Investigation into how concentration of hydrochloric acid affects the rate of reaction with marble chips.

To test our aim I will use different concentrates of hydrochloric acid and add it to the marble chips. I will use 25cm³ of hydrochloric acid and 1 gram of marble chips. I will use a saucepan and fill it up with water, then submerge a test tube in the water making sure there is no air bubbles. The dispensary tube will be put in the test tube submerged in water and attached to a bung. I will measure out 1 gram of marble chips and add them to the conical flask. I will then measure out some molar acid and pour it in the conical flask with the marble chips. The gas that is given off when the two substances react is Carbon Dioxide (CO²). I will put a bung on the conical flask to stop any CO² escaping and attach the dispensary tube to the bung. The stopwatch will be started as soon as a gas bubble emerges out of the dispensary tube. The test tube will start filling up with gas, therefore pushing the water out. When the gas comes out of the bottom of the test tube the stopwatch will be stopped and I will record my results in a table.

As this experiment is very difficult to carry out on my own I will get someone to assist me when starting and stopping the stopwatch.

The different molarities of hydrochloric acid I will use are 0.5, 1.0, 1.5, 2.0, and 2.5. These are corresponding to ensure that I will get sufficient results. I will repeat each experiment three times, this way my averages will be very accurate. I intend to take 15 readings from the stopwatch. These will be in my result table.

Apparatus

The apparatus I will be using is the following:

* Saucepan

* Test tube

* Marble chips

* 0.5, 1.0, 1.5, 2.0 and 2.5 molar acids

* Weighing scales - (correct to 2 decimal places)

* Conical flask

* Measuring cylinder

* Bung

* Dispensary tube

* Stopwatch

Safety Aspects

In order for me to carry out my experiments safely and as accurately as possible there will have to be some guidelines I need to adhere to. I must wear safety glasses at all times as I am working with dangerous acids which could harm my eye's. I will be very careful that no substances enter my body via any cuts or grazes. I will keep acid off my face to prevent swallowing.

Accuracy

To ensure my experiment is as accurate as possible I will measure the solutions very accurately. I will do the same when measuring the marble chips, the weighing scales I will be using are correct to 2 decimal places. I think 2 decimal places are accurate enough for this experiment as I am only using the weighing scales to measure the marble chips.

I will repeat the experiment three times to make sure my average consists of a good range of results. The hydrochloric acid goes up by 0.5 molar every time so our results will not be too similar. A good range of results will be produced. If I find any anonymous results I will record them but then I will repeat the same test to see if I get a result which follows some sort of pattern.

I will record my results accurately to 2 significant figures.

Diagram

This is a diagram of how I will set up my experiment

Saucepan full of water

Dispensary Tube

Test tube

Bung

Conical flask

gram of Marble chips and

25cm³ of Hydrochloric acid

Fair Test

To ensure my investigation a fair test, I must:

* Check my measurements of the hydrochloric acid are all correct to 25cm³

* Check my measurements of the marble chips are all 1gram

* Make sure there is never any water in the test tube submerged under water

* Start and stop the stopwatch on time each time I carry out an experiment

Preliminary Test

I did a preliminary test to get a rough idea of what results I may be missing when I draw a graph. We carried out the preliminary test to the plan and my results are as follows:

Concentration of molar acid

Units are measured in minutes for CO² to displace water in test tube

st Test

2nd Test

3rd test

0.5m

.0m

5.01/4.55

4.05

4.26

.5m

.29

2.18

.57

2.0m

.08

0.49

0.58

2.5m

0.18

0.13

0.21

The red font is anomalous so I repeated it. The spaces that are shaded grey in my table were abandoned because it took over the whole lesson time.

Here is a table of averages so I can draw a graph from my results; I have converted from minutes to seconds so it is easier to draw a graph. When calculating my averages I have rounded the seconds off to the nearest whole number.

Concentration of molar acid

Average

(seconds)

0.5m

.0m

301/257

.5m

01

2.0m

43

2.5m

0

I will draw a graph of my results:

I have drawn some circles on my graph; these are where I can obtain extra results in my real investigation.

Obtaining Evidence

Results

There was a big gap in my graph where I am not sure what happens to the curved line. My extra results will show me what happens. The preliminary test helped me to find what results I need to now find to make my graph complete. This will also give me more evidence to support my prediction and it could act as an extension to my investigation.

The extra results I will try to find are 1.125, 1.375, and 1.75 I will find these by mixing molar solutions. This is how I will make the solutions:

Here is a table to show my extra results:

Concentration of molar acid

Units are measured in minutes for CO² to displace water in test tube

st Test

2nd Test

3rd Test

.125m

3.26

2.83/3.11

3.16

.325m

2.25

2.13

2.31

.75m

.19

.11

.26

I will draw a table of averages to enable me to construct a graph using all the results I have found. I will convert the results from minutes to seconds so it is easier for me to plot points on my graph.

Concentration of molar acid

Averages (seconds)

.125m

70/191

.325m

34

.75m

71

Analysis

I will now draw a graph of all my results.

From the extra results I have found my graph is a lot more accurate. The extra results are shown circled.

There are some anomalous results that are labelled A and B. I plotted these results to show how different the anomalous results are to the results I used. When my graph flattens off at the bottom of the curve, point C, this shows that the reaction can not get any faster with the molarities of hydrochloric acid we had to use.

Conclusion

From my results I can prove that my prediction was correct because as the concentration increases it takes a shorter time to react. The evidence from my graph shows that there are more particles present to collide in the higher concentrate causing the rate of reaction to be faster.

Therefore the conclusion I have gained from the results and graphs of this investigation supports the prediction I made with my scientific knowledge - "...as the concentration of the acid increases the rate of reaction will accelerate causing Carbon Dioxide to be given off at a faster rate."

I have found out that the surface area of small marble chips exposed to the hydrochloric acid particles means that there is more particles exposed therefore speeds up the rate of reaction. If the marble chips have a large surface area there is not as many particles exposed which means that the rate of reaction will not be as quick. Refer to diagram 1, page 1.

Evaluation

The results I obtained were sufficient and I think the extra results held a lot of accuracy. The procedure I used to carry out the experiments was very good. The only problem I encountered from the method I used was the anomalous results I could have got the anomalous results by inaccurate measuring. I could therefore improve my investigation by double checking the measurements of solutions.

The anomalous readings I acquired were redone and I produced accurate results, which can be showed by the fluency in my graph. The anomalous readings could be because the temperature may have dropped in the room, or because the surface area of the marble chips decreased. My results were similar to the results of others, which reassures me that the evidence I obtained was correct within my group. When I repeated experiments, the results I achieved showed little difference (little difference suggests accurate results).

I am happy with the conclusion I got as I collected reliable evidence, which is sufficient enough to support my conclusion. I was very precise as I used weighing scales correct to 2 decimal places, which I think was an appropriate scale. I also used a measuring cylinder when measuring solutions. The distribution of all the results on my final graph (page 8) was spread out evenly. The points were all very close to the smooth curve which showed the best fit. This proves accuracy and therefore reliability. If I left the anomalous results then my conclusion would not be as accurate and my graph would not show an accurate curve.

The experiment could have been affected to affect the results by temperature, inaccurate measurements and changing the size of different apparatus - i.e. changing the size of the test tube would have changed the amount of gas required to produce a bubble outside the tube.

To improve my experiment I would use gas syringes rather than a test tube full of water. I could also use different molarities of the acid to extend my investigation. These two options would improve the accuracy and reliability of my conclusions.

9