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Moles

Moles. Chemical Compounds Unit Notes #4. Avogadro’s Number. [602,200,000,000,000,000,000,000] Atomic masses are measured in amu For real-life purposes, grams are more useful Avogadro discovered a number that converts between amu and grams: 6.022 x 10 23 (“Avogadro’s Number”)

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Moles

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  1. Moles Chemical Compounds Unit Notes #4

  2. Avogadro’s Number [602,200,000,000,000,000,000,000] • Atomic masses are measured in amu • For real-life purposes, grams are more useful • Avogadro discovered a number that converts between amu and grams:6.022 x 1023 (“Avogadro’s Number”) • There are 6.022 x 1023amu per 1 gram

  3. Moles • 6.022 x 1023 of something = 1 MOLE of it(Avogadro’s number!) • We use moles to count atoms, just like we use dozens to count eggs. • This little guy is also a mole. http://www.showbiz411.com/2012/04/11/gawkers-fox-mole-says-hes-still-working-not-caught

  4. How big is a mole? 602,200,000,000,000,000,000,000 • In seconds: 4 million times longer than the earth has existed • In snowflakes: a layer of snow across the entire USA deep enough to cover even the tallest skyscraper • In money: $87 trillion to every person in the world

  5. Using Moles • Since atoms are so tiny, we usually talk about moles instead. • Subscripts in a chemical formula can refer to individual atoms OR moles of atoms • H2O = 2 H atoms + 1 O atom • H2O = 2 moles H + 1 mole O • By looking at the subscripts, we can determine the mole ratio in the formula • H2O = 2 H : 1 O

  6. Moles and Atoms • There are 12 eggs in one dozen. • How many eggs are there in 2.5 dozens? • How many dozens are there in 36 eggs? • How do we figure this out?

  7. Moles and Atoms • To count atoms in a certain number of moles, we multiply by Avogadro’s number. • Ex) How many atoms are in 2 moles of Ca?2 moles x 6.022x1023 = 1.104x1024 atoms • To count moles in a certain number of atoms, we divide by Avogadro’s number. • Ex) How many moles are in 4.3x1022 atoms of Fe?4.3x1022 atoms / 6.022x1023 = 0.0714 moles

  8. Molar Mass • 1 atom and 1 mole of atoms (of the same element) will have masses that are the same number in amu and grams • 1 atom of carbon: 12.01 amu • 1 mole of carbon: 12.01 g • The same is true for compounds! • 1 molecule of H2O: 18.02 amu • 1 mole of H2O : 18.02 g • The mass (g/mol) of one mole of a compound or element is called its MOLAR MASS • The molar mass is the formula mass in grams.

  9. Molar Mass • Linebackers have a “molar mass” of 300 lbs/linebacker. • How many lbs are 3 linebackers? • How many linebackers are there in 1500 lbs? • How can we figure this out?

  10. Molar Mass • To calculate the mass of a certain number of moles, we multiply by the molar mass. • Ex) What is the mass of 1.2 moles of Ca?1.2 moles x (40 g/mol) = 48 g • To calculate the number of moles in a certain mass, we divide by the molar mass. • Ex) How many moles are in 71.0 g of Rb?71.0 g / (85 g/mol) = 0.835 moles

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