How to Survive Organic Chemistry Lab

backyardchem May 22, 2010 School
The introductory organic chemistry lab course can be daunting! But with this tutorial, you'll learn some insightful tips and tricks that will help you get a good grade in any organic lab class. This advice comes from the experience of both a student and teacher's assistant.
How to Survive Organic Chemistry Lab

As a chemistry major, I have had experience both taking and teaching undergraduate organic chemistry lab courses. I have noticed what it takes for a student to be successful in what can be a very stressful lab environment so I thought I would share my knowledge with you.

First let's start out with some common anxieties that students have to deal with in chemistry lab:

1) Finishing the experiment on time. Depending on the day, this can be a difficult task. I will give you many tips and tricks as to how work swiftly but carefully.

2) Getting a good yield. This is a major concern of students who are overly anal. There are some common practices that can increase your yield by a couple of percentage points, but most of the yield is determined by the nature of the reaction. More on this later.

3) Spilling or breaking equipment. I'll teach you only to be super careful when you need to be super careful. This will reduce much of your stress in the chemistry lab and save you time as well.

4) The reaction not working. Some students consistently think that their experiment is going to be the only one that is not going to work. The first thing you should know is that all the labs are designed and optimized to work as well as they possibly can. But nevertheless, I can give you some advice that will help you decrease your chances of complete failure.

5) Writing a good lab report. There are some basic things in an organic chemistry lab report that most students always seem to forget.

Ok so now I'll try my best to address each of these concerns specifically.

1) Finishing the experiment on time

a. Read and digest the contents of the pre-lab.

Read the pre-lab the night before you do the experiment and organize in your head what different steps you will be doing. For your very first lab, you will most likely have to think about the steps in greater detail, but once you gain familiarity in various techniques, you will be able to think about your upcoming experiment in simpler terms. It is very important that when you read the experiment you think about what chemicals and what glassware and other supplies you will need. This will save you tons of time as you will not have to be constantly referring to the lab instruction manual during the lab period. During the class, you should mostly only be going back to the instruction manual to look at specific numbers that are given (mass of reactants, volume of solvents, temperature of reaction, etc.).

b. Minimize the number of trips you make.

In organic chemistry lab, much of what separates the fast students from the slow students is the rate at which the experiment is set-up. In many experiments such as distillation, setting up the glassware and all of the proper equipment can take an hour or longer. There then might be a period of downtime where all of the students have to wait for a reaction to occur (let's say another hour). So it is super important to get the reaction started as soon as possible. Therefore, setting up your glassware in a timely fashion is key. In order to do this, when you go to get your supplies, carry more than one thing at once! This might seem like a silly piece of advice, but you would be surprised to know how many students I see carrying back a single Erlynmeyer flask to their hood and nothing else! When you race to the glassware storage areas to pick up your flask, think about everything else that you might need to go with it. Graduated cylinder to measure out what is going into the flask? If yes, well then you probably need a pipette and a pipette bulb to dispense liquid into the graduated cylinder. Buchner funnel to filter into the flask? If yes, well then you need filter paper to go on top of your funnel.


c. Make use of downtime.

Often times, there is a lot of time when you will be waiting for a reaction to occur. These can be 10 minutes blocks of time or even several hours. This is a good time to catch up and write down things in your lab notebook. Writing everything in your notebook as you go can slow you down substantially. Instead look for blocks of time that you can use to write a lot of information down at once. If you still have extra time after that, don't just lollygag around! Plan out what you will need for the next steps. You can use this time to grab the necessary glassware and even to measure out the appropriate amount of reagents and solvents that you will need next.


d. Estimate when you can.

This is one thing that I make sure to emphasize to my students. Think about if you really need an exact amount of a certain chemical even though the instructions may say so. A prime example deals with the use of drying agents. Let's say the instruction manual tells you to "dry the organic layer with 2.50g anhydrous sodium sulfate." Now, the slow student would spend 5 minutes at the scale weighing out exactly 2.50g of sodium sulfate or as close as he or she could manage. The medium-paced student would realize that the amount of drying agent you use does not have to exact and would go and weigh out anything from 2-3g. The fast student, however, would know that it is entirely unnecessary to weigh out the amount of sodium sulfate and that once the drying agent stops clumping, enough has been added.


You also can estimate when you are adding solvents. For example if a procedure calls for 50mL of ethanol to run a reaction in, it's not going to do any harm if you only have 49mL. Estimation is okay as long as you write down exactly what you did in your lab notebook.


e. Multi-task when you are comfortable.

At first, you will be wanting to give 100% of your attention to everything you are doing because of a lack of experience as to what to expect. However, once you gain more knowledge, you will be able to take on more than one task at the same time. This is especially important when you are running a column. Here, it will save you tons of time if you run your TLC analysis while you are pushing solvents through your column.


f. Store frequently used solvents.

If you anticipate that you'll need lots of different solvents in your lab. There's no harm in storing a good size of these solvents in your hood. Use Erlynmeyer flasks and label them quickly. If you put the solvents in a beaker, then they will evaporate more rapidly.


g. Clean up at the end, not as you go.

You should inquire as to whether or not you will be docked if you are messy when working in your fume hood. If it's alright, then it is much more efficient to store all of the glassware and equipment that you are done using in the corners of your hood where they will not get in the way. Then, after you are done for the day, you can clean everything up at once. This saves a lot of time since the instinct is to clean as you go. (Cleaning, however, is something good to do when you have downtime.)

2) Getting a good yield.


Whatever you do, don't fake your yield. I've known students to say that there reaction yielded a product of 80% when the highest I, as a teaching assistant, had ever gotten was 40%! So definitely, don't artificially inflate your yield. If you think your yield is low, then explain in as detailed terms as you can why you think so. Hopefully, your lab performance grade is not based upon yield, but about the nature of your report and your explanations.


Good habits that will increase your chances of getting a better yield include making sure that your glassware is clean especially before adding the key reagents. Another important thing is to make sure that your reaction is at the requisite temperature during the entire duration of heating.


You also can make sure that you don't loose too much of your product to physical processes by washing anything your product has touched with plenty of solvent and then evaporated it down. There is no harm in doing this but make sure you don't go overboard on how much solvent you use or else you will be evaporating for hours.

3) Spilling or breaking equipment.


Unfortunately, this is a sad reality of the game. However, there are some precautions you can take. If there is anything at all that seems jammed or stuck, then you should ask your teacher what to do because chances are you probably are using the wrong piece. In addition, if you are using any type of ground-glass joints, make sure to use grease, because this will prevent the pieces from sticking together. Don't think that this step is unnecessary. Also, if you have a complicated glassware set-up going on, make sure that everything is well clamped and that you are not moving anything that is not well-supported. As a general rule, don't force things in too place. This is usually a bad sign. Finally, I should say that I break glassware the most frequently when I have a lot of glassware in my hood and it is crowded. In this situation, it is very easy to knock something over accidentally. For this reason, it is important to either keep your hood clean or put glassware that you are not using safe away in the corner of the hood.

4) The reaction not working.


Making sure that your glassware is fairly clean is a good first step to ensuring that at least you get some product from your reaction. TLC is also an extremely useful tool in determining if you have some product. So if you can perform TLC, it is generally a good idea to do this as soon as possible so that you may monitor your reaction carefully. Another good idea is to double check that you are actually adding the correct reagents. Some chemical names can be very similar to one another. Some examples are manganese sulfate vs. magnesium sulfate or ether vs. petroleum ether.

5) Writing a good lab report


Along with any other instructions, be sure to include what your yield was and why you think what it was. For this explanation, it is best to include by physical and chemical rationales. You should try to come up with any side reactions that might be occurring. In addition, you should explain in detail all of the analytical results you used to determine the purity and identity of your product (TLC, IR, NMR, melting point, physical appearance, etc). This is important evidence that you must draw on throughout your lab report.


As a final word of encouragement, I will tell you this. If you are unsure as to whether a possible explanation you are writing in your lab report is correct, include it anyways! You can always preface it with "it is possible that." In chemistry, a lot of different things can happen to some extent (everything is in equilibrium!) so chances are on your side that a certain reaction or explanation you posit is valid, at least to some extent.


Good luck with it! Enjoy your chemistry lab! Chemistry is supposed to be fun!

 

 

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