1. STOICHOMETRY MATH REVIEW

2. DO NOW 4/22/16 Water H 2 0  How many hydrogen molecules are there in one molecule of water?  How many oxygen molecules are there in one molecule of water?  What is the amu (atomic mass units) of water?

3. ATOMS & COMPOUNDS  To get the weight of an individual atom look at the periodic table and find the atomic mass of the atoms  For compounds add the atomic weights in the compound together

4. WATER H 2 0  How many hydrogen molecules are there in one molecule of water? 2  How many oxygen molecules are there in one molecule of water? 1  What is the amu (atomic molecular unit) of water? 18.015 amu  2 X 1.0079amu = 2.106  1 X 15.999amu = 15.999  + 18.015 amu

5. ALUMINUM SULFATE AL 2 (SO 4 ) 3  Al = 2 atoms= 2 x 26.982amu= 53.964  S = 3 atoms= 3 x 32.066amu= 96.198  O = 12 atoms= 12 x 15.999amu= 191.988 342.15 amu

6. THE MOLE  6.02 x 10 23  Avagadro’s number, a really big number  It stands for a certain number of things (atoms or molecules)  For an element it is the atomic weight using grams instead of atomic mass units (amu)  For a compound it is the formula weight in grams instead of amu

7. THE MOLE  The bridge between microscopic and macroscopic  6.02 x 10 23 particles  1 mol  atomic/formula weights in grams  If you have one of these you can calculate the other two

8. WATER  Weight of a water molecule is 18.015 amu  1 mole of water is the formula weight in grams  You can then say the weight of a mole of water is 18.015grams  You can also say that 18.015 grams of water contains 6.02 x 10 23 H 2 0 molecules or 1 mole of water That is composed of two moles of hydrogen and one mole of oxygen

9. HOW MANY WATER MOLECULES ARE THERE IN 5.50 MOLES OF WATER?  5.50 mol X 6.02 x 10 23 molecules/mol = 3.31 x 10 24 molecules

10. 5/2/16 Do Now  What is the molar mass of NH4?  One mole of NH4 equals how many grams? Objectives  Be able to calculate the molar mass of a compound given the chemical formula or chemical name  Be able to calculate how many moles in an element, molecule or compound  Be able to calculate the % composition and empirical formula Tasks  notes  practice problems

11. MOLAR MASS OF NH4

12. FINDING FORMULA OF COMPOUND  Use mole concept to calculate empirical formula of a compound using percentage  First  Let’s assume you have 100grams of the compound so we can use percentages as weights  Then convert the weight of each element to moles

13.  What is the empirical formula for a compound with 26.4% Na, 36.8% S and 36.8% O  Convert %(percent) to weight in grams  26.4/100 Na; 36.8/100 S; 36.8/100 O  26.4gr Na36.8gr S 36.8gr O

14.  Calculate the mole for each element  26.4gr Na x 1mol Na = 1.15mol 22.9gr 36.8 gr S x 1mol S = 1.15mol 32.06gr 36.8gr O x 1mol S = 2.30mol 15.99gr

15.  Write the empirical formula, changing the subscripts to whole numbers when necessary  Reduce each mole, divide each by 1.15  1Na 1S 2O = NaSO 2