Today is lab day! Your students will investigate the buffering properties of eight substances including several biological mixtures such as egg white and chicken liver puree.
This lab will take 45-50 minutes and will run over if your students don't stay on task. Get them started promptly and keep them focused with time warnings every 10-15 minutes.
Make sure you give yourself plenty of time to get all the samples prepared for this lab, there are quite a few! Remember that each group will use a total of 50mL from each solution and some groups will probably mess up their test so have some extra stock on hand.
The lab is divided into acidic and basic testing sections. Each section makes use of a 0.1M solution of either HCl or NaOH. The students will test the pH of the solutions after addition of HCl or NaOH and record the data in a table. Then they plot the data and examine the change in pH to determine the buffering capacity of each solution.
Try to gauge your students understanding of what a buffer is as you supervise the lab. If they don't know what it is and what purpose buffers serve in biological systems they'll feel disconnected and lose interest. If they have a good idea of what's going on this can be a fun lab since it lets them examine the properties of real life compounds.
You may see some variation between your students results and the example results we provide in the Teacher's Key. In the case of the biological samples, in particular, this is expected and not a reason to take points away.
Buffers can be a tricky subject for students to understand. These videos should help if you have a few in need of additional explanation. They both focus on the pH of our blood, which ties them nicely to biology.
Here are your free materials for this lesson!
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