DO NOW: Table of Contents 5) Empirical Formula Notes 1/9 6) Empirical Formula Worksheet/Homework 1/9 What is the percent of Sulfur in H2SO4? What is the percent of Carbon is C12H22O11? How many mol are there in 12.9 mol of Chlorine Gas? How many grams are there?

Unit: Chemical Quantities Day 6 - Notes Unit: Chemical Quantities Determining the Empirical Formula from Percent Composition

After today, you will be able to… Calculate the empirical formulas for various compounds given their percent makeup

Empirical Formula Determination from % Composition To determine empirical formulas from % composition follow these steps: Assume 100.0g of the compound (change % into grams) Convert g moles for each element using molar mass Divide each mole answer by the smallest mole answer If you do not have a whole number, multiply by the smallest whole # to get a whole # ratio. Skip to this step if you already have a whole number ratio from #3. These whole #s are the subscripts for each element.

To sum up these steps here is a poem for my favorite little chemists: “Percent to mass Mass to Moles Divide by small Multiply by whole!”

Example: What is the empirical formula for a compound that is 21 Example: What is the empirical formula for a compound that is 21.2% N, 6.10% H, 24.3% S, and 48.4%O? 21.2gN 6.10gH 24.3gS 48.4gO 1 mol N 14.01gN 1.51 x = = 2 0.758 1 mol H 1.01gH 6.04 x = = 7.97~ 8 N2H8SO4 0.758 1 mol S 32.07gS 0.758 x = = 1 0.758 1 mol O 16.00gO 3.03 x = = 4 0.758

Example: What is the empirical formula for a compound that is 69 Example: What is the empirical formula for a compound that is 69.8% Fe and 30.2% O? 1 mol Fe 55.85gFe 1.25 69.8gFe 30.92gO x = = 1 (2) = 2 1.25 1.89 1 mol O 16.00gO x = 1.5 (2) = = 3 1.25 Fe2O3

WORKSHEET #5 What is the empirical formula for a compound that is 67.6% mercury, 10.8% sulfur, and 21.6 % oxygen?

Time to Practice! Complete WS HOMEWORK: Time to Practice! Complete WS

Calculate the Empirical Formula of the Following: 25 points 50 points 100 points 68.4 % Cr and 31.6 % O?   63.5 % silver, 8.20 % nitrogen, and 28.3 % oxygen? A 170.00 g sample of a compound contains 29.84g sodium, 67.49g Chromium, 72.67g Oxygen 67.1% zinc and the rest is oxygen? 44.82% Potassium, 18.39% Sulfur, and 36.79% Oxygen. A 60.00 g sample of tetraethyl lead is 38.43g Lead, 17.83g Carbon, 3.74g Hydrogen