Microsoft Word - Composition_Report.docx
Percent Composition
Name:
Part A – The Chemistry of Baking
#1). What is the chemical formula for Baking Soda?
#2). What is the molecular weight of Baking Soda?
#3). Is Baking Soda a pure substance or a blend?
#4). Is Baking Powder a pure substance or a blend?
#5). For every one Baking Soda Molecule, how many Ca
on Dioxide Molecules are
generated in the reaction with acid?
Baking Soda Trial Baking Powder Trial
Mass of beaker, empty
test tube & Acid
Mass of beaker, test
tube, sample & Acid
(Before Reaction)
Mass of beaker, test
tube, sample & Acid
(After Reaction)
Total Mass of
Sample
Total Mass of CO2
Generated
#6). How many moles of Ca
on Dioxide gas are generated? Show your work.
Baking Soda Baking Powde
#7). How many moles of Ca
onate Ion is that equivalent to in both of your samples?
Baking Soda Baking Powde
#8). What is the Mass of Ca
onate? Show your work
Baking Soda Baking Powde
#9). What is the Percent Ca
onate? Show your work
Baking Soda Baking Powde
#10). What is the Percent of Baking Soda, that is in Baking Powder based on the data?
Show your work.
Part B – Identifying an Unknown
What is your Unknown Number?
Trial #1 Trial #2 Trial #3
Mass of beaker,
test tube & Acid
Mass of beaker,
test tube, sample
& Acid (Before
Rxn)
Mass of beaker,
test tube, sample
& Acid (After Rxn)
Total Mass of
Sample
Total Mass of CO2
Generated
Based on the calculation steps completed in Part A, complete the table for the data from
Part B
Trial #1 Trial #2 Trial #3
Moles of CO2
Mass of
Ca
onate Ion
Percent
Ca
onate
#11). What is the average Percent Ca
onate of your Sample? Show your work.
Your unknown is one of the pure compounds listed below. Complete the table and
determine the identity of your unknown based on the pure percent ca
onate values
Name Formula Molecular
Weight
% Ca
onate
Calcium
Ca
onate
Potassium
Ca
onate
Sodium
Bica
onate
Sodium
Ca
onate
Sodium
Ca
onate
Monohydrate
#12). What is the identity of your unknown?
#13). These reactions are preformed with a large excess of HCl. If some of
the HCl had spilled on the bench without your knowledge, and is not delivered to the
test tube, how would this affect the calculated % Ca
onate Value? Explain your
easoning.
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Percent Composition
Part A – Baking Chemistry
• Observe the reactions in the following video:
• https:
www.youtube.com/watch?v=Pl7VmOoT16I
• Record the precise mass of the Beaker and Acid with the empty test tube, full test tube before
eaction and the test tube after reaction for the reaction of baking soda with acid
• Record the precise mass of the Beaker and Acid with the empty test tube, full test tube before
eaction and the test tube after reaction for the reaction of baking powder with acid
• From these mass readings, the total mass of baking soda and baking powder can be determined,
as well as the mass of Ca
on Dioxide that escapes
• Using these values, determine the moles of Ca
on dioxide, mols Ca
onate, mass Ca
onate
and percent ca
onate for each reaction
• Using the ca
on dioxide generated from the Baking Powder reaction, convert this to a mass of
Baking Soda to determine its percentage in Baking Powder.
Part B – Unknown Ca
onates
• On Blackboard, choose one of the Unknown files and record the unknown number
• Follow the video link on the unknown file to watch a triplicate reaction of an unknown
ca
onate with acid
• For each trial, record the precise mass of the Beaker and Acid with the empty test tube, full test
tube before reaction and the test tube after reaction
• Using these value, the percent ca
onate can be determined for each trial, and an average
obtained
• Determine the theoretical percent ca
onate of the different known samples, and then compare
your value to the theoretical ones.
• Which ever theoretical percent ca
onate value is closest to your own, this would be the
identity of your unknown sample
https:
www.youtube.com/watch?v=Pl7VmOoT16I
Microsoft PowerPoint - Percent composition Lecture Slides.pptx
PERCENT COMPOSITION
CHEMICAL REACTIONS
Chemical reactions start with reactants and end with products, but how much of one
or the other there is, requires careful measurements and calculations
Last lab was a Qualitative experiment where compounds and ions were identified
This lab is a Quantitative experiment, where the reaction itself is known, but the
amounts are unknown and need to be determined
The last part of the report, then uses the quantitative measurement to compare with
other known samples, in order to determine the sample identity
Your sample identity will be the one which has a theoretical percent ca
onate closest
to your measured unknown
MEASUREMENTS
Due to the small sample sizes used, this experiment utilizes a digital microbalance
This balance has significance out to 4 decimal places, therefore all mass
measurements should be recorded to 4 decimal places, giving 4, 5 or even 6
significant figures.
COMPOSITION OF MOLECULES
Molecules are made up of different elements, held together by chemical bonds or
through electrostatic interactions (positive and negative ions).
In determining the percent composition, you need to determine how much of
everything together there is, and then how much there is of each component
Use the example of water H2O
Water contains three atoms: Two Hydrogen atoms & one Oxygen atom
While the ratio of Hydrogen in the molecule is 2:1 and Oxygen is 1:1, the two atoms
have different atomic masses
The molecular weight and atomic mass is used to determine how much of the overall
amount is hydrogen, and how much is oxygen.
THE MOLE
A mole is simply a number (6.02 x 1023)
To solve for the moles of a compound, the
atomic/molecular weight is used
The atomic/molecular weight is a ratio of
grams per 1 mole
To solve a problem, you would cross multiply
Number Name Number Value
Couple 2
Dozen 12
Score 20
Gross 144
Mole 6.02 x 1023
Given Moles,
solve for Mass
Given Mass,
solve for Moles
The unit of moles, multiplied
y the unit of grams over
moles, causes the moles to
cancel and the answer is in
the unit of grams
The unit of grams, multiplied
y the unit of moles over
grams, causes the grams to
cancel and the answer is in
the unit of moles
ATOMIC & MOLECULAR WEIGHT
An Atomic Mass, or Molecular Weight is the physical mass of a substance that is needed, to
contain one mole of atoms or molecules
The molecular weight of a compound is determined by the individual atomic masses of all
the elements combined
One Copper atom has an atomic mass of 63.55g/mol based on the periodic table.
Copper (II) Sulfate has the formula of CuSO4, and the molecular weight is the sum of the
atomic weights for each atom
Atom Quantity Atomic Mass Total
Copper (Cu) 1 63.55g/mol 63.55 x 1 = 63.55
Sulfur (S) 1 32.06g/mol 32.06 x 1 = 32.06
Oxygen (O) 4 16.00g/mol 16.00 x 4 = 64.00
Copper = XXXXXXXXXX
Sulfur = XXXXXXXXXX
Oxygen = XXXXXXXXXX
CuSO4 = 159.61g/mol
What would the molecular weight be for Copper Sulfate Pentahydrate (CuSO4 * 5H2O)?
PERCENT COMPOSITION FROM FORMULA
If the chemical formula for a compound is known, the percent composition of each
component can also be determined, based on the atomic and molecular weights
Sodium Bica
onate
NaHCO3
1 Na @ 22.99g/mol = 22.99g/mol
1 H @ 1.008g/mol = 1.008g/mol
1 C @ 12.01g/mol = 12.01g/mol
3 O @ 16.00g/mol = 48.00g/mol
NaHCO3 = 84.008g/mol
1
First determine the molecular
weight of the entire compound
2 The determine the molecular or atomic mass of the component.
If you want to determine the percent Sodium, it would be the atomic mass of
sodium (22.99g/mol)
If you want to determine the percent Ca
onate, it would be the molecular mass
of Ca
onate (60.01g/mol)
3 Now you would know mass of the total compound as well as the mass of the
individual component.
You can then perform the percentage calculation
100% %
100% %
60.01
84.008 / 100% 74.43%
22.99
84.008 / 100% 27.37%
PERCENT COMPOSITION -
EXPERIMENT
REACTION
This reaction involves the ca
onate anion, reacting with the acid H+ cation, to
produce water and ca
on dioxide gas
Any ca
onate sample will react in the same way
The ions of ca
onate and H+ are reacting, and the other ions are Spectators,
meaning they are not involved in the actual reaction
→
→
→
The sodium Ca
onate reacts with 2 acid
molecules to form ca
on dioxide, water and salt
The sodium ca
onate and acid are both
dissolved in water, meaning the
eak apart,
and so does the sodium chloride product
Both the sodium ions and the chloride ions did not
change, and therefore are not part of the reaction.
These are spectators and only the ca
onate ion, and
acid H+ ion react to form water and ca
on dioxide
gas
SAMPLE MASS
In the experiment, you need to determine how much the total sample weighs
This is done by weighing by difference.
The mass of everything except the sample is recorded, and then the sample is added
After