Empirical Formula of a Compound

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Presentation transcript:

Empirical Formula of a Compound

Molecular Formula (MF) actual formula shows the number of atoms of each element that make up a molecule or a formula unit

Empirical Formula (EF) simplest formula of a compound shows the lowest whole number ratio of the elements in a compound can be determined from - the molecular formula or - percentage composition of the compound

Using Molecular Formula - Examples Substance Molecular Formula (MF) Empirical Formula (EF) Butane C4H10 C2H5 Glucose C6H12O6 Benzene C6H6 Water H2O

Using Molecular Formula - Examples Substance Molecular Formula (MF) Empirical Formula (EF) Butane C4H10 C2H5 Glucose C6H12O6 CH2O Benzene C6H6 CH Water H2O

Using Percentage Composition - Examples Calculate the EF of a compound that is 85.6 % carbon and 14.4 % hydrogen. Answer: Assume that you are using a 100 g sample of the compound and complete the next calculations. Use a table for your data.

Using Percentage Composition - Example #1 Lowest Whole Number Element Mass % m (g) Molar Mass M (g/mol) Moles n (mol) LWN Ratio EF C H

Using Percentage Composition - Example #1 Lowest Whole Number Element Mass % m (g) Molar Mass M (g/mol) Moles n (mol) LWN Ratio EF C 85.6 12.01 H 14.4 1.01 Recall: n = m M

Using Percentage Composition - Example #1 Lowest Whole Number Element Mass % m (g) Molar Mass M (g/mol) Moles n (mol) LWN Ratio EF C 85.6 12.01 7.13 H 14.4 1.01 14.3 Recall: n = m M

Using Percentage Composition - Example #1 Lowest Whole Number Element Mass % m (g) Molar Mass M (g/mol) Moles n (mol) LWN Ratio EF C 85.6 12.01 7.13 H 14.4 1.01 14.3 Calculate LWN ratio by dividing: molar amount lowest molar amount

Using Percentage Composition - Example #1 Lowest Whole Number Element Mass % m (g) Molar Mass M (g/mol) Moles n (mol) LWN Ratio EF C 85.6 12.01 7.13 H 14.4 1.01 14.3 Calculate LWN ratio by dividing: molar amount lowest molar amount

Using Percentage Composition - Example #1 Lowest Whole Number Element Mass % m (g) Molar Mass M (g/mol) Moles n (mol) LWN Ratio EF C 85.6 12.01 7.13 7.13 = 1.00 H 14.4 1.01 14.3 14.3 = 2.01 Calculate LWN ratio by dividing: molar amount lowest molar amount

Using Percentage Composition - Example #1 Element Mass % m (g) Molar Mass M (g/mol) Moles n (mol) LWN Ratio EF C 85.6 12.01 7.13 7.13 = 1.00 H 14.4 1.01 14.3 14.3 = 2.01 H2 Empirical Formula: CH2

Using Percentage Composition - Examples 2. Calculate the EF of a compound with the following % composition: 32.4 % Na, 22.6 % S and 45.0 % O 3. Calculate the EF of TNT, with the following % composition: 37.0 % C, 2.20 % H, 18.5% N and 42.3 % O Hint: see table 6.2 (p210)