Some Tips on Writing Lab Reports

Written by Wun Chiou

(A Former UCLA First-Year Lab Courses Teaching Assistant)


A lab report is more than just something you turn in to (hopefully) get a good grade. It's your opportunity to show that you understand what is going on in the experiment, which is really the most important part of doing it. In addition, I think it's actually very good practice for getting across your thoughts about the science you are doing in a manner that the reader can understand.

What you write in your laboratory notebook is an actual account of what you have done in a given experiment, like a very detailed diary. You should be able to come back to it at some point, read what you wrote before, and reproduce what you did before. So should anyone else reading your notebook, for that matter. That way, if you make some amazing discovery, like blue aspirin is better than white aspirin (btw: don't eat anything in, from, or created in lab to see if this is right), you will have a permanent record of it to remind you of your greatness. There are three basic parts to a lab report: pre-lab, in-lab, and post-lab. In this document, I've written some helpful tips that might help you through your lab-report woes. I won't include everything you have to do (you should look on VOH for the report guidelines), but just a few key ideas.



I. Introduction

The introduction discusses the problem being studied and the relevant theory. Ideally, it would take up about 4-5 sentences. The main idea here is to give the reader an idea of what you are going to do in a short paragraph. There are different styles to do this. You should try to write it in your own words, rather than paraphrasing or quoting the lab manual (but if you have to, be sure to include the appropriate references). It's always a good idea to read the entire experiment in the manual before you begin your introduction. I suggest the following:

Background sentences: state why you want to do the experiment, why is it relevant, what other kinds of similar experiments have been done in the past.

Goal: In one sentence, state what you are going to do in the experiment and what you hope to find. This is probably the most important part of the introduction. You should also list explicitly any main chemicals with which you are dealing (vinegar, aspirin, NaOH) and any techniques you will be utilizing (titration, recrystallization, spectrophotometry, etc.). For example, "In this experiment, we will determine the buffer capacity of a weak acid buffer of acetic acid / acetate ion by titration with both a strong acid, HCl, and a strong base, NaOH."

Other procedures or theory: If you need to elaborate on some of the techniques you stated in your goal (or couldn't state in your goal), you can write a couple more sentences about them afterwards. Or you can add anything else that you might think is relevant, like additional major procedural steps you will take.

Keep it short!


II. Procedural Flowchart

This part of the pre-lab should take no more than one page. A good flowchart should give a reader an immediate idea of what's need to be done in the laboratory except in a less detailed format. Think of a flowchart as a "road map" of the experiment. It gives a reader a "pictorial" representation of the experimental procedure. In general there are two major steps when constructing the flowchart. First, read the experimental procedure carefully. Second, rewrite the procedures in a flowchart format. Keep in mind that the flowchart should be brief and cover all the steps in a simple and easy to follow manner. There should be no complicated sentences or paragraphs in the flowchart. You will have to do a lot of rewriting in order to simplify the procedures into a flowchart format. This is exactly why we want you to do it. This gives you a chance to THINK about what you read and how to rewrite it in a way that can be implemented into a flowchart.

Always remember to reference where the experimental procedures are coming from in the pre-lab report.

Please DO NOT simply copy the entire procedure (or majority of the procedure) and make it looks like a flowchart.


I. Data-taking

Always write in pen. You can't really erase anything, anyway, because of the carbon paper below it. White-out is a big no-no, too.
Always record data directly into your lab notebook. I know some people like to be neat, and have nice formatting and all that, but it's more important to make sure you record all of the data immediately in case you forget what you wanted to say later or you forget to copy other data into your notebook.
Never scratch something out completely. Yeah, nobody's perfect and of course also nobody wants to be reminded of that, but you may discover that you were right in the first place, and now you wish you could read what you wrote before. Also, if you make a mistake it's a good idea to keep a record if it so you (or someone else trying to do your experiment) can remember to not make the same mistake twice.


II. Observations

In addition to writing down all those numbers (data), you should keep an eye (nose, ear, etc.) on what is actually happening in the experiment. If you add one thing to another and it evolves a gas, gets hot or cold, changes color or odor, precipitates a solid, reacts really quickly or slowly, or anything noticeable, you should write down that observation in your lab notebook. Other things to consider including are: make and type of any machine you are using, concentrations of all the standards you used, and etc. One of the reasons you are doing this goes back to what I said about mistakes earlier. An experiment is exactly that: an experiment. If it turns out that you get an unexpected result, you can go back and trace your observations to see where the error occurred. If you don't have any observat
ions, this is really hard to do. The bottom line: write what you do and do what you write.


I. Data again?

Recopy your data from the in-lab here in a nice neat format (tables are usually nice and neat). This is your chance to organize it into a more readable form now that you are done with the experiment and impress the TA with your organizational skills.


II. Calculations

It's a good idea to write out all the formulas you use in your calculations. Personally, I like to work through the problem using just the formula, and then plug in the numbers at the end to get my final answer. Also, show all of your work.
One more point is to be sure to include the units when you are doing a calculation, and don't drop the units halfway through the calculation. This is actually a pretty powerful tool because if your answer has the wrong units you know you must have made an error somewhere along the way. Conversely, if your answer has the correct units, you could still be wrong, but at least you are on the right track (and probably much of the time your answer is correct, too!) You can even do the calculation using just units and no numbers and see if the units cancel out in the right way to test if you method is good (this is called dimensional analysis).

III. Conclusion

The conclusion is alot like the introduction except, instead of a summary of what you are going to do, it's a summary of what you did. The reason you have a conclusion is because your lab report might be long and the reader may not remember all the important points that you stated. Also, it gives you a chance to explain anything that might have gone wrong or could be improved, as well as propose future experiments. Like the introduction, it should be short and to the point. Again, these are only my suggestions, but here's what I think you should always include:

What you did: Reiterate your procedures briefly (including any changes you made).

What you found: Restate any results that you may have calculated (with errors if applicable). You don't need to include the raw data, but if you calculated an average over several trials, state the average (not each trial). Usually you want to report the results as x +/- y (like 2.345 +/- 0.003), where y is the absolute error in x. Another option, if you calculated the relative error, is x +/- z% (like 2.345 +/- 0.5%), where z is the relative error.

What you think: What do your results mean? Are they good? Bad? Why or why not? Basically, comment on the results. If your experimental error (RAD, RSD) is small or large compared to the inherent error (the error in the standards and equipment used), comment on what this means, too.

Errors: Speculate on possible sources of error.