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MOLE RELATIONSHIPS IN CHEMICAL REACTIONS

(An Experimental Approach)

• 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

• 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) 155.37 GRAMS

• (2) WEIGHT (MASS) OF FILTER PAPER _3.52 GRAMS

• (3) WEIGHT (MASS) OF BEAKER + FILTER PAPER

AND DRY CONTENTS 164.58 GRAMS(4) WEIGHT (MASS) OF IRON USED 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)

• RATIO OF Fe REACTED TO MOLES OF Cu FORMED

0.0896 MOLES Fe / MOLES OF Cu FORMED (CALC. #2)

• 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 ?