1. Check Your Homework from Monday Before completing the notes for today on Percentage Composition, check you work from Monday. The four problems at the end of the note sheet on Formula Weight follow. You will need this information to complete the problems at the end of today’s notes. If you need those problems, they are included at the end of the power point for Formula Weight that is also located in this folder on our class web page. TOMORROW, please be ready to turn in your work from MONDAY and TODAY (be sure they are on separate paper)!

2. Problems from the end of the Formula Weight Note Sheet

4. 3. Sodium Potassium Permanganate Tetra Hydrate, NaK(MnO 4 ) 2 * 4 H2O 1 mole NaX22.990 g=22.990 g/moles 1 mole Kx39.098 g=39.098 g/mole 2 moles Mnx54.938 g= 109.876 g/mole 8 moles Ox15.999 g=127.992 g/mole 8 moles Hx8.0632 g=8.0632 g/mole 4 moles Ox15.999 g=63.996 g/mole +________________ 372.0152 g/mole = 372.015 g/mole

6. Percentage Composition An Analytical Chemistry Technique

7. I CAN calculate the PERCENTAGE COMPOSITION of a compound from Formula Weight data.

8. Percentage Composition An analytical chemistry technique used in studying composition of substance is Percentage Composition. In Percentage Composition, Formula Weight (Molar Mass) data is used to determine the overall contribution the mass of each element makes to the mass of a compound.

9. Calculating Percentage Composition Determine the FW (MM) of the compound. Divide the TOTAL MASS of each element by the FW for the compound. Multiply the results by 100 to convert to a percentage. Add all percentages to check the answer…it should be VERY CLOSE to 100% (may be slightly off due to rounding).

10. Practice Problem What is the percentage composition of Magnesium Hydroxide, Mg(OH) 2 ? STEP 1. Calculate the FW: 1 mole Mg X 24.035 g = 24.305 g/mole 2 moles O X 15.999 g = 31.998 g/mole 2 moles H X 1.0079 g = 2.0158 g/mole + _____________ 58.3188 g/mole (Since this isn’t the last step, don’t round to SF here) You will need these TOTAL masses for each element in the next step!

11. STEP 2. Divide EACH ELEMENT’S TOTAL MASS by the FW: Mg = 24.305 g X 100 = 41.676 % 58.3188 g O = 31.998 g X 100 = 54.867 % 58.3188 g H = 2.0158 g X 100 = 3.4565 % 58.3188 g STEP 3. Add all the %s : 41.676 + 54.867 + 3.4565 = 99.99956 % = 100%

12. ASSIGNMENT For each of the 4 problems on yesterday’s assignment, calculate the PERCENTAGE COMPOSITION of each element! Be sure to do your work on SEPARATE PAPER. You will be turning in the problems from Monday (end of FW note sheet) and today’s problems tomorrow (Friday 1-16-15).