Dianna Li
General Chemistry 4A
3-5-12
How does the concentration of hydrochloric acid affect the rate of reaction of
magnesium carbonate and hydrochloric acid?
INTRODUCTION
According to collision theory, for a chemical reaction to occur, there must be
collisions between the reacting molecules. Thus, it stands to reason that
increasing the concentration of an aqueous reactant will increase the frequency of
collisions between the reacting molecules, thereby increasing the rate of
reaction. The aim of this experiment is to discover whether this theory applies to
the reaction between hydrochloric acid and magnesium carbonate; that is, how
the concentration of hydrochloric acid affects the rate of reaction.
The reaction between hydrochloric acid and magnesium carbonate is as follows:
MgCO3 + 2HCl
–>
MgCl2 + H2O + CO2
Hypothesis:
The rate of reaction will increase as concentration of hydrochloric acid increases
because there are more molecules of hydrochloric acid to react with the
magnesium carbonate, which means the chance of molecules colliding and
reacting increases.
Variables:
Independent variable: Concentration of hydrochloric acid
Dependent variable: rate of reaction, calculated by measuring change in mass of
solution
Controlled variables: Mass and surface area of magnesium carbonate, mass of
hydrochloric acid, time recorded, temperature of solution, and environmental
settings
Materials:
- 0.1, 0.5, 1.0, and 2.0 mol/dm3 samples of hydrochloric acid; 150 mL
each (3 trials for each concentration)
- 50 mL graduated cylinder(s)
- 6 grams of magnesium carbonate; split into samples of 0.5 g each
- plastic weighing dish
- mortar and pestle
- 100 mL conical flask(s)
- electronic balance
- timer
- safety goggles
- apron
Procedures:
1. Put on safety goggles and apron.
2. Measure 50.0 mL of 0.1 mol/dm^3 hydrochloric acid into a graduated
cylinder. Pour the sample into a conical flask. Mass the flask and the acid.
3. With the magnesium carbonate powder, determine 0.5 grams of
magnesium carbonate. As the initial mass of the solution (carbonate + acid
+ flask), add together the mass of the flask (acid) and the mass of the piece
of carbonate.
4. Place the flask onto the electronic balance and prepare the timer.
5. Pour in the sample of magnesium carbonate and start the timer.
6. In intervals of 30 seconds, record the mass of the solution. Stop recording
at 5 minutes
7. Repeat steps 2-6 three times to get three trial readings.
8. Repeat steps 2-7 for each concentration (0.1, 0.5, 1.0, 2.0 mol/dm^3).
9. Calculate the average masses at each time interval of each trial (of the
same concentration) (see sample calculations).
10. Plot the average masses of each 30-second interval on a line graph (Time
vs. Mass).
11. Draw a curved trend line for the data and draw lines tangent to the curve at
30 seconds and 2 minutes.
12. Find the instantaneous rate of change of the mass at 30 seconds and 2
minutes (see sample calculations).
13. Repeat steps 9-12 for each concentration to get four different rates of
change.
14. Plot these four rates of change on a bar graph to visualize the effect of
concentration on the rate of reaction.
Procedure Explanation:
Measuring the change in mass of the solution in intervals lets us calculate the
amount of substance that has already reacted over time, and thus allows us to see
how the rate of reaction changes over certain time intervals for different
concentrations of hydrochloric acid.
DATA COLLECTION
Qualitative observations: magnesium carbonate has dull color, bubbles forming
at bottom of the flask (CO2), magnesium carbonate dissolving at top
Table 1.1: Data collection for 0.1 moldm-3 hydrochloric acid.
Time (s)
± 0.005
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
Trial 1
Mass (g)
± 0.001
145.697
145.691
145.689
145.686
145.686
145.685
145.684
145.684
145.683
145.683
145.682
145.682
145.681
145.681
145.681
145.680
145.680
145.680
145.679
145.679
145.679
Trial 2
Mass (g)
± 0.001
143.434
143.428
143.426
143.424
143.423
143.422
143.421
143.420
143.419
143.419
143.419
143.418
143.418
143.418
143.417
143.417
143.417
143.416
143.416
143.416
143.415
Trial 3
Mass (g)
± 0.001
143.614
143.609
143.606
143.604
143.602
143.600
143.599
143.597
143.595
143.594
143.593
143.592
143.591
143.590
143.589
143.588
143.588
143.587
143.586
143.585
143.584
Average
Mass (g)
± 0.001
144.248
144.243
144.240
144.238
144.237
144.236
144.235
144.234
144.232
144.232
144.231
144.231
144.230
144.230
144.229
144.228
144.228
144.228
144.227
144.227
144.226
Table 1.2: Data collection for 0.5 moldm-3 hydrochloric acid.
Time (s)
± 0.005
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
Trial 1
Mass (g)
± 0.001
146.130
146.102
146.082
146.078
146.076
146.074
146.073
146.071
146.070
146.069
146.068
146.067
146.066
146.065
146.064
146.064
146.063
146.063
146.062
146.062
146.061
Trial 2
Mass (g)
± 0.001
143.013
142.986
142.966
142.960
142.957
142.955
142.953
142.952
142.951
142.950
142.949
142.948
142.947
142.946
142.945
142.944
142.944
142.943
142.942
142.942
142.941
Trial 3
Mass (g)
± 0.001
143.306
143.272
143.257
143.252
143.249
143.246
143.243
143.242
143.240
143.238
143.236
143.235
143.234
143.233
143.232
143.231
143.230
143.229
143.228
143.228
143.227
Average
Mass (g) ±
0.001
144.150
144.120
144.102
144.100
144.094
144.092
144.090
144.088
144.087
144.086
144.084
144.083
144.082
144.081
144.080
144.080
144.079
144.078
144.077
144.077
144.076
Table 1.3: Data collection for 1.0 moldm-3 hydrochloric acid.
Time (s)
± 0.005
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
Trial 1
Mass (g)
± 0.001
146.772
146.743
146.724
146.716
146.712
146.710
146.708
146.706
146.705
146.704
146.703
146.702
146.701
146.700
146.699
146.698
146.697
146.696
146.695
146.695
146.694
Trial 2
Mass (g)
± 0.001
143.754
143.723
143.710
143.702
143.699
143.695
143.693
143.692
143.690
143.689
143.687
143.686
143.685
143.684
143.683
143.681
143.680
143.679
143.678
143.677
143.676
Trial 3
Mass (g)
± 0.001
143.725
143.691
143.680
143.674
143.670
143.667
143.664
143.662
143.660
143.658
143.657
143.655
143.654
143.652
143.651
143.650
143.649
143.647
143.646
143.645
143.644
Average
Mass (g)
± 0.001
144.750
144.719
144.705
144.697
144.694
144.691
144.688
144.687
144.685
144.684
144.682
144.681
144.680
144.679
144.678
144.676
144.675
144.674
144.673
144.672
144.671
Table 1.4: Data collection for 2.0 moldm-3 hydrochloric acid.
Time (s)
± 0.005
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
Trial 1
Mass (g)
± 0.001
146.627
146.563
146.554
146.552
146.550
146.548
146.547
146.546
146.545
146.543
146.542
146.540
146.539
146.538
146.537
146.536
146.535
146.534
146.533
146.532
146.531
Trial 2
Mass (g)
± 0.001
143.524
143.467
143.459
143.457
143.455
143.453
143.452
143.450
143.449
143.448
143.446
143.445
143.443
143.442
143.441
143.440
143.439
143.438
143.436
143.435
143.434
Trial 3
Mass (g)
± 0.001
143.179
143.121
143.109
143.107
143.105
143.103
143.102
143.101
143.100
143.098
143.096
143.095
143.093
143.092
143.091
143.090
143.089
143.088
143.087
143.086
143.085
Average
Mass (g)
± 0.001
144.443
144.384
144.374
144.372
144.370
144.368
144.367
144.366
144.365
144.363
144.361
144.360
144.358
144.357
144.356
144.355
144.354
144.353
144.352
144.351
144.350
Table 1.5: Compared averages for different concentrations of hydrochloric acid
0.1
0.5
1.0
2.0
moldm-3 moldm-3 moldm-3 moldm-3
Time (s)
± 0.005
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
Mass (g)
± 0.001
144.248
144.243
144.240
144.238
144.237
144.236
144.235
144.234
144.232
144.232
144.231
144.231
144.230
144.230
144.229
144.228
144.228
144.228
144.227
144.227
144.226
Mass (g)
± 0.001
144.150
144.120
144.102
144.100
144.094
144.092
144.090
144.088
144.087
144.086
144.084
144.083
144.082
144.081
144.080
144.080
144.079
144.078
144.077
144.077
144.076
Mass (g)
± 0.001
144.750
144.719
144.705
144.697
144.694
144.691
144.688
144.687
144.685
144.684
144.682
144.681
144.680
144.679
144.678
144.676
144.675
144.674
144.673
144.672
144.671
Mass (g)
± 0.001
144.443
144.384
144.374
144.372
144.370
144.368
144.367
144.366
144.365
144.363
144.361
144.360
144.358
144.357
144.356
144.355
144.354
144.353
144.352
144.351
144.350
Total Δg
0.022
0.074
0.079
0.093
DATA PROCESSING
Graph 1.1: Change in mass vs. time for reaction between 0.1 moldm-3
hydrochloric acid and magnesium carbonate
144.25
Mass of Flask + Solution (g)
144.245
144.24
144.235
144.23
144.225
0
50
100
150
Time (s)
200
250
300
Graph 1.2: Change in mass vs. time for reaction between 0.5 moldm-3
hydrochloric acid and magnesium carbonate
144.15
Mass of Flask + Solution (g)
144.14
144.13
144.12
144.11
144.1
144.09
144.08
144.07
0
50
100
150
200
Time (s)
250
300
350
Graph 1.3: Change in mass vs. time for reaction between 1.0 moldm-3
hydrochloric acid and magnesium carbonate
144.75
Mass of Flask + Solution (g)
144.74
144.73
144.72
144.71
144.7
144.69
144.68
144.67
0
50
100
150
Time (s)
200
250
300
Graph 1.4: Change in mass vs. time for reaction between 2.0 moldm-3
hydrochloric acid and magnesium carbonate
144.45
144.44
Mass of Flask + Solution (g)
144.43
144.42
144.41
144.4
144.39
144.38
144.37
144.36
144.35
144.34
0
50
100
150
Time (s)
200
250
300
Graph 2: Comparison in instantaneous rates of change for different
concentrations of hydrochloric acid at 30 seconds
0
Rate of Reaction (g/s)
-0.0001
-0.0002
-0.0003
-0.0004
-0.0005
-0.0006
Concentration (mol/dm3)
Graph 3: Comparison in instantaneous rates of change for different
concentrations of hydrochloric acid at 2 minutes
0
Rate of Reaction (mol/dm3)
-0.00001
-0.00002
-0.00003
-0.00004
-0.00005
-0.00006
-0.00007
-0.00008
-0.00009
Concentration (mol/dm3)
Note: In the case of this experiment, the lower the numerical value for the rate of
reaction, the faster the reaction was, because we were measuring the loss of
mass. Thus, a higher negative value would mean a higher rate of reaction.
Table 2: Comparisons of rates of reaction at 30 and 120 seconds for different
concentrations (rates of reaction: g/s)
0.1 moldm- 0.5 moldm- 1.0 moldm- 2.0 moldmTime (s)
30
120
3
3
3
3
-0.000157
-0.0000286
-0.000571
-0.0000387
-0.000571
-0.00008
-0.00045
-0.0000313
CALCULATIONS
To find the instantaneous rate of reaction at a certain time interval, draw a tangent
line to the graph at that point, and calculate the slope.
Averaging trials: (Trial 1 + Trial 2 + Trial 3)/3
Sample: 2.0 moldm-3 hydrochloric acid at 0 seconds
(146.627 + 143.524 + 143.179)/3
slope =
Example: 0.1 moldm-3 hydrochloric acid at 30 seconds
g/s
CONCLUSION:
The aim of the experiment was not achieved, and according to this experiment,
our hypothesis was incorrect. However, although the data we found suggests that
the collision theory does not apply to the reaction between magnesium carbonate
and hydrochloric acid, the experiment had a gaping fault too severe for us to
make such a statement (see evaluation). According to the results, the rate of
reaction was highest (higher negative value for rate of reaction means faster
reaction rate) for 1.0 moldm-3 hydrochloric acid at both 30 and 120 seconds.
There seems to be a correlation between the higher concentration and higher
reaction rate, with the exception of the results of the 2.0 moldm-3 hydrochloric
acid, which was lower than both 0.5 and 1.0 moldm-3 acid.
EVALUATION:
We expected a positive correlation between concentration and rate of reaction,
and this was generally reflected in our results, with the exception of the results
for the 2.0 moldm-3 hydrochloric acid. Quantitatively, the reaction rate of the 2.0
moldm-3 hydrochloric acid at both time intervals was much lower than that of the
0.5 and 1.0 moldm-3 acid. This may have been because the 2.0 moldm-3 acid
reacted so fast with the magnesium carbonate that by 30 seconds there wasn’t
enough to keep reacting. If we had calculated the initial rates of reaction, it may
have produced more accurate results. If we assume this theory, then the collision
theory still applies. If we were to redo this experiment, we would use lower
concentrations of hydrochloric acid, with smaller concentration differences, for
example, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 moldm-3. This would probably provide results
that more accurately follow the collision theory.