Moles Chemical Compounds Unit Notes 4 Avogadros Number

Moles Chemical Compounds Unit Notes #4

Avogadro’s Number [602, 200, 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 1023 amu per 1 gram

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. showbiz 411. com/2012/04/11/gawkers-foxmole-says-hes-still-working-not-caught

How big is a mole? 602, 200, 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

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 H 2 O = 2 H atoms + 1 O atom H 2 O = 2 moles H + 1 mole O By looking at the subscripts, we can determine the mole ratio in the formula H 2 O =2 H: 1 O

Moles and Atoms There How are 12 eggs in one dozen. many eggs are there in 2. 5 dozens? How many dozens are there in 36 eggs? How do we figure this out?

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. 022 x 1023 = 1. 104 x 1024 atoms To count moles in a certain number of atoms, we divide by Avogadro’s number. Ex) How many moles are in 4. 3 x 1022 atoms of Fe? 4. 3 x 1022 atoms / 6. 022 x 1023 = 0. 0714 moles

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 H 2 O: 18. 02 amu 1 mole of H 2 O : 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.

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?

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