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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. - PowerPoint PPT Presentation
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Calculations The math of chem. rxns.
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!
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!
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
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
18.06 x 1023atoms He x 1 mol He = 3 mol He 6.02x1023 atoms He
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/mol Cl (mass of Cl) – So, it is 58.46 g NaCl/mol NaCl
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
• 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
END
• 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
Ex. Gram -> Mol -> Molecule
• How many molecules are there in 1.0 grams of O2?
• How many atoms is that?
1.0 g O2 x 1 mol O2 x
32.00 g O2
6.02 x 1023molec. O2 =
1 mol O2
1.9 x 1022 molec. O2
• 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%
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% !)