Measuring Chemical Quantities

Ways to Count Term # Items Pair Quartet Octet Dozen Ream Gross Case

Ways to Count Each of the relationships on the previous page can be written as an equality and used to create conversion factors These relationships are common place and we perform these calculations without much thought

Ways to Count Class Exercise

Ways to Count Methane Molecules

Counting Atoms and Molecules Atoms and molecules are very small Reactions happen at the particle level so number of atoms and molecules is important Term introduced to represent a specific quantity of atoms or molecules The chemists “dozen”

The Mole 1 mole = 6.02 x 1023 particles Avogadro’s Number (N)

The Mole The number equal to the number of carbon atoms in exactly 12 grams of carbon-12. One mole of a substance contains 6.02 x 1023 particles of that substance.

How big is a mole? + A mole of…. sand grains would cover the US in ~ 1 cm of sand cells is about the number of cells in the human body grapefruit would have approximately the same volume as the Earth (~500 large grapefruit will fit in 1 cubic meter; VEarth = 1.1 x 1012 km3) dollars would take 20 billion years to spend at 1 million dollars a second data from Wikipedia 12/28/06, updated 12/22/06 and Flinn ChemFax, 10/27/03

Mass Ratios # C atoms Mass (amu) # H atoms mass C mass H Mass Ratio 1 1 x 12 = 12 1 x 1 = 1 12 amu 1 amu 12 2 2 x 12 = 24 2 x 1 = 2 24 amu 2 amu 10 10 x 12 =120 10 x 1 =10 120 amu 10 amu 6.02 x 1023 (N) N x 12 6.02 x 1023 (N) N x 1 N x 12 amu N x 1 amu

Conclusion Average atomic mass of any element in grams is the mass of one mole of that element 1 mole C = 12.01 g 1 mole Mg = 24.31 g 1 mole S = 32.06 g

Terms Synonyms: Definitions: gram atomic mass gram atomic weight molar mass Definitions: Gram atomic mass is the mass, in grams, of one mole of the element Molar mass is the mass, in grams, of one mole of a substance

Counting by Weighing Establish number of items in a given weight M&Ms are sold by weight but there are ~same number of M&Ms per package Aspirin is sold by number, but the bottles can be filled by weight, rather than by counting average atomic mass can help us count atoms

1 mole = average atomic mass (in grams) Mole Calculations Two relationships: 1 mole = 6.02 x 1023 atoms 1 mole = average atomic mass (in grams) Use these relationships to form conversion factors Mole calculations are just like converting from miles to meters or grams to pounds

Mole Relationships Particles 1 mole = 6.02 x 1023 Mole Volume Mass 1 mole = 22.4 L At STP 1 mole = molar mass (in grams)

Pathways to Calculating Moles-Mass-Number molar mass 1 mole 1 mole molar mass 6.02x1023 particles 1 mole 1 mole 6.02x1023 particles Mass # Particles