Precision and Accuracy - Video Tutorials & Practice Problems

The efficacy of any calculation or experiment is based on the principles ofÂ precision andÂ accuracy.Â

Precision, Accuracy and Error

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Precision and Accuracy

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So we're gonna say here that even though we try to be as accurate as possible, every measurement or calculation we do in chemistry has some level of uncertainty. Now this uncertainty we call experimental error. So basically any type of calculation we do is never going to be perfect. Some of the circumstances leading to this imperfection are within our control while others are not. Now before we talk about the different types of errors, we first have to talk about how can we look at our data, our calculations and determine are they good or not? We're gonna say when we investigate the quality of an experimental decision or calculation, we have to take into consideration two major principles. We're gonna say the first major principle um deals with the reproducibility of our calculations. This is called precision Precision is just a way of looking at our data or calculations and see how close they are to one another. If I've ran an experiment 10 times and gotten 10 results, how close are those 10 results to one another. This can often times lead us to determine if our calculations are correct or not. Now, in terms of simplicity we can look at a dartboard on this dark board, we have three strikes. These three strikes are very close to one another. So we'd say the reproducibility is very high. We say that our strikes here are precise because they're very close to one another. Now the second principle deals with how close are measured calculation is to the actual value. So this is accuracy. Now in this image we have our dark board still all the strikes are dead center. If dead center represented our actual value or true value, we'd say that these strikes are very accurate. We could also say that their precise as well because they're all very close to one another. We could say here that this would be a very accurate and precise um list of strikes, The one above would be precise but not necessarily accurate because although they land in the general same general area, none of them hit the bull's eye. So they're not accurate. Now. Later on, we'll learn that we can calculate how good our our calculations are, how reproducible and precise they are by looking at the standard deviation of these values, but that's for later on for now just realize that when it comes to any calculation, it's never going to be perfect. That's because there are things that we may have done incorrectly and they're also circumstances within the experiment which make it impossible to be totally accurate and sometimes not very precise of the two precision is the one that we can try our best to control accurate. Sometimes may not be totally within our control. Knowing this, take a look at example, one look through the experiment that this individual has done to determine if it's precise or accurate. Once you figure that out, come back and take a look at how I approach the same question

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Precision and Accuracy

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So here it states, a student must measure the weight of a sodium bicarbonate compound and obtains the following measurements. 23.12 g 23.26 g 23.8 g and 23.17 g. If the true weight of the compound is 18.1 g. What can be said about the students results. Now we can see that the four measurements done by the student all hover around 23 g or so because all the numbers are very close to one another. We can say that the measurements themselves are precise. However, they are far away from the value of 18.1 g, which is the true weight of the sodium bicarbonate compound. So because of that, we can say that they are not accurate. So the measurements themselves, they would say are not accurate because they're far away from 18.1 g, but are still precise since they're very close to one another. So here we say that the answer choice would be c later on, as we deal with more complex numbers and look at things such as uncertainty will become more difficult to determine if measurements are truly precise or not. In those cases will rely on other concepts such as standard deviation or grubbs test in order to determine the precision involved in any type of measurements and calculations that we undergo for now, guys in this example though, it's clear that our numbers, although they're close to one another and precise, they're still not accurate because they're far away from the 18 g that we really want away.

As the number and complexity of calculations increases it will become more essential to rely on standard deviation to determine their precision.