Percent Composition, Empirical And Molecular Formulas

Percent Composition, Empirical andMolecular Formulas

Law of Definite ProportionsThis law states that the elements in achemical compound are always presentin the same proportions by mass.For example, the mass% of oxygen inwater is always 88.8% and the mass ofhydrogen is 11.2%.

Calculating Percentage Composition- relative mass of each element in a compoundi) Using Mass DataEx. A compound with a mass of 50g is found tocontain 32.3g of zinc and 17.7g of sulfur.What is the percentage composition of thecompound?

ii) Calculating % Composition using formula

Calculating Percentage CompositionEx. b) Determine the percentagecomposition of Ca3(PO4)2.Homework:Practice: p.286 #1,2 and p.287 #3Questions: p. 288 #1,2,4,5,7

FormulasEmpirical formula: the lowest wholenumber ratio of atoms in a compound.Molecular formula: the true numberof atoms of each element in theformula of a compound. molecular formula (empirical formula)n molecular formula C6H6 (CH)6 empirical formula CH

Formulas(continued)Formulas for ionic compounds areALWAYS empirical (lowest wholenumber ratio).Examples:NaClAl2(SO4)3MgCl2K2CO3

Formulas(continued)Formulas for molecular compoundsMIGHT be empirical (lowest wholenumber ratio).Molecular: H2OC6H12O6C12H22O11Empirical: H2OCH2OC12H22O11

Empirical Formula Determination1. If given percentages of elements,assume you have 100 grams of thecompound. Determine moles of eachelement in 100 grams of thecompound.2. Divide each value of moles by thesmallest of the mole values.3. Multiply each number by an integerto obtain all whole numbers.

(Divide bysmallestandmultiply tomakewhole)(Divide byMolar Mass)

Sample Problem #1 Using a Table: What is theempirical formula for a compound with 48% C,8% H, 28% N and 16% O?Mass(g)(Molar Mass)(Moles)Divide by smallest mole

Example #2: What is the empiricalformula if there is 8.4g of Carbon, 2.1gof Hydrogen and 5.6g of Oxygen?

Empirical Formula DeterminationEx.3 Adipic acid contains 49.32% C, 43.84% O,and 6.85% H by mass. What is the empiricalformula of adipic acid?Solution: Treat % as mass (assuming wehave 100g), and convert grams to moles.49.32 g carbon 1 mol carbon 4.107 mol carbon12.01 g carbon6.85 g hydrogen 1 mol hydrogen 6.78 mol hydrogen1.01 g hydrogen43.84 g oxygen 1 mol oxygen 2.74 mol oxygen16.00 g oxygen

Empirical Formula Determination2. Divide each value of moles by thesmallest of the values.Carbon:4.107 mol carbon 1.502.74 molHydrogen: 6.78 mol hydrogen2.74 molOxygen: 2.472.74 mol oxygen 1.502.74 mol

Empirical Formula Determination3. Multiply each number by aninteger to obtain all whole numbers.Carbon: 1.50x 23Hydrogen: 2.50x 25Empirical formula: C3H5O2Oxygen: 1.00x 22

Finding the Molecular FormulaThe empirical formula for adipic acidis C3H5O2. The molar mass of adipicacid is 146 g/mol. What is themolecular formula of adipic acid?1. Find the molar mass of theempirical formula - C3H5O23(12.01 g) 5(1.01) 2(16.00) 73.08 g

Finding the Molecular FormulaThe empirical formula for adipic acidis C3H5O2. The molar mass of adipicacid is 146 g/mol. What is themolecular formula of adipic acid?M 3(12.01 g) 5(1.01) 2(16.00) 73.08 g2. Divide the molar mass of the molecularformula (given) by the mass calculated for theempirical formula.146 273

Finding the Molecular FormulaThe empirical formula for adipic acid isC3H5O2. The molar mass of adipic acid is146 g/mol. What is the molecular formulaof adipic acid?3. Multiply the empirical formula by thisnumber to get the molecular formula.146 273(C3H5O2) x 2 C6H10O4

Finding the Formula of a Hydrate A hydrate is any salt that has water chemically bondedto the ions in the crystal structure is a hydrate orhydrated crystal.– Copper(II) sulfate pentahydrate is a hydrate.– Hydrated copper(II) sulfate is deep blue in color.– Other examples include: Calcium chloride dihydrate CaCl2 2O Chromium (III) nitrate hexahydrate Cr(NO3)3 6H2O

What is the compound called afterthe water has been removed? Anhydride (noun)– The light blue powder is the anhydride. Anhydrous (adjective)– Anhydrous copper(II) sulfate is left inthe test tube after heating (waterremoved)

Percent Composition and Formula of Hydrate A 5.0 gram sample of Cu(NO3)2 nH2O is heated, and3.9 g of the anhydrous salt remains. What is thevalue of n?1. Amount of water lost5.0 g hydrate- 3.9 g anhydrous salt1.1 g water2. Percent of water1.1 g water x 100 22 %5.0 g hydrate3. Amount (moles) of watern 0.22 x 18.02 4.04. The formula isCu(NO3)2 4H2OOR USE CHART METHOD

Empirical Formula Determination Ex.3 Adipic acid contains 49.32% C, 43.84% O, and 6.85% H by mass. What is the empirical formula of adipic acid? mol carbon g carbon g carbon mol carbon 4.107 12.01 49.32 1 mol hydrogen g hydrogen g hydrogen mol hydrogen 6.78 1.01 6.85 1 mol oxygen g oxygen g oxygen mol oxygen 2.74 16.00 43.84 1 Solution: Treat .