In honor of Homecoming,
two special cartoons…
Thursday, Oct. 10th: “A” Day (GO BEARS!)
Friday, Oct. 11th: “B” Day
Agenda
Finish Lab: “Stoichiometry and Gravimetric
Analysis”
In-Class Assignment:
Chapter 9 review, pg. 329-331: #1-8, 13-15, 21a,
24a, 27b, 29b, 31, 34, 37
Homework:
Concept Review
Chapter 9 Test/Concept Review due:
Thursday 10-17/Friday, 10-18
Reminder: Late concept reviews WILL NOT
be accepted!
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
Get your beaker, paper towel, filter paper and
dried precipitate out of the drying oven and
record the total mass (#5).
1.Organizing Data
 Write a balanced equation for the reaction.
Na2CO3 (aq) + SrCl2 (aq) → 2 NaCl (aq) + SrCO3 (s)
 What kind of reaction was this?
Double Displacement
 What is the precipitate?
SrCO3 (strontium carbonate)
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
2. Examining Data
Calculate the mass of the dry precipitate
(#6) by subtracting the mass of the filter
paper (#3) and the mass of the beaker with
paper towel (#4) from the total mass of
beaker, paper towel, filter paper, and dried
precipitate (#5).
Record the mass of the dry precipitate in
table. (#6)
Use the molar mass of SrCO3 to calculate
the number of moles of precipitate formed.
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
3. Examining Data
 Use the mole ratio from the balanced
equation in question #1 to change
moles SrCO3
moles Na2CO3.
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
4. Evaluating Methods
 Calculate the #moles of SrCl2 that were added
if there was 0.30 mol SrCl2 in every liter of
solution.
 Was SrCl2 or Na2CO3 the limiting reactant?
Na2CO3
 Would this experiment have worked if SrCl2
was the limiting reactant?
No, we wouldn’t be able to determine how
much Na2CO3 was in the vat if we had
excess Na2CO3 left over after the
reaction.
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
5. Evaluating Methods
 Why was the SrCO3 rinsed in step 11?
To remove any impurities.
 What soluble impurities could have been on
the filter paper along with the precipitate?
NaCl
 How would the results vary if the precipitate
had not been completely dry?
The mass would have been greater due to
the mass of the water.
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
6. Applying Conclusions
 Start with the #moles of Na2CO3 from
question #3 and use the molar mass of
Na2CO3 to change
moles Na2CO3
grams Na2CO3
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
7. Applying Conclusions
 How many grams of Na2CO3 are present in
the 575 L drum?
 Hint: you just calculated how many grams
of Na2CO3 were in the 15 mL sample. Use
that information as a conversion factor.
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
8. Evaluating Methods
 We used a 0.5M solution, which means that
there was 0.795 g Na2CO3 for every 15 mL
(this is the theoretical yield)
 Use your answer from question #6 as the
actual yield and calculate the percentage
yield:
Actual yield
X 100%
Theoretical Yield
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
Don’t forget your reflection statement:
Was your hypothesis correct?
What were some sources of error in the lab?
How could you minimize these sources of errors
in future trials?
Did this lab help you to understand how
stoichiometry could be used outside of the lab?
Your reflection statement should be a paragraph
with complete sentences!
Finish Lab:
“Stoichiometry and Gravimetric Analysis”
Make sure your table of contents is updated
and put your lab folders back in the bin to be
graded.
In-Class Assignment/Homework
Chapter 9 review, pg. 329-331:
#1-8, 13-15, 21a, 24a, 27b, 29b, 31, 34, 37
Next time: Jeopardy review
Chapter 9 Test/Concept Review due:
Thursday, Oct. 17th
Friday, Oct. 18th