Molar Mass Practice Calculate the molar mass of the following: Hydrogen Fe Iron II sulfate

Percent Composition

Percent Composition – the percentage by mass of each element in a compound Percent = _______ Part Whole x 100% Percent composition of a compound or = molecule Mass of element in 1 mol ____________________ Mass of 1 mol x 100%

Percent Composition Determine the percentage composition of sodium carbonate (Na 2 CO 3 )? Molar MassPercent Composition % Na = 46.0 g 106 g x 100% =43.4 % % C = 12.0 g 106 g x 100% =11.3 % % O = 48.0 g 106 g x 100% =45.3 % Na = 2(23.00) = 46.0 C = 1(12.01) = 12.0 O = 3(16.00) = 48.0 MM= 106 g

Percent Composition Determine the percentage composition of ethanol (C 2 H 5 OH)? % C = 52.13%, % H = 13.15%, % O = 34.72% _______________________________________________ Determine the percentage composition of sodium oxalate (Na 2 C 2 O 4 )? % Na = 34.31%, % C = 17.93%, % O = 47.76%

Percent Composition Calculate the mass of bromine in 50.0 g of Potassium bromide. 1. Molar Mass of KBr K = 1(39.10) = Br =1(79.90) =79.90 MM = g ___________ g = x 50.0g = 33.6 g Br 2.

Empirical and Molecular Formulas

Formulas Empirical Formula – formula of a compound that expresses lowest whole number ratio of atoms. Molecular Formula – actual formula of a compound showing the number of atoms present Percent composition allow you to calculate the simplest ratio among the atoms found in compound. Examples: C 4 H 10 - molecular C 2 H 5 - empirical C 6 H 12 O 6 - molecular CH 2 O - empirical

Formulas Is H 2 O 2 an empirical or molecular formula? Molecular, it can be reduced to HO HO = empirical formula

Calculating Empirical Formula An oxide of aluminum is formed by the reaction of g of aluminum with g of oxygen. Calculate the empirical formula. 1. Determine the number of grams of each element in the compound g Al and g O 2. Convert masses to moles g Al 1 mol Al g Al = mol Al g O 1 mol O g O = mol O

Calculating Empirical Formula When a g sample of iron metal is heated in air, it reacts with oxygen to achieve a final mass of g. Determine the empirical formula g Fe 1 mol Fe g Fe = mol Fe g O 1 mol O g = mol Fe Fe = g O = g – g = g 1 : 1 FeO

Calculating Empirical Formula A sample of lead arsenate, an insecticide used against the potato beetle, contains g lead, g of hydrogen, g of arsenic, and g of oxygen. Calculate the empirical formula for lead arsenate g Pb 1 mol Pb g Pb = mol Pb gH 1 mol H g H = mol H g As 1 mol As g As = mol As g Fe 1 mol O g O = mol O

Calculating Empirical Formula The most common form of nylon (Nylon-6) is 63.38% carbon, 12.38% nitrogen, 9.80% hydrogen and 14.14% oxygen. Calculate the empirical formula for Nylon-6. Step 1: In g of Nylon-6 the masses of elements present are g C, g n, 9.80 g H, and g O. Step 2: g C1 mol C g C = mol C g N1 mol N g N = mol N 9.80 g H1 mol H 1.01 g H = 9.72 mol H g O1 mol O g O = mol O

Calculating Empirical Formula The most common form of nylon (Nylon-6) is 63.38% carbon, 12.38% nitrogen, 9.80% hydrogen and 14.14% oxygen. Calculate the empirical formula for Nylon-6. Step 3: mol C = mol C mol N = mol N 9.72 mol H = 11.0 mol H mol O = mol O 6:1:11:1 C 6 NH 11 O

Calculating Molecular Formula A white powder is analyzed and found to have an empirical formula of P2O5. The compound has a molar mass of g. What is the compound’s molecular formula? Step 1: Molar Mass P = 2 x g = 61.94g O = 5 x 16.00g = g g Step 2: Divide MM by Empirical Formula Mass g g = 2 Step 3: Multiply (P 2 O 5 ) 2 = P 4 O 10

Calculating Molecular Formula A compound has an experimental molar mass of 78 g/mol. Its empirical formula is CH. What is its molecular formula? C = g H = 1.01 g g 78 g/mol g/mol = 6 (CH) 6 = C 6 H 6