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Marble Chips and Hydrochloric Acid.

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Introduction

Marble Chips and Hydrochloric Acid PLANNING AIM To find if changing the concentration of an acid will increase or decrease the rate of the reaction when marble is dissolved in hydrochloric acid. With the equation CaCO3 + 2HCl CaCl2 +H2O + CO2 HYPOTHESES A reaction occurs when particles collide. This process is based on random particle movement. So therefore, the more particles you have in a space, the more likely they are to collide. Therefore making the reaction accelerate. This theory can be proved if you compare the rates of reaction with marble in hydrochloric acid. 'If the acid is of a higher concentration, the reaction will be quicker.' Also if the particles have more energy, they will be travelling faster, making them collide more frequently. PREDICTION When the concentration of acid increases, more gas will be given off faster. I know this from my trial experiments. METHOD Since I will be working with strong acid, I will wear safety goggles while conducting the experiment. I will use Marble chips all of a small size. I can use a sieve to make sure they are all roughly similar size- about 7mm diameter. The amount of acid I have decided on is 10ml. And so the amount of marble must be in excess - 3g. I can measure the speed of the reaction by how much gas is given off. I can measure this in cm3 in a gas syringe. when the experiment takes place, I will take the reading every 10 second to get a good graph for the results. If the reaction goes very quickly, I will take the readings every five seconds. I will use acid of 0.5, 1, 2, 3, and 4 molar concentrations. SInce I only have acess to acid of 1,2 and 4 molar concentrations, I will have to dilute some acids with de-ionised water to produce 0.5 and 3 molar concentration acid. ...read more.

Middle

We have decided to keep the mass and size of the marble chips constant throughout our pre investigation, as it will be easier to only have the two changing variables; the concentration and volume of the hydrochloric acid. In this pre investigation we are going to focus on testing different volumes, of the weakest concentration of acid and of the strongest concentration of acid. This is because we will not have enough time to investigate every possible combination of volumes and concentrations. 5g of medium sized marble chips with 10cm� of 0.25m hydrochloric acid Time (seconds) Volume of gas released (cm�) 10 - 20 - 30 - 40 - 50 - 60 - 70 - 80 - 90 - 100 - 110 - 120 - 130 - 140 - 150 - 160 - 170 - 180 - This table shows that 10cm� of hydrochloric acid is an inappropriate volume to use as no reaction occurred. This is because there were not enough particles travelling at a fast enough speed to create enough collisions to induce a reaction. 5g of medium sized marble chips with 20cm� of 0.25m hydrochloric acid Time (seconds) Volume of gas released (cm�) 10 - 20 - 30 - 40 - 50 - 60 - 70 - 80 - 90 - 100 - 110 - 120 - 130 - 140 - 150 - 160 - 170 - 180 - This table again shows that the volume and concentration of acid we have used are unsuitable, as no reaction has taken place within our 180 second limit. As a result, we will have to continue investigating different volumes and concentrations of hydrochloric acid. 5g of medium sized marble chips with 30cm� of 0.25m hydrochloric acid Time (seconds) Volume of gas released (cm�) 10 - 20 - 30 1 40 3 50 6 60 8 70 10 80 12 90 14 100 16 110 18 120 19 130 21 140 22 150 23 160 24 170 25 180 26 You can see from ...read more.

Conclusion

As the concentrations decreased the different sizes in the particle chips became more apparent, this was because there were a wider range of results, before we calculated the average. The size of the surface area had less of an effect on the higher concentrations of acid because the reaction was taking place so quickly and this was because if the marble chips had a slightly larger surface area, then there would have been a greater chance of successful collisions causing the reaction. Another factor that may have slightly affected the accuracy of our results was that we did not use hydrochloric acid from the same bottle for each experiment. This may have caused slight variation in the results, as the concentrations may have varied a little. Possible suggestions for ways to improve our experiment * To improve our experiment we could have added the marble chips to the acid instead of pouring in the acid onto the marble chips. Doing it in the way we did, which was pouring the acid onto the marble, started the reaction before all of the acid was present and therefore gave an unfair advantage of starting the reaction early. * Instead of performing the experiment in the way that we did, we could have used a balance and weighed the amount of mass that was lost during the experiment, rather than measuring the volume of the CO released. * To measure the volume of carbon dioxide we could have used a gas syringe, which would have given us a more accurate reading of the volume, which in turn would make our results slightly more accurate. * To ensure that the total surface area of the marble chips were exposed and available for reaction throughout the experiment, we could have used a magnetic stirrer, to stir the solution and make sure that the maximum available surface area was exposed. To further this investigation we could experiment with other concentrations between our 0.25m and 2m boundaries. As these would give us a wider and more accurate set of results. ...read more.

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4 Stars
Response to the question
The candidate has carried out a well-planned experiment to investigate the effect of changing concentration on rate of reaction. The experiment was well planned with a stated hypothesis, with clear direction on how this was to be tested. The reports conclusion is limited, with a evaluation used to look at laboratory procedures and improvements. The conclusion would be improved by linking it more closely to the aim of the experiment, stating the effect of concentration on rate of reaction. Although they have investigated the question well, they have failed to fully answer it in a well-balanced conclusion.

Level of analysis
The candidate has a good understanding of the rate of a chemical reaction and covers the majority of factors that effect it. The candidate used diagrams effectively to show both particles in solution and the effect of activation energy. The analysis of the data was of a good standard using specific references to results and stating the change in rates of reactions. It is well written however needs to link their results back to the scientific theory for rates of reaction. They could improve this by explicitly stating the effect of changing the concentration on particle numbers and therefore the probability of products being formed from successful collisions between particles. The method is described generally and should be improved by stating specifically how the experiment was set up and carried out. It should be possible to carry out the experiment again from these directions. They have evaluated their experimental method and suggested possible improvements, to develop this further they should include the impact of these changes on the experimental method and results. Some data that did not lie on the line of best fit was identified, however there was no evidence of these values being re-investigated to improve the reliability of the data.

Quality of writing
Their spelling and grammar is variable, there are a number of spelling errors and incorrect chemical formulae. The equation for the reaction is incorrect and not balanced and carbon dioxide is often written as carbon monoxide. There are some problems with the layout of the experimental report. The evaluation should have come before the conclusion. The method had a diagram however this should include labels. (the conclusion is 'hidden' within the analysis section). Despite these issues, they have described their investigation well.

Marked by teacher Cornelia Bruce 01/12/2012

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