Benzoic Acid Blizzard in a Bottle A Holiday Lab

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1 Benzoic Acid Blizzard in a Bottle A Holiday Lab In this lab, you will learn about how some solutes that are only partly soluble can be forced to fully dissolve with heat. When a solute has dissolved as much as it possibly can, and no more will dissolve no matter how much you stir it, the solution is said to be "saturated." If you take a saturated solution and heat it, the extra solute will dissolve. When you then cool the solution, the extra solute that dissolved with heat will once again precipitate. The lab you are doing today is a beautiful application of that principle of solubility. Procedure 1. Obtain a hot plate and 250 ml beaker. Heat about 75 mls of tap water on the hot plate, but do not allow it to boil!! While the water is heating, obtain between 0.9 and 1.1 grams of benzoic acid. 2. Place the benzoic acid into the heated water. Turn up the heat and stir the mixture until the benzoic acid completely dissolves and makes a solution. Remove the solution from the hot plate and allow it to begin cooling. 3. Take your Holiday figure and your VERY DRY AND CLEAN baby food jar over to the hot glue station. Hold the figure by its head with your hand. Use your other hand to put some hot glue on the bottom of the figure, then immediately place the figure on the bottom of the baby food jar. Hold it for a few seconds so it stays in place. Allow the glue to cool for several minutes. 4. Watch your benzoic acid solution as it begins to cool, and you will see beautiful snowy looking crystals appear. Allow the solution to completely cool to room temperature (if you don't, the figure usually falls off). 5. After your solution is cool, and the figure has been glued, stir the snow mixture a few times, then quickly pour it into the baby food jar, on top of your holiday figure. You will not fill the jar with this procedure. Then slowly add tap water to fill the jar to the brim (use the graduated cylinder, don't try doing it directly from the faucet). 6. Place your cap on. If all is well, you should be able to turn the snow scene upside down and watch your figure get buried in the blizzard!! 7. Something you can try when you get home is to use some silicon adhesive around the edge of the jar lid to seal it completely.

2 Miniature Explosions with Hydrogen Gas Bubbles In this lab, you will be making hydrogen gas and oxygen gas and making bubbles from various mixtures of the two to try to find the ideal mixture. The two gases will be mixed in a syringe and injected into bubble solution to make bubbles filled with the mixture. The bubbles will then be lit with a lighter. Procedure 1. For this lab, you will need to produce a syringe full of oxygen as we have done before and a syringe full of hydrogen as explained next. Produce ml of hydrogen gas by reacting.07 mg of magnesium with 8 ml of 1.0 M HCl. When the reaction is complete, point the syringe upward and remove the cap. Point the syringe downward into a neutralization tank and release the excess liquid. 2. Press the syringe plunger down until it is at the 50 ml mark. For the data to work out properly, you must start with 50 ml. Get a plastic weighing boat and fill it half way with bubble solution. Inject 10 ml of the hydrogen gas through the bubble solution to make a small mound of bubbles. Ignite the bubbles. In your data table, note the relative loudness of the bang. The loudness is directly related to the completeness of the reaction. 3. For each time that you release 10 ml of the gas, you will replace it with 10 ml of oxygen and repeat the bubbling and igniting. In doing this, you will be decreasing the percentage of hydrogen and increasing the percentage of oxygen each time. You are attempting to find the stoichiometrically correct ratio of hydrogen to oxygen. Repeat this procedure until your oxygen is gone. Pre-Lab Questions 1. Write the balanced equation for the combustion of hydrogen. (Hint: only product is water) 2. From your balanced equation, in 10 ml of gas, how many ml would be hydrogen and how many would be oxygen in a perfect stoichiometric mixture? 3. Calculate what percent each of the mixtures that you will be making are hydrogen. (For example, trial #1 is 100% H 2, trial #2 has 40 ml H 2 and 10 ml of O 2 = 80% H 2, trial #3 is.80(40)= 32 ml of H 2 (64%) and 18 ml of O 2 (36%)) Have these percentages in your data table before you come to lab. Post-Lab Questions 1. Prepare a chart with a column for the percent H 2 and the relative loudness of the explosion. 2. With which mixture did you get the loudest bang? 3. How did your actual answer compare to the theoretical answer (pre-lab #2)? 4. How do you explain your answer to #3?

3 Iron Determination I have just received a note from Dr. Vijay, of Veggiepros Inc. I have not included a copy of his note as he uses rather forceful language; he is rather upset. His company has been accused by the Thai Authority of Food and Drug Inspection (TAFDI) of false advertising in the sale of iron supplement tablets. The label on the bottle of these tablets indicates that every tablet contains 200 mg of iron as iron(ii) sulfate, while the TAFDI claim to find no more than 160 mg per tablet. Both the TAFDI and Veggiepros have agreed to hire us to settle this dispute. It is our job to determine the quantity of iron in each of the tablets. I would like you to work in the groups that you established during the training for the titrational analysis. Your first step is to develop as a group a titration procedure to determine the amount of iron in the tablets. I would like to see a copy of this procedure and a list of required materials by the end of this chemistry meeting. In this titration reaction the Fe2+ ions react with permanganate ions, MnO4- and acid, H+, according to the following equation: MnO 4 1- (aq) + 8 H 1+ (aq) + 5 Fe 2+ (aq) Mn 2+ (aq) + 5 Fe 3+ (aq) + 4 H 2 O (l) Purple reactant Colorless product The purple MnO4- ion becomes colorless when it reacts with the Fe2+ ions. The endpoint of the titration (that is, when all the Fe2+ ions have been used up) is that point when the purple color of MnO4- no longer disappears after addition to the iron solution. The iron tablet also contains chalk powder, sucrose, and other minor ingredients. In order to prepare this tablet for analysis you will need to grind it and transfer it to a volumetric flask. I recommend using 2 tablets and in addition, the tablets should be dissolved in 1 M H2SO4. I suggest using some of the acid to help you transfer your tablet to the flask. The final solution should have a final volume of 100 ml. Analyze ml samples of your iron solution. Titrate with M potassium permanganate. Remember that you have reached the endpoint of the titration when the purple color of the permanganate just begins to stay - this indicates that all of the Fe2+ ions have reacted. Do at least three determinations although you may have to do more to ensure that your values are within 0.3 ml of each other Present your data in the form of a table to record the volumes of MnO4- that you have used during the titrations. I recommend that across the top of your table you make at least three columns, one for each of the titrations you have performed. You can label the columns as "Trial I", "Trial II" and "Trial III". Down the left-hand-side of your table you will need to indicate 3 rows: "final reading MnO4- (ml)"; initial reading MnO4- (ml); volume of MnO4- used (ml). The following steps will help you in your calculations: 1. Determine the number of moles of MnO4- used to react with 10.0 ml Fe2+ solution (you know the volume and concentration). 2. Calculate the number of moles of Fe2+ that reacted (use the reaction equation).

4 3. Calculate the number of moles that would have reacted in 50.0 ml of Fe2+ solution (since this contains 1 tablet). 4. The number of moles of Fe2+ is the same as the number of moles of FeSO4. Calculate the mass of FeSO4 in 1 tablet. 5. Convert the mass to milligrams. I would like your group to hand to me a report at the end of the lab period with your conclusions about whether you feel Veggiepros is guilty of false advertising. You should make this conclusion based on your data and how confident you feel about your results. In order to determine your level of confidence you need to ask yourself what are the sources of error and are they large enough to account for differences in the experimental mass of iron and the advertised mass of iron.

5 Cheek/Onion Lab Comparing Animal & Plant Cells Name Date Background One of the types of science that scientists do is called qualitative science. In this type of science scientists often spend their energy trying to describe a new phenomenon or a new type of organism. One of the goals of this science program is to have students OBSERVE and DESCRIBE cells in a variety of organisms using microscopes and hand lenses. In this lab, you will observe and describe cells in two different organisms: humans (animals) and onions (plants). MATERIALS: Onion, razor blade, forceps, dissecting scissors, toothpick, probe, glass slide, cover slip, water, Lugol solution (for staining onion cells), methylene blue (for staining cheek cells), water, light microscope, pencil, Lab Book. METHOD: Part I: HUMAN CHEEK CELLS A. Clean your glassware and microscope as usual. B. Place a drop of diluted methylene blue (or Lugol solution) on the center of the slide. C. Using the blunt or rounded end of the toothpick, scrape the inside of your cheek near the back of your mouth just above your lower teeth. Some of the cheek cells will stick to the toothpick. D. Place the end of the toothpick with the cells on it into the drop of stain. Twirl the toothpick slowly and gently for a few seconds, just long enough to dislodge the cells. E. Put on a cover slip as you did when making other wet mounts. F. Look for single cells or small groups of cells. The cells will appear as pentagons (similar to a rectangle but with five sides). The nucleus will be dark brown or blue depending on the type of stain you used. The cytoplasm will stain more lightly than the nucleus. The cell membrane will be darkly stained on the outside edge of the cell. Don t waste your time looking at any small bits of food that might have been transferred from your mouth along with the cells. You can recognize food particles because they look like threads or rods. G. Make a ½ page drawing of the slide under high power and label it Figure 1. Be sure to capture a few single cheek cells AND a small group of cells that are attached to each other. Part II: ONION SKIN CELLS A. Clean your glassware and microscope as usual. B. Place a drop of Lugol solution on the center of the slide. Place a drop of water on the slide next to the drop of stain. C. Using the toothpick, mix the two drops together. D. To obtain your specimen, get a single piece of onion from your teacher. E. Remove a piece of very thin transparent tissue which looks like skin from the onion. Use the forceps to peel the tissue from the onion. Try to obtain as large a sheet of onion tissue as possible from the onion.

6 F. Use your small dissecting scissors and/or razor blade to cut the tissue into a small square section, about a 1 cm. x 1 cm. square. G. Place the sample on the slide and use the toothpick, probe, and forceps to smooth out the specimen in the drop, if necessary. Folds or wrinkles will make it very difficult to see the cells precisely. H. Cover the specimen with a cover slip. Use the toothpick to tap out any air bubbles you see. I. The cells will appear as thin rectangles (not perfect, they kind of have pointed ends). The nucleus will be dark brown. The cytoplasm will stain more lightly than the nucleus. The cell wall will be darkly stained on the outside edge of the cell. Notice how the onion cells are almost identical and how they fit together in a tight geometric pattern. J. Make a ½ page drawing of the slide under high power and label it Figure 2.