Molarity describes the concentration of a solution in moles of solute divided by liters of solution. This measure of concentration is most often used when discussing the solubility of a solid in solution. Grams per liter represent the mass of solute divided by the volume of solution, in liters. Thank you so much for your help so far, and for your continued help.California State Standard: Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, parts per million, and percent composition. I've looked over my calculations over and over, and I can't see where I messed up, leaving me with a figure with is off by exactly a power of 10. For this brand of toothpaste, the ISE probe read 8mV, so I solved for c like so:Īnd then we needed to figure out the %w/w or %w/v, depending on how it was listed on the tube, and compare it to the listed value on the tube. We established a calibration curve with a regression line y=-51.99x - 173.88, where y=measured voltage (mV) and x=the log of the concentration (logc). So I've got to be messing up the calculations somewhere, right? The only procedural error that could result in an error like that would be messing up the dilution, right?įor this lab, we used an ISE to determine. Which is off by approx a power of 10 when compared to the listed fluoride concentration on toothpaste labels (0.14%). So 0.9681g is the mass of a liter of the toothpaste. Submitted by littlecaitling on Sun, - 22:00 Īlright, I got so far as figuring out the grams of NaF before, that was 0.0013g. % w/v = mass of NaF / 1 liter of toothpaste x 100 I'm not familiar with a % w/v, but it should be calculated in the same manner: % w/w = mass of NaF / mass of 1 liter of toothpaste x 100 If you were going to do the %w/w (weight/weight), you would use the density to calculate the mass of one liter of toothpaste (or whatever volume you chose above if you didn't use 1 liter). Once you know the moles of NaF, you then find the mass of that number of moles by multiplying by the molecular weight.
By assuming 1 liter of solution, the molarity and the number of moles of solute (NaF) are numerically equal.
To make you calculations easier, assume that you have a 1 liter of the toothpaste (you can assume any volume). Moles of solute = molarity x liters of solution Molarity = moles of solute / liters of solutionĪnd rearranged it algebraicly to solve for moles of solute:
First you need to take the equation for molarity:
0 kommentar(er)
