To find the effects of change of the variable on a reaction between Magnesium and Hydrochloric acid
Aim: To find the effects of change of the variable on a reaction between Magnesium and Hydrochloric acid
Reactions occur when Hydrochloric acid particles collide with the Magnesium. They all work by increasing the number of Magnesium collisions. There are a number of factors that change the speed of a reaction:
* Temperature
* Concentration of Hydrochloric acid
* Surface area
* Addition of a catalyst
To make a choice for this experiment we have to choose which is the most feesable in the circumstances.
Temperature: Temperature will affect the rate of reaction because an increase will speed up the movement of the Particles so that they collide more frequently. However, it is not a good option in the circumstances because the required amount of variations is 5, and using an icebox, room temperature and heating (we would not be able to keep different levels of heat constant) gives us only three variations. In addition, the reaction between a metal and an acid is exothermic, so the temperature of the experiment would not be the same half way through as at the beginning.
Surface area: Increasing the surface area of the magnesium would increase its amount of exposure to the Hydrochloric acid at one time, therefore increasing the rate of reaction. However, it is quite difficult to measure the surface area accurately enough to say that one specimen is exactly double (i.e.) the surface area of another
Catalyst: There is no substance that can speed up the rate of reaction whilst staying separate from Magnesium and Hydrochloric acid.
Concentration: You can accurately measure the concentration of an acid in Molars (M). If you increase the concentration of the Hydrochloric acid, then the rate of reaction is increased, proportionally.
I am going to use a total of six concentrations:
* 0.0 Molars
* 0.5 Molars
* 0.75 Molars
* 1.0 Molar
* 1.5 Molars
* 2.0 Molars
I will use for each a solution of water (neutral), and Hydrochloric acid (2 M). This is the table to show how the different strengths were achieved:
Concentration achieved (M)
Amount of water (ml)(%of sol)
Amount of HCl (ml)(%of sol)
0.0
50 (100%)
0 (0%)
0.5
37.5 (75%)
2.5 (25%)
0.75
31.25 (66.5%)
8.75 (33.5%)
.0
25 (50%)
25 (50%)
.5
8.75 (25%)
37.5 (75%)
2.0
0 (0%)
50 (100%)
To make this simpler: in the 0.75M, I used an 80ml test tube to make the soloution 5/8 Hydrochloric Acid and 3/8 Water, then poured 50ml of it into a test tube, so the results above are the precise (although not the ones we used) amounts needed to achieve these concentrations
Graph Prediction:
Rate
Y=X
Concentration
Because an increase in concentration is proportional to ...
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8.75 (33.5%)
.0
25 (50%)
25 (50%)
.5
8.75 (25%)
37.5 (75%)
2.0
0 (0%)
50 (100%)
To make this simpler: in the 0.75M, I used an 80ml test tube to make the soloution 5/8 Hydrochloric Acid and 3/8 Water, then poured 50ml of it into a test tube, so the results above are the precise (although not the ones we used) amounts needed to achieve these concentrations
Graph Prediction:
Rate
Y=X
Concentration
Because an increase in concentration is proportional to an increase in rate, I predict that the graph will show a linear result. Eventually there will be an optimum rate, where the line becomes horizontal, although not in the duration of this experiment.
Measure of rate: Mg(s) + 2HCl(aq) MgCl +H
2 2
Magnesium + Hydrochloric = Magnesium Chloride+ Hydrogen
Acid
To decide what the method of measuring the rate will be, we have to look at the products of the experiments:
Magnesium Chloride: You can measure what speed the Magnesium 'disappears' in the flask as it turns into Magnesium Chloride. This would mean weighing a piece of Magnesium and then leaving it for a specific amount of time and finding the difference. However, this would leave you with only one result and you could not make it accurate by studying its progress.
Hydrogen: You could measure the amount of Hydrogen produced in two ways:
. You could measure the declining weight of the flask, which would be very difficult and very inaccurate because hydrogen weighs so little.
2. You can show the volume of Hydrogen produced, visibly using a gas syringe, which would be quite accurate.
I am going to choose to use the gas syringe, as the results will be clearer and more accurate.
Preliminary work:
I decided to do some preliminary work to determine what balance of acid and metal will give the most workable result (i.e is not to fast, does not go off the scale).
Amount of acid (M)
Amount of Magnesium (cm)
Time till syringe stopped moving (secs)
00
6
5
50
6
0
25
6
20
50
7
5
50
7.5
0
50
8
5
We chose to use 8 cms of Magnesium and 50 ml of Hydrochloric acid, because this was the one that gave us the best opportunity to record more results as it produced more Hydrogen than the others, but didn't go off the scale on the gas syringe and wasn't too fast.
Fair test: To make this experiment fair, we need to consider these factors: Although we are not using the other variables as a measure in this experiment, they are still present and can affect the result considerably. Heat needs to be kept constant, and the surface area of the Magnesium strip and the concentration of the Hydrochloric acid need to be the same each time the experiment is repeated. The Magnesium is the same thickness and is cut from the same cross-section to insure that the level of impurity (if any) is always the same.
Safety: To make the experiment safe, we will use goggles, and will only use instruments that could not be corroded by the substances used.
Diagram:
Results:
Experiment 1: 0.0 molars, 50ml Hydrochloric acid, 80mm Magnesium,
Time (seconds)
Volume of Hydrogen produced (cm3)
Average of 2 and 3
Experiment6.1
Experiment6.2
Experiment6.3
30
3
6
6
6
Experiment 2: 0.5 molars, 50ml Hydrochloric acid, 80mm Magnesium,
Time (seconds)
Volume of Hydrogen produced (cm3)
Average of 1 and 2
Experiment 5.1
Experiment 5.2
0
0
0
0
30
1
2
2
60
22
20
21
90
30
29
30
20
37
35
36
50
44
44
44
80
50
50
50
210
57
57
57
240
62
63
63
270
67
67
67
300
72
72
72
330
76
75
76
360
80
77
79
390
83
81
82
Time
(seconds)
Volume of Hydrogen produced (cm3)
Average of 1&4
Experiment4.1
Experiment4.2
Experiment4.3
Experiment4.4
0
0
0
0
0
0
3
3
4
3
3
3
6
5
5
6
6
6
9
6
7
8
8
7
2
8
9
1
9
9
5
1
1
4
1
1
8
2
3
7
3
3
21
5
7
21
5
5
24
7
20
24
6
7
27
9
22
27
20
20
30
21
24
30
22
22
33
23
25
33
25
24
36
25
27
36
27
26
39
27
30
40
29
28
42
29
32
44
32
31
45
31
34
48
34
33
48
33
36
50
36
35
51
35
39
53
38
37
54
37
42
56
40
39
57
40
44
58
41
41
60
41
47
61
44
43
63
43
49
64
47
46
66
46
50
67
49
48
69
48
52
68
51
50
72
49
54
70
54
53
75
51
57
73
55
53
78
53
59
74
57
55
81
55
61
76
60
58
84
57
63
79
63
58
87
63
64
80
64
65
90
67
65
81
66
65
93
63
67
83
67
65
96
65
69
83
68
67
99
67
70
83
70
69
02
68
71
83
71
70
05
69
72
83
72
71
08
70
74
83
73
72
11
72
75
83
75
74
14
73
76
83
76
75
17
74
77
83
77
76
20
75
78
83
78
77
23
76
79
83
79
77
26
77
82
83
80
79
29
78
84
83
81
80
32
79
84
83
82
81
Experiment 3: 0.75 molars,
Experiment 4: 1 molar, 50ml Hydrochloric acid, 80mm Magnesium,
Time
(seconds)
Volume of Hydrogen produced (cm3)
Average of 2 and 3
Experiment3.1
Experiment3.2
Experiment 3.4
Experiment3.4
0
0
0
0
0
0
3
4
4
5
6
5
6
5
8
0
0
9
9
6
0
3
5
2
2
9
2
20
23
6
5
2
5
23
29
9
8
5
27
31
34
29
21
9
30
36
39
33
24
22
35
40
47
38
27
25
40
45
52
43
30
29
44
50
57
47
33
32
49
55
63
52
36
37
50
60
67
55
39
40
55
62
71
59
42
42
59
65
77
62
45
45
63
67
81
65
48
50
66
69
83
68
51
54
70
75
83
73
54
56
71
76
83
74
57
61
73
76
83
75
60
65
76
76
83
76
63
67
79
76
83
78
66
70
80
76
83
78
69
75
81
76
83
79
72
78
81
76
83
79
75
80
81
76
83
79
78
82
81
76
83
79
81
83
81
76
83
79
84
85
81
76
83
79
Experiment 5: 1.5 molars, 50ml Hydrochloric acid, 80mm Magnesium
Time
(seconds)
Volume of Hydrochloric acid produced (cm3)
Average of 2 and 3
Experiment2.1
Experiment2.2
Experiment2.3
Experiment2.4
0
0
0
0
0
0
3
0
0
0
8
0
6
22
25
23
22
24
9
35
35
34
35
35
2
48
50
46
43
48
5
62
62
63
62
63
8
72
69
72
71
71.5
21
81
84
83
79
83.5
24
81
84
84
85
84
Experiment 6: 2 molars, 50ml Hydrochloric acid, 80mm Magnesium
Time (seconds)
Volume of Hydrogen produced (cm3 )
Average of 2 and 3
Experiment1.1
Experiment1.2
Experiment1.3
Experiment1.4
0
0
0
0
0
0
3
20
30
20
20
20
6
40
43
40
50
41.5
9
45
70
70
65
70
2
58
83
82
83
82.5
Rate of reaction table based on these results:
Concentration (M)
Rate of reaction (cm3 /sec)
0
0
0.5
0.5
0.75
.0
.7
.5
3.8
2
6.3
Evaluation:
Diffuculties in method: At the beginning of each experiment, there was a short time between the Magnesium being put into the Hydrochloric Acid and the securing of the bung on the top of the conical flask, when some of the Hydrogen escaped.
Difficulties in measurements: Due to the speed of the reaction, it was very difficult to take accurate readings at the agreed intervals, so sometimes we were a bit late recording our results, causing some of the results not to fit exactly on the curve.
We measured the length of Magnesium to one millimetre, but that still prouduces quite a substantial ammount in leway, as it is quite possible to have produced up to approximately 5mm3 extra each time. It is the same when measuring the Hydrochloric acid, because we used measuring cylinders of approx 1cm radius, so even the smallest error in measurement can make quite a lot of difference to the result of the experiment.
Keeping things constant through the results and during the experiment
Temperature: We recorded different results on different days, which means that the temperature is variable throughout the course of our experiments. The temperature effected each experiment, and as we did not record the temperature on each day, it is impossible to tell how much difference it made to the overall picture.
Result reliability: Many anomoulous results were produced. The ones recorded here are significantly out of line with the others.
Experiment 1: the first point was not anomolous, but the gradient of the line from 0-60 seconds is vastly different from 60 onwards, so it is not counted.
Experiment 2: (390,82)
Experiment 3: (86.5,65), (90,65)
Experiment 4: (6,9), (9,12), (12,16), (15,19)
Experiment 5: none
Experiment 6: (12, 82.5)
Conclusion:
The final graph shows my prediction was correct in some aspects but not others. It is true (as shown in the graph) that as the concentration increases the rate of reaction increases. However the line is not y=x but a smooth curve with no anomoulous results, so it is not proportional.
Conclusion verification
To corroborate my conclusion I could experiment with different methods of recording the results and investigate the properties of the substances used to suggest why the rate of increase is not proportional.