Experiment 23: Factors Affecting Reaction Rates
Chemistry for Engineers Lab 1109-01
The University of Texas Rio Grande Valley
Fall 2019
Hector Alonso Garcia
Introduction:
Chemical kinetics is the study of chemical reaction rates, how reaction rates are controlled, and
the pathway or mechanism by which a reaction proceeds from its reactants to its products. The
rate of a chemical reaction is expressed as a change in the concentration of a reaction (or
product) as a function of time. There is a direct relationship involved, hence, the greater the
change in concentration, the faster the rate of reaction.
The purpose of this lab is to study the various factors that affect the rates of chemical reaction.
Acids such as 3 M H2SO4 , 6 M HCl, 6 M CH3COOH, and 6 M H3PO4 are involved through the
use of metals like zinc, magnesium and copper. Within the following lab, different factors that
can be controlled are investigated. Such factors include:
➢ Nature of the reactants
➢ Temperature of a chemical system
➢ Presence of a catalyst
➢ Concentration of the reactants
➢ Surface area of the reactants
A catalyst is a substance that speeds up a chemical reaction, but is not consumed by the reaction;
hence a catalyst can be recovered chemically unchanged at the end of the reaction it has been
used to speed up, or catalyze.
Experimental Section:
Procedure A - Nature of the Reactants
1. Four small test tubes were obtained, and labeled with 3 M H2SO4 , 6 M HCl, 6 M
CH3COOH, and 6 M H3PO4. Each test tube was then half-filled with the proper acid and
place in a test tube rack. Approximately, a 1-cm strip of magnesium ribbon was inserted
into each tube, and the reaction rates were compared. Observations were then recorded on
a seperate sheet of paper.
2. A set of three labeled test tubes were half-filled with 6 M HCl. 1-cm strips of zinc,
magnesium and copper were obtained, and inserted separately into each of the test tubes.
The reaction rates of each metal in HCl was then compared and observations were
recorded.
Procedure B - Temperature of the Reaction: Hydrochloric Acid -- Sodium Thiosulfate Reaction
System
1. Using a pipette, approximately 2 mL of 0.1 M Na2S2O3 was transferred into each of the
set of three, clean test tubes. Into another second set of three test tubes, 2 mL of 0.1 M
HCl was transferred. All test tubes were then labeled with the corresponding substance.
The first pair of Na2S2O3 - HCl pair test tubes was combined at room temperature. Then,
a second pair of test tubes were placed in an ice bath. Lastly, a third pair of test tubes
were placed in a warm water bath at 60℃. Each pair of test tubes were in their own
2.
3.
4.
5.
environment until a thermal equilibrium state was established.
A timer was obtained by one lab partner, in order to monitor the reaction rate. The first
Na2S2O3 - HCl pair of test tubes were quickly combined and the timer began shortly after.
The mixture was then agitated for several seconds, and the timer went on until the
cloudiness of the sulfur had appeared in the test tube. Through the use of a timer and
thermometer, the time lapse and room temperature was recorded.
Focusing on the ice bath, the HCl solution was quickly poured into the Na2S2O3 solution
as the timer began once again. The mixture was agitated again for several seconds, and
the timer continued until the cloudiness appeared again. The time lapse and the
temperature of the bath was recorded.
From the warm water bath, the HCl solution was quickly poured into the Na2S2O3
solution, as the same steps in parts 2 and 3 were repeated once again. Both the time lapse
and temperature was recorded.
A graph of temperature versus time was made using the appropriate online software.
Procedure C - Temperature of the Reaction: Oxalic Acid -- Potassium Permanganate Reaction
System
1. Approximately 1 mL of 0.01 M KMnO4 (in 3 M H2SO4) and 4 mL of 3 M H2SO4 was
transferred into a set of three, clean test tubes. Into a second set of three test tubes, 5 mL
of 0.33 M H2C2O4 was transferred.
2. A KMnO4 - H2C2O4 pair was selected and the H2C2O4 solution was poured into the
KMnO4 solution. A timer was used to start the time, and the mixture was then agitated.
The time was recorded for the purple color of permanganate ion to disappear. The room
temperature was then recorded.
3. A second KMnO4 - H2C2O4 pair of test tubes was then placed into warm water at 40℃
until the thermal equilibrium was established. The H2C2O4 solution was then poured into
the KMnO4 solution. The same steps were repeated in order to record the time and
temperature.
4. Part 3 was repeated but the temperature was now increased to 60℃. The appropriate data
was recorded.
5. A graph of temperature versus time was made using the appropriate online software.
Procedure D - Presence of a Catalyst
1. Approximately 2 mL of a 3% H2O2 solution was placed into a clean test tube. 1 or 2
crystals of MnO2 was added to the solution and observed.
Procedure E - Concentration of Reactants: Magnesium -- Hydrochloric Acid System
1. Into a set of four different test tubes, 5 mL of 6 M HCl, 4 M HCl, 3 M HCl and 1 M HCl
was transferred into each tube and labeled. The mass of each solution was determined
with four 1-cm strips of magnesium. The number of moles of magnesium in each strip
was calculated.
2. The first magnesium strip was added to the 6 M HCl solution. The time for all traces of
magnesium to be gone was recorded. The experiment was then repeated with the
remaining three strips.
Calculations:
*Report Sheet/handwritten calculations attached*
Analysis/Discussion of Results:
Experiments done in this lab were done to test how each factor affects the rate of a chemical
reaction, the nature of the reactants, concentration, temperature, surface area and when a catalyst
is present. In addition, these experiments also tested the effects of temperature and concentration
when it comes to the equilibrium of a reaction. The nature of the reactants were tested by using
metals such as magnesium with the addition of the five different acids. It was seen that the
concentration of a substance will change the collision/reaction rate. There were errors
experienced in the lab. The rate of the reaction is supposed to generally decrease as temperature
is increased, but that was not the experience with the observations of this lab. The cause of this
error could be due to human error.
In the Hydrochloric Acid-Thiosulfate Reaction System the time versus temperature graph did not
show the information that was it was supposed to show. As time increased, the temperature did
not increase. There was an abnormal plot of data where temperature would be low and time
would be low, but then temperature would be in the middle and then time would be very high.
When the temperature was very high there was very low time. The abnormal time amount with
the medium temperature doesn’t correlate to what was supposed to occur.
In the Oxalic Acid-Potassium Permanganate Reaction System there was a better correspondence
between the temperature of the reaction and the reaction time. This graph represented what was
supposed to occur: as the temperature increased, there was a decrease in the reaction time.
In the Magnesium-Hydrochloric Acid System the mol HCl/mol Mg were the same for 6M and
the 4M concentration of HCl. there wasn’t too much of a correlation between the 3M
concentration of mol HCl/mol Mg and the 1M mol HCl/mol Mg
Conclusion:
The following lab concluded how different metals could affect its reaction rates. Metals such as
magnesium, zinc and copper were utilized in different situations with the presence of acids in
order to depict the different factors of reaction rate. This lab showed that factors like temperature
and rate of reaction increase proportionally due to a greater number of collisions. Although there
were some errors associated with this experiment, it was successful in determining the
relationship between different factoring that can affect the reaction rate.
Laboratory Questions:
*The following lab does not contain any laboratory questions*