Presentation on theme: "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?"— Presentation transcript:
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? 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 12 u (atomic mass units). What is the actual mass of a C atom? Answer: approx. 2 x 10 -23 grams; 0.00000000000000000000002 g (protons and neutrons each weigh about 1.7 x10 -24 grams) Two problems 1.Atomic masses do not convert easily to grams 2.They can’t be weighed (they are too small)
W hat Is a Mole and Why Are Moles Used? A mole is simply a unit of measurement. Units are invented when existing units are inadequate. Chemical reactions often take place at levels where using grams wouldn't make sense, yet using absolute numbers of atoms/molecules/ions would be confusing, too.
What Is a Mole and Why Are Moles Used? Cont’d Like all units, a mole has to be based on something reproducible. A mole is the quantity of anything that has the same number of particles found in 12.000 grams of carbon-12. That number of particles is Avogadro's Number, which is roughly 6.02x10 23. A mole of carbon atoms is 6.02x10 23 carbon atoms. A mole of chemistry teachers is 6.02x10 23 chemistry teachers.
Food for thought… It's a lot easier to write the word 'mole' than to write '6.02x10 23 ' anytime you want to refer to a large number of things! Basically, that's why this particular unit was invented!! Okay... you may not find it too convenient when you are first learning how to use it, but once you become familiar with it, a mole will be as normal a unit as, say, a dozen or a byte.
The Mole With these problems, why use atomic mass at all? 1.Masses give information about # of p +, n 0, e – 2.It is useful to know relative mass E.g. Q - What ratio is needed to make H 2 O? A - 2:1 by atoms, but 2:16 by mass It is useful to associate atomic mass with a mass in grams. It has been found that 1 g H, 12 g C, or 23 g Na have 6.02 x 10 23 atoms 6.02 x 10 23 is a “mole” or “Avogadro’s number” “mol” is used in equations, “mole” is used in writing; one gram = 1 g, one mole = 1 mol.
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 10 23 / $1 000 000 000 = 6.02 x 10 14 payments = 6.02 x 10 14 seconds 6.02 x 10 14 seconds / 60 = 1.003 x 10 13 minutes 1.003 x 10 13 minutes / 60 = 1.672 x 10 11 hours 1.672 x 10 11 hours / 24 = 6.968 x 10 9 days 6.968 x 10 9 days / 365.25 = 1.908 x 10 7 years A: It would take 19 million years
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