Chemistry IA
January 2022
How does changing the concentration of hydrochloric acid
affect the rate of reaction of the chemical reaction between
magnesium and hydrochloric acid as measured by the
production of hydrogen gas?
Research Question
How does changing the concentration of hydrochloric acid, in the selected range of 2.00
mol/dm3, 1.50 mol/dm3, 1.00 mol/dm3, 0.75 mol/dm3, 0.50 mol/dm3, affect the rate of reaction
of the chemical reaction between magnesium and hydrochloric acid as measured by the
production of hydrogen gas?
Scientific Context
When analysing chemical reactions, chemists often observe the rate of reaction. The rate of
reaction is defined as the rate of change of the concentration of the reactants or products per
unit time. Rate of reaction is a useful tool to control the rate at which a product is produced,
therefore the rate of a reaction can be observed and analysed in order to get the highest
yield of a chemical reaction and gain as much product as possible. When two particles react,
as explained in the Collision Theory, they collide with each other and, by breaking the
intermolecular bonds, they create new ones with other particles. In order for a reaction to
take place, there must be successful collisions between the particles of the reactants categorised as such if there is enough energy to break the intermolecular bonds and the
proper orientation between particles. There are different factors that influence the probability
of a successful collision occurring, affecting the rate at which they happen. One of these
factors, the one selected to be investigated in this experiment, is the concentration of either
of the reactants.
Figure 1: graphic portraying how increasing the concentration impacts the number of
collisions
Hypothesis
The rate of reaction can be predicted to increase as the concentration of the hydrochloric
acid is increased. This is due to the increase of the number of HCl particles, in a set volume,
that are available to make successful collisions with the magnesium ribbon. As more
particles are present in a constant volume, they are also closer together allowing for more
frequent collisions and a higher probability of a successful collision. The increase of both of
these aspects infers an increase in the rate of reaction as the products are formed more
rapidly. The rate of reaction can be expected to be directly proportional to the concentration
of hydrochloric acid.
Choice of Reaction
As I was deciding which field to explore for the investigation, I was keen on choosing
something which had to do with chemical kinetics which is a very interesting field that allows
for extensive analysis of the data gained through a simple experiment. I choose to
investigate the following reaction:
Mg(s) + 2HCl(l) → MgCl2 (aq) + H2 (g)
as it combines my interest in chemistry with the one of biology. MgCl2 is often used in
dietary supplements to higher the intake of magnesium into the body, and I take one myself
to prevent migraines. Magnesium is part of many metabolic reactions in the body and it is of
great interest to pharmaceutical companies to gain the highest possible yield in the optimum
conditions as to make the supplements with the least amount of wastage. The factors, like
concentration, that impact collisions between particles can be modified to reach a higher
yield.
Variables:
o Independent variable
The concentration of HCl will be changed using the values 2.00 mol/L, 1.50 mol/L,
1.00 mol/L, 0.75 mol/L, 0.50 mol/L. Original planning of the experiment programmed
a decrease of half in between each concentration, but as the results were
inconclusive due to the lack of completion of the reaction and product produced, the
concentration range chosen changed to values closer to each other.
o Dependent variable
The rate of reaction will be measured by observing the time it takes for magnesium to
react with hydrochloric acid to produce 50 mL of hydrogen gas. As the concentrations
of hydrochloric acid are very low, not all reactions are able to create enough product
to fill the glass syringe. 50 cm3 was chosen consequentially to some trial repeats as
the optimal measurement of gas produced. The rate of reaction will then be
calculated using stoichiometric relationships and with the following formula:
𝑟𝑎𝑡𝑒 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 =
∆ 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
∆ 𝑡𝑖𝑚𝑒
.
o Controlled variables
CV#
Controlled
Variable
How it was controlled
Why it was controlled
CV1
Temperature
All solutions and reactions
were done and kept at room
temperature
Changing the temperature
impacts how the energy is
distributed between the
molecules, therefore affecting
the rate of reaction
CV2
Mass of Mg
The amount of magnesium
was kept constant
throughout the experiment
Changing the mass of
magnesium means changing
the concentration, therefore
changing the amount of
particles involved in the
reaction, affecting the rate of
raction
CV3
Surface area of
Mg
The length and amount of
pieces of magnesium was
Changing the surface area
impacts the number of
kept constant throughout
the experiment
molecules exposed to the
hydrochloric acid, therefore
affecting the rate of reaction
CV4
Volume of HCl
solution
The volume was measured
with the same method and
kept constant throughout
the experiment
The ratio between the
hydrochloric acid and
magnesium molecules would
change, therefore affecting the
rate of reaction
CV5
Solvent
Distilled water was used to
make all solutions
throughout the experiment
Different solvents might have
different chemical properties,
possibly impacting the result of
the reaction and reaction rate
CV6
Pressure
The experiment was
conducted at room pressure
By changing the pressure the
collision rate between particles
is changed therefore impacting
the rate of reaction
CV7
Presence of a
catalyst
No catalyst was added in
any reaction in the
experiment
Catalysts lower the activation
energy of a chemical reaction
and therefore speeding up the
rate of reaction
Equipment and apparatus
● Pipette
● Measuring cylinder (100.00±0.5 mL, 25.00±0.25 mL)
● Glass syringe (100±0.5 cm3)
● Beaker (50.0±7.5 mL, 100±12.5 mL, 250±25 mL)
● Test tubes
● Conical flask (125±12.5mL)
● Stand with a clamp
● Rubber cork for test tubes and conical flask
● Magnesium (Mg) ribbon
● Hydrochloric acid (HCl) (2.00 mol/dm3, 1.50 mol/dm3, 1.00 mol/dm3, 0.75 mol/dm3,
0.50 mol/dm3)
● Ruler (15.00±0.05cm)
● Stop clock (5999.99±0.01”)
● Scissors
Figure 2: Glass syringe system connected to conical flask
Method
1. The glass syringe was topped with a rubber cork, attached to a silicone tube that
ends with another cork in order to create a closed system in order to avoid loss of
product in the environment
2. The glass syringe was set up in the clamp on the stand and regulated so that the
values on the syringe were easily readable at eye level
3. The hydrochloric acid solution was prepared in a measuring cylinder of 100mL
4. For the solutions that needed to be diluted, the appropriate ratio was chosen and the
hydrochloric solution was diluted in distilled water (eg. starting with a 2 mol/L
concentration in order to prepare a 1.5 mol/L concentration, the ratio needed is 3:1,
diluting 75 mL of HCl solution in 25 mL of distilled water)
5. The solution was then poured into a separate beaker and stirred to avoid a
concentration gradient inside the beaker
6. 25mL of the solution was measured in a measuring cylinder using a pipette (CV5) at
eye level and then poured into a testing tube
7. 2 pieces measuring 2cm of the magnesium ribbon were cut (CV3, CV4) with a pair of
scissors
8. The solution was then poured into the conical flask
9. The magnesium was then added to the solution in the conical flask to start the
reaction and the flask was immediately closed with the cork connected to the glass
syringe
10. At the same time as closing the conical flask, the start clock was started
11. Observing the glass flask the start clock was stopped once the volume reached 50
mL of hydrogen gas formed
12. Once the volume has been reached the time was recorded and the glass syringe is
emptied
13. The conical flask was then emptied into a beaker
14. The conical flask was then rinsed with water
15. The procedure was repeated 4 times for each concentration (2.00 mol/dm3, 1.50
mol/dm3, 1.00 mol/dm3, 0.75 mol/dm3, 0.50 mol/dm3)
Safety precautions
Source
Danger
Precautions
Magnesium ribbon
Flammable
The magnesium ribbon was kept away
from any source of fire and kept in a
protected environment when the needed
amount was taken. Only small quantities
of the metal were used in the experiment.
Hydrochloric acid
Corrosive
Safety goggles were worn at all times
throughout the experiment. Only low
concentrations and small volumes of the
acid were handled. All equipment was
thoroughly washed before touching it with
exposed skin.
Hydrogen gas
Flammable
The gas was released from the glass
syringe away from any source of fire and
any leftover reaction was placed in a fume
cupboard so that the gas was not
dispersed unsupervised. Only small
volumes of hydrogen gas were produced.
Other
Assistance was used in steps 9 and 10 to
avoid any spillage of the acid on the
working table.
Raw Data
Table 1: Time that is taken each trial for the reaction to produce 50 mL of hydrogen gas
Time (s) ±0.01 s
Experiment
number
Concentration of HCl
(mol/dm3)
T1
T2
T3
T4
1
2.00
14.09
13.79
13.23
12.97
2
1.50
18.17
18.76
17.74
17.76
3
1.00
50.85
61.89
51.87
50.85
4
0.75
132.48
95.94
93.19
86.83
5
0.50
357.68
347.01
314.80
370.96
Processing Data
In order to identify anomalies in the data set standard deviation was used. If the data was
identified to be outside 2 standard deviations from the mean, then the value would be
rejected from further calculations.
Table 2: Mean and standard deviations of each experimental data set and the accepted
range of values
Experimental
data set
Mean (s)
2 standard
deviations (s)
Accepted range of values (s)
1
13.52
±1.02
12.50 ≤ 𝑥 ≤ 14.54
2
18.11
±0.95
17.15 ≤ 𝑥 ≤ 19.07
3
53.87
±10.74
43.13 ≤ 𝑥 ≤ 64.61
4
102.11
±41.21
60.90 ≤ 𝑥 ≤ 143.32
5
347.61
±47.94
299.67 ≤ 𝑥 ≤ 395.55
With the method, no anomalies can be identified following the method as they are all
included in the accepted range and all values are kept for calculations and further analysis of
the data.
Table 3: Average time taken for the reaction to produce 50 mL of hydrogen gas for each
concentration of hydrochloric acid used with respective standard deviations
Average time (s)
Experiment
Number
Concentration of HCl
(mol/dm3)
±0.10 mol/dm3
Value
Standard
deviation
1
2.00
13.52
± 0.51
2
1.50
18.11
± 0.48
3
1.00
53.87
± 5.37
4
0.75
102.11
± 20.60
5
0.50
347.61
± 23.97
Calculation example for the average time:
● Divide the sum of the values by 4
𝑥𝑎𝑣𝑔 =
Σ𝑥
4
Uncertainty of the average time
● Calculated with the standard deviation
Analysis
Table 4: Average time taken for the reaction to produce 50 mL of hydrogen gas for each
concentration of hydrochloric acid used with calculated hydrogen gas concentration with
respective uncertainties
Experiment
Number
Concentration
of HCl
(mol/dm3)
Concentration of H2
produced (mol/dm3)
± mol/dm3
Time (s)
value
uncertainty
value
uncertainty
1
2.00
13.52
± 0.51
0.50
±7.07×10-3
2
1.50
18.11
± 0.48
0.38
±6.25×10-3
3
1.00
53.87
± 5.37
0.25
±5.60×10-3
4
0.75
102.11
± 20.60
0.19
±5.34×10-3
5
0.50
347.61
± 23.97
0.13
±5.16×10-3
Calculations to find the concentration of hydrogen produced (exemplified with data from
experiment 1)
Mg(s) + 2HCl(l) → MgCl2 (aq) + H2 (g)
●
Calculate the moles of HCl by multiplying the concentration and the volumes used in
the experiment (consider the change in units of the volume from cm3 to dm3) and the
affiliated uncertainty
−3
Eg. moles of HCl 2. 00 𝑚𝑜𝑙 𝑑𝑚
3
× 0. 025 𝑑𝑚 = 0. 05 𝑚𝑜𝑙
●
Calculate the moles of H2 by dividing the moles of HCl by two as observed from the
stoichiometric ratio of 1:2 between the two and the affiliated uncertainty
Eg. moles of H2 =
●
0.05 𝑚𝑜𝑙
2
= 0. 025 𝑚𝑜𝑙
Calculate the concentration of H2 by dividing the moles by the volume of H2 measured
(consider the change in units of the volume from cm3 to dm3) and the affiliated
uncertainty
0.025 𝑚𝑜𝑙
Eg. concentration of H2 =
3
0.05 𝑑𝑚
−3
= 0. 50 𝑚𝑜𝑙 𝑑𝑚
Propagation of uncertainty
● For the first two calculations for the concentration of hydrogen, the only uncertainty
that is propagated it the one of the volume measurement of the hydrochloric acid
−4
●
3
solution in the measuring cylinder (±0. 25 𝑚𝐿 = ±2. 5 × 10 𝑑𝑚 )
For the calculation of the concentration from the moles of hydrogen and the volume,
the following formula is used
2
2
( ) ( )
𝑥
∆𝑥
∆𝑦
∆𝑧 = || 𝑦 ||
+ 𝑦
𝑥
Where ∆𝑧 is the uncertainty of the result, ∆𝑥 and ∆𝑦 are respectively the uncertainties
of the moles of hydrogen gas and the volume of hydrogen gas
Eg. from experiment 1
0.025
∆𝑧 = || 0.05 ||
(
−4
2.5×10
0.025
2
) (
+
−4
5×10
0.05
2
)
−3
−3
= ± 7. 07 × 10 𝑚𝑜𝑙 𝑑𝑚
Table 5: concentration of hydrochloric acid and the corresponding rate of reaction of each
experiment when 50 cm3 of hydrogen gas was produced
Experiment
Number
Concentration of HCl
(mol/dm3)
1
Rate of Reaction (mol/dm3s)
value
uncertainty
2.00
3.70×10-2
1.49×10-3
2
1.50
2.10×10-2
6.55×10-4
3
1.00
4.64×10-3
4.74×10-4
4
0.75
1.86×10-3
3.79×10-4
5
0.50
3.74×10-4
2.98×10-5
Calculations to find the Rate of Reaction
● To calculate the Rate of Reaction the following formula was used
𝑟𝑎𝑡𝑒 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 =
●
∆ 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛
∆ 𝑡𝑖𝑚𝑒
The two points considered were the initial time (at 0.00 s) and the initial concentration
of hydrogen gas (0.00 mol/dm3) and the time it took for the reaction to produce 50
dm3 of hydrogen gas. As the change started from two values of 0, the rate of reaction
was calculated by simply dividing the concentration of hydrogen gas by the average
time.
Eg. from experiment 1
0.50
13.52
𝑟𝑎𝑡𝑒 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 =
−2
−3
= 3. 70 × 10 𝑚𝑜𝑙 𝑑𝑚
Propagation of uncertainty
● The uncertainty for each value was calculated using the same formula previously
used
2
2
( ) ( )
𝑥
∆𝑥
∆𝑦
∆𝑧 = || 𝑦 ||
+ 𝑦
𝑥
Where ∆𝑧 is the uncertainty of the result, ∆𝑥 and ∆𝑦 are respectively the uncertainties
of the concentration of hydrogen gas and the average time
Eg. from experiment 1
0.50
∆𝑧 = || 13.52 ||
(
−3
7.07×10
0.50
2
)
+
(
0.51 2
13.52
)
−3
= 1. 49 × 10
−3 −1
𝑚𝑜𝑙 𝑑𝑚 𝑠
Graph 1; Graph of the concentration of hydrochloric acid against the rate of reaction
The trend is shown in the graph shows a linear relationship between the concentration of
hydrochloric and the rate of reactions, as one increases the other also increases.
Further observations can be made as the graph allows to determine the overall order of the
reaction. From the line of best fit shown in the graph, the reaction is likely to be of first order.
The R2 value is exactly 1, which indicates a strong positive correlation between the
concentration of hydrochloric acid and the rate of reaction.
The positive correlation is also observed as there are no points that lie outside of the line of
best fit, indicating that the data is quite precise.
Conclusion
As predicted in the hypothesis, the increase of the concentration of hydrochloric acid
caused an increase in the rate of reaction as the amount of particles increases in the set
volume (25 mL). There is a difference of 0.037 between the rates of reaction of the lowest
and highest concentration, this shows clearly an increase in the rate of reaction and the
graph successfully represents the reaction with a strong positive correlation with each other.
The rate of reaction is directly proportional to the concentration of hydrochloric acid in the
reaction with a linear relationship.
Limitations and improvements
Limitations
Improvement
Not all reactions were completed when 50
mL of hydrogen gas were produced. This
makes the rate of reaction comparison less
precise
Conduct more trials to observe the
maximum volume of hydrogen produced.
Only one point of reference was taken into
consideration.
Measure the time at different volumes, or
measure the volume formed at chosen time
intervals.
For safety, only very low concentrations
were used, allowing for only minimal
change in the rate of reaction and making it
more susceptible to r.
Under safe conditions, use higher
concentrations of hydrochloric acid, to
observe greater change.
The stop clock was manually stopped after
the volume reached 50 mL. Especially for
faster reactions, the time of reaction of the
person stopping is limited, making the
accuracy of the time reading limited.
The reaction could have been recorded
showing the glass syringe and stop clock to
then record more accurate data.
The temperature of the solution was not
measured with a thermometer every time
the reaction was carried out but it was kept
at room temperature implying that the room
was at constant 25ºC.
To accurately keep the temperature
constant, a water bath measured at 25ºC
could have been kept and the temperature
could have been measured every time the
experiment was to be carried out.
Although with 2 standard deviations, no
anomalies were identified, there were
values in the experiments that were outside
of the general trend.
- Experiment 1, trial 4 (12.97);
experiment 3, trial 1 (61.89),
experiment 4, trial 1 (​​132.48)
experiment 5, trial 4 (370.96)
These values might have impacted the final
result of the investigation.
In order to have more accurate data, more
trials should have been carried out to have
more viable data to substitute the data that
does not follow the general trend.
The glass syringe apparatus is not a
completely closed system and does not
assure that no amount of gas is dispersed
Assuring the glass syringe is fully empty
and all corks are tightly secured to the ends
of the syringe before beginning the
in the environment. Any uncontrolled
amount of gas dispersed alters the
accuracy of the reading and the results.
experiment.
Extensions
Possible extensions of this experiment could include
● Manipulating the mass of magnesium; this would be done by changing the amount of
magnesium ribbon that is added to the HCl solution.
● Manipulating the surface area of magnesium; this would be done by changing the
number of separate pieces the magnesium ribbon is cut in.
● Manipulating the temperature the reaction takes place in; this would be done by
heating or cooling down the HCl solution.
All these extensions would observe how different factors affect the rate of reaction. In the
case of the manipulation of the mass of magnesium, it could be added as an extension to
the previous data carried out to find the rate equation and the order in respect of
magnesium. This would allow understanding of how the concentration of each reactant
impacts the rate of reaction.
Bibliography
A Gas Syringe Connected by a Rubber Tubing or Glass Tube ...
https://www.researchgate.net/figure/Figure-1-A-gas-syringe-connected-by-a-rubber-tub
ing-or-glass-tube-to-the-flask_fig1_313662163.
Libretexts. “2.5: Reaction Rate.” Chemistry LibreTexts, Libretexts, 11 Sept. 2020,
https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textboo
k_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Kinetics/02%
3A_Reaction_Rates/2.05%3A_Reaction_Rate.
Mott, Vallerie. “Introduction to Chemistry.” Lumen,
https://courses.lumenlearning.com/introchem/chapter/the-collision-theory/.
Spritzler, Franziska. “10 Evidence-Based Health Benefits of Magnesium.” Healthline,
Healthline Media, 3 Sept. 2018,
https://www.healthline.com/nutrition/10-proven-magnesium-benefits.