Chemistry in Biology Below is a picture of a mitochondrion (top) and a chloroplast (bottom), both of which function due to a pH differences on opposite sides of a membrane. Image thanks to: http://w3.dwm.ks.edu.tw/bio/activelearner/08/ch8c1.html

Directions: This lab is divided into two parts (pH & Buffers and Osmosis) that are relatively unrelated, but will give you some experience with some important applications of chemistry in biological fields. Since this lab is considered an “at-home” lab, you will be required to work with house-hold 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 text below and answer the questions within each part in a word processor document.

Part 1: pH and Buffers Introduction: ? In chapter 2 we learned 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. We also learned that buffers are solutions that resist changes in pH (in other words, they 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 overpowers 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 acids, bases 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 . . . if you are unsure is a cleaner can be used in place of ?windex, email your instructor and ask!

• 4 cups large enough to hold 100 ml or more of water each

• 4 Teaspoons (for stirring)

• Baking soda

• Measuring spoons (1?4 tsp. and 1 tsp. measuring spoons are recommended)

• pH paper and pH scale (in the Lab Materials kit) – see image below

• 50 ml graduated cylinder (in the Lab Materials kit) – see image below

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 a number of 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, quickly determine the pH of each liquid using the pH scale on the pH paper vial (compare colors) and record this value. 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!

Question 1: (5 points) Record the initial pH values you measured for each liquid in your word processor document.

Question 2: (5 points) From the pH values you measured, state which liquid (lemon juice or Windex) is an acid, and which liquid is a base. You may want to refer to chapter 2 in your book for help.

F. Measure out 50 ml of tap