STOICHOMETRY MATH REVIEW

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?

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

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? amu  2 X amu =  1 X amu =  amu

ALUMINUM SULFATE AL 2 (SO 4 ) 3  Al = 2 atoms= 2 x amu=  S = 3 atoms= 3 x amu=  O = 12 atoms= 12 x amu= amu

THE MOLE  6.02 x  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

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

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

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

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

MOLAR MASS OF NH4

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

 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

 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

 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