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Calculations The math of chem. rxns.

Calculations The math of chem. rxns. Mole. What is a mole, again?. A mole is a counting unit, like a dozen. 1 dozen eggs = 12 eggs 1 mole eggs = ? 6.022 x 10 23 eggs! A mole is the same, no matter if it ’ s counting eggs or atoms.

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Calculations The math of chem. rxns.

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  1. Calculations The math of chem. rxns. Mole

  2. What is a mole, again? • A mole is a counting unit, like a dozen. • 1 dozen eggs = 12 eggs • 1 mole eggs = ? • 6.022 x 1023 eggs! • A mole is the same, no matter if it’s counting eggs or atoms. • BUT it is SO large that the ONLY things we count with it are atoms and molecules!

  3. Would you like a mole of $?? • If I gave you one dollar a second, how long do you think it would take for me to give you a mole of dollars? (i.e. $6.022 x 1023) • It would take over 19,100,000,000,000,000 years. • The Earth was formed only 4,600,000,000 years ago! • A mole of dollars (each .0043 in thick) would reach over 7000 light-years!

  4. Calculate number of atoms in two mol Kr. • One mole = 6.02 x 1023 atoms • 2 moles = ? atoms 2 mol Kr x 6.02x1023 atoms Kr = 12.04x1023atoms 1 mol Kr

  5. 18.06 x 1023atoms He x 1 mol He = 3 mol He 6.02x1023 atoms He Calculate number of moles for 18.06 x 1023 atoms of He. • 6.02 x 1023 atoms = 1 mole • 18.06 x 1023 atoms = ? moles

  6. Molar Mass • Remember atomic mass? • Atomic mass of Na = 22.98977 g/mol • (22.99 grams of sodium per mole of sodium) • This is from the periodic table • Now, we learn molar mass: • What is the molar mass of NaCl? • 22.99 g/mol Na + 35.45 g/molCl (mass of Cl) • So, it is 58.46 g NaCl/molNaCl

  7. State the number of moles in 58.4 grams of Carbon. • 12.01 g C = 1 mol C • 58.4 g C = ? mol C • 58.4 g C x 1 mol C = 4.86 mol C 12.01 g C

  8. 12.04 x 1023 molec. x 1 mol H2O x 18.01 g H2O = 6.02x1023 molec. 1 mol H2O 36.02 g H2O 6.02x1023 molec. = 1 mol 12.04x1023 molec. = x mol 1 mol = 18.01 grams on Periodic Table x mol = y grams Calculate mass in grams of 12.04 x 1023 molecules H2O

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  10. atoms-mole-grams • To change atoms to grams OR to change grams to atoms, first calculate the number of moles. • atoms --> mol --> gram • OR • gram --> mol --> atoms • NO atom --> gram or gram --> atom

  11. Ex. Gram -> Mol -> Molecule • How many molecules are there in 1.0 grams of O2? • How many atoms is that? 1 mol O2x 32.00 g O2 6.02 x 1023molec. O2= 1 mol O2 1.0 g O2 x 1.9 x 1022 molec. O2

  12. Percent Composition • Sometimes, you have to calculate what percentage part of a compound is: • % part= part x 100% total • What percent of the total box is one strawberry? • 1/5 x 100% =20%

  13. Calculate % comp for Na2O2 • Mass Na (in Na2O2) = 2 x 22.99 g Na = 45.98 g Na • Mass O(in Na2O2) = 2 x 16.00 g O = 32.00 g O 77.98 g tot. • % Na = 45.98 g x 100% = 58.96% Na 77.98 g • % O = 32.00 g x 100% = 41.04 % O 77.98 g • (or 100% - 58.96% = 41.04% !)

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