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Regents Chemistry

Regents Chemistry. Topic III. Stoichiometry. What’s a Mole???. One mole of ANY specified entity contains 6.022 x 10 23 of that entity. For example:. One mole of donuts contains 6.022 x 10 23 donuts One mole of H 2 O contains 6.022 x 10 23 molecules

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Regents Chemistry

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  1. Regents Chemistry Topic III Stoichiometry

  2. What’s a Mole??? One mole of ANY specified entity contains 6.022 x 1023 of that entity. For example: • One mole of donuts contains 6.022 x 1023 donuts • One mole of H2O contains 6.022 x 1023 molecules • One mole of nails contains 6.022 x 1023 nails • One mole of Fe contains 6.022 x 1023 atoms • One mole of dogs contains 6.022 x 1023 dogs • One mole of electrons contains 6.022 x 1023 electrons

  3. (Covalently bonded)

  4. These are Formula units!

  5. How can we measure a mole? • A mole = 6.022 x 1023 particles • Could be a mole of an ionic compound • contains 6.022 x 1023 formula units (made of ions) • Could be a mole of a molecular compound • contains 6.022 x 1023 molecules (made of elements) • A mole of an element = the average atomic mass listed on the periodic table • A mole of a compound = total mass of the moles in the compound

  6. Finding the Mass of a Mole of a Compound

  7. Example #1

  8. Example #2

  9. Summary • Formula mass - mass of the smallest unit of an ionic compound; sum of atomic masses in amus • Gram Formula Mass - same as formula mass except in grams • Molecular Mass – same as FM except for used for molecular substances • Mole – 6.022 x 1023 particles of anything! Just know it is also the GFM of any substance

  10. Regents Chemistry • Mass, Mole and Particle conversions

  11. The Conversion Flowchart Mass of compound Number of Particles multiply by molar mass multiply by 6.02 x 1023 divide by molar mass Mole divide by 6.02 x 1023 divide by 22.4 liters multiply by 22.4 liters Liters of Gas

  12. Practice mole to mass • How many grams are in 2 moles of CuCl2? • How many grams are in 3.5 moles of H2O 2 moles CuCl2 x 134g per mole = 268 g 3.5 moles H2O x 18g per mole = 63 g

  13. Mass to Mole • How many moles of NO are in 67.0g of NO? • How many moles of KCl are in 125.0g of KCl? 67.0 g NO / 30.0 g per mole = 2.2 moles NO 125.0 g KCl / 74.5 g per mole = 1.68 moles KCl

  14. Regents Chemistry • Finding Percent Composition

  15. What is Percent Composition? • Formulas represent the composition of a substance • If we use the subscripts and atomic masses of the elements, we can find the percent by mass of each element in a substance • Essentially, Percent Composition finds how much of each element is in a substance

  16. How do we do this???? • 1. We can add up the total molar mass of all elements involved in the substance • 2. We next simply divide the total of the element in question by the total molar mass and multiply by 100%

  17. Example #1 • Find the percent composition (in grams) of oxygen in potassium chlorate 2. Divide and multiply by 100% 1. Find the molar mass KClO3 K - 1 mole x 39.1 grams = 39.1 g Cl - 1 mole x 35.5 grams = 35.5 g O - 3 moles x 16.0 grams = 48.0 g %O = 48.0 g x 100% 122.6 g Molar mass = 122.6 g %O = 39.2%

  18. Moles and molecules/formula units • Moles - measured in grams • molecules / formula units - measured in amu (atomic mass units) • So… grams make up moles of a substance • and amu (atomic mass units) make up individual molecules/formula units • Use the same numbers from the PT!

  19. It’s the same process to find the % of amu in a 1 molecule or formula unit! • Find the percent composition (in amu) of oxygen in potassium chlorate 2. Divide and multiply by 100% 1. Find the mass in amu KClO3 K - 1 atom x 39.1 amu = 39.1 amu Cl - 1 atom x 35.5 amu = 35.5 amu O - 3 atoms x 16.0 amu = 48.0 amu %O = 48.0 amu x 100% 122.6 amu Formula mass = 122.6 amu %O = 39.2%

  20. Example #2 • Find the percent composition (in amu) of water in sodium carbonate crystals Na2CO3 • 10H2O 3. Divide %H2O = 180.0 amu x 100% --------------- 286.0 amu %H2O = 62.9% 1. Formula Mass = 286.0 amu 2. Total formula mass of H2O = 180.0 amu worksheet

  21. Regents Chemistry • Mole Relations in Balanced Equations

  22. RECAP • The Law of Conservation of Mass tells us: • Moles (and atoms) in equations must be balanced • Since moles (and atoms) have mass, mass is also balanced (we did this by finding missing mass) • So we have relationship between reactants and products • Thus if we change the moles of reactants (or number of atoms) we change the moles /# of atoms of products..HOW?

  23. Mole Relations • Balanced Chemical Equation: 2C2H6 + 7O2 4CO2 + 6H2O MolesC2H6 MolesO2 MolesCO2 MolesH2O 2 7 4 6 4 14 8 12 1 3.5 2 3

  24. Sample Problem • How many moles of water will be produced from the complete combustion of 3.0 mol of ethane? 2C2H6 + 7O2 4CO2 + 6H2O moles ethane:moles water = 2:6 3.0 mole C2H6 = x 2.0 mole C2H6 6 mole H2O x = 9.0 mole H2O

  25. Finding the Mass Produced • Sample Problem Cont.. • How many grams of water are produced 9.0 mole H2O produced ( ) #g H2O = 9.0 mole H2O 18.0g H2O = 162 g H2O 1 mole H2O

  26. Sample Problem #2 • How many moles of iron (III) oxide are produced from the combination of 6 moles of Fe ? How many grams? 4Fe + 3O2 2Fe2O3 6 mole Fe=x mole Fe2O3 4 mole Fe 2 mole Fe2O3 x= 3 mole Fe2O3 equals 480g Fe2O3

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