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Rice Lab 1. Count out 1 dozen grains of rice and place in container. 2. Repeat until you have 3 containers each holding 12 grains of rice. 3. Mass each dozen and calculate the average mass of 1 dozen grains of rice. (Don’t forget to minus out the mass of container.) 4. Calculate the number of rice grains in 1.94 gram of rice. 5. Mass out rice grains until you reach a mass equal to the mass you calculated above. 6. Count the grains of rice in the sample. 7. Calculate the percent error between the calculated number of rice grains versus the actual number of rice grains. Episode 701 Mole • Avogadro’s number – the mole = 6.022 x 1023 – 602,200,000,000,000,000,000,000 Molar Mass The mass of one mole of any pure substance Episode 701 • Molar mass of an element (g/mol) – Equals the atomic mass of the element in grams • Molar mass of a compound – Equals the sum of the molar masses of the elements making up the compound • Find the molar masses of- – Magnesium 24.3 g/mol – Chlorine 35.5 g/mol – Magnesium chloride • Write formula • Find the atomic mass of each element • Multiply atomic mass by the number of atoms for each element, then total the masses • MgCl2 • 24.3 g/mol + (2 x 35.5 g/mol) = 95.3 g/mol Episode 701 Try it! • Find the molar mass of aluminum oxide (2x 27 g/mol) + (3 x16g/mol) 102 g/mol Episode 701 Remember Rice Lab Calculations… • How many moles of atoms are there in 8.0 grams of Mg? ? moles = 8.0g Mg 1 mol Mg 24.3 g/mol • How many atoms are in 0.7 grams of He? ? atoms = 0.7g He 1 mol He 6.022 x 1023 atoms 4.0 g/mol 1 mol He Episode 701 Formula Units… No Problem • What would the mass of 5.3 x 1022 formula units of calcium iodide? CaI2 Formula Molar Mass 40.1 g/mol + (2 x 126.9 g/mol) 293.9 g/mol ?g CaI2 = 5.3 x1022 fu 1 mol CaI2 6.022 x 1023 fu = 293.9 g CaI2 1 mol CaI2 26 g CaI2 Episode 701 Problem Set 1 • How many atoms are in 3.5 grams of silicon? ? atoms = 3.5g Si 6.022 x 1023 atoms = 7.5 x 1023 atoms Si 1 mol Si 1mol Si 28.1g Si • How many formula units are in 32.6 grams of potassium oxide? ? fu = 32.6 g K20 1mol K2O 6.022 x 1023 fu 94.2g K2O 1 mol K2O = 2.1 x 1023 fu K2O • How many molecules are in 0.25 grams of dinitrogen pentoxide? ? molec = 0.25 g N2O5 1mol N2O5 6.022 x 1023 molec 108 g N2O5 1 mol N2O5 = 1.4 x 1021 mole N2O5 Episode 701