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In this project I am going to investigate rates of reaction of an indigestion tablet when added to hydrochloric acid. The variable I am going to use will be the temperature of the acid.

Extracts from this document...

Introduction

Introduction In this project I am going to investigate rates of reaction of an indigestion tablet when added to hydrochloric acid. The variable I am going to use will be the temperature of the acid. (All background knowledge used in this project was taken from previous experience - notes and experiments from work done in year nine) What are rates of reaction? The rate of a reaction is the speed at which a reactant is turned into the product. Chemical reactions can take place at very different rates (eg. explosions, rock formations). A rate is measured as: A change in something (eg. loss of mass/mass of gas given off) Divided by The time it takes to change/disappear Rates of reactions can be measured in two different ways: * How fast reactants disappear * * How fast products appear Many factors affect rates of reaction: * Surface area The greater the surface area of a solid, the greater the area of the particles that is exposed and likely to collide with other particles, meaning more successful collisions can take place per second. Therefore reaction between acid and a finely powdered salt will take place faster than a reaction between the same acid and a lump of salt. * Concentration of solutions The rate of a reaction increases as the concentration of the solution increases. This is because there are more solute particles to collide with a fixed volume of solvent particles. Therefore more successful collisions take place. The rate of a reaction is directly proportional to its concentration (i.e. as concentration doubles, rate doubles.) (This is assuming that any reactions taking place are not exothermic and that no other variables are changed) * Temperature The rate of reaction increases as the temperature increases. This is because at a higher temperature the particles move around faster (due to heat energy being converted into kinetic energy) ...read more.

Middle

For the same experiment with a gas syringe, I decided against taking one measurement every few seconds as the reaction happened too quickly. I also decided against noting the time every 10cm� gas collected as the reaction was too fast, the gas syringes are not accurate enough and it would be difficult trying to get an accurate time without stopping the stopclock, as I would have to look at both the syringe and the stopclock at the same time. However, when I measured how long it took to collect 25cm� of gas from one tablet in 50cm� of acid it gave me a simple reading of 23 seconds. I decided that this would be a good and clear method provided enough readings were taken to give an accurate representation of any trend. * I tried both crushing the tablets and keeping them whole. Crushing the tablets made the reactions happen so fast (due to an increase in surface area) that changing the temperature made little/no difference to the times I got. However, keeping the tablets whole produced a wide range of clear results. * I tried both different concentrations of acid (4 mols/dm� and 2 mols/dm�). Acid at concentration 2 mols/dm� took a long time to react with one tablet. Increasing the concentration increases the rate of reaction. Therefore, I decided to use acid at 4mols/dm�, as it would react more quickly. I also realised that in both concentrations of acid one tablet took too long (especially at a low temperature) to give adequate results within the time-span I had. * I then found the maximum and minimum temperatures I could reach using my method of heating, and from there determined what would be a good volume of gas to collect (not too quick at the highest temperature, not too slow at the lowest temperature). The minimum temperature I could reach using ice was approximately 10�C, as I had very limited time. ...read more.

Conclusion

This increases the chances of the experiment being inaccurate, as two different people are very unlikely to be completely synchronised. Therefore the gas has time to escape unnoticed at the start of each reaction before the bung is put in. I can see little which could be done about this in future experiments. In both cases (above or below the best-fit line) the experiment would have benefited from a greater number of results being taken at smaller intervals. This would probably have further supported my conclusion and may also have more accurately displayed a less obvious trend such as the one I originally predicted. Taking results in a wider range, (for example from 5�C to 70�C) with repeats to verify accuracy, would have strengthened my evidence. It would only have done this if, as I imagine, a continuing trend showed in the extra results. In all of the experiments, a degree of error in continuity must be taken into account. It is extremely unlikely that the tablets all had the same mass, or that there was the same volume of hydrochloric acid down to the last drop. I tried to make this as accurate as possible, using a burette instead of a measuring cylinder, and only getting the tablets out at the last minute so that they were as whole and un-tampered-with as they could be. If the experiment was to be repeated on a larger timescale, I could measure the mass of the tablets to increase accuracy. It is also impossible to swirl the beaker at exactly the same vigorousness every time, although I tried to keep it as constant as I could. If I was looking to test these results on a much wider scale, I could use other common antacid tablets with similar active ingredients, keeping the type and volume of acid constant. This would prove that the tablets that I used were regular, and didn't just coincidentally produce typical results. Chemistry Coursework - Rates of Reaction Lauren Barnfield 1 ...read more.

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Here's what a teacher thought of this essay

3 star(s)

This is a well research and planned experiment however the limitations to the data (a single repeat of each temperature) lowers its reliability and limit it to a three star rating. There should be at least three repeats for every temperature investigated. There are many strengths to this investigation. It reviews factors which might affect the outcome of the experiment and describes how they have been controlled. It describes the statistical relationships within the situation studied. It suggests improvements to the apparatus or techniques used in the experiment. The practical procedures were clearly described and the appropriate scientific vocabulary was used. To improve this further the conclusion should be justified

Marked by teacher Cornelia Bruce 17/03/2013

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