welcome chem students we’re now on the second video how to write a lab report in this video we’re going to look at the analysis and the conclusion portion what will often refer to as the post lab write-up last time we talked about designing the pre lab what we’re talking about now is what you’re going to do after you’ve collected the data of the experiment in the pre lab portion you designed a data table to collect your data and when you do the lab you are now going to collect that data and of course you need to remember that you are going to use the appropriate precision given by the instrument that you’re working with like most of our balances measure to the thousandth of a gram and so you would want to make sure that you measure to that precision you always want to collect your data in ink remember that you need to do that now there are mainly two different types of analysis that we will do calculations and graphs will start with calculations if you notice the two examples that you see here some very important things to note are number one that the calculation is labeled it says right here what that calculation is mass of water the other thing to notice is that the calculation is shown in detail including having the correct significant figures one of the things that we can mark you off for are your significant figures you need to watch those as you do your calculations the other thing I want to show you is notice that even a simple calculation like a subtraction is listed and so don’t think that a calculation is too unimportant insignificant or small you need to show every calculation that you are doing to determine your results so keep that in mind now I mention about graphs when you are doing a graph you are to follow all of the rules that you have learned about graph design and make sure that those are followed it talks here about how to represent graphs like we’ve already talked about things like showing extrapolation or interpolation lines as dashes make sure that slope calculations are written next to the best fit line and that you’re using points on the line to determine slope you won’t always be doing slope calculations and many times you’ll be asked to determine a best fit line or a best fit curve depending on what the data is what you need to keep in mind is that graphs are part of this subsection called analysis remember the results section consists of two sub sections the data section where you will put your table like this one and the analysis section where your graphs and calculations go that means that a graph is part of the results section and should be included in the results section if you don’t put your graph in this section you will lose a point for a format error if your graph you know if you want to not waste paper and start your conclusion or something on the same page as your calculations for example what you need to make sure that you do is in this part of it and the analysis part of it explain where the graph is to be found like you might say something see graph next page or something like that see graph end of report or last page if you don’t if your graph is not in this part or you don’t indicate where to find it you will lose a point okay let’s move on now to the conclusion portion this is a very important part and one in which students often struggle what I would highly recommend to you is that you read this example that you see here because this shows you the type of information that should be contained in a conclusion now it depends you know exactly what your experiment was what you will do but here are some things that you want to keep in mind as you write the conclusion the conclusion is designed to answer your purpose the purpose of the experiment was why you’re doing the lab so what that means is when you go to write the conclusion you are giving the answer to that purpose for example if you were trying to determine what the percent yield of hydrogen was like that was what our purpose was for this experiment then you need to discuss what the percent yield of hydrogen is that should be very early on in your conclusion discussion always make sure to address the answer to the purpose what did you determine but then you need to explain how you did that and what evidence you have from your results that supports that you see here site evidence you know if we indicate in your conclusion that you know you didn’t cite evidence what that means is you’re not using the data or the analysis that you did to explain how you arrived at your conclusion that is what you have to do use evidence from your analysis from your data in order to explain how you got the answer you got talk a little bit about what you did in the experiment in other words see how in this it says during this decomposition hydrogen and oxygen gas were produced we were able to collect the hydrogen gas using the gas collection tube that was connected to the ring stand so we’re explaining to the reader what we did in order to collect the data and to analyze the data that’s helpful to the reader to understand the process you used to come up with the answer that you got you certainly want to discuss any calculations that you did or refer them to evidence from any graph that you made or any analysis that you did on the graph like a slope like an interpolation something like that needs to be pointed out as part of the evidence for your conclusion so again I would highly recommend that you read through this to see how that’s done additionally we will often ask you to analyze the error and you should talk about the error sometimes you will be asked to do an error analysis that is like a percent error or a percent yield or something like that and then we’ll ask you to explain that error you can see right here it says give legitimate and realistic possible explanation for error do not use these two words please okay that means nothing you know you are a human and you make mistakes so any mistakes you make is human error you need to be more specific about what error that was involved you know in your particular experiment you see here at the end a possible explanation for the error since in this particular case they got a 97 percent yield so why didn’t they get 100 what’s an explanation for that says here some reasons for that are that we did not decompose all of the water which means you wouldn’t produce all of the gas you expected which is why your percent error is too low or some of the gas may have escaped again which would give you an amount of gas that was lower than you expected it to be so you want to be specific about the error one more word on the error a lot of times people will jump straight into a discussion of this is how we messed up that comes at the end before you ever get to that part you’ve got to make sure that you talk about this part what did you find out what is the evidence that supports that what did you do that allowed you to get that evidence that supports your conclusion that needs to be discussed then you can worry about talking about the error that was involved so that’s how you do your lab write-up I would highly recommend that the very you know the first few times that you do this you re watch these videos to make sure and certainly certainly pay attention to any comments or Corrections that are made on the labs that you have done don’t keep doing the same thing over and over again and losing points constantly for the same mistakes which is what we see too often if you have any questions about this make sure that you contact your teacher and ask how to fix those mistakes or to address the questions that you have finally don’t forget again about these helpful hints because they are helpful this is also something that you should look at every single time you do a formal lab write-up alright good luck and we’ll see you next time


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