Presentation on theme: "Percent Composition Empirical Formula Molecular Formula"— Presentation transcript:
1 Percent Composition Empirical Formula Molecular Formula Chemical FormulasPercent Composition Empirical Formula Molecular Formula
2 Percentage Composition the percentage by mass of each element in a compoundof the element
3 Percentage Composition Find the % composition of each element in Cu2S.2 (63.55 g) Cug Cu2S%Cu = 100 =79.85% Cu32.07 g Sg Cu2S%S = 100 =20.15% S
4 Percent Composition 2 (1.01) g H 18.02 g H20 100 = % H = 11.21 % H Find the percent composition of each element in water.2 (1.01) g H18.02 g H20 100 =% H =11.21 % H16.00 g O18.02 g H2O% O = 100 =88.79 % S
5 A. Percentage Composition Find the percentage composition of a sample that is 28 g Fe and 8.0 g O.28 g36 g%Fe = 100 =78% Fe8.0 g36 g%O = 100 =22% O
6 A. Percentage Composition How many grams of copper are in a 38.0-gram sample of Cu2S?Cu2S is % Cu(38.0 g Cu2S)( ) = 30.3 g Cu
7 A. Percentage Composition Find the mass percentage of water in calcium chloride dihydrate.36.04 gg%H2O = 100 =24.51%H2O
8 C2H6 CH3 B. Empirical Formula Smallest whole number ratio of atoms in a compoundC2H6reduce subscriptsCH3
9 B. Empirical Formula1. Find mass of each element. If have %, then assume out of 100 grams.2. Convert the mass to 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.
10 B. Empirical FormulaFind the empirical formula for a sample of 25.9% N and 74.1% O.25.9 g1 mol14.01 g= 1.85 mol N= 1 N1.85 mol74.1 g1 mol16.00 g= 4.63 mol O= 2.5 O
11 N2O5 N1O2.5 B. Empirical Formula Need to make the subscripts whole numbers multiply by 2N2O5
12 CH3 C2H6 C. Molecular Formula “True Formula” - the actual number of atoms in a compoundCH3empiricalformula?C2H6molecularformula
13 C. 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.
14 (CH2)2 C2H4 C. Molecular Formula The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is g/mol?empirical mass = g/mol28.1 g/mol14.03 g/mol= 2.00(CH2)2 C2H4