LAB 7: PERCENT OF WATHER IN POPCORN NAME Introduction Popcorn is one of the world’s favorite snack foods. In the US, Americans consume more than18 billion quarts of popcorn each year. Some nutritionists call it a perfect snack food because it is a whole grain, a good source of fiber and antioxidants, and low in fat. Background The most intriguing part of popcorn is the science behind how it pops. Popcorn is the only grain in the corn family that pops open when exposed to temperatures above 180° C. A popcorn kernel is composed of 3 parts: the pericarp, germ, and endosperm. See Fig. 1. The pericarp is the tough outer shell surrounding a popcorn kernel, and the key to what makes it pop. Inside the pericarp is the germ, or seed embryo. Adjacent to the germ is the endosperm, which contains some trapped water plus soft and hard starch granules that serve as food for the germ when it sprouts. When a popcorn kernel is heated, the trapped water in the endosperm turns into steam, building up pressure inside the pericarp. This pressurized, super-heated steam transforms the soft starch in the endosperm into a gelatinous material. Popcorn pericarp is much stronger than that of all other corn kernels and is able to retain this pressurized steam up to 9.2 atm (135 psi). Above that pressure, the pericarp ruptures, releasing the steam and gelatinous starch that solidifies upon cooling. The resulting popped kernel is 40 to 50 times its original size. To see popcorn pop in slow motion, select from the Popcorn Videos menu at www.popcorn.org. People often wonder what is the ideal percentage of water in popcorn kernels for best popping. Popcorn is harvested in the fall when the kernels’ moisture content is between 16 and 20%. The kernels are then stored in bins where they are dried by forced air until reaching an optimum moisture level of 14%. If the moisture content drops below that value, the size of the popped kernels is smaller and the number of kernels that pop decreases. Figure 1 Corn kernel. Objectives: Find the percent of water in popcorn Calculate the percent composition of popcorn and chemical compounds Materials Canola Oil 20 Kernels of Popcorn Pipet 250 mL Beaker Aluminum Foil Hotplate EXPERIMENT: PERCENTAGE OF H2O IN POPCORN Electronic Balance Beaker Tongs Timer Prelab Questions: You already know a lot about percent. Today you’ll be figuring out some percentages for compounds and mixtures. You can always find percent by using the following formula: 𝑃𝑎𝑟𝑡 ∗ 100 = 𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑊ℎ𝑜𝑙𝑒 1. You get a 58 out of 54 on a chemistry test. i. What is your “part”? ii. What is your “whole”? iii. What percent did you get on the test? Percent Composition - The percent composition of a component in a compound is the percent of the total mass of the compound that is due to that component. To calculate the percent composition of a component in a compound: 1. Find the molar mass of the compound by adding up the masses of each atom in the compound using the atomic mass on the periodic table. 2. Calculate the mass due to the component in the compound you are for which you are solving by adding up the mass of these atoms. 3. Divide the mass due to the component by the total molar mass of the compound and multiply by 100. Examples of Percent Composition Problems a) Calculate the percent composition of carbon in CO2 Molar mass of compound: Mass due to carbon: 12.01 g/mol Percent composition of carbon: b) Calculate the percent composition of carbon in C6H12O6 Molar mass of compound: Mass due to carbon: Percent composition of carbon: 2: a) What is the percent oxygen in water, H2O? b) What is the percent hydrogen in water, H2O? c) Prove you did solved the above parts correctly by adding your percentages – if it’s not 100% you have done something wrong! Procedure: Analysis and Post lab Questions: 1. Calculate the initial mass of the popcorn kernels 2. Calculate the final mass of the popcorn kernels 3. Calculate the percentage of water in popcorn. Initial mass – final mass x 100 = percentage of H2O in un popped popcorn Initial mass 4. Calculate your percent error. If the industry standard 13.5% water in un popped popcorn. % error = l accepted value – experimental value l x 100 Accepted value 5. Quartz has the chemical formula SiO2. What is the percentage composition of each element this compound? 6. Urea, a component in fertilizer, has the chemical formula, CO(NH2)2. What is the percentage composition of each element in this compound? 7. What is the percent carbon (by mass) in CO2? 8. Potassium Phosphate, K3PO4, is used as an electrolyte in many sports drinks. Calculate the percent of phosphate in this compound. 9. Calculate the percent water in CuSO4·5H20. 10. Which of two common ingredients in garden fertilizers, ammonium sulfate, (NH 4)2SO4, or ammonium phosphate, (NH4)3PO4, has a greater percentage of nitrogen? Explain your reasoning using a complete sentence. Percent of water in popcorn Lab– 41 points Note: To receive credit on pre and post lab questions they must include either the question written or the answer provided, or the answer restates the question as part of the answer. 1. _____ 1 pts Lab is entered correctly in the Table of contents 2. _____ 1 pts Lab entered into composition book according to basic lab notebook instructions 3. _____ 1 pt Lab notebook is neat and legible (includes proper sized print, readable ink) 4. _____1 pt Lab area left clean with all materials put back in their proper place 5. _____ 6 pts Prelab questions 1 and 2 are completed according to instructions 6. _____ 8 pts Physical lab and data collection completed by the student within one week of original lab date 7. _____ 3 pts Data table I complete 8. _____ 20 pts Post lab questions 1 – 10 answered correctly with proper sig figs and labels
