chem 101 lab report 4
DESCRIPTION
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Introduction:
The main aim of this experiment is to demonstrate the application of the principles of
stoichiometry and also illustrate the effects of limiting reagents on a chemical reaction.
Stoichiometry, derived from the Greek words stoicheion (meaning element) and metron
(meaning measure) deals with the calculation of masses of the reactants and the products
involved in a chemical reaction.
Many a time, while performing stoichiometric calculations, it is observed that chemical
reactions are carried out when the reactants are not present in amounts as required by the
balanced chemical equation for that reaction. As a result, one reactant is in excess over the
other. This reactant present in the lesser amount gets consumed , after which no further
reaction would take place, no matter whatever be the amount of the other reactant present.
Hence, the reactant that gets consumed limits the amount of product formed, and is therefore
called the limiting reagent.
According to the law of conservation of mass, a balanced chemical equation has the same
number of atoms of each element on both sides of the equation.
Example 1) Unbalanced Chemical Equation: →
Example 2) Balanced Chemical Equation: →
This experiment will also involve a comparison of the actual yield and the theoretical yield
of the chemical reaction. Theoretical Yield is defined as the amount of product that would be
formed from the chemical reaction under idealized conditions while Actual Yield is defined
as the amount of product that would be actually synthesized from the same. The ratio of the
actual yield to the theoretical yield multiplied by 100 yields the percentage yield, indicating
the percentage of the theoretical yield that was formed in the reaction from experimentation.
Percentage Yield= Actual Y ieldTheoretical Y ield 00%× 1
Calculations and Discussions
This experiment involves the double displacement reaction of sodium hydroxide (NaOH)
and Calcium Chloride which is carried out in three phases: the first of which involves)(CaCl2
the precipitation of NaOH, while the others involve finding the limiting reagent and
calculating the theoretical yield respectively.
In order to find the limiting reagent and the actual yield, we would require the molar ratios
of the reactants, which can be obtained from the balanced equation of the reaction which is
as follows:
CaCl NaOH → Ca(OH) NaCl2(aq) + 2 (aq) 2(s) + 2 (aq)
Determining the Limiting Reagent and Calculating the Excess Reagent
a. Calculation of the number of moles of NaOH and CaCl2
Molarity of NaOH=
Molarity of CaCl2=
Sample No. Number of moles CaCl )( 2 Number of moles (NaOH)
Test Tube #1
Test Tube #2
Test Tube #3
Test Tube #4
b. Finding the limiting reagent and calculating the excess reagent
According to the balanced chemical equation of the given reaction
, it could be seen from the stoichiometricCaCl NaOH → Ca(OH) NaCl )( 2(aq) + 2 (aq) 2(s) + 2 (aq)
coefficients that for every mole of sodium hydroxide used, we would require half a mole of
calcium chloride. So, comparing the molar ratios of sodium hydroxide to calcium chloride
from the table, it is safe to conclude that calcium chloride is the limiting reagent in test
tubes 1 and 2 while it is sodium hydroxide, in test tube 4. There is no limiting reagent in
test tube 3 since both compounds are present in the ratio as required by the balanced
equation.
c. Calculation of the Excess Reagent:
Test Tube #1 Test Tube #2 Test Tube #3 Test Tube #4
Excess Reagent --
Number of moles of excess reagent in mol
Mass of excess reagent in grams
Experimentally, the excess reagent was determined by checking the samples which showed
a formation of precipitate and which did not, as is summarized in the excess reagent test in
the data sheet attached at the end of this report.
d. Calculation of Theoretical Yield of Calcium Hydroxide
Calculation of the theoretical yield would require knowledge of the limiting reagents, which
could be obtained from the calculations in section b) .
Also, from the balanced chemical equation for the reaction, we can calculate the molar ratio
of calcium chloride to calcium hydroxide to be equal to 1 (equimolar ratio).
Molar mass of calcium hydroxide = 74 grams.
Theoretical yield, therefore could be estimated as follows:
Sample #1 Sample #2 Sample #3 Sample #4
Number of moles
of
Mass of
e. Actual Yield of Calcium Hydroxide (Obtained by Experimentation)
Below shown is the table of the actual yield of calcium hydroxide obtained in each of the
four samples:
Sample Yield of Calcium hydroxide
Test Tube #1
Test Tube #2
Test Tube #3
Test Tube #4
Actual Yield could be plotted against the volume of calcium chloride used as follows:
From the graph, it is observed that the reaction proceeds until a small plateau region of sorts
appears, indicating that the limiting reagent is causing the reaction to stop. This is applicable
to the first three samples, while the spike in the graph from the third point indicates a
change in the limiting reagent (it was seen that the limiting reagent for the fourth sample
alone was NaOH while it was calcium chloride for the other three samples).
f. Calculation of Percentage Yield
Using the values of actual yield and theoretical yield, the percentage yield for each of the
four samples could be estimated as follows:
Percentage Yield
Sample #1
Sample #2
Sample #3
Sample #4
Data Sheet
Conclusions:
1. The yield of the four samples were recorded by duly following the
required laboratory procedures .
2. The limiting reagent was found to be calcium chloride in the first two
samples, while sodium hydroxide was found to be the limiting reagent
in the fourth sample. The third sample doesn’t have a limiting reagent
as such since the compounds are present in an equimolar ratio.
3. We were able to learn how to take measurements using laboratory
scales, and by avoiding potential fire hazards, thereby expanding our
understanding of measurements and research.
4. We were able to establish experimentally that the limiting reagent
affects the rate of a given chemical reaction.