# What factors affect the rate of decay of a limestone castle?

A local town has a castle. The castle is built from Limestone (Calcium Carbonate). The castle has started to crumble. Some people have blamed the new damage on acid rain and have stated that the damage has increased as pollution has increased. Others blame Global warming and claim that the level of acid in the rain has stayed the same.

Choose ONE factor to investigate to find the reason for the decay of the castle.

The reaction is:

Calcium Carbonate + Nitric Acid ——–> Calcium Nitrate + Water + Carbon Dioxide

Intro

* I decided to investigate the affect that acid rain would have on the limestone, which the castle is built of.

* For this, I decided to do an experiment involving immersing limestone chips in different concentrations of acid.

Hypothesis

I think that the acid will dissolve the marble chips in the experiment that I am about to perform. As I change the independant variable, the rate at which the marble chips dissolve and how much they do in the given time will vary. I think that if the acid concentration is high, then the marble chips will dissolve faster. If the concentration of acid is low or if acid is not present, the marble chips will dissolve slowly. I also think that the reaction between the calcium carbonate (marble chips) and the nitric acid will omit carbon dioxide, as shown in the equation above. This will become apparent whilst doing the experiment. I think that we will be able to see how much carbon dioxide is let off in each component of the experiment, due to how each one reacts.

Apparatus

Marble chips

1 Molar of Nitric Acid

Water trough

100cm3 measuring cylinder

Stopwatch

Beehive jar

Gas jar

Thistle funnel

Water

Glass slide

Step-by-Step Plan

* My independent variable in these experiments will be the acid and its concentration, which I will vary using larger or smaller amounts of acid diluted with water for each component.

* The weight of the marble chips will remain the same.

* The volume of the water will remain the same.

* The marble chips and the acid will be put in a conical flask. This will have a bung in the top, with a thistle funnel inserted so that it will dip in the acid and water solution.

* The thistle funnel will have a cotton wool bud inserted, so that the water and/or acid will be prevented from bubbling up the tube.

* The conical flask will have a tube inserted in it, which will lead to the underneath of the beehive. This is the tube, which the gas will travel down.

* On the top of the beehive jar, where a hole is, is where the gas jar will stand. The gas jar will be filled with water.

* The beehive and the gas jar will stand in a trough filled with water.

* The amount by which the water disappears in the gas jar and goes down due to the gas carbon dioxide transferring to the jar will be monitored in each component of the experiments 1, 2 and 3.

* Throughout the experiments that I am doing, I will be wearing safety goggles to prevent any acid getting in contact with my eyes. Also, an overall will be worn to protect against any spillages.

Variables

For my experiments, I will have to keep some elements the same in order to make this a fair test. The weight of the marble chips will remain at 90 grams for each component of my experiments. The volume of acid and/or water will total at 40cm3 for each component of my experiments. The reaction of the marble chips in the acid will be timed for 2 minutes in each component of the experiments. The set up of the apparatus will be exactly the same for each component with no variations. I will follow these guidelines strictly to ensure the most accurate results as possible. I will do this by measuring the volume of the solution accurately, weighing the marble chips before I proceed with the experiment components and also making sure that my stopwatch is set correctly to 2 minutes before I continue with my experiments.

The only variable that I shall alter between each component is the concentration of water and acid.

Collecting Results

To collect my results, I am going to draw up a table. I am going to divide this table into categories, and do three separate ones for each experiment. I will put different headings on my tables listing the results for each component below. Here is an example of the categories I am using as headings in my tables below:

Vol of water (cm3) Vol of acid (cm3) Height of Jar (cm)

Water decreased in jar – level of CO2(cm) Difference (cm)

To collect my results, I will measure the side of the gas jar with a ruler to show how much the water has gone down by due to CO2 gas entering the jar in cm.

The range of the independent variable is (in cm3):

WATER: 0 – 10 – 20 – 30 – 40

ACID: 40 – 30 – 20 – 10 – 0

The independent variable is from 0 – 40 in both acid and water, as intervals of

10, 20 and 30 cm3 for each. They alternate in each experiment as shown above.

There are five components in each experiment. Therefore, I will be performing the task 5 times to make one single “experiment”, which there are three of in this investigation.

The Experiments

I will try and do my best to ensure as much accuracy as I possibly can throughout the components of experiments 1, 2 and 3. Repeating the experiments 3 times and comparing results ensures an accurate average, as does measuring and ensuring some variables exempt one are of the same value throughout. However, as much as I will try to do this, it is not possible for me to ensure complete and utter accuracy, and the measurements of fluids and marble chips from component to component are bound to vary mildly, which is out of my control as there is a limit to how accurate it is possible to be.

OBTAINING EVIDENCE

Results Tables

I have drawn up some results tables, one for each of the experiments I have done, of which there are three of altogether. Within each of the three experiments are five components.

EXPERIMENT 1

Component Water(cm3) Acid(cm3) Height of jar(cm) Water decreased

in jar – level of CO2(cm)

C.1 40 0 23 1.5

C.2 30 10 ” ” 2.8

C.3 20 20 ” ” 4.0

C.4 10 30 ” ” 5.0

C.5 0 40 ” ” 6.0

Difference(cm) (Difference = Height of jar – Water decreased in jar)

21.5

20.2

19.0

18.0

17.0

EXPERIMENT 2

Component Water(cm3) Acid(cm3) Height of jar(cm) Water decreased

in jar – level of CO2(cm)

C.1 40 0 23 2.0

C.2 30 10 ” ” 3.2

C.3 20 20 ” ” 4.3

C.4 10 30 ” ” 7.6

C.5 0 40 ” ” 8.4

Difference(cm) (Difference = Height of jar – Water decreased in jar)

21.0

19.8

18.7

15.4

14.6

These last results are taken from a colleague’s experiment. They performed the same experiment as I had done.

EXPERIMENT 3

Component Water(cm3) Acid(cm3) Height of jar(cm) Water decreased

in jar – level of CO2(cm)

C.1 40 0 23 1.5

C.2 30 10 ” ” 3.5

C.3 20 20 ” ” 5.5

C.4 10 30 ” ” 6.0

C.5 0 40 ” ” 9.5

Difference(cm) (Difference = Height of jar – Water decreased in jar)

20.5

19.5

17.5

17.0

13.5

AVERAGES FOR ALL THREE EXPERIMENTS (to 1 d.p):

1. 1.7

2. 3.2

3. 4.6

4. 6.2

5. 8.0

Each of the components in all 3 experiments were timed for 2 minutes. This meant that each had the same amount of time to react, making it a completely fair test.

The results are as I did expect. The stronger the acid, the greater amount of CO2 omitted and the stronger the reaction. The marble chips did indeed react with the acid, proving that acid rain must have had an impact on the deterioration of the limestone castle. The weaker, more diluted solutions with little acid did react with the marble chips, but it was not as strong a reaction as with the components using the stronger acid, and it did not omit as much carbon dioxide gas.

ANALYSIS

I have drawn up four graphs to show my results from this experiment. Three show the amount of water in cm that has decreased from the top of the gas jar. The latter shows the averages of the amount of water that has decreased from the top of the gas jar, in other words, the level of CO2.

These graphs can be seen separately on graph paper.

I have studied each graph carefully and have noted that they all have one thing in common with each other. They all have a steady gradient, and the results for each matching component (e.g. component 2 of all experiments 1, 2 and 3) are fairly different from each other. Studying my averages graph, the results are almost a perfect gradient on this, and there are no results that are far out from the trend or line of best fit.

My results fit in with my prediction well. I predicted in my hypothesis that the stronger the nitric acid solution, the more greater the reaction will be, and the more CO2 the calcium carbonate will give off. Looking at the graphs, this is apparent, as in Component 1, the solution is made up entirely of water and you can see that the water in the gas jar has decreased little. This means that little CO2 was given off, which means that the reaction between the marble chips and the acid was not great. However, in Component 5, where the solution is made up entirely of nitric acid with no dilution, there has been a great amount of CO2 given off, because the reaction was stronger. The reaction between the marble chips and the acid in C. 5 was the strongest reaction. This is clearly shown in the gradient of the graphs that I have drawn.

EVALUATION

Studying the graphs, there are no far out anomalous results. However, in Experiment 3, Component 4, the result for that one was slightly off the mark of the line of best fit. I did follow the experiments carefully and was always sure that I achieved the highest standards of accuracy that I possibly could.

Nearly all of the points on my graphs, exempt one, are extremely close to my line of best fit, especially on the averages graph, where some of them are dead on the line.

Results that are not near the line of best fit may be connected to the level of water in the gas jar. As the jar had to be filled up and tipped upside down with a slide preventing spillage, when the slide was released in the trough it may have been possible that a little of the water in the gas jar may have escaped. Therefore, the level of water was lower to start with, which may have contributed to the amount of cm’s that the water had dropped due to CO2 gas. They may also be linked to slipped standards of accuracy in my experiments, but I was almost fully sure that I performed them with my best precision.

I think that to improve the standards of the experiment and to increase the accuracy, each procedure of the experiment should be followed extremely carefully. The variables that should not be changed should be kept entirely equal, such as the timing of the reaction, the weight of the marble chips, the water in the gas jar and the amount of solution. The glass slide used to keep the water in the gas jar when tipped upside down should be released carefully, and only when the gas jar reaches the beehive in the trough should it be released.

To extend my investigation on the decay of the limestone castle, I could repeat the experiment many times over to achieve an even more accurate average. I could also investigate global warming harming the limestone castle, and compare the two types of experiments to see which one would be most detrimental to the limestone castle.