Activity: Moles, Avogadro, and Molar Mass

Name: Jose Rivera Rodriguez Date: 02/24/20 – 02/25/20 Activity: Moles, Avogadro, and Molar Mass Prior Knowledge Questions 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 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 B. Add molecules to the larger balance until its reading matches that of the nano- balance 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