Mr. Quinn & Ms. Tom January 10, 2014

Aim: How can empirical formulas be found from mass percent data?

Do Now:What is 35% of 100?

What is 35% of 72?

Simplify this expression:

Combustion experiments are still done today• Chemicals are burned in a bomb calorimeter this provides data on the

percent by mass of each element

•We are calculating the empirical formula:• Definition: the smallest whole-number ratio between the elements in a molecule or salt

The Steps

1.Determine masses of each reactant.2.Divide masses by atomic mass.3.Divide coefficients by smallest to find ratio

Calculating the formula of LixBry

•5 g of Li becomes 62.5 g of LixBry

Calculating the formula of formaldehyde•C: 40%•H: 7 %•O: 53 %

Calculating the formula of aminoethanol•C: 39%•H: 11.5%•N: 23%•O: 26%

Your Turn!

Exit Ticket• Your calculations lead you to determine that the mole ratio of Cs to O

in cesium oxide is 2:1. What is the formula for cesium oxide?1. CsO2. CsO2

3. Cs2O4. Cs2O2