The Synthesis of Zinc Iodide Purpose: To determine the empirical formula of zinc iodide by synthesizing the ionic compound directly from its elements. In addition, we will verify the law of conservation of mass as well as compare limiting reactant calculations to actual yield of product to obtain percent yield. Introduction Perhaps the simplest type of chemical reaction is the synthesis of a compound from its elements. In this experiment we will produce zinc iodide directly by combining a known mass of zinc with a known quantity of iodine. Since zinc is a transition metal, it could hypothetically have several charges, and thus let us say it could possibly make the compounds ZnI, ZnI2 , or ZnI3 . Your task in this lab is to determine the empirical formula for the compound you make between zinc and iodine, and with this information, determine the percent yield of the reaction. Finally, you will want to use the data you obtained to verify the law of conservation of mass. Let’s think for a minute how you will obtain the identity of the unknown compound. Through careful measurement, you will have the following data: 1. The initial mass of metal 2. The mass of iodine reacted 3. The final mass of metal 4. The mass of compound With this information, one should be easily able to obtain the moles of iodine and zinc reacted, and thus calculate the empirical formula for the compound. Stoichiometry can then be used to evaluate the percent yield. Procedure You want to obtain 2 clean and dry 18x150 mm test tubes. Test tubes are hard to mass on a balance, so what you want to do is place a beaker on the balance and tare it. Then simply place the tube in the beaker and record the mass of the tube. All masses in this experiment need to be recorded to 0.001 g. 1 Obtain some of the granular zinc. Make observations of it and record these below your data table. You need approximately 1.00 g of Zn, but once you place some of Zn in the tube, you will never be able to get it out. Thus, to make sure you do not add too much, simply first weigh some Zn in a weighing boat on the centigram balance. Try to get as close to 1.00 g as possible, but going over a little is fine. After you know the approximate mass, weigh your empty test tube on the analytical balance empty, add the zinc, and then reweigh the tube. The mass of the Zn will of course be the difference in the two masses. We now want to do a similar procedure with iodine. Molecular iodine is one of the most toxic substances you will use this year (see attached MSDS) and to prevent accidental release we need to measure out the iodine in the hood. There you will find iodine in a weighing boat covered with a watch glass. Take a small, clean weighing boat and add some iodine to it. Weigh this iodine on the centigram balance in the hood. If the mass is close to 1.00 g (over 1.00 g is better than 1.00 g, why??), add the iodine to your zinc filled test tube in the hood, and then weigh the mixture on the analytical balance. Again since you are weighing by difference, the mass of the iodine added can be easily determined by subtraction. Obtain your clean 10 ml graduated cylinder. Add to it 3-5 ml of the acidic water you will be using as the solvent for the entire lab (The acidic water is found in small wash bottles throughout the lab. This acidic water is necessary to prevent a side reaction between your metal and water). Add the 3-5 ml to your test tube and begin to gently swirl. Record any observations of chemical reaction. It is critical to continue swirling throughout the reaction for the reaction to happen quickly. Over the course of 10 minutes you should see the reaction mixture clear and return to room temperature. Obtain a second test tube with a glass boiling stone and record the mass of the two together. Decant the soluble product from one test tube to the other (you may use a small funnel if you wish. Remember, any liquid you lose is product!). Then, wash the remaining zinc metal with 3 successive 1ml volumes of acidic water, decanting the water into the other tube to insure all the soluble product is obtained. Place the test tube with excess metal in a labeled beaker and place in the oven to dry. If you are doing the lab at T period, you should stop at this point. Attach a test tube clamp to your tube containing product and gently begin to heat the solution by waving the tube gently and continuously through the blue flame. It is critical that you heat the solution gently while pointed away from you (and others). Otherwise it is highly probable the solution will foam up and bump. Bumping occurs when the solution is heated too quickly and a large bubble of vapor quickly forms and explodes out of the solution. The force of the bubble usually turns your solution into a projectile, causing you to lose product and endangering others as well. IT IS CRITICAL YOU HEAT SLOWLY!!!! You can take turns with your partner heating the solution, but one second of impatience will cost you an hour to two hours of rework. Eventually, the solution will boil off, leaving behind your solid product. Continue to gently heat the product through the whole tube until the color of the product is a pale yellow and 2 no water remains. Listen for the sound of crackling which will be evident when the product is almost dry, and you should heat for a short time after that. Let the product cool until your can comfortably handle it and then reweigh the product on the balance. Remove your excess Zn from the oven and let it cool. Swirl the metal and if it does not adhere to the tube, it is dry. Let it cool and weigh, gently heat the metal in the burner for a few minutes and cool and weigh again. If the masses of the two weightings differ by more than 0.005 g consult the instructor. Place both samples in your drawer. The class will test the samples for electrical conductivity and also try and decompose the solid back into its original elements later in the semester. Analysis 1. With your data, you should verify the law of conservation of mass. Simply compare the masses of your reactants to that of your product. It is likely the two will not match (something you should discuss in your discussion section) 2. You actually have two methods to calculate the amounts of Zn and I in the compound (a) You can assume that all the iodine placed in the tube is in your product, and thus find the amounts of Zn and I in the compound using this information. (b) You have the mass of Zn left over in the reaction as well as the mass of the product. From this you can find the mass of Zn in the compound and hence the mass of I. I think it would be interesting to calculate the percent composition (and hence the empirical formula) using both methods to see which is closer, and then discuss in your discussion which you think is better. Observations you make during the lab may guide you to which is the better method for this experiment. 3. Calculate the percent composition of Zn and I in your compound 4. Calculate the empirical formula of your compound 5. From your empirical formula, write down the balanced chemical equation (with states) for your synthesis reaction, and then calculate the theoretical yield of product from your reactant masses. Using your actual yield, calculate the percent yield of the reaction. Discussion The compound between zinc and iodine should be an ionic compound. How could you prove it is ionic in the laboratory? In addition, do you feel you have verified the law of conservation 3 of mass? Explain. Finally, explain which of the two methods of determining the EF is the “better” one. Are there any experimental observations to support one over the other? Conclusion End the lab by stating the empirical formula of the ionic compound as well as the percent yield of the reaction. 4 FLINN SCIENTIFIC INC. "Your Safer Source for Science Supplies" Material Safety Data Sheet (MSDS) MSDS #: 407.00 Revision Date: November 25, 2002 Section 1 — Chemical Product and Company Identification Iodine Flinn Scientific, Inc. P.O. Box 219 Batavia, IL 60510 (800) 452-1261 CHEMTREC Emergency Phone Number: (800) 424-9300 Section 2 — Composition, Information on Ingredients Iodine CAS#: 7553-56-2 Section 3 — Hazards Identification Gray-black flakes, metallic luster, characteristic odor. Highly toxic by ingestion and inhalation. Irritating and corrosive to skin. Avoid all body contact. FLINN AT-A-GLANCE Health-3 Flammability-0 Reactivity-2 Exposure-3 Storage-1 0 is low hazard, 3 is high hazard Section 4 — First Aid Measures Call a physician, seek medical attention for further treatment, observation and support after first aid. Inhalation: Remove to fresh air at once. If breathing has stopped give artificial respiration immediately. Eye: Immediately flush with fresh water for 15 minutes. External: Wash continuously with fresh water for 15 minutes. Internal: Rinse out mouth, give 1 to 2 cups of water or milk, induce vomiting. Call a physician or poison control at once. Section 5 — Fire Fighting Measures Non-flammable, noncombustible solid. When heated to decomposition, emits toxic fumes of iodide and various iodine compounds. Fire Fighting Instructions: Use triclass, dry chemical fire extinguisher. Firefighters should wear PPE and SCBA with full facepiece operated in positive pressure mode. NFPA CODE None Established Section 6 — Accidental Release Measures Restrict unprotected personnel from area. Sweep up, place in sealed bag or container and dispose. Ventilate area and wash spill site after material pickup is complete. See Sections 8 and 13 for further information. Section 7 — Handling and Storage Flinn Suggested Chemical Storage Pattern: Inorganic #2. Store with acetates, halides, sulfates, sulfites, thiosulfates and phosphates. Store in a cool dry place. Store in a Flinn Chem-Saf bag; the substance sublimes. Frequently oxidizes metal shelves or metal containers in proximity to the iodine. Use and dispense in a hood. Section 8 — Exposure Controls , Personal Protection Avoid contact with eyes, skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and chemical-resistant apron. Use ventilation to keep airborne concentrations below exposure limits. Always wear a NIOSH-approved respirator with proper cartridges or a positive pressure, air-supplied respirator when handling this material in emergency situations (spill or fire). Exposure guidelines: ceiling 0.1 ppm (OSHA) © 2002 Flinn Scientific, Inc. All Rights Reserved. PAGE 1 OF 2 FLINN SCIENTIFIC INC. Iodine "Your Safer Source for Science Supplies" MSDS #: 407.00 Revision Date: November 25, 2002 Material Safety Data Sheet (MSDS) Section 9 — Physical and Chemical Properties Gray-black flakes, metallic luster, characteristic odor. Solubility: Soluble in alcohol and other organic solvents; not in water. Formula: I2 Formula Weight: 253.80 Boiling Point: 185.24 C Specific gravity: 4.98 Melting Point: 113.5 C Section 10 — Stability and Reactivity Avoid contact with magnesium, zinc, ammonia, aluminum, corrodes steel. Reacts violently with acetaldehyde. Shelf Life: Fair; the substance sublimes. Frequently oxidizes metal shelves or metal containers in proximity to the iodine. Section 11 — Toxicological Information Acute effects: Highly toxic, harmful vapor, corrosive, severe lachrymatol, sensitizer, stomach pains, vomiting. Chronic effects: Dermatitis Target organs: Thyroid ORL-HUM LD50: 2-4 gm for an adult IHL-RAT LC50: N.A. SKN-RBT LD50: N.A. N.A. = Not available, not all health aspects of this substance have been fully investigated. Section 12 — Ecological Information Data not yet available. Section 13 — Disposal Considerations Please consult with state and local regulations. Flinn Suggested Disposal Method #12a is one option. Section 14 — Transport Information Shipping Name: Toxic solid, inorganic, n.o.s. Hazard Class: 6.1 Keep away from food UN Number: UN3288 N/A = Not applicable Section 15 — Regulatory Information TSCA-listed, EINECS-listed (231-442-4), RCRA code D002. Section 16 — Other Information Consult your copy of the Flinn Scientific Catalog/Reference Manual for additional information about laboratory chemicals. This Material Safety Data Sheet (MSDS) is for guidance and is based upon information and tests believed to be reliable. Flinn Scientific Inc. makes no guarantee of the accuracy or completeness of the data and shall not be liable for any damages relating thereto. The data is offered solely for your consideration, investigation, and verification. Flinn Scientific Inc. assumes no legal responsibility for use or reliance upon this data. FLINN SCIENTIFIC INC. "Your Safer Source for Science Supplies" Flinn Is No. 1 in Safety flinn@flinnsci.com www.flinnsci.com P.O. Box 219 Batavia IL 60510 (800) 452-1261 Fax (866) 452-1436 © 2002 Flinn Scientific, Inc. All Rights Reserved. PAGE 2 OF 2