Chem Catalyst If a class of 22 students has 15 girls and 7 boys, what percentage of the class is male? What percentage is female?

Today’s Agenda: 1. Catalyst 2. Notes- percent composition/ empirical formula 3. HW: p #32-35

Percent Composition/Mass Percent - The percent by mass of each element in a compound. (mass of part) ÷ (mass of whole) x100

Percent Composition When a 13.60g sample of magnesium oxide is decomposed, 5.40g of oxygen are obtained. What is the percent composition of this compound? 1) Find the mass of each element. 2) Find the mass of the compound. 3) Calculate.

Percent Composition When a 13.60g sample of magnesium oxide is decomposed, 5.40g of oxygen are obtained. What is the percent composition of this compound?

Percent Composition: From Formula 1) Find the total molar mass for each element. 2) Divide by molar mass of compound. 3) Multiply by 100.

Percent Composition from Formula Find the percent composition of propane (C 3 H 8 ).

Percent Composition from Formula: Your turn! Find the percent composition of iron (II) oxide (FeO). Find the percent composition of iron (III) oxide (Fe 2 O 3 ).

Chemical Formulas: Empirical formula: the lowest whole-number ratio of the atoms of elements in a compound Molecular formula: the exact number of atoms of elements in a compound For example, styrene (C 2 H 2 ), and acetylene (C 8 H 8 ) have different molecular formulas but the same empirical formula (CH)

Finding Empirical Formulas: Determining the MOLE RATIO of elements in a compound. 1. Find percent composition (if not given) 2. Divide percent composition by molar mass of the element to get mole ratios 3. Simplify to whole numbers 4. Write the formula with the subscripts

Empirical Formula: Example A compound contains 25.9% nitrogen, and 74.1% oxygen. What is the empirical formula of this compound?

Empirical Formula: Example Calculate the empirical of these compounds: 1) 94.1% O, 5.9% H 2) 67.6% Hg, 10.8% S, 21.6% O