Percentage Composition Halton District School Bord成分百分比荷顿区教育局.pptVIP

Percent Composition Compounds are ALWAYS composed of elements in fixed ratios. This is often referred to as the Law of Definite Proportions. This law states that elements are always present in the same proportions by mass in a compound. I.e. H2O is always 2H:1O any other proportions would not form water. H2O2 is hydrogen peroxide Since compounds always form in fixed proportions, we can calculate the Percent Composition of an element in a compound. Example 1: A sample of a compound is analyzed and found to contain 0.90g of Ca and 1.60g of Cl. The sample has a mass of 2.50g. Find the % composition of the compound. Percentage Composition %Composition= x 100 = % Mass of element Mass of compound Calculate the percentage composition of C3H7NO2 Step 1: Find the molar mass of C3H7NO2 M = 3(12.01) + 7(1.01) + (14.01) + 2(16.00) = 89.11 g/mol Step 2: Find the % of each element by dividing the mass of each element by the total mass %C = x 100 = 40.43 % %H = x 100 = 7.93% %N = x 100 = 15.72% %O = x 100 = 35.91 % 3(12.01) 89.11 7(1.01) 89.11 1(14.01) 89.11 2(16.00) 89.11 What is the percent composition of nitrogen in N2O? Step 1: Find the molar mass of N2O M = 2(14.01) + (16.00) = 44.02 g/mol Step 2: Find the % of each element by dividing the mass of each element by the total mass %N = x 100 = 63.65% %O = x 100 = 36.35 % 2(14.01) 44.02 1(16.00) 44.02 Calculate the mass of aluminium in 28 g of Aluminium Oxide Step 1: Calculate the molar mass of aluminium oxide. Al2O3 M = 2(26.98) + 3(16.00) = 101.96 g/mol Step 2: Calculate the % mass of aluminium in aluminium oxide. %Al = x 100 = 52.92% 2(26.98) 101.96 Step 3: Find the mass of aluminium in 28g of aluminium oxide. mAl = x 28g = 15g 52.92 100 Alternate Solution = Al on top Total on bottom = mAl = 15 g MAl MTotal mA