Fluent Essays

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 water using your graduated cylinder, and pour this water into an empty cup. Add 1 tsp. of baking soda to the water. Repeat with a second cup, so that you have 2 cups of baking soda in water. These 2 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. H. In the two remaining empty cups, add 50 ml of water to each. Determine the pH of the water using a pH strips. Record this value. (The pH of tap water tends to be between 5 and 7). 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. To keep track of this information, you will want to construct a table similar to the one below. When adding base, it is recommended that you measure in terms of numbers of squirts of Windex, and for adding acid, it is recommended you either use a 1⁄4 tsp. or measure in terms of drops of acid added (10 drops at a time would work best). Table of data: � Water with acid Buffer with acid Water with base Buffer with base Drops of acid added pH Drops of acid added pH Squirts of base pH Squirts of base pH 0 0 0 0 ¼ tsp. or 10 drops ¼ tsp. or 10 drops 1 1 ½ tsp. or 20 drops ½ tsp. or 20 drops 2 2 ¾ tsp. or 30 drops ¾ tsp. or 30 drops 3 3 1 tsp. or 40 drops 1 tsp. or 40 drops 4 4 J. Add 10 drops of acid to each of one cup of water and one cup of buffer, and record the new pHs of both solutions. Continue to add acid 10 drops at a time, until you have added a total of 50 drops of acid in one of the water and one of the buffer solutions. Question 3: (5 points) Describe any differences you observed between pH changes in the water and pH changes in the buffer as you added acid. Which changed solution pH faster? 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. Question 4: (5 points) Describe any differences you observed between pH changes in the water and pH changes in the buffer as you add base. Which solution changed pH faster? Question 5: (5 points) Record your table of data (complete with number of drops and pH values) in the word processor document. Question 6: (5 points) If you had to describe what buffers do in your own words, what would you say based on what you just observed? Part 2: Osmosis 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 below 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 and eggs, and can cause food poisoning. It is much easier to wash your hands than it is to fight Salmonella, so take the easier path and wash your hands! Introduction: Osmosis is diffusion 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 fit through (small particles, which are permeable) while others can't (larger particles, which are impermeable). The following applet may assist you in visualizing how osmosis occurs: http://hydrodictyon.eeb.uconn.edu/people/plewis/applets/Osmosis/osmosis.ht ml. 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. You may notice bubbles forming on the egg shells as it 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: CaCO3 (solid) + 2 H+(aqueous) à Ca+2(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. 2. After the eggs have soaked in vinegar for at least 36 hours, using your finger tips, 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, since many eggs have been broken during this step. 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. 3. Immediately after cleaning your raw eggs, prepare the following six solutions, each in a separate cup. This is 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) 80 ml of water 40%-Syrup Solution (Cup 3): 40 ml of corn syrup 60 ml of water 60%-Syrup Solution (Cup 4): 60 ml of corn syrup 40 ml of water 80%-Syrup Solution (Cup 5): 80 ml of corn syrup 20 ml of water 100%-syrup Solution (Cup 6): 100 ml of syrup 4. With a soft paper towel, dab off any extra water from the outside of each egg to dry them. 5. 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 a table, like the one shown below. Cup Initial Dry weight of egg (g) Initial Time Final dry weight of egg (g) Final Time 1 2 3 4 5 7 6. After weighing the egg, 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 you table. 7. Record the time you placed the egg in the solution on your table, as well. 8. Repeat steps 5-7 until all six of the eggs are weighed, and in a cup containing a separate solution. 9. 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. 10. After the eggs have soaked for at least an hour, gently remove one of the eggs gently from its cup, and quickly and gently rinse off any corn syrup from the egg. 11. 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. 12. Repeat steps 10 and 11 for each egg, and record the weights and times for each egg. 13. 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 the area you used to carry out this experiment, and finally, wash your hands thoroughly. Answer the questions below. Question 7: (5 points) Type up your table of data, showing the initial and final weights and times for each egg. Question 8: (5 points) Which solution caused the greatest increase in egg weight mass? Question 9: (5 points) Which solution cause the greatest decrease in egg mass? 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 following questions: Question 10: (5 points) In which direction did water flow (into or out of the egg membrane) for those eggs that increased in mass? Give an explanation for why the water flowed as it did for those eggs that increased in mass (you may wish to refer to pages 84-85 to help answer this question). Question 11: (5 points) In which solutions, if any, did the eggs remain at about the same weight (plus or minus 1 gram)? Question 12: (5 points) In which direction did water flow (into or out of the egg membrane) for those eggs that decreased in mass? Give an explanation for why the water flowed as it did for those eggs that decreased in mass (you may wish to refer to pages 84-85 to help answer this question). Question 13: (5 points) Is the 100% syrup solution hypotonic, isotonic or hypertonic with respect to the contents of the egg membrane? (you may wish to refer to pages 84-85 to help answer this question). Question 14: (5 points) Is the 0% syrup solution hypotonic, isotonic or hypertonic with respect to the contents of the egg membrane? (you may wish to refer to pages 84-85 to help answer this question). Question 15: (5 points) Which percentage solution is closest to being isotonic with the contents of the egg? How can you tell? Question 16: (5 points) Our cells contained a good deal of sugar, and are enclosed by a semi-permeable membrane. What do you think would happen to them if they were placed in pure water? Question 17: (5 points) Look at the red blood cells pictured at the top of page 85 in your textbook. The three pictures show cells that have been placed in a hypertonic, isotonic or hypotonic solution. When a nurse prepares an IV bag for intravenously feeding of sugar and salt into the bloodstream of a patient, he must be very careful to mix the right concentration of sugar and salt in the water. Do you think the concentration of sugar and salt in a typical IV solution is hypotonic, isotonic or hypertonic compared to the concentration of these molecules in the blood cells? Explain your reasoning. Miscellaneous Osmosis and Diffusion Questions Question 18: (5 points) A human lost at sea cannot drink ocean water and survive. Why do you think this might be based on what you learned about in this lab? (Remember, your cells contain salt as well.) Question 19: (5 points) Although animal cells, when put into pure water, will swell to the point of exploding, plant cells won't explode due to their cell structure. What part of the plant cell do you think stops the plant cell from "exploding"? Remember to submit your answers in Canvas! I hope you found your look at chemistry educational and interesting!