Unit 06 The Mole Theory Ch. 4 and 7

Dimensional Analysis ● just converting one thing to another Problem 1 : How many seconds are in a day? sec day What do we know? Let’s solve. Conversion factors: the numerator and denominator are equal ×× = 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 Gram Formula mass – sum of the atomic masses of all the atoms in a formula of a compound

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: multiply the number of atoms by the rounded mass number for each element then add up all of the elements. ◦ N- 2 × 14 = 28 ◦ H- 8 × 1 = 8 ◦ C- 1 × 12 = 12 ◦ O- 3 × 16 = 48 96g How to determine molar mass-

Mole – Mass Relationship Use the following conversion factors: 1mole or molar mass molar mass 1 mole (we have to calculate the molar mass of the substance)

Moles  Grams 2 Ex.) How many grams are in 9.45 moles of N 2 O 3 ? Known: 9.45 moles of N 2 O 3 Unknown: mass (grams) of N 2 O 3 Step 1: calculate the molar mass of N 2 O 3 N = 2 x 14 = 28 O = 3 x 16 = 48 76g Step 2: solve 9.45 moles x 76g = g N 2 O mole

Mass  Moles Ex.) Find the number of moles in 92.2g of Fe 2 O 3 ? Known: mass of Fe 2 O 3 is 92.2g Unknown: moles of Fe 2 O 3 Step 1: Find the molar mass of Fe 2 O 3 Fe = 2 x 56 = 112 O = 3 x 16 = g Step 2: Solve 92.2g x 1 mole = mole Fe 2 O g

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 1.) How many molecules are in 2.0 moles? 2.0 mole 6.02  molecules 1 mole = 1.20  molecules

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

Molar Conversion Examples Find the mass of 2.1  molecules of NaHCO  molecules 1 mole 6.02  molecules = g NaHCO 3 84 g 1 mole

Volume of a Mole of Gas 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

Volume  Moles Ex.) Determine the volume, in liters, if 0.60 mole of SO 2 gas at STP. known: 0.60 mole unknown: volume Start with the known and then use the correct conversion factor to solve for the unknown mole x 22.4 L = L SO 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

Your clothing labels have Percent Composition.

Percent Composition Percent Composition The percent by mass of each element in a compound Information needed: ◦ Formula of the compound ◦ Mass of the elements and the compound % mass = mass grams of element × 100 molar mass (g) of compound

Calculating Percent Composition Calculate the percent carbon in C 3 H 8 - Find the molar mass C = 3 x 12 = 36g H = 8 x 1 = 8g 44g % C = mass(g) of carbon X 100 mass of C 3 H 8 % C = 36g X g % C = X 100 % C = 81.8 or 82%

Now, calculate the percent hydrogen in C 3 H 8 %H = 8g X g %H = X 100 %H = 18.2 or 18%