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The Mole

The Mole. Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second?. Background: Atomic Masses. Look at the “atomic masses” on the periodic table. What do these represent? E.g. the atomic mass of C is 12 (atomic # is 6)

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The Mole

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  1. The Mole Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second?

  2. Background: Atomic Masses • Look at the “atomic masses” on the periodic table. What do these represent? • E.g. the atomic mass of C is 12 (atomic # is 6) • We know there are 6 protons and 6 neutrons • Protons and neutrons have roughly the same mass. • So, C weighs about 12 u (atomic mass units). • TB: why is the atomic mass not exactly 12 on the periodic table? • What is the actual mass of a C atom? • Answer: approx. 2 x 10-23 grams (protons and neutrons each weigh about 1.7 x10-24 grams) Two problems: • Atomic masses do not convert easily to grams • They can’t be weighed (they are too small)

  3. The Mole Withtheseproblems,whyuseatomicmassatall? - Atomic masses give information about # of p+, n0, e– It has been found that 1gH,12gC,or 23gNahave6.02x1023atoms 6.02 x 1023 = a “mole” or “Avogadro’s number” • “mol” is used in equations, “mole” is used in writing; • one gram = 1 g, one mole = 1 mol. • Unit used to measure the amount of molecules/individual particles in a substance

  4. Mollionaire! Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second? A: $ 6.02 x 1023 / $1 000 000 000 = 6.02 x 1014 payments = 6.02 x 1014 seconds 6.02 x 1014 seconds / 60 = 1.003 x 1013 minutes 1.003 x 1013 minutes / 60 = 1.672 x 1011 hours 1.672 x 1011 hours / 24 = 6.968 x 109 days 6.968 x 109 days / 365.25 = 1.908 x 107 years A: It would take 19 million years

  5. Comparing sugar (C12H22O11) & H2O Same 1 gram each 1 mol each volume? No, they have dif. densities. No, molecules have dif. sizes. mass? Yes, that’s what grams are. No, molecules have dif. masses # of moles? No, they have dif. molar masses Yes. # of molecules? No, they have dif. molar masses Yes (6.02x1023 in each) # of atoms? No, sugar has more (45:3 ratio) No

  6. Molar mass • The mass of one mole is called “molar mass” • E.g. 1 mol Li = 6.94 g Li • This is expressed as 6.94 g/mol • What are the following molar masses? S SO2 Cu3(BO3)2 32.06 g/mol 64.06 g/mol 308.27 g/mol Calculate molar masses (to 2 decimal places) CaCl2 (NH4)2CO3 O2 Pb3(PO4)2 C6H12O6 Cu x 3 = 63.55 x 3 = 190.65 B x 2 = 10.81 x 2 = 21.62 O x 6 = 16.00 x 6 = 96.00 308.27

  7. Molar mass • The mass of one mole is called “molar mass” • E.g. 1 mol Li = 6.94 g Li • This is expressed as 6.94 g/mol • What are the following molar masses? S SO2 Cu3(BO3)2 32.06 g/mol 64.06 g/mol 308.27 g/mol Calculate molar masses (to 2 decimal places) CaCl2 (NH4)2CO3 O2 Pb3(PO4)2 C6H12O6 110.98 g/mol (Cax1, Clx2) 96.11g/mol(Nx2, Hx8, Cx1, Ox3) 32.00 g/mol (Ox2) 811.54 g/mol (Pbx3, Px2, Ox8) 180.18 g/mol (Cx6, Hx12, Ox6)

  8. m n M Formula M (g/mol) m (g) n (mol) Equation HCl 0.25 m= n x M H2SO4 53.15 NaCl 3.55 Cu 1.27 Converting between grams and moles • If we are given the # of grams of a compound we can determine the # of moles, & vise-versa • In order to convert from one to the other you must first calculate molar mass m = n x M n = m  M • Thiscanberepresentedinan“equationtriangle” 36.46 9.1 98.08 0.5419 n= m  M 58.44 207 m= n x M 63.55 0.0200 n= m  M

  9. N n NA Converting between grams and number of particles (atoms, molecules, compounds, etc.) • Once you know the amount of a substance (n), you can then calculate t he number of particles (N) by going back to our first equation triangle that includes Avagadro’s number (NA)

  10. N m n n NA M • Determine the number of molecules of water in an ice cube of mass 12.6 g. 1st – convert m  n 2nd – convert n  N A little more tricky • Calculate the number of atoms in 1.00 g of nitrogen. • Calculate the number of chloride ions in 22.2 g of CaCl2

  11. Homework!  • Pg. 226 #2,3 • Pg. 228, 230, 231 – odd numbers • Pg. 235 #31,33 • Pg. 237, 239, 242 – odd numbers

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