* Thermometer (to take the temperature of the room before do each concentration.)
* Weighing scales (to weigh out marble chips).
Method
I am going to change the concentration of the hydrochloric acid to test which concentration is the best. I am going to use the range of 0.25M-2.00M with 0.5M, 1.0M and 1.5M in-between.
I will keep the surface area of the marble chips the same, ( to my best ability, I will keep them around the same size e.g. I will not use marble powder and then use marble chips.) the mass of the marble chips used the same, the temperature of the marble chips, the acid and the room the same and the amount of hydrochloric acid used the same.
I am going to measure the quantity/volume of gas released in five minutes. I will take a reading of how much gas has been released every thirty seconds, as I believe this will show the differences of gas released from start to finish between all concentrations.
To Keep My Investigation Safe:-
I will wear protective glasses incase any acid is splattered. I will also wash my hands after I have touched the hydrochloric acid so that it does not irritate my skin and so I cannot rub it into my eyes.
To Keep My Investigation Fair:-
I will do all of the things that I said I will keep the same in my method. I will repeat the experiments three times and then work out an average, as I believe that this will give me accurate readings and point out an odd results e.g. if after 1 minute on the 0.25M I got 2cm, 2.2cm and 5cm then 5cm would be odd as the other two are close together, so I will not count the 5cm I will take the average from the other two results.
Prediction
I predict that the 2.0 molar acid will have the quickest reaction time and the 0.25 molar will have the slowest reaction time I believe this because the stronger the concentration the more acid molecules there are, so there is a more likely chance of a collision compared to a weaker concentration of acid where there are less acid molecules therefore there is less chance of a collision. I believe that the other concentrations will go in order of highest concentration fastest time, lowest concentration slowest time. So it will go(best-worst time) 1.5, 1, 0.5( See collision theory for a more detailed explanation.)
Preliminary Results
Results To Show The Amount of Gas Given Off In 5 Minutes
Concentration
Volume of gas produced(cm )
of acid(M)
Time(minutes)
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0.5
8
46
58
66
70
75
78
80
82
83
1
15
57
65
74
85
92
101
112
115
115
1.5
22
67
85
90
120
135
147
150
155
156
2
41
106
166
196
213
225
237
245
248
249
My preliminary results show that 0.5M will give the least amount of gas of in 5 minutes and 2M will give the most gas off in 5 minutes. These have given me an idea of what my results for my main experiment will be like. These results also support my prediction and I believe that the collision theory is quite accurate even though it is only a theory as it gives a very good explanation of what should happen and it has happened in my experiment. I am going to include 0.25M in my main experiment as I believe that this will give a better range of results and also increase the accuracy of my results. I will keep the amount of time the same as I believe it was the best amount of time to get an accurate reading. I will do my main experiment results to one decimal place as I believe that this will give me the most precise results. When reading the amount of gas in the cylinder I will take any number that is whole e.g. 14 to be 14.0. To improve my reliability I will repeat each concentration three times as I believe this will give me a reliable average.
Results Table
Results To Show How Much Gas Is Given Off In 5 Minutes
Volume of Gas Collected (cm )
Time in minutes
Test
Concentration
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Number
of acid(M)
Test 1
0.25
12
14
16
25
27
29
30
33
36
38
Test 2
0.25
11
12
15
26
29
34
44
54
56
62
Test 3
0.25
10
11
12
16
23
27
36
42
48
53
Average
0.25
11
12.3
14.3
25.5
26.3
30
33
37.5
46.6
57.5
Test 1
0.5
37
60
78
92
100
101
110
120
127
135
Test 2
0.5
16
40
54
88
107
105
108
118
121
123
Test 3
0.5
12
50
71
84
99
105
118.5
129
138
146
Average
0.5
14
50
69
88
102
103.6
112.1
123.3
128.6
134.6
Test 1
1
9
24.5
47.2
70
91
107
123
137
144
155
Test 2
1
10
22
48.5
70
85.6
110
130
136
140
145
Test 3
1
8
18
50
82
90.2
111
135
141
142
149
Average
1
9
21.5
48.6
74
88.9
109.3
129.3
138
142
149.6
Test 1
1.5
20.5
60.7
105
141
174
210
237
260
283
303
Test 2
1.5
20.2
61
101
141
175
211
239
263
286
306
Test 3
1.5
24
67
105
141
174
210
237
260
283
304
Average
1.5
21.6
62.9
103.6
141
174.3
210.3
237.6
261
284
304.3
Test 1
2
93
193
264
346
435
497
519
563
599
637
Test 2
2
90
200
256
360
431
495
520
568
604
626
Test 3
2
99
198
270
350
450
496
529
571
600
619
Average
2
96
197
263.3
352
433
486
522.6
567.3
601
627.3
Any number highlighted are not counted in the average as I believe that the are either to high, to low or do not fit into the pattern.
Result that I believe is causing the results for this time to be inaccurate.( see level of confidence) I will not include this result in my new average.
I have found out that 2M is the best strength of hydrochloric acid to use when you want a fast reaction, as it released the most gas in 5 minutes compared to 0.5M, 1M and 1.5M.
I can make the statement the stronger/higher molar(M) the acid the faster the reaction and the weaker/lower molar(M) the acid the slower the reaction.
Conclusion
I conclude 2M is the best concentration of acid. You can see this on my graph, my graph shows that 2M is the best concentration of acid out of all the ones that I tested as it had the quickest reaction time compared to all of the other concentrations. You can see this from the graph as 2M has got the steepest slope.
I believe that the activation energy (see background information for detailed explanation) has effected my results. I believe that the concentration of the acid makes it easier for the particles to react. But what does this have to do with the activation energy? Each molecule has a certain amount of energy and for the molecule to react it must collide with another molecule. It must also generate more energy that it already has. In a low concentrated solution, there are less molecules so it hard for a molecule to find other molecules to collide with, but in a high concentrated solution collisions are more frequent and even if the molecule does not collide with enough energy to react it will soon hit another molecule and have a high possibility of reacting.
I predicted that the 2.0 molar acid would have the quickest reaction time and the 0.25 molar would have the slowest reaction time I also said that the other concentrations would go in order of their concentrations, the higher the concentration the more gas there will be released and the lower the concentration the less gas there will be released. I believe my predictions were accurate as I based them on the collision theory and even though it is a theory I believe it is an accurate theory and explains what is believed to happen when reactions take place very well.
0.5M and 1M start off wrong in my opinion as until 3 minutes 0.5M had released more gas where as I believe according to the collision theory 1M should have released more gas and reacted faster, but in the end 1M released more gas. This also happened in the first 30 seconds of the 0.25M where it also released more gas than the 1M. This leads me to believe that the 1M may have been the wrong concentration. It is because of this reason I am going to work out the confidence levels for my results. I will take 0 as 100% accurate and 100 as 0% accurate.
Level Of Confidence
I am going to work out the inaccuracy of my results I will do this by doing the sum
Range multiplied by 100= level of inaccuracy
Average
I have chosen to do the inaccuracy of time 0.5, 1.5, 2.5, 3.5 and 4.5 as I believe that I can get a good reading of how inaccurate my results are by doing a selected number of times.
Time
Concentration
Range of gas
Average Amount of
Times
Equals
(minutes)
of acid(M)
released(cm )
gas released(cm )
100
0.5
0.25
12 10
11
x 100
18.1
1.5
0.25
16 12
14.3
x 100
27.9
2.5
0.25
29-23
26.3
x 100
22.8
3.5
0.25
36-30
33
x 100
18.1
4.5
0.25
56-36
46.6
x 100
42.9
I am going to look at
0.5
0.5
16 12
14
x 100
28.6
my results table and
1.5
0.5
78-54
69
x 100
28.9
highlight the result
2.5
0.5
107-99
102
x 100
7.8
that I believe is too
3.5
0.5
118.5-108
112.1
x 100
9.3
high or too low. I will
4.5
0.5
138-121
128.6
x 100
13.2
then redo this sum
0.5
1
10 8
9
x 100
22.2
not including the
1.5
1
50-47.2
48.6
x 100
5.8
highlighted number.
2.5
1
91-85.6
88.9
x 100
6
3.5
1
135-123
129.3
x 100
9.2
4.5
1
144-140
142
x 100
2.8
0.5
1.5
24-20.4
21.6
x 100
16.6
1.5
1.5
105-101
103.6
x 100
3.9
2.5
1.5
175-174
174.3
x 100
0.6
3.5
1.5
239-237
237.6
x 100
0.8
4.5
1.5
286-283
284
x 100
1
0.5
2
99-93
96
x 100
6.3
1.5
2
270-256
263.3
x 100
5.3
2.5
2
435-431
433
x 100
0.9
3.5
2
529-519
522.6
x 100
1.9
4.5
2
637-619
627.3
x 100
2.8
Level of confidence for sum that I believed was inaccurate I have now changed the range of the gas released at 4.5 minutes.
4.5
0.25
56-48
52
x 100
15.3
This inaccuracy level is a lot lower than the other one. This means that that volume of gas
released was to low, many things could have caused this .e.g. the temperature of the room
could have been lower than when I did the other two experiments.
Evaluation
I believe my results are quite accurate and would be considered reliable as non of my results have a high inaccuracy level or have a 50% chance of being wrong. I have highlighted the results that I believe are wrong on my results table and have not included them in my averages. On my graph my points go up in curves or in some sort of curve. I have joined all of the point on my graph together but on some of my curves I have done a curve of best fit, I have done this because it will show me if any results are slightly wrong. If you look at the green curve for 0.5M you will see that the points at 2 and 2.5 minutes look slightly to high, the curve of best fit shows where the points should have been.
The trend I see from the graph is that the higher the concentration of the hydrochloric acid the steeper the slop of the graph is. I believe that the way in which I carried out my experiment was good as I followed my method exactly. To improve the accuracy of my method I could have said I would use a bulb pipette or a graduate pipette as these are more accurate than a measuring cylinder, I could make sure that the marble chips all have the same surface area because the marble chips with the bigger surface areas could have reacted more than the marble chips with the smaller surface areas. I could have also make sure that the room was the same temperature for each experiment because if the room was hot for one experiment and cold for another then the results would be inaccurate as the molecules would have been moving and reacting at different speeds.
The results I have support my conclusion and my prediction, as what I predicted would happen did happen. The order of the concentrations for the most gas released in 5 minutes was also accurate, as it was in the order that I predicted.
To extend my investigation I could test if the temperature had any effect on the amount of gas released, I believe this would provide me with the relevant information about what the optimum temperature is for a reaction to take place. I could then test the optimum concentration and the optimum temperature together and see how much gas is released in 5 minutes and compare it to the separate results of the concentration and temperature.
