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The mole

The mole. Describing the quantity of chemicals. Amount. There are different ways of describing the amount of something: By number 6 grains of rice 17 people 4358 languages. By mass 5 pounds of potatoes 200 milligrams of aspirin my weight is 82 kilograms. By volume a cup of milk

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The mole

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  1. The mole Describing the quantity of chemicals

  2. Amount • There are different ways of describing the amount of something: • By number • 6 grains of rice • 17 people • 4358 languages • By mass • 5 pounds of potatoes • 200 milligrams of aspirin • my weight is 82 kilograms • By volume • a cup of milk • 2 Liters of Coke • buckets of rain • By concentration • heavy fog • dense chocolate • thick syrup

  3. Measuring amount • The way to measure amount often depends on the thing being measured. One counts: • Pillows by: • Milk by: • Cargo by: • But if one knows how to convert the values, any way can work: • 68746 grains of rice = One cup of rice = 127 grams of rice Number Volume Mass

  4. Mole • Because atoms and molecules are, in many ways, uniform, they can be described using just one value: the mole number. • Moles can then be converted in any other way to measure amount (number, mass, volume or concentration) with conversion factors.

  5. Mole conversions • A mole of a chemical is defined as “the amount of a chemical whose mass will equal its atomic weight” • So: 1 mole of chemical X * atomic weight X = mass (in grams) of X • And, the number of atoms needed to do that is pretty defined. It is a big number, and is called Avagadro’s number: 1 mole of chemical X * 6.02 x 1023 = number of X chemicals

  6. Mole conversions, continued • While the volumes of solids and liquids varies a lot, gas behavior is pretty uniform. 1 mole of gas chemical X * 22.4 Liters/mole = volume of gas X • Concentrations can be measured in many ways, but most often it is measured by how many moles are in a Liter of solution. 1 mole of chemical X / 1 Liter solution = concentration (Molar, M) of chemical X

  7. Molar Mass • Since most chemicals are made of more than one atom, their “atomic mass” is really the sum of ALL the atoms atomic masses. • This sum is called “Molar Mass” • Depending on how the compound is put together, it can also be called: • Molecular weight or mass or… • Gram formula weight or mass • The units are grams/mole

  8. Calculating Molar Mass • Find the atomic weights of the individual atoms. • Multiply them by their subscripts (which tell one how many atoms are in the compound.) • Add them all together • H2O = (1*2) + 16 = 18 grams/mole • H2SO4 = (1*2) + 32 + (16 * 4) = 98 grams/mole • C6H12O6 = (12 * 6) + (1 *12) + (16 * 6) = 180 g/mol

  9. Summary of Conversions Concentration / Liters Solution * 6.02 x 1023 * Molar Mass Mole Number Mass * 22.4 Liters/mol Volume of Gas

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