COPYRIGHT SAUTTER 2003
MOLE RELATIONSHIPS IN
CHEMICAL REACTIONS
(An Experimental Approach)
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WHAT IS A CHEMICAL REACTION?
A PROCESS IN WHICH NEW SUBSTANCES ARE FORMED!
WHAT HAPPENS DURING A CHEMICAL REACTION?
ATOMS AND/OR MOLECULES ARE REARRANGED!
WHAT FUNDAMENTAL LAW APPLIES TO ALL CHEMICAL
REACTIONS?
• THE “LAW OF CONSERVATION OF MASS”
• WHAT IS THE “LAW OF CONSERVATION OF MASS”?
• THE COMBINED MASS OF THE REACTANTS ALWAYS
EQUALS THE COMBINED MASS OF THE PRODUCTS!
ALL CHEMICAL EQUATIONS MUST BE BALANCED.
WHY??
• THE “LAW OF CONSERVATION OF MASS” REQUIRES IT SO THAT NO
ATOMS ARE GAINED OR LOST DURING A CHEMICAL REACTION!
• STEP ONE IN WORKING WITH ANY CHEMICAL
EQUATION IS TO BE SURE IT IS BALANCED!!
• WHAT DO THE COEFFICIENTS IN BALANCED EQUATIONS
REPRESENT?
• THE COEFFICIENTS OF THE REACTANTS SHOW
HOW MANY MOLECULES ARE REACTING AND
THE COEFFICIENTS OF THE PRODUCTS SHOW
HOW MANY MOLECULES ARE FORMED.
THE EXPERIMENT WE WILL DO TODAY WILL
SHOW HOW WE CAN DETERMINE THE NUMBER OF
MOLECULES WHICH REACT AND THE NUMBER OF
MOLECULES WHICH ARE FORMED IN A REACTION
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IN OUR EXPERIMENT, WE WILL REACT IRON WITH COPPER II SULFATE
PENTAHYDRATE.
IN THIS EXPERIMENT YOU WILL BE REQUIRED TO CALCULATE THE
NUMBER OF MOLES OF SUBSTANCES USED. DO YOU REMEMBER HOW
TO CALCULATE MOLES FROM GRAMS?
MOLES = GRAMS OF SUBSTANCE / MOLAR MASS *
*MOLAR MASS IS DETERMINED FROM THE PERIODIC TABLE.
WHAT IS THE MOLAR MASS OF IRON?
DID YOU SAY 55.8 GRAMS PER MOLE?
WHAT IS THE MOLAR MASS OF COPPER?
DID YOU SAY 63.5 GRAMS PER MOLE?
• YOU SHOULD HAVE!!!
Experimental Procedures:
STEP 1: Weigh a clean, dry beaker and set the balance 25.00
grams ahead. Carefully add copper II sulfate pentahydrate
until the balance just balances.
Experimental Procedure:
STEP 2: Add 100 ml of distilled water and stir until the
copper sulfate is completely dissolved.
Experimental procedure:
STEP 3 – Weigh a clean, dry beaker and set the balance 5.00
grams ahead. Carefully add iron filings until the balance just
balances. You now have 5.00 grams of Fe.
Experimental Procedure:
STEP 4 – Add the iron filings to the copper sulfate solution
and stir. Place the mixture on low heat for 5 to 10 minutes.
Notice the magnetic properties of the iron.
Experimental Procedure:
STEP 5: Carefully pour the liquid through a weighed filter paper while
leaving as much as the solid as possible in the bottom of the beaker.
Wash the solid with distilled water and pour the wash water through
the filter paper. When the filtering is complete, place the filter paper in
the beaker with the solid and dry over night in an oven.
Experimental Procedure:
STEP 6 – The next day remove the beaker and contents from the
oven and weigh it. Notice that no magnetic properties remain when
it is tested.
MAGNETIC
PROPERTIES HAVE
DISAPPEARED !
A REVIEW OF THE PROCEDURE
1 Fe(S) + 1 CuSO4 (Aq)  1 Cu (S) + 1 FeSO4 (Aq)
EXPERIMENTAL DATA
(Sample Data)
• (1) WEIGHT (MASS) OF THE REACTION BEAKER (BEAKER
ORIGINALLY CONTAINING THE CuSO4)
• (2) WEIGHT (MASS) OF FILTER PAPER
• (3) WEIGHT (MASS) OF BEAKER + FILTER PAPER
AND DRY CONTENTS
(4) WEIGHT (MASS) OF IRON USED
155.37 GRAMS
_3.52 GRAMS
164.58 GRAMS
5.00 GRAMS
CALCULATIONS
HOW MANY MOLES ARE CONTAINED IN THE 5.00 GRAMS
OF IRON USED IN THE EXPERIMENT?
• MOLES = GRAMS OF SUBSTANCE / MOLAR MASS
• MOLES = 5.00 GRAMS OF Fe / 55.8 GRAMS PER MOLE
• THERE ARE 0.0896 MOLES OF Fe CONTAINED IN 5.00 GRAMS OF
IRON
• A BALANCED EQUATION FOR THE REACTION OF IRON WITH
COPPER II SULFATE PENTAHYDRATE IS:
1 Fe(S) + 1 CuSO4 (Aq)  1 Cu (S) + 1 FeSO4 (Aq)
WHICH TELLS US THAT FOR EACH MOLE OF IRON, ONE MOLE OF
COPPER SHOULD BE FORMED.
THEREFORE 0.0896 MOLES OF IRON SHOULD GIVE 0.0896 MOLES
OF COPPER (A ONE TO ONE RATIO)!
LET’S CHECK !
CALCULATIONS (CONTINUED)
(Try these calculations with your data if you have done the
experiment or use the given sample data in frame #12)
• FINDING THE GRAMS OF PRODUCT FORMED:
• (1) MASS OF BEAKER +CONTENTS (DATA ENTRY #3)
– MASS OF BEAKER + FILTER PAPER ( DATA ENTRY #1 + #2)
MASS OF PROUCT FORMED IN REACTION
• (2)MOLES OF PRODUCT FORMED = MASS OF PRODUCT / MOLAR MASS
MASS OF PRODUCT (CALC. #1) / 63.5 GRAMS PER MOLE (Cu)
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RATIO OF Fe REACTED TO MOLES OF Cu FORMED
0.0896 MOLES Fe / MOLES OF Cu FORMED (CALC. #2)
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A RATIO OF Fe TO Cu IS ONE TO ONE AS PREDICTED BY THE
BALANCED EQUATION SHOULD BE CONFIRMED !!
EXPERIMENTAL ERRORS:
IF THE EXPERIMENT NOT GIVE A 1 Fe TO 1 Cu RATIO AS
PREDICTED BY THE BALANCED EQUATION, WHY ?
• CAN YOU THINK OF SOME POSSIBLE REASONS ?
• (1) INCORRECT WEIGHING OF THE IRON OR THE COPPER
REACTANTS
• (2) REACTION OF THE IRON AND COPPER SULFATE WAS
INCOMPLETE
• (3) IMPROPER FILTERING OF THE PRODUCT
• (4) WASHING OF THE PRODUCT WAS NOT COMPLETE
• (5) PRODUCT SAMPLE WAS NOT COMPLETELY DRIED
• ANY OTHERS ?