How will changing the concentration of hydrochloric acid influence the
reaction rate between calcium carbonate and hydrochloric acid?
RATIONALE
In chemistry, rate of reaction is defined as the speed in which a chemical reaction occurs. It can be
measured as the concentration of products formed or reactants consumed within a unit of time in
the reaction (Laidler, 2020). Chemical reactions are the interaction between chemicals where the
reactant molecule bonds are broken, and new bonds are formed within molecules to form a new
product (Anonymous, 2019). According to collision theory, bonds are broken and formed through
molecules or atoms colliding with one another. Collision theory states that for a reaction to occur,
molecules need to collide with sufficient energy, known as activation energy, and at the correct
orientation, in order for the bonds to break (Wu, 2022). The rate of chemical reactions may differ
depending on the reaction. There are many factors that may impact reaction rate, including
concentration, pressure, temperature, agitation, and the presence of a catalyst (Helmenstine, 2020).
Anderson (2022)’s original experiment investigated the reaction rate between calcium carbonate
chips and hydrochloric acid.
CaCO3 (s) + 2 HCl (aq)  CaCl2 (aq) + CO2 (g) + H2O (l)
The reaction rate was determined by measuring the mass loss of the reaction flask every 10 seconds
over the course of a set timeframe. The mass loss was caused by the reactant molecules being
converted to CO2. The original experiment used hydrochloric acid at 2M only, and therefore
provides little insight on the impact of hydrochloric acid concentration on reaction rate. Thus, this
experiment was modified by changing the concentration of hydrochloric acid used, to investigate
whether changing the concentration of hydrochloric acid would impact the reaction rate of this
experiment.
According to (Key, 2019), a higher reactant concentration leads to a greater number of successful
collisions within a time period, thus increasing reaction rate. This is because a higher concentration
of reactant molecules means there is an increased opportunity for reactant molecules to collide,
thus increasing collision frequency (Dillon, 2017). Therefore, it is hypothesised that as the
concentration of hydrochloric acid increases, the reaction rate will also increase.
RESEARCH QUESTION
How will changing the concentration of hydrochloric acid influence the reaction rate between
calcium carbonate and hydrochloric acid?
MODIFICATIONS TO METHODOLOGY
The original experiment by Anderson (2022) investigated the rate of calcium carbonate reacting with
hydrochloric acid, as measured by the mass loss experienced every 10 seconds over the course of 5
minutes.
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However, modifications were made to the methodology to accommodate the new research
question.
-
-
Measuring the mass loss (g) of the calcium carbonate and hydrochloric acid reaction /carbon
dioxide with the hydrochloric acid concentrations at 0.25M, 5M, 3M, 6M, along with 2M as
according to the original methodology. This modification was important as the wide range of
concentrations ensured that sufficient data could be collected, so that trends, patterns, and
relationships could be analysed and interpreted back to the research question.
Three trials were conducted for each concentration rather than one as according to the
original methodology. This modification was important in ensuring that the results were
consistent and reliable. This also allowed for identification of anomalies or random errors.
SAFETY & ETHICAL CONSIDERATIONS
The safety considerations outlined in the original experiment were adhered to (Anderson, 2022)
Additionally, there are some further safety and ethical considerations that must be adhered to in this
modified experiment:
Safety/Ethical Consideration
Justification
Exercise caution when handling/using
Hydrochloric acid can be extremely
hydrochloric acid.
corrosive and cause severe skin burns,
eye damage, and respiratory irritation
(Global Safety Management, 2015). This poses
a considerable risk in this experiment as
the modified methodology uses HCl
with concentrations of up to 6M.
Ensure the appropriate safety attire is
worn and rinse the affected area with
water in the case of direct contact.
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RAW DATA
0,7
Average Mass Loss (g)
0,6
0,5
0,4
0,3
0,2
0,1
0
-50
-0,1
0
50
100
150
200
250
300
350
Time (seconds)
0.25M
0.5M
2M
3M
6M
Figure 1: A scatter plot graph showing the average mass loss (grams) over 300 seconds at different HCl
concentration levels. The error bars represent the absolute uncertainty at each time of measurement.
Figure 1 shows a general increase in average mass loss over time for each concentration, with the
greatest total mass loss of approximately 0.61g for the 6M concentration, and the lowest total mass
loss of 0g for the 0.25M concentration. This suggests that as the concentration increases, a higher
average mass loss is experienced.
DATA PROCESSING AND ANALYSIS
The raw data was processed using Microsoft excel to calculate the average mass loss, absolute
uncertainty, relative uncertainty, reaction rate for each concentration, and average rate for each
concentration with error propagation. Absolute uncertainty was calculated to represent the range in
which the true value is likely to be. This was used to determine the accuracy and therefore the
validity of the data. Relative uncertainty was calculated from the absolute uncertainty values to put
the error of a measurement into perspective, by calculating the uncertainty compared to the size of
the measurement. This was used to determine the precision and therefore reliability of the results.
The average mass loss, reaction rate, and average rate were calculated to graph the results for
trends analysis.
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Table of Sample Calculations
Table 1: A table of sample calculations that display the statistical analysis techniques used in this investigation. The 2M 40
seconds data was used to demonstrate the sample calculations.
Formula used
Sample Calculation
Concentration of Dilution (mL)
C1 V1 = C2 V2
C1 V1 = C2 V2
3V1 = 2 × 50
3V1 = 100
V1 = 33.33mL
Average Mass Loss (g)
=
𝑥̅(2𝑀 40𝑠𝑒𝑐𝑠) =
trial1 + trial2 + trial3
3
𝑥̅(2𝑀 40𝑠𝑒𝑐𝑠) = 0.04 g
Absolute Uncertainty (g)
=±
=±
𝑥̅(𝑚𝑎𝑥̅) − 𝑥̅(𝑚𝑖𝑛)
2
=
Uncertainty
× 100
Average
error propagation (g/s)
=
=
Average Mass Loss
Time
Average rate for concentration with
0.01
× 100)
mass
0.01
Total Time ± (
× 100)
time
Total Mass Loss ± (
0.01
× 100
0.04
= 25%
Reaction Rate (g/s)
=
0.05 − 0.03
2
= ±0.01 𝑔
Relative Uncertainty (%)
=
0.05 + 0.04 + 0.03
3
0.04
40
= 0.001 g/s
0.001
0.3033333 ± (
× 100)
0.3033333
=
0.001
280 ± (
× 100)
280
0.3033333 ± 0.32967
=
280 ± 0.00036
= 0.00108 ± 0.33003
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Graphs of Processed Data
0,0045
0,004
Rate of Reaction (g/s)
0,0035
0,003
0,0025
0,002
0,0015
0,001
0,0005
0
-0,0005
0
50
100
150
200
250
300
350
Time (seconds)
0.25M
0.5M
2M
3M
6M
Figure 2: A scatter plot graph showing the average rate of reaction (g/s) over 300 seconds at different HCl concentration
levels.
No discernible trend for reaction rate over time for concentrations 0.5M or 3M can be observed in
figure 2, with data points showing inconsistent fluctuations in the reaction rate over time. However,
for the concentration of 6M, the graph shows a sharp increase in reaction rate from 0g/s at 0seconds
to 0.0039g/s at 50 seconds, before demonstrating a more gradual increase of 0.0003g/s between 50
seconds to 100 seconds (0.0039g/s to 0.0042g/s), then gradually decreasing from 0.0042g/s at 100
seconds to 0.002g/s at 300 seconds (0.0022g/s). The 2M concentration also follows this trend, with a
sharp increase from 0g/s at 0 seconds to 0.00067g/s at 10 seconds before gradually increasing to
0.0011g/s at 60 seconds (0.00043g/s), then decreasing from 0.0011g/s to 0.00051g/s at 300 seconds.
(0.00059g/s). Figure 2 shows no change in reaction rate over time for 0.25M concentration. This
coincides with the aforementioned collision theory that for a reaction to occur, reactant molecules
need to collide with sufficient activation energy, with a higher concentration of molecules resulting in
a higher change of reactant molecules colliding. As the 0.25M solution contains the lowest number of
reactant molecules, there is a reduced chance of successful collisions occurring (Dillon, 2017).
Table 2: Table showing the total average rate at different concentrations, and
absolute uncertainty for each concentration.
Table 2 shows extremely high
levels of absolute uncertainty for
each concentration above 0.25M,
with each uncertainty value
significantly greater than the
average reaction rate value. For
instance, the 0.5M concentration
had an average rate of 0.00036
±0.93783.
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0,003
R² = 0.974
Average Rate (g/s)
0,0025
0,002
0,0015
0,001
0,0005
0
0
1
2
3
4
5
6
7
Concentration of HCl
Figure 3: A scatter plot graph with a linear trend line showing the overall average rate (g/s) at different HCl concentration
levels. The R2 value shows the accuracy of the fit of the trend line to the points.
1
0,8
Average Rate (g/s)
0,6
R² = 0.974
0,4
0,2
0
-0,2
0
1
2
3
4
5
6
7
-0,4
-0,6
-0,8
-1
Concentration of HCl
Figure 4: Error bars applied to graph from figure 3.
Analysis of Data
Due to the aforementioned theory suggesting that a higher concentration results in a higher rate of
reaction (Key, 2019, it was theorized that the results would show an overall increase in average rate,
as the HCl concentration increased. Figure 3 supports this theory, as it demonstrates a steady
increase of the average reaction rate as the HCl concentration increases, with the average rate
increasing from 0g/s ±0.00033 at 0.25M to 0.0024g/s ±0.165 at 6M (0.0024g/s total). A linear trend
line was applied to the data points with an R2 value of 0.9726, suggesting the trend line was a close fit
for the points, and thus shows a very strong correlation between the concentration of HCl and
average reaction rate. The 0.5M point and 2M point deviates slightly from the trend line, however
the other points appear to fit the trend line extremely well.
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Outliers were removed from the raw data for the 0.5M concentration, as highlighted in yellow in the
appendices. This was because the mass loss recorded was greatly different to the other trials, for
instance a mass loss of 0.3g was recorded compared to 0.01g and 0.03g at 20 seconds, and therefore
was likely due to measurement error. Removing the outliers would reduce variation within the data,
and therefore increase accuracy. The absolute uncertainty for each concentration were outlined
using error bars, as demonstrated in figure 4. All concentrations show considerably long error bars,
indicating the uncertainty of the data points are extremely high, and thus may be far from the
theoretical value. The longest error bars were present at 0.5M, spanning from approximately 0.94 to
-0.94g/s, which suggests that the accuracy of the data was extremely low. The shortest error bars
were present at 6M, spanning from approximately 0.17 to -0.17g/s, however compared to the
average rate values, as also seen in table 2, this still suggests extremely low accuracy of the data at
this concentration.
Significant overlap of the error bars is seen between all HCl concentrations, with the greatest
overlap present for 0.5M and 2M, overlapping from suggesting that the difference in reaction rate for
all concentrations, particularly between 0.5 and 2M were likely not statistically significant. However,
further statistical analysis would be required to justify this.
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EVALUATION
Limitation
Effect on reliability/validity
Suggested Improvement
The amount and density of
May have impacted the
Use of a reusable foam plug,
cotton wool used to plug the
amount of carbon dioxide
would ensure a consistent
neck of the beaker may have
product able to escape from
amount of product would be
changed for each trial, as the
the beaker for each trial, thus
able to escape the beaker.
investigation took place over
randomly impacting the
several days.
reliability of the experiment.
The hydrochloric
This reduced the validity as
concentrations were manually
the calculations for the volume solutions would ensure
diluted
were rounded to 2 decimal
utmost accuracy with
places – thus the volume for
concentration, thus reducing
each mixture may not have
systematic errors.
Use of pre-diluted HCl
been accurate, systematically
reducing the accuracy of the
molarity.
The high levels of absolute
uncertainty, along with the
extremely long error bars as
demonstrated in figure 4, are
indicative of extremely low
accuracy, potentially from this
limitation.
The mass for the scale used in
This impacts the reliability as
Ensure scales are calibrated
one of the trials kept
the scale fluctuations were
beforehand to ensure they are
fluctuating, suggesting that the
random, thus randomly
accurate. Additionally, using
reading was inaccurate and
impacts the reliability. Impacts
the same scale for each trial
inconsistent.
the validity as the scale
would ensure the scale masses
measurements did not reflect
recorded are more consistent,
the true mass
thus improving the precision.
This may have occurred for
trials with concentrations
0.5M and 3M as many
fluctuations were seen for
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these concentrations in the
data in figures 1 and 2.
As the trials were not
This would have affected the
conducted successively,
validity of the data, as the
external factors such as room
external factors may have
temperature were
impacted the mass loss
inconsistent.
simultaneously with the
independent variable.
This is demonstrated by the
outliers as seen in the raw
data for 0.5M at 20 seconds,
as whilst trial 1 and trial 3
experienced mass loss of 0.01g
and 0.03g respectively, trial 2
experienced a mass loss of
0.3g.
Suggested Extensions
-
-
Performing the experiment with HCl concentrations exceeding 6M to investigate whether
the trends identified in figure 3 will continue, or whether the reaction rate would plateau.
This extension would give a greater insight in the extent that the concentration of reactants
impacts reaction rate, and at what point does increasing the concentration no longer impact
reaction rate.
Redirecting the research question by changing the surface area of CaCO3 used. This
extension would explore whether different surface areas of CaCO3 would impact the rate of
reaction, and whether changing the surface area of CaCO3 would have a greater impact on
the rate of reaction than changing the HCl concentration.
CONCLUSION
In conclusion, the data strongly supports the hypothesis that changing the concentration of HCl
influences the reaction rate between CaCO3 and HCl. A positive linear trend was established
between increasing HCl concentration and the average reaction rate, with a total increase of
0.0024g/s from 0.25M to 6M. This data demonstrates that changing the concentration of HCl will
influence the reaction rate to a slight extent. Furthermore, the high R2 value of 0.9726 is indicative of
a strong correlation between the HCl concentration and average reaction rate. However, numerous
limitations are evident, such as the randomly fluctuating trends, and the extremely high absolute
uncertainty values, as shown by error bars, which was likely caused by the aforementioned random
and systematic errors. The methodology could be improved using the above stated improvements to
improve the reliability and validity of the data. Furthermore, the aforementioned extensions provide
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guidance on how the research question could be further developed, to gain a greater insight on the
topic.
Wordcount: 1991
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APPENDICES
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BIBLIOGRAPHY
Anderson, C., 2022. Reaction Rate between Marble Chips and Hydrochloric Acid
measured through mass loss, Brisbane: St Margaret's Anglican Girls School.
Anonymous, 2019. Chemical reactions. [online] Education.vic.gov.au. Available
at:
<https://www.education.vic.gov.au/school/teachers/teachingresources/disciplin
e/science/continuum/Pages/chemreactions.aspx> [Accessed 16 August 2022].
Dillon, S., 2017. The Rates of Chemical Reactions. [online] Chem.fsu.edu.
Available at:
<https://www.chem.fsu.edu/chemlab/chm1020c/Lecture%208/01.php>
[Accessed 17 August 2022].
Global Safety Management, 2015. Safety Data Sheet - Hydrochloric Acid, 6M.
[online] Geneseo.edu. Available at:
<https://www.geneseo.edu/sites/default/files/202203/6M%20Hydrochloric%20Acid%20SDS.pdf> [Accessed 20 August 2022].
Helmenstine, A., 2020. Factors That Affect Reaction Rate - Chemical Kinetics.
[online] Science Notes and Projects. Available at:
<https://sciencenotes.org/factors-that-affect-reaction-rate-chemical-kinetics/>
[Accessed 20 August 2022].
Key, J., 2019. Factors that Affect the Rate of Reactions. [online] Opentextbc.ca.
Available at: <https://opentextbc.ca/introductorychemistry/chapter/factorsthat-affect-the-rate-of-reactions/> [Accessed 12 August 2022].
Laidler, K., 2020. reaction rate | Facts & Formula. [online] Encyclopedia
Britannica. Available at: <https://www.britannica.com/science/reaction-rate>
[Accessed 14 August 2022].
Wu, S., 2022. HSC Chemistry – Collision Theory in Equilibria | Science Ready.
[online] Science Ready. Available at:
<https://scienceready.com.au/pages/collision-theory-in-equilibria> [Accessed
10 August 2022].
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