Tuesday , June 2 2020
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How to Write a Chemistry or Physics Lab Report

hi and welcome to you really do love science calm my name is Jen and I’ll be your tutor for today today we’re going to talk about how to write a lab report now I want you to remember that every single teacher is different and so each teachers way your teachers way is the right way to do a lab report for example some teachers will say oh your lab report must be hand written on notebook paper another teacher might say oh your lab report has to be on graph paper of course because you’re going to be doing tables and charts and graphs and another teacher might say graph paper what do you mean graph paper of course you have to type your lab report on the computer and and print it out and so each teachers way is different and just keep in mind that your teachers way this year is the right way to do it there are some things though that all teachers seem to agree on when writing a lab report and so those are the things that I put together here in these instructions and this particular template is going to be available on my website that you really do love science comm so that you can print it out and read the instructions later and let me show you the entire lab report template it should look like this this is the one you can print out on my website with all the instructions at the top where it says lab report you want to be able to put the title of your lab report determining the relationship and I’m just making this up between an object’s density and its ability to float capitalize that a right there and I’m just going to make sure that this particular sentence is centered as the title and there we go make sure it’s centered you probably don’t want to have the words lab report at the top your teacher might like that but just ask your teacher so here we have your name Joe science student with the date and the name of your teacher and period 7 or Bell 7 or hour 7 whatever you say now do you remember the scientific method the scientific method included five steps step one is to make observations step two is to form a hypothesis about a situation and number three test the hypothesis like doing an experiment number four is to record your measurements in your data and number five form a conclusion about the hypothesis so the scientific method is sort of like the precursor to your lab report the lab report that you write will be very much like the scientific method in the sense that you state a purpose then you test it and you record your data and then you form a conclusion so it’s very much like the scientific method and so the purpose of your laboratory experiment you can use it just one or two sentences in the purpose for example the purpose of this laboratory experiment was to determine whether there is any relationship between an object’s density and its ability to float in water and really that’s all you need for the purpose so we can get rid of my instructions here and there we go a purpose can be one or two sentences just stating why you’re doing the experiment the next part of the lab report is your procedure so so far you’ve got your title with your name and date at the heading and then you state your purpose and now you’re getting into your procedure now the procedure tells the steps that you did to complete the laboratory experiment you want to ask your teacher though do I need to list every step in the procedure or should I assume that you know the procedure that we followed and I don’t have to get into every detail I’ve had teachers say oh no you have to write out every step so that somebody reading your lab report if they wanted to they could redo your lab in every detail that you did another teacher says no no I was here when you did the lab I know what you did you don’t have to write out every step for me so again make sure you ask your teacher ask your teacher also if you should write in the past tense telling what you did like a story or if you should write it like a set of instructions that someone else could follow if they did the lab separately from you now there are two types of ways to write a paragraph there’s a difference between active voice and passive voice active voice sounds like this we then added three drops of phenolphthalein to the solution it sounds like a normal sentence but then some teachers want you to use passive voice and you get rid of the pronouns the personal pronouns like you and we and I and instead you write it this way three drops of phenolphthalein were then added to the solution notice that you can’t really tell who did the step in the procedure it’s just that it was done so when you end up with a procedure you should normally have a set of steps of what you completed during the lab and it can be numbered like that next is your data section now your data those are your measurements that you make during the lab and your observations as well this is where your tables and charts go sometimes your teacher will have you do three or four trials of the same exact measurement this is to ensure accuracy it’s kind of like if you were measuring a plank of wood because you were making something like a cabinet and before you cut the wood you made sure you measured it twice or three times just to be sure that you measured it correctly well it’s the same thing with laboratory experiments you want to do three or four trials of the same measurement to make sure you did it correctly and you didn’t accidentally make a mistake so your data tables might have trial 1 and trial 2 with your measurements listed in each row now what if you have several trials and three let’s say three of your measurements agree with each other but then there’s this one measurement that’s way off and it just doesn’t agree with the other measurements and it seems like it’s wrong because it’s way off in science we call that an outlier usually most scientists delete the outliers the pieces of data that are way off because they know that something went wrong either they made a mistake or maybe their equipment malfunctioned at that moment hopefully you won’t have any outliers in your measurements but if you do have an outlier a piece of data that’s obviously wrong ask your teacher whether you can delete it because if you keep it in your data tables and then it ends up in your calculations in your results section it can really throw your results off because it’s an obviously wrong piece of data now I want you to be careful with your units in your data tables units are things like grams when you’re measuring or milliliters when you’re measuring volume or centimeters when you’re measuring length and you know what debt units are but here’s how you put them in the data tables so let’s get rid of all of my instructions right here and let’s just create a data table I’m going to show the ribbon here with all of these features look up here at the top where it says home insert page layout click on insert and underneath the word insert there’s a table feature if you click on the word table all of a sudden this grid opens up you get to pick how many rows and how many columns you would like in your table so let’s just pretend right now we might want to delete some but let’s make it nice and big with five rows and five columns now once it’s created as soon as you let go of the mouse the data table appears let’s say you want to adjust the table because you don’t like that it’s sitting all the way over on the left side of the page watch this you can expand it and make it stretch out but when you expand it you’ve only expanded that one column and it didn’t expand everything so and let’s say we want it to be a little bit maybe a little bit bigger this way so if you want it to be proportional and not deformed what you want to do is select the entire table by clicking on your mouse select the whole thing and then go up here to the very top over here it says table tools and underneath the table tools it says design and layout click on layout and then go to these buttons right here these buttons allow you to distribute the columns and distribute the rows evenly so I’ve selected the entire table I want to distribute my columns evenly isn’t that nice and now I want to distribute all of my rows evenly and there I have a nice even data table so that’s how you create the data table again insert table and you select the rows and columns now we’re ready to add data to our tables I made this up but let’s pretend that we’re studying whether certain objects sink or float I decided we could use a penny so the first object is a penny and then we’ll say an ice cube and then the third object is going to be a Styrofoam Styrofoam ball and I only want to measure three objects and their ability to float so I’m going to get rid of this entire row now watch if you type something in a field and then you highlight the row and you just hit the delete button all it does is delete the text that’s in that field so I’m about to hit the delete button see how it just got rid of the text in order to delete an entire row what you’ll do is you’ll highlight the row so you can go up to the table tools here not under design but actually under layout come right over and see this delete button now click on the delete button and it says do I want to delete just one cell or column or a row or the entire table I just want to delete the bottom row so I click on that and then the bottom row is gone so I’m just teaching you how to adjust your table so here we have these objects I guess I don’t need a colon there and then over here I’m going to say I want to measure the mass of the object the volume and its ability to float and then I’m going to scoot this over a little bit further so that will be big enough and I’m going to get rid of this column now let’s say I want the text on these top header rows this row right here to be nice and centered I go back to home and I click on the center tab so that these headers are all nicely centered and now I’m going to fill in some data now we know that mass is measured in grams we have several choices in some data tables and as a matter of fact I’m going to make all of this data centered as well so let’s say the Penny’s mass is two point four nine grams you have a choice of putting grams right there in E each cell with the number but what’s commonly done with data tables instead of entering the G for grams each time what you want to do after the word mass you do parentheses and then you list the unit so that says mass in grams the parentheses means it’s in grams okay so I’ve got the pennies mass is two point four nine grams at volume we’re going to measure volume for solids it’s going to be in cubic centimeters and for liquids it’s going to be in milliliters but all of these objects are solids so we are going to measure the volume of these objects in cubic centimeters now the three needs to be a superscript up high so we go up here and we click on x squared and that gives us the superscript feature then you click on it again to come back to regular font the ability to float is just going to be a yes or no and let’s pretend that we did this lab and know the penny couldn’t float and oh yes the IceCube was floating nicely in the Styrofoam ball yes it floated nicely now let’s fill in these volume measurements and for the penny and there’s no way that you would know this I’m just making up these numbers as if you had measured these things for the penny we’re going to say point three four nine cubic centimeters for the ice cube 12 cubic centimeters and for the Styrofoam ball we actually measured the diameter of the Styrofoam ball we cut that in half to get the radius and then we did the equation for the volume of a sphere the volume of a sphere is 4/3 PI R cubed the diameter was four centimeters the radius was therefore 2 centimeters and in the calculator when I calculated 4/3 times pi times the radius which is 2 centimeters cubed I end up with a volume of 33.5 one cubic centimeters and so this is an example of a data table it’s complete every field or every cell is filled in sometimes these cells these little blank areas are called fields in other programs so cells and fields are basically the same thing and so we have a nice complete data table here and most data will be in the form of a table but there’s some data that you could record in the form of a paragraph or some other form of chart that you could where you could put your measurements or your observations for example now we move on to the results section the results section is where you show your calculations you’re going to talk about what you figured out with your data what did the data tell you now we have an example here about density and floating so we’re going to calculate all of the different objects densities and we might make a new table showing the densities and we’ll compare those densities to the object’s ability to float the density formula you should know it’s density equals mass over volume you’re going to ask your teacher hey do I have to show my calculations and what I mean by that is density equals mass divided by volume and then you’re going to plug in numbers so let’s say for the penny we say density equals and we’ve got a mass of two point four nine grams and a volume of the penny was zero point three four nine cubic centimeters so you’re going to show you work this way you might be able to do it by hand on regular notebook paper and then once you do the calculation the density of the penny turned out to be seven point one three grams per cubic centimeter and that was using a calculator so do you see how we showed our calculation ask your teacher if you have to show your work for every single calculation in the lab or are you allowed to show it once to prove to her that you know how to do the calculation and then for the to the calculations you just do it on your calculator or on scratch paper but you don’t have to show it in the lab report so that’s different for every teacher once you have a calculation at least one shown then what you want to do is create a results table sometimes there’s a results table sometimes there’s not there are some results that are just paragraph form but in this lab we are going to and let me take this data table and see if I can copy the whole thing I’m going to right click see if I can copy this entire table down here see if it works it did work so now we will instead of showing the mass and the volume because those were measurements that we made I’m now going to say the density of the object and the density of the object would be in grams per cubic centimeter again okay so once we calculated the pennies density it turned out to be seven point one three and we again you don’t put the units in the field just at the top in the header and for the ice cube we took mass divided by volume and for the ice cube the density is point nine one six seven zero point nine one six seven and for the Styrofoam ball the density turned out to be point zero point three zero zero grams per cubic centimeter and so do you see how after you do calculations those are your results and so we created a results table now this section in your results section is also a place where you’re going to explain your sources of error the things that didn’t go perfectly now in every lab there are going to be mistakes or measurements that weren’t exactly right sometimes you have equipment that’s old for example maybe used a balance that’s very old and it was wobbly and it never really could get evenly balanced or perhaps the thermometer was old and you could see the red fluid which is alcohol in the thermometer but you could also see a little air bubble in there so the thermometer was not reading accurately or maybe there’s human error maybe you made a mistake when you were reading the graduations which are the markings on the thermometer or on the beaker or on the flask or maybe you spilled some of the substance just slightly or maybe when you transfer the substance from the filter paper into the volumetric flask not all of it actually made it into the flask just because some of it stuck to the paper there’s all kinds of reasons why your results are not perfectly accurate and so in the results section you want to explain first by calculations whether your results were accurate and then you want to explain in words about whether your results were accurate and why the reasons why now after you create your results table and report the numerical results you then want to be able to talk about whether your results were good or not and there are two ways to evaluate your results first you have accuracy and accuracy is whether you got the right answer accuracy is how close you were how close your results were to the accepted value and when I say accepted value I mean there was a right answer or there was a density for example for styrofoam that you could look up in a book and it was an accepted value for the density of styrofoam that you knew to be the true density of styrofoam and so you’re wondering well how close did we get to that accepted value and accuracy is measured by percent error now percent error is basically the difference between your results and the accurate result or the accepted value and the equation for calculating percent error goes like this you take the absolute value of the difference between your result and the correct result of the accepted value you find that difference you divide it by the accepted value and then you multiply by 100 I took the absolute value on top because I don’t want my percent in the end to turn out to be a negative percent so let me give you an example here let’s say that the correct density according to a textbook of a certain metal is 9 grams per cubic centimeter but in your lab you took measurements in your results section you did density equals mass over volume and you calculated the density to be nine point two seven grams per cubic centimeter so you were off by point two seven grams per cubic centimeter so here’s how you calculate your percent error you take the difference between your results and the accepted value it doesn’t matter which one comes first you’re just finding the difference between the two so 9.00 minus nine point two seven which is point two seven or if you want you could say nine point two seven which was your result minus 9.00 which is the accepted value which is a negative answer but because you’re taking the absolute value of that difference it doesn’t matter that you ended up with a negative value on top so you take the difference between the right answer and your answer divide it by the right answer the nine point zero zero was the accepted value and multiply that whole thing by a hundred to get your percent error see how easy that is this is a way of measuring how accurate your results were and if you have anything under 10 percent error then it means you really did a good job in your lab sometimes I don’t include all the units in my calculations but some teachers want you to include units next to every single number so make sure you do what your teacher asks you to do now you could end up with a lab where your percent error is something crazy like eighty percent that would mean that either you did the calculations wrong or your equipment malfunctioned or maybe something spilled and you were not able to get a good result in college if your percent error is high you actually could fail the lab and get a very bad grade but in high school usually the teacher will accept an explanation as to why the results turned out bad or inaccurate in other words if you understand the calculations that you did the measurements that you made and the purpose of those measurements and calculations and if you can explain the purpose and why the results were off base or your percent error was high your teacher will usually accept that as good enough because she knows you understood the concepts so ask your teacher if a high percent error is going to ruin your grade or if you can just explain your sources of error so when your error is high make sure you spend extra time explaining what could have gone wrong in your experiment once again its percent error that measures how accurate you were in other words how close you were to the correct value or the correct answer but then there’s something else about your results that your teacher might want you to explain the second way to evaluate your results is called precision and precision is about consistency so precision answers the question how consistent were your measurements or your results now remember that you could be consistent and you could still get the wrong answer for example if you have a bathroom scale and every time you step on the scale it’s 5 pounds off but it’s consistently 5 pounds off well that’s a scale that’s not accurate but it is consistent and so precision and accuracy are very different and when you say your results were precise you’re saying that you were consistent it’s best to have both good accuracy and good precision consistency is important because it usually means that you are being careful when you did the lab and you weren’t doing different procedures you were actually doing the same procedure each time very carefully precision is measured by percent deviation and percent deviation has a different equation so with percent deviation you really are telling how close or how far your measurements were from each other in other words how consistent you were so here’s how you calculate whether your measurements were consistent if you didn’t have any big outliers if most of your measurements and your calculations were pretty close to each other then your percent deviations will be low which means good consistency good precision if you had one measurement that was way off then your percent deviation for that trial might be higher and a high percent deviation means that something else went wrong that result or that calculation or that measurement deviated from the others and for that trial you might have a higher percent deviation if your results are consistent it means you were careful and that’s why percent deviation matters the way to calculate consistency is called percent deviation first you get the average of all your results let’s say we did four trials in the lab and we did four sets of calculations and we ended up with four different sets of density values and I just made up these numbers here in order to get the average all we do is we add them all up divided by four and there we go there’s an average and again this is for some kind of a liquid I just made this up so I used a calculator and I got the average percent deviation talks about how far off was each measurement from the average of all your measurements or the average of all your results so you’ll take the result from one trial and you’ll subtract it from the average of all your results get the absolute value of that divided by the average and multiplied by a hundred so let’s do this for the example trial one looking back up here the density of trial 1 the density of the fluid turned out to be 0.9 0 6 grams per milliliter let’s plug that in down here subtract the average result which we found to be zero point nine three one grams per milliliter take the absolute value of that which is 0.025 divide that by the average point nine three one and multiplied by 100 that gives us two point six nine percent deviation for that trial I used absolute value on top again so that I wouldn’t get a negative percent in my answer you’ll have to do percent deviation for each trial if your teacher does want you to do present deviation to show your consistency at the very end your teacher might want you to write a few sentences about your results not just show the calculations and so you’ve got your percent error and your percent deviation numbers but then you want to add a few sentences about the quality of your accuracy which was measured by percent error and your precision which was measured by your percent deviation you can say something like our data was fairly consistent with deviations ranging only from 2 percent to 6 percent and so that’s your results section you’ll end up with a results table something like this one up here that we did you’ll show calculations either above the table or below the table you’ll do your percent error calculations then you’ll do your percent deviation calculations and then you’ll add a paragraph or a few sentences discussing your results whether your results were good or not and finally your sources of error and so your results section is really the biggest part of your lab report because it includes your calculations your results tables charts or graphs and you should ask your teacher if she wants you to graph your results your calculations regarding your accuracy which is your percent error your calculations regarding precision which is based on percent deviation a few sentences discussing whether your results were good or bad and your sources of error the sources of error are what we’ve talked about already what might have gone wrong or what might have thrown off your results your conclusion is kind of fun and short and easy because all you get to do all you have to do is just answer the question that you stated in the purpose was there a relationship between an object’s density and its ability to float tell what you discovered so you could say something like this based on our observations our data and calculations we found a clear relationship between an object’s density and its ability to float in water specifically we discovered that objects with density is higher than the of water sink and objects with densities lower than the density of water are able to float in water remember if your teacher wants you to use passive voice then you’d say something like this based on the data and calculations that were made a clear relationship between an object’s density and its ability to float was observed notice that you’re not saying who did it you’re not saying I did it or we did it you’re just saying that the relationship was observed so now you know how to do a lab report and I just have a few reminders for you lab reports are not hard to do but they take so much longer than you ever think they’re going to take it’s not something you can do at your lunch time or between classes you really they’re like school projects you really need to set aside at least one evening to do a lab report properly especially the results section takes time I want you to be careful I want you to do your calculations twice and check all your work and please be very very neat make sure you do everything your teachers way if your teacher disagrees with me on something then forget about what I said and do it her way or do it his way and above all I want you to be safe in your lab follow the procedure carefully don’t fool around too much you can have fun but don’t do anything stupid that could get somebody hurt and so be safe wear your goggles even though they’re silly looking and I hope you get an a on your lab report

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