The Mole Theory

Dimensional Analysis A way to solve problems by converting or using the units of the items involved Converting one thing to the another – amount has not changed Conversion factors: the numerator and denominator are equal so they are basically equal to ‘1’ – used to solve for unknowns in dimensional anaylsis problems

Dimensional Analysis Problem 1 : How many seconds are in a day? sec day What do we know? Set up Conversion Factors: Let’s solve. ×× = 86,400 sec 1 day

Dimensional Analysis Problem 2: You're throwing a pizza party for 15 and figure each person might eat 4 slices. How much is the pizza going to cost you? You call up the pizza place and learn that each pizza will cost you $14.78 and will be cut into 12 slices. You tell them you'll call back. How much money is the pizza going to cost you, which in math terms is: cost (in dollars) per party, or just $/party x 4 x 15 = $ party

How do you measure matter? -Counting (dozen, 3/$1, 6 pack) -Mass ( 1 lb, 4 oz, 57g) -Volume (liter, gallon, pint, quart) In chemistry- this is all measured by a measuring unit called the mole.

Mass of a Mole o Molar Mass- the mass of a mole of any element or compound (in grams) o Also called: o Formula mass – sum of the atomic masses of all the atoms in a formula of a compound o 1 Mole = Molar Mass o Conversion Factors: 1 MoleORMolar Mass Molar mass1 Mole

How to determine molar mass- The atomic mass expressed in grams- rounded to whole number (ones place) Examples:  C =  Cl =  O =  F = 12g 35g 16g 19g

For compounds- Add together all the atoms that make up the compound Examples: SO 3 = How to determine molar mass- 1 S atom  3 O atoms 32g + 16g + 16g + 16g = 80g

What is the gram formula mass of ammonium carbonate (NH 4 ) 2 CO 3 ? Take inventory: ◦ N- 2 × 14 = 28 ◦ H- 8 × 1 = 8 ◦ C- 1 × 12 = 12 ◦ O- 3 × 16 = 48 96g How to determine molar mass-

Number of particles in a Mole What is a representative particle? How the substance normally exists: 1 mole = 6.02 × representative particles (also called Avogadro’s Number) 1.Atom- rep. particle for most elements 2.Molecule- rep. particle for covalent compounds and diatomic molecules “BrINCl HOF” 3.Formula unit- rep. particle for ionic compounds

Converting from moles –› particles Analogy: 1 dozen = 12 eggs Conversion Factors: 1 dozen or 12 eggs 1 dozen For moles and particles: 1 mole = 6.02 × rep particles– therefore Conversion Factors 1 mole OR 6.02 × particles 1 mole

How to solve mole problems: 1. Determine known and unknown. Known: 1.25 × atoms Mg Unknown: moles 2. Determine the conversion factor(s) needed. 3. Multiply the known by the appropriate conversion factor(s) so units cancel. 4. Calculate answer 2.08 × moles or.208 moles 6.02 × particles 1 mole or 1.25 × atoms Mg 1 mole 6.02 × atoms How many moles are in the number of molecules? Sample problem: 1.25 × atoms Mg 1 mole 6.02 × particles

The Mole and Avogadro’s Number How many molecules are in 2.0 moles? 2.0 mol 6.02  molecules 1 mol = 1.20  molecules

How many moles are in 6.02 × ? 6.02 × particles 1 mol 6.02 × particles = 1 mol The Mole and Avogadro’s Number

Volume of a Mole of Gas The Volume of a gas varies with a change in temperature or pressure. Measured at standard temperature and pressure (STP)  0°C at 1 atmosphere (atm) 1 mole of any gas occupies a volume of 22.4L Conversion Factors: 1moleOR22.4 L 22.4 L1 mole

All the conversion factors you need to know! Representative Particles 1 mole 6.02 × particles 1 mole Mass 1 Mole OR Molar Mass Molar mass 1 Mole OR 1 moleOR22.4 L 22.4 L1 mole Volume

Molar Conversion Examples Find the mass of 2.1  molecules of NaHCO  molecules 1 mol 6.02  molecules = 290 g NaHCO g 1 mol

Your clothing labels have Percent Composition.

Percent Composition The percent by mass of each element in a compound Information needed: ◦ Formula of the compound ◦ Gram atomic mass of its elements % mass = grams of element in 1 mol compound × 100 molar mass of compound

Calculating % Composition Calculate the % composition of C 3 H 8. % C = mass of C × 100 = 36g X 100% = = 81.8% 44g % H = mass of H × 100 = 8g × 100% = = 18% grams of compound 44g