Acid Rain Case

Acid Rain is rain, snow or fog that is polluted by acid in the atmosphere and damages the environment. When fossil fuels are burned they release mostly CO2, but they also release two harmful gases, sulphur dioxide and various nitrogen oxides. The sulphur dioxide, SO2, comes from the sulphur impurities in the fossil fuels. However, the nitrogen oxides are created from a reaction between the nitrogen and the oxygen in the air, caused by the heat of the burning. When these gases mix with clouds they form dilute sulphuric acid and dilute nitric acid. This then falls as acid rain. Cars and power stations are the main causes of Acid Rain.

Acid Rain has effects on plants, soil and even buildings. The acid reacts with the limestone and then the limestone begins to erode.

From previous knowledge, I know that limestone has the chemical formula CaCO3. Limestone, chalk and marble are all calcium carbonate. When an acid reacts with a metal carbonate (such as calcium carbonate) the fizzing shows that a gas is produced. That gas is carbon dioxide, CO2. Adding hydrochloric acid to a rock sample is one of the tests for a carbonate rock, like marble, chalk or limestone. It is also why these rocks are greatly affected by acid rain.

The word equation is for this reaction between calcium carbonate and hydrochloric acid is:

Calcium carbonate + hydrochloric acid –> calcium chloride + carbon dioxide + water

The chemical formulae for this reaction between calcium carbonate and hydrochloric acid is:

CaCO? + 2HCL –> CaCL2 + CO2 + H2O

The rate of reaction can be calculated by measuring amount of Carbon dioxide gas that is obtained by the syringe.

There were various types of apparatus which I included:

Goggles Syringe Stop clock Measuring cylinder Spatula

Hydrochloric Acid Marble-Powder and Chip Boiling tube Bung

Preliminary experiment.

Before actually beginning my investigation, I will firstly carry out a preliminary investigation. This will help me to see the improvements that I can make after the experiment. I will be able to see possible downfalls and failures in my method, work out appropriate quantities of chemicals to use and generally improve the quality of the final experiment.

Below is the set up apparatus that I will use for the preliminary experiment and the actual experiment:

The preliminary experiment is performed so that I can predict the volume of acid, the mass of the chip and powder and the length of time that I will be timing for.

1. Firstly, I set up the apparatus.

2. I will specify a curtain mass of marble using a balance and I will place it into the boiling tube.

3. Then, I will measure a quantity of acid and quickly add it to the boiling tube whilst after quickly placing the bung onto the top of the tube.

4. I will record the amount of CO2 gas which is given off, every curtain amount of time. This will produce a rate of reaction.

For many experiments the rate of reaction can be changed by altering curtain variables. For this reaction there is no catalyst, therefore we cannot alter this variable. However there are three main variables that could be changed:

Temperature of the acid – this would be varied by starting off with the acid at room temperature (around 24 C) and then using acid with temperatures of 30 C, 40 C and 50 C.

Concentration of the acid – the concentration would be varied three times, using hydrochloric acid with concentrations of 0.5M, 1M and 2M.

Surface area of the calcium carbonate – the surface area would be varied by using different sizes of calcium carbonate.

I will predict that the 2m acid and the powder will be the fastest reaction as the acid is more compact with acid particles in the same volume of water. This helps more successful collisions take place between the particles. The more collisions there are the increased rate of reaction.

I found out that I should use 1 gram of mass for the chip and powder marble and 30cm of acid. This is because the reaction is not too fast or slow. I can get an acceptable number of results recorded. I will be using three different concentrations of acid, 0.5m, 1m and 2m.(m=molar) The time I will be using will be starting at when the syringe starts to move up to 180 seconds.

I will be keeping the amount of acid the same and the mass of the marble so that I conduct a fair test. The temperature was kept at 24C-25C.

Results

0.5m with chip 0.5m with powder

Mass of chip = 1.0g Mass of powder = 1.0g

Time (s)

Volume (cm)

10

2

20

4

30

5

40

6

50

7

60

8

70

9

80

16

90

17

100

18

110

20

120

21

130

22

140

24

150

25

160

26

170

27

180

31

Volume of acid = 30cm Volume of acid = 30cm

Time (s)

Volume (cm)

10

14

20

17

30

19

40

20

50

22

60

23

70

23

80

25

90

29

100

34

110

35

120

37

130

38

140

38

150

38

160

39

170

40

180

40

1 m with chip 1 m with powder

Mass of chip = 1.0g Mass of powder = 1.0g

Volume of acid = 30cm Volume of acid = 30cm

Time (s)

Volume (cm)

10

21

20

30

30

36

40

38

50

39

60

31

70

42

80

43

90

43

10

44

110

44

120

44

130

44

140

44

150

44

160

44

170

44

180

44

Time (s)

Volume (cm)

10

4

20

5

30

6

40

9

50

12

60

15

70

18

80

21

90

24

10

27

110

31

120

34

130

37

140

40

150

44

160

47

170

50

180

52

2 m with chip 2 m with powder

Mass of chip = 1.0g Mass of powder = 1.0g

Volume of acid = 30cm Volume of acid = 30cm

Time (s)

Volume (cm)

10

5

20

9

30

13

40

16

50

22

60

26

70

33

80

36

90

46

10

46

110

46

120

51

130

54

140

57

150

57

160

57

170

57

180

57

Time (s)

Volume (cm)

10

0-60

20

“

30

“

40

“

50

“

60

“

70

“

80

“

90

“

10

“

110

“

120

“

130

“

140

“

150

“

160

“

170

“

180

“

Conclusion.

After completing my experiment my results show me that as the concentration of the acid is increased, the reaction takes place faster and more gas is produced in a shorter space of time. Due to this I found that the 2M hydrochloric acid (the strongest concentration of acid I used) produced the most gas in the shortest time. The 0.5M hydrochloric acid (the weakest concentration of acid I used) produced the least amount of gas in the longest time period.

I can clearly see from the graph that the 2M hydrochloric acid gave the fastest reaction and produced the most gas in the shortest space of time, because the gradient of the curve is the steepest and goes far higher than the other curves showing that a larger amount of gas was produced because the ‘gas produced’ axis is the ‘y’ axis. The fact that the 2M acid had the steepest curve shows that the reaction was fastest because a large amount of gas was produced (high on the y axis) and in a short space of time (short on the x axis). This will give a steep gradient on the graph.

The 0.5M hydrochloric acid gave almost the opposite curve when the results were placed on a graph. Not much gas was produced in a long space of time and so the slope was very gentle and low on the graph.

The 2M hydrochloric acid produced the most gas in the shortest amount of time and was generally a quicker reaction due to its significant difference in particle arrangement compared to the 0.5M and 1M hydrochloric acid. The more concentrated 2M hydrochloric acid has more acid particles in the same volume compared to the 1M and 0.5M acid. This means there are more available acid particles to react with the calcium carbonate. The reaction will be quicker when using the 2M acid because there are more particles available to react with. The calcium carbonate particles can react with more acid particles quickly as they are easily accessible, whereas in the 0.5M acid, there are few acid particles in a volume and so some calcium carbonate particles will have no acid particles to react with, causing the reaction to be slow and uneventful.

All reactions will only occur if there is enough energy to make it happen. This minimum energy is known as activation energy. Activation energy is the minimum energy for which two reacting particles must collide for a reaction to take place. When particles collide they slow down, stop, and then fly apart again. This will occur regardless of whether they have enough energy to react. In an unsuccessful collision the particles separate unchanged, but in an effective collision the activation energy barrier is crossed and the particles that separate are chemically different from those that came together.

I think my results are definitely sufficient to support my prediction. They equal everything I predicted and I am very pleased at how well they turned out.

Evaluation

I think that the experiment went very well. All my results matched my prediction and everything went ‘according to plan’. The gas produced by each acid had a steady increase however; there were a few rogue points. Overall I achieved what I set out to do.

I would have liked more time on the experiment to make sure everything was perfect, though. Due to the short time limit we were quite rushed in completing the experiment.

There were a few aspects of the experiment that could have been improved to make the experiment even more accurate. For a start the experiment was undertaken over a few days. Each day had a different temperature and so this would have affected the results. If one day had been hotter than the others the heat would have influenced one reaction to take place faster. Also due to the fact that the experiment lasted a few days, different equipment was being used each day. Some gas syringes were slightly stiffer than others and so wouldn’t move out as fast. If on one day you had a very stiff gas syringe that wouldn’t move very easily and on another day you had a very loose gas syringe, then the results would be very different as the loose gas syringe would give results that say that the reaction happened very fast and the stiff gas syringe would give results that say the reaction was slow. To prevent this from happening the experiment should have been undertaken and finished on the same day, using exactly the same equipment as you started with for each acid.

The initial part of the reaction when the acid first reacts with the calcium carbonate is very fast. A lot of gas is produced at the beginning of the reaction. However the way the apparatus are set up means that when you pour the acid onto the calcium carbonate, there are a few seconds when the gas is able to escape before the gas syringe is connected to the test tube. To avoid this from happening a test tube containing the calcium carbonate should be placed inside a beaker containing the hydrochloric acid. They must not be touching, as the reaction would then start. Then the gas syringe will be connected to the beaker. When the reaction is ready to start, the beaker is knocked so that the test tube falls over, consequently causing the reaction to take place as the acid and carbonate would mix. Then when the initial gas is produced it will all be ‘caught’ as the gas syringe is already in place.

The surface area of the calcium carbonate should also have been kept equal. The same number of equally weighted chips should have been used. E.g. all 1g chips. This way the reaction is fair and accurate, as a large surface area will cause the reaction to take place faster. Keeping all the surface areas the same would have kept the experiment fair. However to do this would have taken a long time and we only had a limited amount of time.

Another way of keeping the temperature the same would have been to do the experiment in a water bath. This would have allowed us to do the experiment over a few days as well.