Chemistry in biology lab
Learning Objectives:
• To learn about some applications of chemistry in biology.
• To learn about pH and buffers, and examine the action of buffers.
• To learn about osmosis.
This lab is divided into two parts (pH & Buffers, and Osmosis) that are relatively unrelated, but will give you experience with some
important applications of chemistry in biology. Note: Part 2 of this lab (Osmosis) needs to be started AT LEAST 36 hours before you
plan to collect your data.
Note: PARTS OF THIS LAB TAKE MORE THAN A DAY TO COMPLETE, SO YOU CANNOT JUST DO THIS LAB THE NIGHT BEFORE IT IS DUE!
Since this lab is considered an "at-home" lab, you will be required to work with household chemicals. Be sure to take proper
precautions (i.e. wear your safety goggles that came in your Lab Materials kit). You will need to gather some of the materials on your
own, and these materials are highlighted in red lettering in the materials list. Be sure to get the red highlighted materials before
attempting to do the lab. Once you have all the necessary materials, read the instructions and answer the questions in the lab
worksheets (these answers will be cut and pasted into the appropriate area in WebStudy before the posted due date).
Part 1: pH and Buffer
Background: We learned during the chemistry section of this class that the pH scale is used to measure the amount of hydrogen ions
+
(H ) in a solution. Acids have a pH below 7, bases have a pH above 7, and neutral solutions have a pH of 7. Remember: a lower number
means MORE hydrogen ions and thus more acidic. We also learned that buffers are solutions that resist changes in pH. In other words,
buffers stay at about the same pH, even if you add some acid or base to them (although you can get them to start changing pH if you add
a lot of acid or base and overpower the buffers). Our blood has buffers in it, which is why we can eat acidic lemons without having to
worry too much about lowering our pH! In this section, you will test the pH of two household items—lemon juice and Windex (or other
window cleaner)—and determine whether they are acidic, basic or neutral solutions. Then, you will compare how these two solutions
change the pH of water and of a buffer solution (made with baking soda and water).
Materials:
•Lemon Juice
• Windex or other similar window cleaner
• 4 cups large enough to hold 100 ml or more of water each
• 4 teaspoons (for stirring)
•Baking soda
•Measuring spoons (¼ tsp. and 1 tsp. measuring spoons are
recommended)
•pH paper and pH scale (in the Lab Materials kit) – see image
•50 ml graduated cylinder (in the Lab Materials kit) – see image on
next page
Record your answers in the lab worksheet.
pH paper and pH scale
Procedure:
A. Place your materials on a table covered with newspaper or some other protective
covering.
B. Be sure to put on protective clothing and your goggles found in the Lab Materials kit,
and be careful with the liquids!
C. Count out several pieces of pH paper, and place them on the newspaper.
D. Pour a tiny amount of lemon juice into a stirring spoon and dip one of the strips of pH
paper in the liquid. Once you have spotted the pH paper with lemon juice, quickly
determine the pH of the juice using the pH scale on the pH paper vial (compare colors)
and record this value in the worksheet. You may discard used pH paper in the trash.
E. Repeat step "D" for the Windex cleaner by squirting a little Windex into a clean stirring
spoon. Be sure to record the pH value. Note: Do not mix your liquids! Do not place
dirty spoons or pH paper into any of the liquids you are using! Also, use a clean spoon
with each new liquid!
Record the initial pH values you measured for each liquid in Table 1 of the lab
worksheet.
50 ml graduated cylinder
F. Measure out 50 ml of tap water using your graduated cylinder, and pour this water into
a clean, empty cup. Add 1 tsp. of baking soda to the water. Repeat with a second cup, so that you have two separate cups, each
containing baking soda in water. These two solutions will be your buffer solutions (the reason you made two buffer solutions is that
you will later add acid to one and base to the other).
G. Stir the buffer solutions until they are completely dissolved. Determine the pH of each buffer solution by dipping a piece of pH paper
into the solution and immediately comparing the color to the pH color-scale. Record the pH values of the buffer solutions (Entry 2).
H. In the two remaining empty cups, add 50 ml of water to each. Determine the pH of the water using the pH strips. Record this value.
(The pH of tap water tends to be between 5 and 7) (Entry 2).
At this point, you should have a total of four cups, two containing 50 ml of buffer and two containing 50 ml of water. You also should
know the pH of each of these solutions. You are now ready to move on to the next step.
I. You will be adding lemon juice (acid) or Windex cleaner (base) to one of each of the buffers and water solutions (see picture below), and
then stirring each solution with a spoon to make sure it mixes well. You need to keep track of the amount of acid or base added to
each solution, as well as the new pH of the solutions after each addition (Entry 3; Table 1).
J. Add 10 drops of acid to one cup of water and 10 drops of acid to one cup of buffer, and record the new pHs of both solutions.
Continue to add acid 10 drops at a time (be sure to test pH after each 10 drops and to record this value), until you have added a total
of 50 drops of acid to one of the water and one of the buffer solutions.
K. While keeping the two untouched solutions for the next step, discard the two solutions you just added acid to down the drain, and
wash the cups thoroughly.
L. Now you will add base to the two remaining cups (one of water and one of buffer). Add 10 drops of base to each of the remaining
cups of water and buffer, and record the new pHs of both solutions. Continue to add base 10 drops at a time while testing and
recording the pH, until you have added a total of 50 drops of base to both.
Part 2: Osmosis
Warning: The following steps require that you handle raw eggs. Be certain to wash your hands thoroughly with soap and water
after each handling of the raw eggs, as the bacterium Salmonella is often found on poultry and eggs, and can cause food poisoning.
Materials:
• 6 cups or jars for holding liquids
• 6 raw eggs (DO NOT break the eggs. . . you might also consider using 1 or 2 extra eggs just
in case)
• Karo corn syrup or imitation maple syrup (like Log Cabin syrup)
• Zip-lock bags
• 1 liter of white vinegar (the cheaper the better!)
• Paper towels
• Large container with top (to hold the 1 liter of vinegar and eggs)
• Large dry bowl
•50 ml graduated cylinder (in the Lab Materials kit)
•Spring scale (in the Lab Materials kit) – see image to the right
Introduction:
Spring scale
Osmosis is the diffusion of water across a semi-permeable membrane. If a membrane is
semi-permeable, this means some molecules and ions can move across it, while others can't.
The reason for this is simple—semi-permeable membranes have tiny holes in them which
some particles can pass through (small particles, which are permeable) while others can't (larger particles, which are
impermeable). To help you understand, watch the online animation at
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
You do NOT have to submit your answers to me from this animation site!
In this next section, you will examine the process of osmosis using different corn syrup solutions and raw eggs. Preparation of the
eggs takes at least 36 hour's wait, so be sure to start your lab early! You may also wish to prepare an extra egg or two, in case
one should break.
Procedure:
1. Pour the vinegar into the large container, and submerge the eggs completely in the vinegar. Put the lid loosely on top of the
container, and let the container sit undisturbed for at least 36 hours. (Sometimes the process gets done sooner and sometimes
it takes longer; it really depends on room temperature so do watch it occasionally)
You may notice bubbles forming on the egg shells as they sits in the vinegar. This is because the vinegar (a 5% acetic acid
solution) is reacting with the calcium carbonate (CaCO3) that the egg shells are made from. Calcium carbonate is commonly used
by organisms to build hard structures, like shells, bones and teeth (including our bones and teeth!). When treated with acid,
calcium carbonate undergoes the following chemical reaction:
+
+2
CaCO3 (solid) + 2 H (aqueous)  Ca (aqueous) + CO2 (gas) + H2O(liquid)
The bubbles are carbon dioxide (CO2) gas, a product in this reaction. Geologists often use this same reaction to identify
limestone—rock typically made from the fossilized shells of ancient organisms. When acid is dropped onto a sample of limestone
(or bone, or anything made from calcium carbonate) the above reaction occurs forming CO2 bubbles, while rocks made from
different substances won't bubble.
Record your data in Table 2 of the lab worksheet.
1. After the eggs have soaked in vinegar for at least 36 hours, use your fingertips to quickly and GENTLY rub off any remaining
white coating under running water, and place the clean, raw eggs in a dry bowl or container. Don't rub too hard, though, or
you’ll risk breaking an egg. If you see a lot of white shell left on the egg and cannot rub the shell off easily, just let the egg soak
in vinegar some more.
2. Immediately after cleaning your raw eggs, prepare the following six solutions, each in a separate cup. This process can make a
mess and you won't get exact volumes, just estimate as best you can. For those solutions containing both water and corn
syrup, make sure the two liquids mix completely by stirring the solutions with a clean spoon. Number the cups with 1-6, as
indicated below:
0%-Syrup Solution (Cup 1): 100 ml of water
20%-Syrup Solution (Cup 2): 20 ml of corn syrup (use your graduated cylinder to measure out the syrup) and 80 ml of water
40%-Syrup Solution (Cup 3): 40 ml of corn syrup and 60 ml of water
60%-Syrup Solution (Cup 4): 60 ml of corn syrup and 40 ml of water
80%-Syrup Solution (Cup 5): 80 ml of corn syrup and 20 ml of water
100%-syrup Solution (Cup 6): 100 ml of syrup
3. With a soft paper towel, GENTLY dab off any extra water from the outside of each egg to dry them.
4. Without delay, weigh one of the dry eggs by gently placing it in a Ziploc bag and using your spring
scale to weigh the bag and egg, as shown below. Estimate the initial mass of the egg to the nearest
tenth of a gram (example: 70.2 g). Record the mass of the dry egg in Table 2 of the lab write-up
worksheet.
5. After weighing the egg, carefully place it into one of the cups containing solution. Be sure that the
egg is submerged in the solution as much as possible (some eggs will float—this is fine). Record
which solution you put the egg in next to the dry mass of the egg on Table 2.
6. Record the time you placed the egg in the solution on your table, as well.
7. Repeat steps 5-7 until all six of the eggs are weighed, and each is in a cup containing a separate solution.
8. Allow the eggs to sit in the solutions undisturbed for at least 1 hour, although you are welcome to wait even longer for more
dramatic results.
9. After the eggs have soaked for at least an hour, gently remove one of the eggs from its cup, and quickly and gently rinse off
any solution from the egg.
10. Dry the washed egg with a paper towel, and weigh the egg again using a zip-lock bag and your spring scale. Record the new
weight and the time for your egg in Table 2.
11. Repeat steps 10 and 11 for each egg, and record the weights and times for each egg in Table 2.
12. When you have completed your table, dispose of the eggs and solutions down the drain (DO NOT EAT THE EGGS!!!!).Wash all
the dishes and your graduated cylinder thoroughly with soap and water (the graduated cylinder CANNOT be placed in the
dishwasher!). Wash your the area you used to carry out this experiment, and at the end wash your hands thoroughly.
The change in mass of the eggs was due almost entirely to water diffusing into or out of the eggs. Water molecules are small, and
therefore able to move through the tiny holes in the semi-permeable egg membrane. The corn syrup, however, is made of large
molecules, as are most of the contents of the raw egg. These larger molecules are not able to move across the egg membrane.
With this information in mind, answer the questions in your lab write-up worksheet.