Warm-up March 22nd 9.67 moles of KCl = __________________ grams KCl 3.4 x 1032 molecules of NO2 = ____________ grams NO2 52.22 grams of CO=________________L CO at STP

Percentage Composition Percent Composition- the percentage by mass of each element in a compound

Percentage Composition Find the % composition of Cu2S. 127.10 g Cu 159.17 g Cu2S %Cu =  100 = 79.852% Cu 32.07 g S 159.17 g Cu2S %S =  100 = 20.15% S

Percentage Composition Find the percentage composition of a sample that is 28 g Fe and 8.0 g O. %Fe = 28 g 36 g  100 = 78% Fe %O = 8.0 g 36 g  100 = 22% O

Percentage Composition Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O? 36.04 g 147.02 g %H2O =  100 = 24.51% H2O

What is the percent composition of each element in Copper (II) Phosphate

Find the percent composition of each element in: Warm-up Find the percent composition of each element in: Fe(NO3)3 K2SO4

Warm-up March 22nd Convert 4.5 g CO2 = _________ mol CO2 460 L CO = _________ g CO 1.56 x 1021 molecules NO = ______ L NO

C2H6 CH3 Empirical Formula Empirical Formula- Smallest whole number ratio of atoms in a compound C2H6 reduce subscripts CH3

To Find Empirical Formula 1. Find mass (or %) of each element. 2. Find moles of each element. 3. Divide moles by the smallest # to find subscripts. 4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.

Empirical Formula Qualitative analysis shows that a compound contains 32.38% Na, 22.65%S, and 44.99%O. Find the empirical formula of this compound. 32.38 g Na x 1 mol Na = 1.408 mol Na = 1.993 22.99 g Na 0.7063 22.65 g S x 1 mol S = 0.7063 mol S = 1 32.07 g S 0.7063 44.99 g O x 1 mol O = 2.812 mol O = 3.981 16.00 g O 0.7063

Empirical Formula Empirical Formula Na2SO4

Empirical Formula Find the empirical formula for a sample of 25.9% N and 74.1% O. 25.9 g N x 1 mol N = 1.85 mol N = 1 N 14.01 g N 1.85 mol 74.1 g O x 1 mole O = 4.63 mol O = 2.5 mol O 16.00 g O 1.85 mol

N2O5 N1O2.5 Empirical Formula Need to make the subscripts whole numbers  multiply by 2 N2O5

Warm-up November 7th Solve each: 3.45 moles CO = _________ g CO 45.6 Liters NO2 = __________ molecules NO2 Calculate the percent composition of each element in Al(NO2)2

CH3 C2H6 Molecular Formula ? Molecular Formula- “True Formula”, the actual number of atoms in a compound CH3 empirical formula ? C2H6 molecular formula

Calculating Molecular Formula 1. Find the empirical formula. 2. Find the empirical formula mass. 3. Divide the molecular mass by the empirical mass. 4. Multiply each subscript by the answer from step 3.

Calculating Molecular Formula The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is 28.1 g/mol? Empirical formula mass = 14.03 g/mol 28.1 g/mol 14.03 g/mol MF = EF = 2.00 (CH2)2  C2H4

Calculating Molecular Formula If 4.04 g of N combine with 11.46 g O to produce a compound with a formula mass of 108.0 amu, what is the molecular formula of this compound? !st you must find the Empirical Formula 4.04 g N x 1mol N = .288 mol N = 1 14.01 g N .288 11.46 g O x 1 mol O = .7163 mol O 2.5 16.00 g O .288

Calculating Molecular Formula Empirical Formula (N1O2.5)2 = N2O5 N= MF mass = 108.0 = 1 EF mass 108.0 (EF)n = (N2O5)1

Calculating Molecular Formula The Molar mass of a compound is 92 g/mol. Analysis of a sample of the compound indicates that is contains 0.606 g N and 1.390 g O. Find its molecular formula. .606 g N x 1 mol N = .0436 mol N = 1 14.01 g N .0436 1.390 g O x 1 mol O = .08688 mol O = 1.993 16.00 O .0436

Calculating Molecular Formula Empirical formula = NO2 MF mass = 92 = 2 EF mass 46 (NO2)2 = N2O4