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An experiment to investigate the rate of reaction between

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An experiment to investigate the rate of reaction between marble chips and hydrochloric acid The aim of this experiment is to find the factors that affect the rate of reaction between calcium carbonate and hydrochloric acid. The equation for this reaction is shown below. Calcium Carbonate + Hydrochloric Acid --> Calcium Chloride + Water + Carbon Dioxide The variables that I believe are most likely to have an effect in my experiment are: 1. Temperature 2. Concentration (of hydrochloric acid) 3. Surface area (of marble chips) 4. A catalyst However instead of investigating all four variables, I have chosen to investigate how different concentrations of hydrochloric acid affect the rate of reaction between marble chips and hydrochloric acid. My prediction for this experiment is that as the concentration of hydrochloric acid increases, the rate of reaction will also increase in direct proportion. My reasons behind the above prediction are that so a reaction can take place, the particles of the substances reacting have to collide. If they collide with enough energy then they will have enough energy in order for them to react. If the concentration of hydrochloric acid is increased it will, in turn, increase the number of particles in a given volume, in contact with the marble chips. This will lead to more collision, so the rate of reaction will increase also. ...read more.


After 25 seconds I will pour the solution through a sieve, making sure only the marble chips are remaining. I will then get some paper towels and dry off the marble chips. I will then re-weigh the marble chips and record the results. I will repeat this method for the other concentrations. I will also repeat each concentration if any of my results seem irregular. Results * Experiment 1 Concentration (molar) Mass before (g) Mass after (g) Mass change (g) Rate of reaction 2.0 4.99 4.54 0.45 1.35 1.6 5.0 4.64 0.36 1.08 1.2 5.04 4.71 0.33 0.99 0.8 4.98 4.76 0.22 0.66 0.2 4.99 4.84 0.15 0.45 * Experiment 2 Concentration (molar) Mass before (g) Mass after (g) Mass change (g) Rate of reaction 2.0 5.02 4.6 0.42 1.26 1.6 5.01 4.62 0.39 1.17 1.2 5.01 4.65 0.36 1.08 0.8 5.00 4.82 0.18 0.54 0.2 4.98 4.88 0.10 0.3 * Average results Concentration (molar) Average rate of reaction 2.0 1.3 1.6 1.125 1.2 1.035 0.8 0.6 0.2 0.375 Analysis From my graph I can see that as the concentration of hydrochloric acid increased as did the rate of reaction. This is because when the particles reacted they collided with enough energy to make them react. As the concentration of acid increased, the number of particles increased, and so there were more particles in contact with the marble chips. ...read more.


My results were consistent but feel with more repeats they could have been even more consistent and also more reliable. I would also use a larger number of different concentrations, and so I would be left with a more reliable and accurate conclusion. An alternative experiment I could have done was to test one of the other variables I stated earlier in this write up. I may then be in a better position to draw a more detailed conclusion. So, for example, I could investigate the surface area of marble chips and how it affects the rate. If I were to complete this experiment I would separate the chips using their size of their surface area. I would then go on to weigh out equal amounts of the chips using their different sizes. Then I would measure out the same 5 solutions of hydrochloric acid, using the same concentration. I would then add the smallest chips to the first solution, time them for 20 seconds, and then sieve them. I would then precede on to dry them with a paper towel, and then weigh them. I would repeat this method for the different sizes of marble chips. I do however find that my results are sufficient enough to draw a firm conclusion because my results were consistent as I did use a repeat. However I do have anomalies and sources of error within my experiment. If I were to repeat my experiment using the improvements I have already explained above, I feel my conclusion would be much more reliable. ...read more.

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Response to the question

The author has successfully carried out an experiment to test their hypothesis about how the rate of reaction changes with concentration. They have used their existing scientific understanding to make their hypothesis, which they then showed to be correct. They ...

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Response to the question

The author has successfully carried out an experiment to test their hypothesis about how the rate of reaction changes with concentration. They have used their existing scientific understanding to make their hypothesis, which they then showed to be correct. They have mentioned other factors which could affect the rate of reaction, and, although they only tested one, considered how these could have affected their results, for example how they struggled to keep the surface area of the marble chips the same, which could have lead to errors in their results. They also suggest a good way of removing this source of uncertainty if they were to repeat the experiment. They have clearly responded well to the task.

Level of analysis

The author has discussed the trend shown in their results and compared this to their original hypothesis. They have then considered the causes of unusual results in their experiment, and suggested ways to improve this. However, we are always advised to show all our workings and calculations, which the author has neglected to do – this makes it more difficult to understand how they worked out the rate of reaction. This could also have been mentioned in the method section. I would also have repeated the experiment a few more times, which would enable me to calculate anomalies in the data and therefore discuss these in my analysis. However, this calculation may not be essential, depending upon the exam board (always read the mark scheme beforehand to check you are covering all the points). Despite these minor issues, they clearly understand the chemistry of the experiment and have discussed how they came to their hypothesis and conclusion clearly.

Quality of writing

The author’s quality of written communication is excellent, with very few grammatical or spelling mistakes. They have presented their report well, with headings and diagrams, and made good use of bullet points, tables, and graphs. Therefore, the report is easy to read and therefore easy to mark! However, the method section could have been written in numbered bullet points rather than one long paragraph, which would have made it clearer and easier to follow, and I would have included the “Before I begin to set up my experiment, I will make sure all hair is tied back, and put on safety glasses.” Into a separate ‘safety considerations’ section, as it is not part of the method. I would also have included a balanced equation of the reaction, as conventional in the write up of an experiment. However, the report is very well written and easy to read for the most part, and therefore they are unlikely to have lost many marks for these small mistakes.

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