Investigate how the rate of reaction changes with the surface area.

Fair Test:

To keep this experiment a fair test you must keep the weight of the marble chippings the same each time you do the experiment. Keep the same amount of hydrochloric acid each time. Make sure you change your hydrochloric acid and marble chippings in your second experiment, because your old one may be contaminated.

Prediction:

I think that the rate of reaction will speed up when the surface area increases. I think this because the surface area also affects the rate of the physical and chemical change. Surface area has to do with the number of exposed surfaces available for physical or chemical changes to take place. Look at the pictures below.

Does the sugar cube have more or less surface area than the group of sugar crystals? Of course the sugar crystals have more surface area. Each surface of each crystal is exposed. In the sugar cube many of the sugar crystals are not exposed until the outer crystals on the cube have dissolved. So the rate of physical or chemical change will be faster with the group of sugar crystals due to increased surface area.

A catalyst is a substance that can cause a change in the rate of a chemical reaction without itself being consumed in the reaction; the changing of the reaction rate by use of a catalyst is called catalysis. Substances that increase the rate of reaction are called positive catalysts or, simply, catalyst, while substances that decrease the rate of reaction are called negative catalysts or inhibitors. Catalysts are important in industry because they can speed up reactions even at low temperatures. A catalyst can save money because less fuel is used.

Concentration - If there is more of a substance in a system there is a higher chance that molecules will collide and speed up the rate of the reaction. If there is less of something... there will be fewer collisions and the reaction will probably happen at a slower speed.

Temperature - When you raise the temperature of a system the molecules bounce around a lot more (because they have more energy). When they bounce around more they are more likely to collide. That means they are also more likely to combine. When you lower the temperature the molecules are slower and collide less. That temperature drop lowers the rate of the reaction.

Pressure - Pressure affects the rate of reaction especially when you look at gases. When you increase the pressure the molecules have less space to move around. That greater concentration makes them collide with each other more often. When you decrease the pressure molecules don't hit each other as much and there are fewer collisions. That lower pressure lowers the rate of reaction.

All this information is relevant to my investigation, as I now know what would happen to the molecules when using different variables.

Obtaining Results:

I set up the apparatus as shown in the plan. I took the precautions to wear goggles because I was handling acid. I followed the steps I had laid out in the plan with the changes that I made after the preliminary work. I was careful not to start timing as I poured in the acid. This is because the gas released wouldn't be produced by reaction but the displacement of air by the acid.

To keep the experiment a fair one, I had to keep all the variables apart from temperature the same. The variables were:

Amount of materials used

Surface area of marble chips

I made sure I used the same mass of marble chips each time and the same volume of hydrochloric acid too. To keep the surface area of the marble chips the same, I made sure all the marble chips I used were large therefore I had a similar surface area.

I only did this experiment once.

Time (seconds)

Carbon dioxide produced (cm?)

small surface area

Carbon dioxide produced (cm?) large surface area

0

6

7

20

6

6

30

2

20

40

5

26

50

9

33

60

21

41

70

25

50

80

29

59

90

33

67

00

36

76

10

40

85

20

44

92

30

47

00

40

52

n/a

50

55

n/a

60

59

n/a

70

64

n/a

80

66

n/a

90

71

n/a

200

74

n/a

210

77

n/a

220

83

n/a

230

85

n/a

240

89

n/a

250

92

n/a

260

97

n/a

270

00

n/a

Analysis:

I used the results obtained to plot a graph of the time it took to fill 100cm? of carbon dioxide in the gas syringe. The graph shows that the larger the surface area the faster the reaction takes place. In my prediction I said that the larger the surface area the faster the reaction happens. When I mixed hydrochloric acid with marble chippings each surface of each crystal is exposed. But with the larger piece of marble many of the crystals are not exposed until the outer crystals on the marble have dissolved. This fits in my hypothesis too.

The graph shows that the line is steeper for the larger surface area.

I conclude that as the surface area is larger the rate of chemical reaction increases.

Graph on graph paper.

Evaluation:

In my opinion the investigation went OK. I think I did take the sufficient amount of reading but of course it would have helped if I had another set of results and made an average to be more accurate... I had a few anomalous results these may have been because the conical flask could have got shaken, which would have speeded up the reaction but I have circled the anomalous results on my graph. These can be explained by simply a poor reading.

If I had to do the investigation again I would do the experiment several times and set and average for more accurate results.

There are many possible extensions to this experiment. I could try to use other carbonates and react them with hydrochloric acid. I could try different acids also and see what happens. All these could help me broaden my knowledge on rates of reaction.