An investigation to find out how the concentration of acid affects the rate of the reaction between HCl and CaCO3

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An investigation to find out how the concentration of acid affects the rate of the reaction between HCl and CaCO3

Skill Area P: Planning Experimental Procedures

Introduction and Preliminary Work

I am attempting to find out what affect the concentration of hydrochloric acid has on the rate of the reaction between HCl and marble chips (calcium carbonate). The equation of this reaction is as follows:

CaCO3 (s) + 2HCl (aq) --> CO2 (g) + CaCl2 (aq) + H2O (l)

calcium + hydrochloric--> carbon + calcium + water

carbonate acid dioxide chloride

There are many factors which can affect the rate of a reaction. The temperature of the acid will have an impact on how quickly a reaction occurs. I carried out a preliminary experiment on the affect of temperature as the variable, by using water baths and thermometers to obtain four different water temperatures in which the flask containing acid and marble chips was placed. I used four different water temperatures from 20°C to 50°C, going up in 10°C each time. I carried out two tests for each temperature, and noted the change in mass every minute for ten minutes as the chips dissolved, and I took an average of the two sets of results. I found that, the higher the temperature of the water bath, the faster the reaction happened. This was because, as the kinetic theory explains, a high temperature gives the particles of the reactants more energy to move (and react) faster. I am not choosing to use this factor in my current investigation because it was quite difficult to obtain accurate results, as the water baths didn't always maintain the correct temperature. This caused a few errors in my results.

I also did a preliminary experiment in the same way on the effect of the size of the calcium carbonate chips on the rate of the reaction. This was an experiment that proved that the larger the surface area of the chips (i.e. the small sized marble chips), the faster the reaction took place. The mass decreased faster with a large surface area because the acid particles met the particles of the marble chips more often, causing an increased rate of reaction. I chose not to carry out an improved version of this experiment because there is only a small range of sizes of chips that I could have used, which are small, medium and large. This decreases the accuracy of results because the range of surface areas is fairly small, and the large chips, for example, could vary slightly in actual size.

I have chosen to do an investigation on the concentration of acid because I can use a good range of concentrations - five different acid concentrations ranging from 0.1 molar to 2 molar. This will increase the accuracy of my results. I have also done extensive preliminary work on this particular factor. I used only three concentrations of hydrochloric acid, so I will make my work better this time by investigating five. Here are the results from my previous experiment:

0.5M concentration:

Time (minutes)

Mass (grams)

st Test

2nd Test

Average

0

2

3

4

5

6

7

8

9

0

29.73

29.69

29.65

29.63

29.62

29.61

29.61

29.60

29.60

29.60

29.60

29.03

28.97

28.92

28.91

28.89

28.88

28.88

28.87

28.87

28.86

28.86

29.38

29.33

29.29

29.27

29.26

29.25

29.25

29.24

29.24

29.23

29.23

Average total decrease in mass over 10 minutes = 0.15g

M concentration:

Time (minutes)

Mass (grams)

st Test

2nd Test

Average

0

2

3

4

5

6

7

8

9
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0

28.50

28.40

28.40

28.40

28.40

28.40

28.40

28.30

28.30

28.20

28.20

30.00

29.90

29.90

29.80

29.80

29.80

29.80

29.70

29.70

29.70

29.60

29.25

29.15

29.15

29.10

29.10

29.10

29.10

29.00

29.00

28.95

28.90

Average total decrease in mass = 0.35g

2M concentration:

Time (minutes)

Mass (grams)

st Test

2nd Test

Average

0

2

3
...

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