I am making a 0.1 M KCl (molar mass 74.551) solution for an experiment. To measure the mass of the KCl, I will use an analytical balance that is only accurate to ± 0.01 g. I place a piece of paper on the balance and set the tare to read 0.00. I then put the KCl on the balance until it reads 6.79 g. What is the uncertainty in this mass?

I am making a 0.1 molar potassium chloride solution for an experiment. To measure the mass of the potassium chloride, I will use an analytical balance that is only accurate to plus or minus 0.01 grams. I place a piece of paper on the balance and set the tare to read 0.00. I then put the KCL on the balance until it reads 6.79 grams. What is the uncertainty in this mass? So in this question here, they're telling me, that the mass of the potassium chloride that I have is 6.79. All of these masses have this much uncertainty because they're using this particular analytical balance. So it'd be 6.7 9 grams, plus or minus plus or minus 0.01. Now, the way it works is we zero, the amount that's on the balance. We place our thing on there and we see what it is. Here, this is similar to weight by difference. So it'd be 6.79 plus or minus 0.01 grams minus 0.00 plus or minus 0.01 grams. Okay. So we're kind of taking a mass by difference approach in order to figure out what our final uncertainty will be with our given sample of potassium chloride. Now, here because the operation is subtraction, remember that we're going to subtract our measurements. Initially, we're going to get 6.79 but then what we're going to do is we're going to figure out what our absolute uncertainty is And based on the real rule, we'll know what our final digits will be for our measurement. So, we have here for total absolute uncertainty, we take the square root, take those measurements on those uncertainties, square them and add them together. So here when we do that, we get within here 0.0002. And when we take the square root of that, that's going to give us 0.014142. So here, we're going to say plus or minus 0.01 and a little 4 here just to deal with any rounding errors, that may occur. So we'd say that this is our final answer with our absolute uncertainty. Now, knowing this portion connects us to practice question 2. So attempt to do practice question 2 with the information that we obtained from up above. Once you've attempted it on your own or even if you didn't attempt it on your own, just come back and look at the next video where I tackle this practice question 2.