1. The Mole Chapter 11

2. Counting units 1mole = 6.02 x 10 23 particles Particles Names Atoms, formula units (ionic compounds), molecules (covalent compounds)

3. Mole to Particle Conversions How many molecules of water are there in 2.4 moles of water? How many moles of copper contain 3.5 x 10 18 copper atoms?

4. Volume and the Mole According to Avogadro, the mass of one mole of a gas at STP is always 22.4L regardless of the gas’ identity. STP = Standard Temperature and Pressure (0 o C and 1 atmosphere)

5. Mass and the Mole The mass of one mole of a substance is unique to that substance and is based on the sum of the atomic masses of the elements in that substance. 1 mole of lead = 207.2g1 mole of water = 18.0g 1 mole of copper = 63.6g Mass of H 2 O = mass of two hydrogen atoms + mass of one oxygen atom

6. Percent Composition by Mass Sum of the product of the number of each atom and their masses divided by the total mass of the compound What is the percent composition of Mg(BrO 4 ) 2 ? 1(mass Mg) + 2(mass of Br) + 8(mass of oxygen) = Mass of Mg(BrO 4 ) 2

7. Empirical Formula Chemical formula which contains the lowest whole number ratio of atoms Ionic formulas always contain the lowest whole number ratios Covalent compounds do not always contain the lowest whole number ratios What is the Empirical Formula of the following compounds? C 6 H 12 O 6 H2O2H2O2 C3H9O6C3H9O6

8. Determining the Empirical Formula of a Compound What is the empirical formula for a compound which contains 25.9% nitrogen and 74.1% oxygen by mass? 1.Covert % to mass (if needed) 2.Convert mass to moles 3.Divide each molar quantity by the lowest number of moles 4.Multiply by the smallest number needed to create a whole number ratio (if needed) Assume a 100g sample. In that sample 25.9 g is nitrogen and 74.1g is oxygen NxOyNxOy N 1.85 O 4.63 N 1 O 2.5 N 1x2 O 2.5x2 N2O5N2O5

9. Which of the following are empirical formulas and which represent molecular formulas? C2H8N2C2H8N2 H 3 PO 4 C2H8C2H8 CH 4 C 8 H 12 O 4 Li 2 SO 4

10. Simple Molecular Problems What is the molecular formula of a compound with an empirical formula of CH 2 O and a molecular mass of 90g/mol? 1.Determine the empirical mass 2.Divide the molecular mass by the empirical mass to determine how much larger the mass of the molecule is compared to the empirical formula 3.Multiple the subscripts of each element in the empirical formula by the factor determined in #2 CH 2 O =1(12g)+2(1g)+1(16g) = 30g C 1x3 H 2x3 O 1x3 C3H6O3C3H6O3

11. Longer Molecular Problems 1.Determine the molecular formula 2.Given the molecular mass, determine the molecular formula Determine the molecular formula of a compound that has a mass of 34g and contains 94.1% oxygen and 5.9% hydrogen by mass.