Hydrogen Bubbles Investigation.

In the 2nd diagram there hare twice the number of acid particles, which means twice the collisions with the magnesium, therefore more hydrogen is produced.

Apparatus

Use

Burette

Measuring the amount of hydrogen produced

Burette Holder

Holding the burette securely in place

Clamp Stand

To hold the burette holder and the burette

Plastic Trough

Filled with water to prevent hydrogen escaping

Stopwatch

To time the reaction

Measuring cylinder

To measure accurately the amounts of acid and water

Delivery tube

To carry the hydrogen into the burette

Thermometer

To ascertain the temperature every minute

Protective goggles

To protect eyes from being harmed by the reaction

Conical flask

To carry out the reaction

Ruler

To measure the length of the magnesium ribbon

Apparatus

Diagram

Method

. Firstly, I set up all the apparatus as shown above in the diagram.

2. Then I filled the burette to the top with water and turned it upside down in the trough of water, trying not to let any air inside the burette.

3. I then secured the burette in place using a burette holder and a clamp stand.

4. I placed a delivery tube up the burette, while placing the other end in a conical flank, held in by a bung. The conical flask is where the reaction will take place.

5. Following this, I prepared 25cm3 of 2 molar Hydrochloric acid and a 2cm piece of magnesium ribbon.

6. I double-checked that everything was prepared and made sure I had a stopwatch and a reliable results table to record my results.

7. Then I placed the magnesium ribbon and the 2M Hydrochloric acid into the conical flask, (in that order), began the stopwatch and recorded my results every 5 seconds.

My preliminary results are displayed below.

Concentration (M)

Volume of Hydrochloric Acid (cm3)

Time

Volume of Hydrogen (cm3)

Length of Magnesium

2

25

5

5

2

2

25

0

1

2

2

25

5

1

2

2

25

20

1

2

2

25

25

1

2

2

25

30

1

2

These results show me that using a 2cm piece of magnesium will produce a set of very unreliable results. These results below show that an 8cm piece of magnesium would be much more reliable as this is only with 0.5 Molar acid:

Volume of Hydrogen (cm3)

Time (seconds)

st attempt

2nd attempt

3rd attempt

Average

0

0

0

0

0

0

3

2

4

3

20

7

6

7

7

30

1

9

0

0

40

3.5

2

3

3

50

7

6

6

6

60

20

8

8

9

So, my preliminary results tell me that I would attain the best results using and 8cm piece of magnesium. I will be able to vary the concentration to see how the reaction speeds up and slows down.

All of my results are displayed on the next page. Each attempt displays the amount of Hydrochloric acid collected in cm3:

Results

0.50M

Volume of Hydrogen Collected (cm3)

Time(s)

st attempt

2nd attempt

3rd attempt

Average

0

0

0

0

0

0

3

2

4

3

20

7

6

7

7

30

1

9

0

0

40

3.5

2

3

3

50

7

6

6

6

60

20

8

8

9

0.75M

Volume of Hydrogen Collected (cm3)

Time(s)

st attempt

2nd attempt

3rd attempt

Average

0

0

0

0

0

0

9

7

8

8

20

7

5

5

6

30

24

22

23

23

40

30

29

28

29

50

36

37

33

35

60

42

43

41

42

.00M

Volume of Hydrogen Collected (cm3)

Time(s)

st attempt

2nd attempt

3rd attempt

Average

0

0

0

0

0

0

0

3

1

1

20

21

26

23

23

30

35

39

33

36

40

47

51

45

48

50

56

61

57

58

60

62

65

64

64

In a first attempt, the stronger acids of 1.25M and 1.5M used up the Magnesium quicker, proving difficult to measure every 10 seconds. I decided to measure every 5 seconds instead to increase the accuracy of my results.

.25M

Volume of Hydrogen Collected (cm3)

Time(s)

st attempt

2nd attempt

3rd attempt

Average

0

0

0

0

0

5

25

20

22

22

0

40

35

38

38

5

50

50

52

51

20

60

61

61

61

25

66

69

69

68

30

71

72

71

71

35

71

73

71

72

40

71

73

71

72

45

71

73

72

72

50

72

73

73

73

55

72

74

73

73

60

72

74

73

73

.50M

Volume of Hydrogen Collected (cm3)

Time(s)

st attempt

2nd attempt

3rd attempt

Average

0

0

0

0

0

5

29

28

30

29

0

50

52

51

51

5

65

67

66

66

20

73

72

74

73

25

76

75

77

75

30

79

78

79

79

35

78

80

79

79

40

80

82

80

80

45

81

84

82

82

50

82

84

83

83

55

82

85

83

83

60

83

85

83

84

Analysis

Judging by my results, when I increased the concentration of hydrochloric acid, the reaction went faster.

A more visual representation is included on my graph attached to this sheet of results. It displays a line for each of the 5 molarities. Also included on the graph is a gradient line, drawn on each molarity line. I can use this gradient line to work out the initial rate of the reaction. I have done this for each line to calculate the initial rate. Below is a table of the rate for each concentration. I will draw a graph of this also. The equation for working out the rate is y/x, where y = volume of HCL and x = time.

Rate of reaction = volume of hydrogen

time

Rate (cm3/s)

Concentration (M)

0.3

0.50

0.8

0.75

.1

.00

3.8

.25

5.1

.50

The reason for this pattern in my results is all to do with particles and collision theory, as I have previously mentioned.

In this diagram of 1M acid, there are 2 acid particles (H+ ions) and 2 water particles. Because of this, there is less chance of a reaction taking place between the acid and the magnesium. There will only be a few collisions.

25cm3 2M acid

In the diagram above there are now twice as many acid particles, so the chance of reaction is greater and there will be many more collisions.

My average result for 1M acid after 60 seconds is 64 seconds, which is considerably slower than my average result of 84 seconds for 2M acid after 60 seconds. Why this happened is all down to particle theory, explained above. This proves that higher molar acids have many more particles (H+ ions) that lower acid particles and this is why they react faster.

Evaluation

I think my experiments went as well as could be expected. I feel that I attained a high degree of accuracy when recording results. My results portray the effect of collision theory well and explain how higher molar acids react faster than lower molar acids.

I did not notice any anomalous results but on my graph 1.25M and 1.5M had a considerably larger initial rate that the other concentrations and if I carried this investigation on I would probably look into this further.

To improve my results yet further, a gas syringe could be used to collect the gas instead of a measuring cylinder. This would improve the accuracy of my results because less hydrogen can escape from the gas syringe as would in our experiment.

During class time, my teacher carried out an experiment analysing how concentration affects the speed of chemical reaction. He used calcium carbonate chips and various concentrations of HCL. The diagram and results are displayed below:

Concentration (M)

Time taken to fill tube with gas(s)

0.5

909

.0

258

.5

30

2.0

20

These results reinforce my results and prove that my collision theory is correct.