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 Ie H ID: 731988
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Percent CompositionSlide2
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 peroxideSince compounds always form in fixed proportions, we can calculate the Percent Composition of an element in a compound.
%Composition= x 100 = %
Mass of element
Mass of compoundSlide3
Steps for Finding Percent Composition
Find molecular mass of whole moleculeDivide the mass of each type of atom by the molecular mass and multiply by 100 to make into a percent.Slide4
Calculate the percentage composition of C
3H7NO2Step 1: Find the molar mass of C3H7NO2 M = 3(12.01) + 7(1.01) + (14.01) + 2(16.00) = 89.11 g/mol
%Composition= x 100 = %
Mass of element
Mass of compoundSlide5
Step 2: Find the % of each element by dividing the mass of each element by the total mass
Calculate the percentage composition of C3H7NO2
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What is the percent composition of nitrogen in N
2O?Step 1: Find the molar mass of N2O Mr = 2(14.01) + (16.00) = 44.02 g/molStep 2: Find the % of each element by dividing the mass of each element by the total mass
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Calculate the mass of aluminum in 28 g of Aluminum Oxide
Step 1: Calculate the molar mass of aluminum oxide. Al2O3 Mr = 2(26.98) + 3(16.00) = 101.96 g/molStep 2: Calculate the % mass of aluminum in aluminum oxide.
Slide8
Calculate the mass of aluminum in 28 g of Aluminum Oxide
Step 3: Find the mass of aluminum in 28g of aluminum oxide using the percent aluminum.
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% Composition Check Point
What is the percent composition of carbon in carbon monoxide?What is the percent composition of oxygen in carbon monoxide?Calculate the mass of oxygen in 42.8g of carbon monoxide.Slide10
% Composition Check Point
What is the percent composition of sulfuric acid (H2SO4)?What percentage of rubidium in rubidium selenide?Calculate the mass of fluorine in 24.1g of strontium fluoride.