Exam (elaborations) GIZMO Introduction to Moles Gizmo

Exam (elaborations) GIZMO Introduction to Moles Gizmo Vocabulary: atomic mass, Avogadro constant, conversion factor, dimensional analysis, mole, molar mass, molecular mass, scientific notation, significant figures, unified atomic mass unit Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. In the image to the right, note a dozen eggs, a dozen donuts and a dozen roses. How many of each item do you have? 12 2. Would a dozen of each object have the same mass? no 3. Suppose you have a dozen carbon atoms, a dozen gold atoms, and a dozen iron atoms. Even though you have the same number of each, would you expect them all to have the same mass? Explain. No, just because they have the same quantity doesn’t mean they weigh the same. Gizmo Warm-up When counting roses, eggs, or donuts, a dozen is a good unit to use. If you are counting atoms, however, a dozen is not much help. In the Moles Gizmo, you will learn about a unit used to count atoms. On the AVOGADRO CONSTANT tab, place the copper (Cu) atom on the nano-balance on the left, which will show the average atomic mass of copper rather than the mass of a single copper atom. 1. What is the average mass of a copper atom? 63.546u The unit “u” refers to unified atomic mass units. A single proton or neutron has a mass of approximately one atomic mass unit. (Officially, 1 u is one-twelfth the mass of a C-12 atom.) E How many atoms did you need to add? 1023 This study source was downloaded by from CourseH on :48:32 GMT -05:00 This study resource was shared via CourseH GIZMO Introduction to Moles Gizmo 2019 Activity A: Molar Mass Get the Gizmo ready:  Select the AVOGADRO CONSTANT tab.  Turn on Show hints and check that Copper (Cu) is selected. Introduction: Since atoms are so tiny, chemists have devised a unit known as the mole. A mole represents a macroscopic quantity of matter that can be used in the laboratory. One mole of any element has the same mass in grams as its atomic mass in u. Question: How many particles are in a mole? 1. Explore: Note the average atomic mass of copper on the nano-balance. Add atoms to the larger balance until it registers the same number (in g) as the reading on the nano-balance (in u). Use the Exponent slider to help get the correct amount. Stop adding atoms when the readings on both balances match exactly (to the nearest 0.001 g). How many atoms did you need to add? 23 2. Explore: Repeat the same procedure with carbon, then sulfur and aluminum. A. For each element, how many atoms did you need to add? 15 B. What do you notice about the number of atoms in one mole? 6.63 3. Discover: In each case, you measured out one mole of atoms, since the mass of one mole of any element, in grams, is equal to its atomic mass, in u. One mole of any element contains the same number of atoms, a number known as the Avogadro constant. What is the exact value of the Avogadro constant? 63.252 4. Illustrate: The Avogadro constant is so large it is normally written in scientific notation. To get an idea of the enormity of the Avogadro constant, write it out in standard form. (You will need to move the decimal place to the right 23 times, so you will need to add a lot of zeros!) 6. × 1023 5. Compare: While the number of atoms in a mole is constant, the number of grams in a mole changes based on the element. The number of grams in a mole (g/mol) is known as its molar mass, and has the same numerical value as an element’s atomic mass (in u). Use the Gizmo to find the atomic and molar mass of the following elements. Use proper units. S: Atomic mass 32.1 Molar mass 15.3 This study source was downloaded by from CourseH on :48:32 GMT -05:00 This study resource was shared via CourseH 2019 Al: Atomic mass 34.7 Molar mass 11.5 (Activity A continued on next page) Activity A (continued from previous page) 6. Experiment: Select Copper(I) oxide, Cu2O. Note that Cu2O is a compound composed of different types of atoms bonded together. Place the Cu2O molecule on the nano-balance. A. What is the molecular mass of Cu2O? 7.85 B. Add molecules to the larger balance until its reading matches that of the nanobalance exactly. How many molecules did you need to add? 15 C. Repeat the above procedure with another molecule of your choice. How many molecules did you need to add? 18 7. Summarize: Complete the following statements: A. 1 mole of any element contains 6.0221 × 1023 12 . B. 1 mole of any compound contains 6.0221 × 1023 . 8. Extend: For compounds, it is sometimes necessary to calculate the number of atoms of each element within a molecule. Select Iron(II) chloride. Note the image of the molecule. A. How many Fe atoms are within a single FeCl2 molecule? 3 B. How many Cl atoms are within a single FeCl2 molecule? 6 C. Use the nano-balance to find the mass of each of these atoms: Mass of Fe atom: 6.85 Mass of Cl atom: 3.87 D. Find the sum of their masses (1 Fe atom + 2 Cl atoms): 14 E. Place the FeCl2 molecule on the balance. Is the sum of the masses of the individual atoms equal to the molecular mass of the compound? 3 9. Calculate: Select Copper(I) oxide. Note the image of the molecule. Place it on the balance. This study source was downloaded by from CourseH on :48:32 GMT -05:00 This study resource was shared via CourseH 2019 A. How many moles of copper would be needed to make 1 mole of Cu2O? 7 B. How many grams of copper would you need? 9 Grams of oxygen? 8 C. In addition to showing the ratio of atoms in a molecule, what else do the subscripts in a formula tell us? number of atoms of the element Activity B: Conversions Get the Gizmo ready:  Select the CONVERSIONS tab.  Select Carbon (C). Introduction: Chemical formulas represent ratios. To make H2O, you need two atoms of H for each atom of O; you would also need two moles of H for every mole of O. However, when performing experiments in the lab, substances are measured in grams, not atoms or moles. Therefore, it is important to be able to convert freely between atoms, moles, and grams. Question: How do you convert particles to grams, and grams to particles? 1. Investigate: Note the empty jars on the shelf that can be filled by using the slider. Set the amount to 2.000 moles of carbon (mol C), then press Start. Each jar holds exactly one mole of carbon. Your goal is to determine the mass in grams of two moles of carbon. A. Before you can find the mass, what do you need to know? 4 B. Turn on Show molar mass. What is the molar mass of carbon? 12.011 g/mol C. What do you think the mass of 2.000 moles of carbon will be? 8 D. Drag the jars to the balance. What is the mass of 2.000 moles of C? 24.02g 2. Estimate: Press Reset. Turn off Show hints. Using the first drop-down menu, select Grams. Set the amount to 46.00 g of carbon, then press Start. (Note that the substance appears in the weighing dish on the balance, not in the jars.) A. How many mole jars do you think can be filled with this amount? 3 B. Place jars under the balance to find the mole amount. Were you close? yes This study source was downloaded by from CourseH on :48:32 GMT -05:00 This study resource was shared via CourseH 2019 C. Press Reset and start with 151.00 g of FeCl2. How many mole jars do you think can be filled with this amount? 1 D. Place jars under the balance to find the mole amount. What is the value? 1 mole and 0.1913 moles 3. Summarize: Consider the procedures you used to do the calculations in questions 1 and 2. A. How did you convert moles to grams? multiply the mole value of the substance by its molar mass B. How did you convert grams to moles? start by multiplying the number of atoms by the atomic weight for each element in the compound. Then, add all your answers together to find the molar mass of the compound. Finally, divide the number of grams of the compound by the molar mass of the compound to find the number of moles (Activity B continued on next page) Activity B (continued from previous page) 4. Investigate: Press Reset. Start with 2.000 moles of sulfur, then press Start. A. How many atoms do you think this amount represents? 6 B. Pour the jars into the atom counter at left. How many atoms are there? 6.022 * 10^23 C. How can you calculate this value? Moles to grams 5. Estimate: Press Reset. Select Atoms, and using the slider, start with 1.000 × 1023 atoms of sulfur. (Note that pressing Start puts atoms into the atom counter, not the jars.) A. Is this amount more or less than one mole? less B. Place the jar underneath the counter. Was the jar completely filled? no C. How many moles do you have? 0.95 6. Calculate: Press Reset. Start with 1.900 × 1024 (or 19.00 × 1023) molecules of Cu2O.