How the Concentration Affects the Rate of the Reaction

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Title Page Number Diagram of Apparatus Introduction Risk Assessment ` Table of Results Line of Best Fit Graph Error Bars Graph Gradients Graph Analysis • Error Bars Analysis Evaluation • Improvement Assessment • Improved Experiment. • Reliability References Introduction: For this data analysis project, I conducted and experiment to investigate how the concentration of an acid affects the rate of the reaction.

I have set up the experiment’s equipment as shown on figure 1.

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As you can see by figure 1, I have used the reaction between sodium thisoulphate solution and hydrochloric acid (HCL) to come up with results that will help me draw conclusions regarding the effects of the concentration of the acid. I decided to use this particular reaction due to the fact that the product of the reaction between sodium thisoulphate and hydrochloric acid (HCL) is precipitates of sulphur which tend to turn the solution cloudy.

As a result, the cross beneath the conical flask (see figure 1) would disappear/ become difficult to be seen when the reaction has taken place. Therefore, the idea is that 50 cm? of sodium thisoulphate are made to react with 5 cm? of hydrochloric acid that is of different concentration each time. The concentrations of hydrochloric acid used varied from 0. 1 to 5 moles. Afterwards, the cross is observed through the top of the conical flask until it because invisible. The time of which this happens is then recorded and monitored using a stopwatch.

The symbol equation of this reaction is as follows: The above symbol equation shows the reaction: Sodium thisoulphate reacts with hydrochloric acid to form sodium chloride, water, precipitate of sulphur as well as sulphur dioxide. The results that I recorded from this experiment were poor. This is because they were not entirely accurate and did not make sense. As a result, my teacher gave me a different set of results that were recorded at different temperatures to analyse and help me write up.

The table of results (table 2), shows the results obtained at 3 different trials of the same experiment. The reason behind repeating the experiment 3 times is to ensure that the result’s reliability is of a satisfactory level. After the experiment was conducted, I looked back at the equipment I used as well as the steps I carried out during the process. I did so to recognize the risks associated with carrying out such experiments. To prevent or minimize such risks in future experiments, I conducted a risk assessment that is shown on the following page: Risk Assessment Risk |Damage |Prevention Method | |Hydrochloric Acid (HCL) |Hydrochloric acid is corrosive. |Eye protection must be worn at all times during | | |Therefore it can damage skin. |the experiment. | | |It can also damage eyes. |Ensure it does not come into contact with skin | | | |and if it does rinse thoroughly. |Conical Flask (glass) |Can roll down the bench |

Make sure apparatus made of glass are not | | |Broken glass can cut/damage skin. |chipped. | | | |Wear gloves if possible | | | |Be careful when handling glass. | | | | | | | | |Sodium Thisoulphate |Inhalation may cause irritation and coughing. |Avoid contact with eyes and skin. | | |Skin and eye contact might cause irritation and |Do not inhale on purpose. | |damage | | |Paper |1. A risk of a paper cut is possible. |1. Careful while handling paper and if paper cut| | | |occurs rinse and do not come in contact with | | | |hydrochloric acid. Risk Assessment (Table 2) Analysis: Outliers: Table 2 summarises the results of this experiment. As you can see, a couple of outliers have occurred during the experiment. I decided that a difference of more than 30 seconds between a result and the others obtained from repeating the same experiment indicates that this result is an outlier. Therefore the two outliers are ringed on table 2, so that they are made clear. For instance, the results recorded for the third experiment using 0. 1 moles concentrated hydrochloric acid is 583 seconds.

This is clearly an outlier due to the fact that the other results are 683 and 626 seconds, making the result of 583 seconds clearly distant and therefore is classed as an anomaly. Another outlier that has occurred is the result for the 3rd trial using 4. 0 moles hydrochloric acid. Here the outlier is 132 seconds, while the other trials show results that vary from 160 to 165 seconds. Graph Analysis: The first graph (figure 2) states the averages of the recordings. I have used a line of best fit on this graph to identify the trends between the results.

Firstly, the graph shows overall that the experiment has gone as expected. This is because it looks very similar to the graph in the chemistry text book as well as ones found on the internet. The general trend that is shown by this experiment (as seen on figure 2) is that as the concentration of the hydrochloric acid increase, the rate of the reaction also increases, as the reaction takes less time to take place. Therefore, the experiment shows that the concentration of the acid is directly proportional to the rate of the reaction. From 0. to 0. 5 Moles: As you can see by figure 2, when 0. 1 moles of hydrochloric acid were used, the reaction was at its slowest, taking 656 seconds to take place. From 0. 1 to 0. 5 moles, the rate of the reaction increased significantly with the reaction only taking around half the time: 379 seconds to take place. At the start, the line of best fit has a gradient of 0. 000152 moles per second (m/s). I worked this out using the equation x/y = 0. 1/656 = 0. 000152 m/s. At 0. 5 moles, the gradient of the graph increases rapidly to 0. 00132 m/s.

This calculation reinforces that the reaction is at its slowest at the beginning with the sulphur precipitate taking the least amount of time to cloud the solution and causing the cross to become invisibile. This is because a low concentration of hydrochloric acid means that not as much molecules are available to collide, making molecular collision much less likely (). From 0. 5 to 1 Moles: From 0. 5 to 1 moles, the time taken for the reaction to take place decreases further as the rate of the reaction increases. Therefore the precipitate of sulphur is taking less time to form ().

The gradient of the graph also increases as a result to 0. 00357 m/s. I have worked this out using the same equation as above: x/y= 1/280. This indicates that the rate of the reaction keeps on increasing as the concentration of the hydrochloric acid increases. From 1 to 2 Moles: By increasing the concentration of the acid from 1 to 2 moles, the rate of the reaction kept on increasing by taking less time for the reaction to occur. This is again shown by the line of best fit on figure 2, which at this point in the graph has a gradient of 0. 0913 m/s (x/y = 2/219), which is nearly triple the gradient stated previously. The rate of the reaction is a measure of how quickly this reaction is taking place. As you can see by the negative correlation between the time and the molarity of the acid shown on figure 2, the rate of the reaction keeps on increasing as the concentration of the hydrochloric acid is increasing. This result is supported by the collision theory. This theory indicates that for a reaction to occur, the particles or molecules must collide with each other to form a reaction.

Infact, they need to collide hard enough for the reaction to become a successful one as well, since only a certain fraction of the total collisions actually result in a chemical change (). When those successful collisions occur, they have enough activation energy to break existing bonds and form new bonds, resulting in a chemical reaction and a new product being formed (). Increasing the concentration of a solution means increasing the amount of molecules that are available in that solution.

Therefore, increasing the concentration of the hydrochloric acid from 1 to 2 moles is increasing the amount of molecules in the acid that would be available to collide and cause a reaction. Therefore, this means that there would be more particles per dm?. The fact that more particles are available explains why the rate of the reaction becomes faster. This is because the more particles there are, the more successful molecular collision would be happening, which increases the rate of which the reaction occurs. This aspect of the collision theory is illustrated by the diagram below:

The Collision Theory (figure 5) (). As you can see by the diagram above, the amount of collisions happening per second is a major factor that determines how quickly or slowly the rate of the reaction goes. Therefore a high concentration increases the chances of collisions and consequently results in an increase in the rate of the reaction. From 2 to 4 Moles: When increasing the concentration of the hydrochloric acid again from 2 to 4 moles, the trend still obeys the collision theory as far as the increase in the rate of the reaction is concerned.

This is reinforced by the dramatic gradient increase to 0. 025 m/s (x/y = 4/163), which is shown by figure 2 as well as 4. According to the collision theory, it is expected that when the concentration of the hydrochloric acid doubles, the rate of the reaction will tend to double as a result too. On the other hand this does not seem to be the case in this experiment, since the time take for the reaction to take place when 2 moles hydrochloric acid was used is 219 seconds, while it is 163 seconds when 4 moles hydrochloric acid is used.

This indicates that the reaction happening at this experiment was not a perfect one. This could be as a result of human error or other factors affecting the rate of the reaction, which will be discussed later. From 4 to 5 Moles: Finally, by increasing the concentration of the hydrochloric acid used from 4 to 5 moles, the rate of the reaction was increased to become at its highest during this experiment, with the steepest gradient of 0. 035 m/s (x/y = 5/141).

This implies that the amount of successful molecular collisions here are the highest with the sulphur precipitate clouding the solution in the quickest rate of time (141 seconds). Thus, the cross disappeared at the quickest rate as well. Error Bars Analysis: The second graph (figure 3) is a graph of error bars. Error bars show the range of results. I have drawn this graph since it is a visual account of the experiment’s reliability and so, it would help me decide whether the experiment was accurate enough or not. As you can see, the size of the error ars on figure 3 varies from small to large ones. I have decided that a bar range of 5 small squares on the graph is a reasonable maximum to detect the experiments accuracy. So, any range bars that vary above 5 small squares show inaccurate set of results. The error bars drawn on figure 3 show that the results obtained from 0. 1 to 0. 5 moles are rather inaccurate. This is because the error bars illustrated for those set of results are relatively big, showing a difference of from 6 to 10 small squares. This implies that those results with big error bars are quite poor and lack accuracy.

However, the rest of the experiments show relatively small error bars. In addition, the error bars seem to be getting smaller and smaller with a bar range that varies below 5 or 4 small squares. This proves that the results keep getting more and more accurate towards the end of the experiment which makes. Overall I believe that the results of this experiment are 71% accurate. This is because 5 out of 7 of the error bars had a small range, leaving 2 out of 7 of the error bars with rather big range bars. Evaluation: