. And then you might state what be the unit here ? And what people will normally say equal this cost 1.00 molar. When you see this capital meter correct over here, that be the unit for more molarity merely they ‘re in truth speak approximately the number of mole of solute per liter of solution. And we be act.

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