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Ch 6 Avogadro’s Number

Ch 6 Avogadro’s Number.

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Ch 6 Avogadro’s Number

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  1. Ch 6 Avogadro’s Number • The first person to have calculated the number of molecules in any mass of substance was Josef Loschmidt (1821-1895) an Austrian high school teacher, who in 1865 calculated the number of molecules in one cubic centimeter of gaseous substance under ordinary conditions of temperature of pressure. • The number was later changed to Avogadro’s number by Jean Perrin, a Noble Laureate, in a paper which won him the Nobel Prize.

  2. Discovering NA • The best modern values for what we now call "Avogadro's Number" are the result of the x-ray diffraction measurement of lattice distances in metals and salts. • Today's best experimental value of   6.022 141 99 x 1023 atoms per mol is the best average for measurements using the best methods available.

  3. Ch 6 The Mole • The number represented by Avogadro’s constant is referred to as the mole (mol). • It’s value for our calculations is 6.022e23 mol-1. • The mole represents the number of atoms present in a mass equal to the atomic mass of an element. • Therefore in 4.003 grams of helium there are 6.022e23 atoms of helium. In 32.07 grams of Sulfur, there are 6.022e23 atoms of sulfur. • The mole is a general representation used to represent something that is always equal to NA.

  4. Ch 6 Molar Mass • A mole represents not only a specific number of elemental particles but also can be used for compounds and formulas. • The molar mass of a compound is numerically equal to the sum of the masses of atoms in the formula. • The molar mass of H2O is 18.02 g/mol. Therefore, in 18.02 grams of water there are 6.022e23 molecules of water. • Therefore, the mole (6.022e23) acts as a bridge between the mass of an atom or compound and the actual number of particles present.

  5. Ch 6 Mole-Gram Conversions • It is useful to use Avogadro's number and the mole to convert between atoms, moles, and grams of both product and reactant.

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