Exam (elaborations) GIZMO Moles, Avogadro, and Molar Mass

Exam (elaborations) GIZMO Moles, Avogadro, and Molar Mass 1. In the image, note a dozen eggs, a dozen donuts and a dozen roses. How many of each item do you have? 12 eggs, 12 donuts, and 12 roses. 2. Would a dozen of each object have the same mass? No 3. Suppose you have a dozen silver atoms, a dozen oxygen atoms, and a dozen lithium atoms. Even though you have the same number of each, will they all have the same mass? Explain. They will not all have the same mass because although there may be an equal amount of each one, they don’t all weigh the same or take up the same amount of space. Gizmo Warm-up 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? 63.546 u The unit “u” refers to unified atomic mass units. (Officially, 1 u is one-twelfth the mass of a C-12 atom.) 2. To know how many atoms are in a gram of copper, use the larger balance on the right. Press Add atoms to put a scoop of atoms in the weighing dish, and keep adding until the balance registers between 1 and 2 grams. If you don’t seem to be making much progress, adjust the exponent using the slider, which will make the scoop size bigger. How many atoms did you need to add? 9.6 x 10^21 atoms of copper This study source was downloaded by from CourseH on 07-25-2021 06:39:58 GMT -05:00 This study resource was shared via CourseH GIZMO Moles, Avogadro, and Molar Mass 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? 6.0221 x 10^23 atoms of copper 2. Explore: Repeat the same procedure with carbon, and aluminum. A. For each element, how many atoms did you need to add? Carbon: 6.022 x 10^23 atoms and Aluminum: 6.022 x 10^23 B. What do you notice about the number of atoms in one mole? The number of atoms for one mole is the same no matter the element. 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? 6. x 10^23 4. Compare: 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. Sulfur: Atomic mass 32.065 u Molar mass 32.065 G/Mol Aluminum: Atomic mass 26.982 u Molar mass 26.982 G/Mol 5. 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? 143.091 G/Mol This study source was downloaded by from CourseH on 07-25-2021 06:39:58 GMT -05:00 This study resource was shared via CourseH B. Add molecules to the larger balance until its reading matches that of the nanobalance exactly. How many molecules did you need to add? 6.0222 x 10^23 molecules C. Repeat the above procedure with another molecule of your choice. How many molecules did you need to add? Iron (III) hydroxide, Fe(OH)3 (Molecular Mass: 106.866 G/Mol) = 6.0221 x 10^23 molecules 6. Summarize: Complete the following statements: A. 1 mole of any element contains 6.0221 × 1023 molecules. B. 1 mole of any compound contains 6.0221 × 1023 molecules. 7. 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? 6.0221 x 10^3 atoms B. How many Cl atoms are within a single FeCl2 molecule? 6.0221 x 10^3 atoms C. Use the nano-balance to find the mass of each of these atoms: Mass of Fe atom: 55.845 u Mass of Cl atom: 35.453 u D. Find the sum of their masses (1 Fe atom + 2 Cl atoms): 126.751 u 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? No, y ou need two Cl and one Fe to match FeCl2 8. Calculate: Select Copper(I) oxide. Note the image of the molecule. Place it on the balance. A. How many moles of copper would be needed to make 1 mole of Cu2O? 6.0221 x 10^23 B. How many grams of copper would you need? 127.092 g Grams of oxygen? 16 g This study source was downloaded by from CourseH on 07-25-2021 06:39:58 GMT -05:00 This study resource was shared via CourseH C. In addition to showing the ratio of atoms in a molecule, what else do the subscripts in a formula tell us? The subscripts in a formula also tell us what is in a molecule like the amount needed for compounds. 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? Molar Mass 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? 1 x 10^24 D. Drag the jars to the balance. What is the mass of 2.000 moles of C? 1.204 x 10^24 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? 6 B. Place jars under the balance to find the mole amount. Were you close? No This study source was downloaded by from CourseH on 07-25-2021 06:39:58 GMT -05:00 This study resource was shared via CourseH C. Press Reset and start with 151.00 g of FeCl2. How many mole jars do you think can be filled with this amount? 4 D. Place jars under the balance to find the mole amount. What is the value? 1.1913 3. Summarize: Consider the procedures you used to do the calculations in questions 1 and 2. A. How did you convert moles to grams? You convert the moles to grams by times the number of grams into moles. B. How did you convert grams to moles? You convert the grams to moles by dividing the grams to moles. 4. Investigate: Press Reset. Start with 2.000 moles of sulfur, then press Start. A. How many atoms do you think this amount represents? I think the atoms this amount represents is 1.204 x 10^24 B. Pour the jars into the atom counter at left. How many atoms are there? There are 1.204 x 10^24 atoms. C. How can you calculate this value? I calculate the value by multiplying Avogrado’s number by 2. 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? The amount is less than one mole. B. Place the jar underneath the counter. Was the jar completely filled? The jar was not completely filled. C. How many moles do you have? I have 0.1661 moles. 6. Calculate: Press Reset. Start with 1.900 × 1024 (or 19.00 × 1023) molecules of Cu2O. A. Calculate the number of moles: 3.2 moles B. Use the Gizmo to verify your calculation. Were you correct? 3.1551 moles, I was close. C. Is the method for converting molecules to moles the same as that for atoms? The method is not the same. 7. Summarize: Consider the procedures you used to do the calculations in questions 4 and 5.