Looking at the graph it is clear that the reaction is faster with medium chips, but the data collected is much more erratic than with the large chips. But all in all I think I will choose to use the medium chips. Also both sets of marble chips were able to react with 0.2 M HCL; hence I have found the two limits of my concentrations, 2M and 0.2. I have also decided that the optimum mass and type of the marble chips is 10g of medium sized chips.
Experimental Variable:
For my investigation I have chosen acid concentration as my variable, as this I believe will give me the best possible set of results, and should be easier to obtain. I believe this to be so, because it reduces the need to heat up the acid which is firstly, because hot acid is hazardous and dangerous, and secondly, it can be very inaccurate, as it requires a water bath to be set up, and then reading off a thermometer, which will increase the risk of human error. All other factors I will keep constant.
I intend to have 6 different concentrations of Hydrochloric Acid of the following molarities:
2M
1.6M
1.2M
0.8M
0.4M
0.2M
Also I intend to keep the volume of acid the same throughout all my experiments, this shall be 50 cm3, and I have determined this to be the optimum amount from preliminary experiments.
I only intend to collect results for the first 60 seconds of the experiment every 5 seconds as this will give me the best set of results possible so that I can draw and accurate and correct experimental conclusion. As after the first 60 seconds the molarity (concentration) of the solution would have changed, as the reaction would have taken place and some of the particles of the acid would have reacted.
Apparatus and Materials:
500 ml of 2M HCL, 500ml of Distilled Water, Electronic Scales, Bung, Marble Chips, 50 cm3 measuring cylinder, 20 cm3 measuring cylinder, 1 cm3 tite pipette, conical flask, beakers, stop watch
Experimental Hazards:
- Hydrochloric acid is corrosive
- My cause burns, and the vapour is very irritating to the respiratory system.
- 2M > Solution > 6.5M are irritant
- Dangerous with Calcium and other reactive metals
- General precautions to be taken when using HCL, and eye protection to be worn
Method:
i) measure out 50 cm3 of the correct molarity solution (check table above) into the using a measuring cylinder or smaller cylinders into a conical flask, using the correct amounts of distilled water and 2.M HCL
ii) place on scale, and reset the scale using the ‘tare’ function so that it reads 0.00g
iii) measure out 10.0g of medium sized marble chips in a weighing boat using the scales
iv) add the pre-weighed medium sized Marble chips into solution, start stop watch simultaneously
v) note down the mass of the solution every 5 seconds, as it goes down from 10g for the first 60 seconds
vi) thoroughly rinse out all the used glassware in preparation for the next experiment.
vii) repeat the above procedure 3 times for each stated concentration, remember to note all the results down on a data collection sheet
viii) use the formula below to calculate the mass lost during the experiment.
10.00 – mass of solution = mass lost (g)
Diagram:
Prediction:
I predict as the concentration increase the rate of reaction will increase in direct proportion.
I predict that the rate of reaction will double for every double in concentration
I believe that this is the right prediction because as if you increase the concentration you increase the number of reacting particles. So for example if I had 50cm3 of 0.4M HCL I would have ‘x’ {‘x’ representing the number of reacting particles} number of reacting particles, so if I had the same volume 0.8M HCL I would have ‘2x’ reacting particles which means that there are twice as many reacting particles which should double the rate of collisions and hopefully double the rate of successful collisions. So with a double in the rate of the successful collisions there should be a double in the rate of reaction, i.e. mass lost (g), this is because the greater the rate of reaction, it more ‘individual’ reactions are taking place, and hence more Carbon Dioxide will be given off, hence a greater mass lost.
Results:
The tables below, show the results obtained from the experiments
Initial Rates vs. Variable:
Conclusion and Analysis of Evidence:
Due to the fact that the rates of reaction gradient data could be interpreted in two ways either in a linear or exponential fashion, I have deicide to draw two conclusions and then decide which one is the best.
Exponential Conclusion:
Looking at the graph showing rate of reaction against concentration, it is clear that as the concentration increases the rate of reaction increases. The rate of reaction increases in indirect proportion to the concentration. Therefore I can conclude that:
The rate of reaction will increase in indirect proportion in relationship to the increase in concentration.
I believe that this is the right conclusion to this experiment as when looking at the graph showing rate of reaction against concentration, it clearly shows that the rate of reaction is increasing in indirect proportionality. A curved line can be drawn through the points and, hence, indirect proportionality.
N.B. The data from the table below has been taken from the exponential graph showing rate of reaction against concentration.
Average Increase: 168 %
I believe that the results obtained from my experiment partially prove my prediction, as I predicted that ‘the rate of reaction will double for every double in concentration’. This is simply proved by the table above. The data shown proves the prediction to an extent but not fully as the average increase is 168 % meaning a1 2/3 increase in the rate of reaction for every 200 % for every increase in concentration. So I can conclude that my prediction was partially proved.
This is because when the concentration is lower, there are less reacting particles, therefore less collisions, and hence there are less successful collisions, hence fewer reactions take place. But when we increase the number reacting particles i.e. increases the concentration of HCL we increase the number of reacting particles in proportion, as the concentration is the number of moles present. So with more reacting particles there should be an increase is the number of successful collisions, hence more reactions, which means that the rate of reaction will increase. So with double the number of reacting particles the rate of reaction should double.
Linear Conclusion:
After analysing the points on the graph, it is clear that the data points could be interpreted in a linear fashion. As the concentration increase so does the rate of reaction in linear fashion. The rate of reaction vs. the concentration increases in a linear fashion, hence I can draw the following conclusion.
The rate of reaction will increase in a linear relationship to the increase in concentration.
I believe that this is the correct conclusion as the linear line almost passes straight through 4/6 data points meaning that it is a very accurate line for the data collected. Hence meaning that there is a linear relationship between the concentration increase and the rate of reaction increase.
I believe that the data collected proves my prediction of the rate of reaction will double for every double in concentration’. And I believe that this is simply proved by the table below
N.B. The data from the table below has been taken from the linear graph showing rate of reaction against concentration.
Average Increase: 200 %
Looking at the table above I can ‘safely’ say that the data collected clearly proves my prediction as I predicted that as the concentration doubles {200 % increase} the rate of reaction will double in direct proportion. This has clearly been shown to be the case, and hence I can say that my prediction is proved.
This is because when the concentration is lower, there are less reacting particles, therefore less collisions, and hence there are less successful collisions, hence fewer reactions take place. But when we increase the number reacting particles i.e. increases the concentration of HCL we increase the number of reacting particles in proportion, as the concentration is the number of moles present. So with more reacting particles there should be an increase is the number of successful collisions, hence more reactions, which means that the rate of reaction will increase. So with double the number of reacting particles the rate of reaction should double.
After analysing both conclusions, I can say that the best conclusion for the data is the linear conclusion as this only meant 2 large anomalies, off the final line of best fit, but it is not the case with the exponential graph, as there are 3 large anomalies, so based on the number of anomalies ‘created’ by the line of best fit, I can say that it is fair to conclude that the best conclusion for the data is the linear conclusion.
The data collected even though erroneous at points is enough to prove my conclusion as the lines of best fit were mainly drawn using the latter points but obviously taking into account the location of the other points. So I believe that the data is strong enough to draw the conclusions, and strong enough to support my prediction.
Evaluation:
I believe that the procedure used to collect data for my investigation was a excellent indication of how the rate of reaction varies, with the two reactions. Although the majority of my graphs were accurate and had nice smooth lines, there are too many potential errors; procedural and experimental to be 100% sure of the results. But I still believe that the data collected is still strong enough to substantiate my conclusion, because after analysing the flaws in the experiment, and taking into account a margin for human error the results are still strong enough to support my conclusion.
But when you look deeper into the investigational data, it can be seen that there are some anomalies, in the data that I have collected. They are now listed below:
- 20, 60 seconds on 0.8M Graph
I believe that these anomalies were simply caused by the mis-reading of the data. But of the latter anomaly, could be due to the interpretation of the graphs, it would be arguable to say that the line should pass through this point and hence make 55 seconds an anomaly, even though it would have an effect on the rate of reaction gradient. So I believe that it is fair to say that the latter anomaly is just human errors.
I can conclude that these anomalies are just figures that have been mis recorded by human error. These results would not have greatly altered the final rate of reaction gradient calculation, and hence no major influence would have been made on the final rate of reaction vs. concentration graph.
- 25, 30, 35, 45 and 55 seconds on 0.4M Graph
Looking at the five anomalies, it is clear that the data points are in the incorrect places. As they are obviously not on the line of best fit, I believe that these anomalous points could have been due to several reasons. Mainly, human error, probably due to mis-reading of data shown, as at this point the rate of reaction is still increasing at quite a quick rate, hence means that the display on the scales would have been ever changing. Paired with the fact that it was important to note the stopwatch time at the same time as scale readings, readings may have been taken too early or late, and this would have affected the figure collected.
But taking into consideration the position of these points it can be noted that these points would not have made a great impact on the initial rate of reaction curve, hence it would not have greatly impacted the gradient, thus no huge change would have been required on the graph showing rate of reaction vs. concentration.
- 15, 20, 30, and 35 seconds on 0.2M Graph
I believe that these anomalous results were caused by the human error and mis readings of the scales and stop watch, like the previous anomalous points on the previous experiment; 0.4M.
These anomalous points could have been due to several reasons. Mainly, human error, probably due to mis-reading of data shown, as at this point the rate of reaction is still increasing at quite a quick rate, hence means that the display on the scales would have been ever changing. Paired with the fact that it was important to note the stopwatch time at the same time as scale readings, readings may have been taken too early or late, and this would have affected the figure collected.
But once again taking into consideration the location of these points it can be clearly noted that these points had not real major influence over the rate of reaction and thus no real affect on the final rate of reaction vs. concentration graph.
Also there were anomalous points on the final graphs showing the rate of reaction vs. concentration graph. On both graphs the points were 0.2M, 0.4M and 0.8M, but as we decided in the conclusion we were going to accept the linear conclusion, 0.8M becomes less of an anomaly. I believe that these anomalous points were caused by the fact that the initial rate of reaction for both these points were incredibly high which meant the line of best fit had a very steep initial gradient, which affected the final gradient and hence the final graph.
I believe the source of this problem lies in the fact that the majority of the marble chips reacted within the first 10-15 seconds, meaning that in the reaming time the reaction was much slower, i.e. the rate of reaction was not evenly dispersed.
After analysing the anomalous results it is clear to see that they could have affected the final result, but not by that much and even if we discount those points we could still come up with a similar final line of best fit and hence a similar conclusion, and hence I can say that my conclusion is proved.
Looking at the identified anomalous results it is clear to see that all the anomalous results have been collected in the lower concentrations this is because the rate of reaction was very slow, and this meant that the readings on the scales were not totally accurate as the scales only read to 2 decimal places, and hence, if the reaction was slow, it was take a long time for the mass lost to be recognised by the scales.
I believe that all-in-all my experiment was very accurate and hence, the reasonable results. But there are several ‘unreliable’ aspects to my experiment and these are listed below:
- The scales used to measure the mass lost during the experiment only read to 2 decimal places, this meant that if the reaction was slow, and the mass lost was in the 3 decimal places, the scales would not have shown that and therefore could not have been noted down.
This also posed a problem when weighing out the mass of the marble chips, so the chips could have been 10.005g or 9.995g, which would have made a slight difference to the final result.
- The acid used during the experiment was of varying temperature, due to the time of day the experiments were taking place the outside temperature. But I hade hoped to keep the temperature constant, I did not measure the temperature of the acid every time before each experiment, but with hindsight, I believe that this is an action I should have taken. Therefore the higher the temperature, the greater the rate of reaction and visa versa, this means that some reactions would have gotten and ‘unfair head start’, die the temperature difference.
- Even though the size of the marble ships were stated to be of medium size by the supplier, the sizes of the chips did vary, from being powdered because of ‘erosion’ in the container, to being of the larger size. This meant the surface area of the chips varied, and hence gave some experiments an advantage.
- Also I believe that some of the marble chips could have piled up when they were added to the solution and hence this would have lead to them not having all the surface area open to the reactive particles and hence a slower rate of reaction would have been achieved. Even though the overall average size would have been the same, some experiments would carried out with smaller chips and some would have been carried out with larger chips.
- Also there are some minor discrepancies to the procedure, as the reaction is an exothermic reaction and hence if the flask was not washed out thoroughly and hence cooled, the acid may have been heated slightly by the flask.
- Also when drawing a rate of reaction tangent to the graphs it is clear to see that it could have been possible that different people would have interpreted the data points differently and hence different tangents would have been drawn and hence different gradients calculated and hence a different final graph drawn.
Therefore I believe that the experiment that I designed could be changed in the following ways to make it more accurate:
- Use scales that read past 2 decimal places, hence more accurate readings.
- Ensure that all the starting temperatures of the acid are the same, and if either hot or cold then cool them down to the right temperature.
- Ensure that all supplied marble chips are of uniform size.
- Carry out more experiments at the same and different concentrations; as this would allow more data points to be plotted on the final graph hence a more accurate picture.
- Maybe use a digital meter to read the results and hence only have to interpret the data collected.
But after analysing all the problems that could have occurred in the experiment, I still believe that this was the best way for collecting the data for my investigation. As it provided me with enough data to draw a strong and conclusive conclusion.
After considering the experimental procedure carefully, I believe that it is strong enough for me to be able to discount the anomalies, and still be sufficiently strong enough for me to support my conclusion. This is because looking at the graph showing rate of reaction against concentration, even if I removed the three points I could still draw a similar graph, maybe not as accurate, but still accurate enough for me to prove my conclusion.
To improve my experiment I suggest the following further work, I suggest that even more repeats should be carried out and hence more accurate results can be obtained. I also suggest that more concentrations should be used as this would allow us to obtain even more data points and plot even better lines of best fit. I also believe if the digital meters were available that we only measured the first 30 seconds but every second or two seconds which would have meant that the anomalies later on in the experiment would be discounted. Also with more data points a more accurate line of best fit can be drawn.
Also I believe that the method of using a gas syringe to collect the gas given off could be used as it would allow us to measure the gas given off and relate that data to the mass lost data by means of several simple calculations. (moles and gases).
Also it could be argued that as my repeats for the experiment we carried out at different times of day and different days, it would have allowed for external influences to influence the final result, these external influences, could be different batch of marble chips, different temperature of acid and different equipment, with different collaborations, meaning ever so slightly different readings. Also as we carried out repeats on different days it would have allowed us to