Hydrochloric Acid Concentration & Marble Chip Reaction Speed

I am going to see if changing the concentration of acid affects the speed at which it reacts with marble chips.

Marble chips + Hydrochloric acid ( Carbon dioxide + Water + Calcium chloride

CaCO3 + HCl ( CO2 + H2O + CaCl2

I will measure how much gas is given off by using a tally counter to count how many bubbles of gas are given off and measuring the volume of gas produced.

Diagram:

Apparatus:

5g medium marble chips

50ml HCl

2 measuring cylinders

Conical flask

Bung and plastic tubing

Tub of water

Clamp

Stopwatch

Tally Counter

Method:

* Set up apparatus as shown, minus the HCl.

* Add the HCl and make sure the bung is inserted as soon as all the HCl is in the flask. Also, make sure the stopwatch is started then, so that none of the reaction is missed.

* Start measuring the volume of gas, taking readings every 10 seconds. Start the tally counter after a minute so that all the air from the conical flask is expelled and not mistaken for CO2.

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* Take 8 readings and repeat the experiment twice so that you have 3 sets of readings. Use the average readings.

Fair Test:

I will keep the mass of marble chips the same in each experiment and I will use medium-sized marble chips so that the surface area does not affect the rate of reaction.

I will be measuring the volume of gas produced and also how many gas bubbles are given off.

Prediction:

I think that the higher the molar of HCl, the quicker the reaction will be.

I think this because there will be more HCl particles in the 2m than the 1m, for example, and so the HCl particles will be able to collide with the marble chips more and, therefore, react quicker.

Safety:

You must wear safety goggles when doing this experiment because acid is being used. This will burn and could blind you if it goes in your eyes. Make sure spillages are cleaned up immediately with the correct substance.

Results:

Time (secs)

1m

1.25m

1.5m

1.75m

2m

BB

V (cm?)

BB

V (cm?)

BB

V (cm?)

BB

V (cm?)

BB

V (cm?)

10

10

2

9

2

17

5

26

4

34

10

20

22

5

20

8

31

12

45

15

48

21

30

32

8

32

12

42

21

58

29

62

30

40

43

11

45

18

59

27

78

38

84

45

50

51

16

57

25

68

37

81

51

99

59

60

59

23

70

29

79

48

99

69

111

74

70

72

30

85

37

98

57

109

78

130

91

80

81

36

92

46

114

79

119

91

143

116

BB=No. of bubbles

V (cm?)=Volume of gas produced (cm?)

Analysis:

My results show that the higher the concentration of acid, the faster the reaction and so my prediction was correct. I can see this from my graphs because the higher the concentration of acid used, the steeper the curves were to describe the volume of gas or amount of bubbles produced. This is because there are more acid particles in the higher molar of acid and, therefore, they collide with the marble chips more and the reaction is quicker. On my graphs I drew the curves of best fit. For the volume of gas produced, most of the results stuck fairly close to the curve. The 1.75 molar results showed that more gas was produced than I would have thought because the plotted points weren't near the curve at all. For the amount of bubbles produced, none of the points were near the curve of best fit, especially the 1.75 molar results.

Evaluation:

I think that most of my experiment was accurate and the method was appropriate. Having said this, I think that something may have been wrong with the 1.75 molar acid because on both graphs the results are irregular. If I did this experiment again I would make sure that the acid was exactly what it was supposed to be. I think that I took enough readings because the averages were pretty much as expected and the graphs looked like I thought they would. I think that there should have been a holder in the end of the measuring cylinder because the plastic tubing kept moving around and it was difficult to get in. Having said this, I would have to make sure that the water could still come out, so a bung would be inappropriate.