The Mole: A Measurement of Matter Prentice-Hall Chapter 10.1 Dr. Yager

Objectives Describe methods of measuring the amount of something Define Avogadro’s number as it relates to a mole of a substance Distinguish between the atomic mass of an element and its molar mass Describe how mass of a mole of a compound is calculated

You often measure the amount of something by one of three different methods — by count, by mass, and by volume.

The Mole A mole is the SI unit of counting A mole equals 6.02 x 1023 of anything 602,000,000,000,000,000,000,000 Avogadro’s Number Average atomic mass (amu) is equal to molar mass, the mass of one mole of a substance. Formula weight and molecular weight are the mass of one mole of an ionic and molecular compound, respectively.

The Other Mole

A mole of any substance contains Avogadro’s number of representative particles, or 6.02  1023 representative particles. The term representative particle refers to the species present in a substance: usually atoms, molecules, or formula units.

Mole Examples 1 mole of “Vanadium” = 6.02 x1023 atoms 50.941 g of “Vanadium” = 6.02 x1023 atoms 1 mole of “Vanadium” = 50.941 g 1 mole of “Helium” = 6.02 x1023 atoms 4.0026 g of “Helium” = 6.02 x1023 atoms 1 mole of “Helium” = 4.0026 g

# of moles = (2.17 x1023 particles) / (6.02 x 1023 = 0.360 moles particles/mol) = 0.360 moles

Moles to Number of Particles

# of “S” atoms = (1.14 mol)(6.02 x 1023 atom/mol) = 6.86 x 1023 atoms # of “O” atoms = 3 x (1.14 mol)(6.02 x 1023 atom/mol) = 20.6 x 1023 atoms Total = 6.86 x 1023 + 20.6 x 1023 = 2.75 x 1024 atoms

Mass of a Mole of an Element Molar mass is the mass of one mole of an element, expressed in grams/mol. You can find the molar mass of an element under its atomic symbol on the periodic table.

The molar mass of carbon, sulfur, mercury, and iron are shown.

Converting Grams to Moles If given grams, divide by average atomic mass to get moles: 15 g of “Mo” = 15 g/95.94 g/mole = 0.156 moles 15 g of “H” = 15 g/1.0079 g/mole = 14.88 moles

Mass of a Mole of a Compound To calculate the molar mass of a compound: find the number of grams of each element in one mole of the compound. then add the masses of the elements in the compound.

Use values of molar mass (g/mol) for each element from the periodic chart. Thus 1 mol of SO3 has a mass of 80.1 g.

Molar Masses of Glucose, Water, and Paradichlorobenzene

P = 30.97 g/mole Cl = 35.45 g/mole Molar Mass = 30.97 g + 3 x 35.45 g = 137.33 g

1. Three common ways of measuring the amount of something are by count, by mass, and by temperature. by volume. by area. by density.

1. Three common ways of measuring the amount of something are by count, by mass, and by temperature. by volume. by area. by density.

2. A mole of hydrogen gas, H2(g), contains 6.02 x 1023 molecules. atoms. amu. grams.

2. A mole of hydrogen gas, H2(g), contains 6.02 x 1023 molecules. atoms. amu. grams.

3. The atomic mass of fluorine is 19.0 amu, so the molar mass is 19.0 g. 6.02 x 1023 amu. 6.02 x 1023 g.

3. The atomic mass of fluorine is 19.0 amu, so the molar mass is 19.0 g. 6.02 x 1023 amu. 6.02 x 1023 g.

4. Calculate the molar mass of ammonium nitrate. 45.02 g 80.05 g 60.06 g 48.05 g

4. Calculate the molar mass of ammonium nitrate. 45.02 g 80.05 g 60.06 g 48.05 g