GEN CHEM 1 | Percent Composition & Empirical and Molecular Formula

Percentage Composition

shows the percentage of each constituent element in a given compound

Percentage Composition Formula

[(molar mass of element) x (subscript of element)]/[molar mass of compound] x 100

Steps in Calculating Percent Composition

1. Determine the molar masses of the compound and the needed element.

2. Multiply the molar mass of the element to the subscript.

3. Divide the product by the molar mass of the compound.

4. Multiply it to 100.

Empirical Formula

It is the simplest formula that represents the lowest whole-number ratio of the atoms in the compound. It does not necessarily represent the actual number of atoms.

Molecular Formula

It is the true formula as it shows the actual number of atoms in a compound.

Deriving the Empirical Formula from the Percent Composition.

1. List down the elements given, and their respective % and molar masses.

2. Convert the percents to mass, assuming 100g of the compound was produced. Then, multiply the % of each mass to 100g to get their respective mass.

3. Get the moles of each element by dividing the mass by the molar mass.

4. Find which is has the smallest mole. Divide all of the computed moles by the smallest moles to get the subscript. Round off to the nearest whole number if needed.

Deriving the Empirical Formula from the Total Mass

1. List down the elements given, and their respective % and molar masses.

2. Get the moles of each element by dividing the mass by the molar mass.

3. Find which is has the smallest mole. Divide all of the computed moles by the smallest moles to get the subscript.Round off to the nearest whole number if needed.

Deriving the Molecular Formula

1. Get the empirical formula of the compound.

2. Determine the molar mass of the empirical formula.

3. Divide the MF Molar Mass with the EF Molar Mass. Round of the quotient to the nearest integer.

4. Multiply the integer to the subscripts of each element in the