Chapter 11 The Mole

Measuring Matter: THE MOLE Mole (mol): unit to measure the amount of a substance. 1 mol = 6.02 x 1023 particles = Avogadro’s # 6.02 x 1023 particles = 602,000,000,000,000,000,000,000 Particles can be atoms, molecules (covalents), formula units (ionics), e-, or ions depending on the substance

Measuring Matter: THE MOLE Ex: 1 mol Elephants = 6.02 x 1023 elephants 1 mol M&M’s = 6.02 x 1023 M&M’s 1 mol Cu = 6.02 x 1023 Cu atoms 1 mol H2O = 6.02 x 1023 H2O molecules 1 mol NaCl = 6.02 x 1023 NaCl formula units You can convert between moles, atoms, molecules, formula units, particles, etc. using conversion factors

To convert from moles (atoms, molecules, formula units) to particles, multiply by Avogadro’s Number To convert from particles (atoms, molecules, formula units) to moles, divide by Avogadro’s Number.

The Mass of a Mole (Elements) Molar Mass: Mass (g) of 1 mol of any pure substance Units of molar mass are g/mol Conversion Factor: For elements: 1 mol = atomic mass number Ex: What is the mass of 3.0 mol Mn? 3.0 mol Mn x 54.94g Mn = 164.8 g Mn 1 mol Mn

The Mass of a Mole (Compounds) Molar mass of a compound is the sum of the molar masses of all elements making it up. Ex: H2O 2 mol H atoms x 1.008 g H = 2.016g H 1 mol H 1 mol O atoms x 15.999 g O = 15.999g O 1 mol O Molar Mass water = 2.016 + 15.999 = 18.015 g

The Mass of a Mole (Compounds) Multiply the number of atoms of an element by it’s atomic mass. Do this for all elements, then add them up. CCl2F2 C = 12 x 1 = 12; Cl = 2 x 35.45 = 70.9; F = 2 x 19 = 38 12 + 70.9 + 38 = 120.9 g Al2O3 Al = 2 x 26.98 = 53.96; O = 3 x 15.99 =47.97 53.96 + 47.97 = 101.93 g H2SO4 H = 1.008; S = 32.07; O = 4 x 15.99 = 63.96 1.008 + 32.07 + 63.96 = 97.04 g

Try These ….. What is the mass of 2.5 mol fluorine? 2.5 mol F x 19.0 g = 47.5g F 1 mol F How many moles are in 325 g C? 325 g C x 1 mol C = 27.1 mol C 12.0 g C How many moles are in 34.4 g N? 34.4 g N x 1 mol N = 2.46 mol N 14.0 g N

Converting Between mol + mass of Compds Always start by calculating the molar mass, then use conversion factors to get the necessary units What is the mass of 2.6 mol H2O? Molar mass = 18.015g 2.6 mol H2O x 18.015 g H2O = 46.839 g H2O 1 mol H2O What is the mass of 6.94 mol CCl2F2 ? Molar Mass = 120.9g 6.94 mol CCl2F2 x 120.9 g CCl2F2 = 839.04 g CCl2F2 1 mol CCl2F2

Converting Between mol + mass of Compds How many mol H2O are in 599.653 g? Molar mass = 18.015g 599.653 g H2O x 1 mol H2O = 33.286 mol H2O 18.015 g H2O How many mol CCl2F2 are in 692.222 g? Molar Mass = 120.9g 692.222 g CCl2F2 x 1 mol CCl2F2 = 5.73 mol CCl2F2 120.9 g CCl2F2

Percent Composition % Comp = (mass element/mass compound)x 100 A 100g sample of XY contains 55g X and 45g Y. What is the % composition of each element? X = (55g X/100g XY) x 100 = 55% X Y = (45g Y/100g XY) x 100 = 45% Y A 200g sample of CO2 contains 67g C and 133g O. What is the % composition of each element? C = (67g C/200g CO2) x 100 = 33.5% C O = (133g O/200g CO2) x 100 = 66.5% O

Using % Comp to Find Molecular Formulas Steps: Convert mass of each element to moles. Divide moles of each element by the smallest number of moles available to get mole ratios If ratios are not whole numbers, multiply to make them whole. Write the empirical formula Divide known molar mass (represents molec formula) by the molar mass of emp formula Multiply your subscripts by that number to write the molecular formula same