Percentage Composition

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Percentage(%) Composition:

Percentage(%) Composition

Percent Composition:

Percent Composition Compounds are ALWAYS composed of elements in fixed ratios. This is often referred to as the Law of Definite Proportions. Identifies the elements present in a compound as a mass percent of the total compound mass.

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Indicates the relative amount of each element present in a compound. The mass percent(% Composition) is obtained by dividing the mass of each element by the total mass of a compound and converting to percentage.

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%Composition= x 100 = % Mass of element Mass of compound

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This law states that elements are always present in the same proportions by mass in a compound. I.e. H 2 O is always 2H:1O any other proportions would not form water. H 2 O 2 is hydrogen peroxide Since compounds always form in fixed proportions, we can calculate the Percent Composition of an element in a compound.

Calculating percentage composition:

Calculating percentage composition Step 1 : Calculate molar mass Step 2 : Divide the subtotal for each element’s mass by the molar mass. Step 3 : Multiply by 100 to convert to a percentage.

Example 1:

Example 1 Calculate the molar mass of water, H 2 O. Step 1 H- 2(1.01) = 2.02 O- 1(16.0) = 16.0 ________ 18.02

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Step 2 & 3 2.02/18.02 X 100 = 11.21% 6.0 /18.02 X 100 = 88.79 % Water is composed of 11.21 % hydrogen and 88.79 % oxygen.

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?:

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?

Calculate the percentage composition of C3H7NO2:

Calculate the percentage composition of C 3 H 7 NO 2 Step 1 : Find the molar mass of C 3 H 7 NO 2 M = 3(12.01) + 7(1.01) + (14.01) + 2(16.00) = 89.11 g/mo l

Step 2: Find the % of each element by dividing the mass of each element by the total mass:

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?:

What is the percent composition of nitrogen in N 2 O? Step 1: Find the molar mass of N 2 O 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:

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:

Calculate the mass of aluminium in 28 g of Aluminium Oxide Step 1: Calculate the molar mass of aluminium oxide. Al 2 O 3 M = 2(26.98) + 3(16.00) = 101.96 g/mol

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Step 2: Calculate the % mass of aluminium in aluminium oxide. %Al = x 100 = 52.92% 2(26.98) 101.96

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Step 3: Find the mass of aluminium in 28g of aluminium oxide. m Al = x 28g = 15g 52.92 100

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Alternate Solution = Al on top Total on bottom = m Al = 15 g M Al M Total m Al m Total 2(26.98) 101.96 m Al 28g

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18 The empirical formula gives the ratio of the number of atoms of each element in a compound. Compound Formula Empirical Formula Hydrogen peroxide H 2 O 2 OH Benzene C 6 H 6 CH Ethylene C 2 H 4 CH 2 Propane C 3 H 8 C 3 H 8

Percentage Composition:

19 Percentage Composition Glucose has the molecular formula C 6 H 12 O 6 . What is its empirical formula, and what is the percentage composition of glucose? Empirical Formula = smallest whole number ratio CH 2 O

Percentage Composition:

20 Percentage Composition CH 2 O Total mass = 12.01 + 2.02 + 16.00 = 30.03 %C = 12.01/30.03 x 100% = 39.99% %H = 2.02/30.03 x 100% = 6.73% %O = 16.00/30.03 x 100% = 53.28%

Percentage Composition:

21 Percentage Composition Saccharin has the molecular formula C 7 H 5 NO 3 S. What is its empirical formula, and what is the percentage composition of saccharin? Empirical Formula is same as molecular formula MW = 183.19 g/mole %C = (7 x 12.011)/183.19 x 100% = 45.89% etc.

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