EXP 14 - ChemLectures

EXP 14
Baking Soda & Stoichiometry
Name: _______________________________
Student ID: ___________________________
Chem 50 — De Anza College
The goal is to find the percent yield from the decomposition reaction of sodium hydrogen
carbonate (NaHCO3). Then to determine the percent of sodium hydrogen carbonate in an
unknown mixture, using stoichiometry and dimensional analysis. Review the discussion
and example calculations for this experiment on page 157-159 of your lab manual.
!
2 NaHCO3 (s) → Na2CO3 (s) + H2O (g) + CO2 (g)
eqn #1: balanced equation for decomposition of sodium hydrogen carbonate
Part A of this lab involves testing the process, to see if we can experimentally determine
the amount of NaHCO3 in the test tube. We compare our results to theory to see how
well the experiment performs and report that comparison as percent yield.
Part B of this lab involves heating our unknown mixture and using the observed
difference in mass and our understanding of stoichiometry to determine how much
NaHCO3 was in the original mixture. We report this as the percent NaHCO3 in the
unknown substance.
We were not able to conduct this experiment. Instead of collecting your own data for this
lab, you are being provided with the attached data. This data will serve as your “data”
section for your experiment report.
Copyright ChemLectures™ 1992-2015
Exp # 14
Name: ________________________________
Student ID: ____________________________
Chemistry 50 Prep Chemistry
De Anza College
Experiment Title: Baking Soda (Stoichiometry)
Unk#: ____
Bench / Locker : _____/_____
(write N/A if no unknown for this experiment)
This square for use by instructor.
_______
quiz A
_______
quiz B
_______
report
_______
total
Unknown Composition or Identity:
A report must be submitted receive credit for your participation in all lab
experiments. You may only report on experiments in which you fully participated.
Reminder: Experiment reports generally include the following sections.
section should start with a new page and be clearly labeled.
Each
➡ COVER PAGE (this page)
➡ PRE-LAB
➡ Provide clearly expressed answers to the questions on pages 161-162 from
your lab manual.
➡ DATA
➡ Data has been provided for this experiment. Use the filled out data table
provided as your data for this experiment.
➡ CALCULATIONS
➡ Provide your calculations for determining the percent yield of sodium
carbonate in Part A. A calculation guide is included.
➡ This demonstrates that we can rely on the amount of amount
determined by experiment, when we use this same process in part B.
➡ Provide your calculations from Part B for determining the percent sodium
hydrogen carbonate in the unknown. A calculation guide is included.
➡ CONCLUSIONS
➡ Give your average percent yield from part A.
➡ Give your determined percent NaHCO3 from your unknown.
➡ QUESTIONS
➡ Clearly present answers to questions from pages 165-166 from your lab
manual.
ta
>t
EXPERIMENT
14
NAME
DATE
SECTION
PRELABORATORY
ASSIGNMENI*
1. Providethe key tenn that conespondsto eachof the following definitions.
(a) therelationship
of quantities(i.e.,massof substance
or voiumeof sas)in a
chemicalreactionaccordingto thebalancedchemicalequation
(b) themassof 1 moleof anysubstance
expressed
in grams
(c.) a procedurefor obtainingthe massof a sampleby frst welghinga container
andthenweighingthecontainerwith the sample
(d) a
thevoiumeof a gasby measuring
thevolume
oI^technique-for-determining
wafer 1t dlsDlaces
(e) the amountof productexperimentallyobtainedfrom a reaction
(f) the amountof productthat is calculatedfrom a given amountof reactant
(g) the actualyield comparedto the theoreticalyield expressedasa percent
Key Terms: actualyield,_molarmass(l\4M),percentyield, stoichiometry,theoreticaiyield,
volumeby displacement,
weighingby difference
2. How do you tell whenthebakingsodasampleis decomposed
completely?
3. Is it possibleto obtaina percentyield of Na2CO3thatis greaterthan1002o?
4. Whataremajorsources
of experimental
error?
* Answersin Appendix J
Copyright
O 2013Pearson
Education
Decomposing
Baking
Soda 161
Referto
with heatto produce0.991^g-Na2C^O3.
.5. A 1.555-9salnpleof bakingsodadecomposes
yield
Na2co3.
of
theoretical
the
for
14.1andshowthecalculation
Example-Exercise
What is the percentyield of sodiumcmbonate,NazCO:?
of 0.325'g.Refer
sodais heatedandhasa nrass-loss
6.
- A 1.473-sunknownmxture with baki4g
in themixture.
percentage
NaHCO3
the
io iiua1o't" B""r"lse 14.2andshowthdlalculation for
7. What safetyprecautionsmustbe observedin this experiment?
14
L62 Experiment
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DATA
Part A: Percent Yield of Na2CO3
Trial #1
Trial #2
mass Test Tube
10.860 g
10.753 g
mass Test Tube + NaHCO3 (before heating)
12.894 g
12.648 g
mass Test Tube + Na2CO3 (after heating)
12.116 g
11.924 g
Part B: Percent NaHCO3 in Unknown
Trial #1
Trial #2
“B”
“B”
mass Test Tube
10.653 g
10.782 g
mass Test Tube + Unk Mixture (before heating)
12.342 g
12.607 g
mass Test Tube + residue (after heating)
11.874 g
12.102 g
Unknown ID
Copyright ChemLectures™ 1992-2015
CALCULATIONS
Part A: Percent Yield of Na2CO3
Calculate by difference the mass of your starting NaHCO3.
Calculate by difference the mass of Na2CO3 produced (experimental or actual yield) This
is the only matter left in the test tube.
Determine the theoretical yield (mass of Na2CO3 theory says would have been produced).
Determine the percent yield (ratio of theory to actual yield) of Na2CO3. And average
percent yield of the two trials.
Trial #1
Mass of starting NaHCO3
Experimental Yield Na2CO3
Theoretical Yield Na2CO3
Percent Yield Na2CO3
Copyright ChemLectures™ 1992-2015
Trial #2
Average
CALCULATIONS
Part B: Percent of NaHCO3 in Unknown Mixture
Calculate by difference the mass of your starting mixture.
Calculate by difference the mass of H2CO3 (H2O + CO2) produced. This is how much
matter was lost from our starting material after we heated it.
Using the H2CO3 produced, calculate how much NaHCO3 must have been in the original
sample.
Determine the percent of NaHCO3 in the original sample. Report an average percent for
the two trials.
Trial #1
Mass of starting mixture.
Mass of H2CO3 (H2O + CO2) produced.
Theoretical Starting Amount of NaHCO3
Percent of NaHCO3 in starting mixture.
Copyright ChemLectures™ 1992-2015
Trial #2
Average
NAME
SECTION
L. A I .225-9sampleof purelithium hydrogencarbonaleis decomposed
by heatingto produce
0.660g lithium carbonate.Calculatethe theoreticalyield andpercentyield of Li2CO3.
2LiHCO3(s)
;
LizCO:(s) + HzO(g) + COz(g)
A 1.205-9samplemixture of lithium hydrogencarbonateis decomposed
by heating.If the
masslossis 0.275g, what is the percentageof LiHCO3in the unknownmixtwe?
2LiHCO3(s)
;
LizCO:(s) +
HzCOa(g)
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BakingSoda
Decomposing
L6s
with heatto give lithium chlorideandoxygengas.If-l^.115 g of
-3. Liihium ctilorateis decomposed
how manymltliten of oxygengasis releasedat STP?
tidrium ctrtorateis decompbsed,
2LiClOg(s)
1
2lic1(s) + 3oz(g)
4. Lithium metalreactswith waterto give lithium hydroxideandhydrogengas.If-75.5mL of
hydrogengasis producedat STP,whatis themassof lithiummetalthatreactedl
2 Li(s) + 2 HzO(l) -J
2 LiOH(aq) +
HzG)
5. (optional)The Solvayprocessis usedto manufacturebakingsoda NaHCO3,Inthe process,
bbz, lri:, rtzo, andNaCl reactto producebaking soda.If 25.0L CO2and20.0 L NH3 react
at STp, with excesswaterandsodiumclrloride,what is the limiting r€actant?Calculatethernass
of baking sodaproduced.
[email protected])+ NHIG) + H2O(1) + NaCl(s) -+
ulluung KeacElnt
NaHCOg(s)+ NILCl(aq)
MassNaHCO:
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166 Experiment
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