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Investigation Planning

The aim of my investigation is to find out how the concentration of an acid affects the rate of reaction on marble chips.

The factors which might affect how well the investigation will work are:

„h The temperature

„h The concentration of the acid

„h The surface area (size of the chips)

„h Adding a catalyst (this is possible but not for this reaction)

„h The mass of the carbonate (amount of chips)

„h Different acids.

I want very accurate results so I am going to repeat my experiment two times and take an average. Each time I do the experiment I am going to measure the rate of reaction at five different concentration levels at intervals of ten seconds so that I can demonstrate a proportional relationship between these two factors. I will also measure the factors, which I hope to keep constant so that I can prove they did not change and affect the experiment.

The equipment I will need to carry out the experiment is: a gas syringe, a chronicle flask, a burette, a 10cm cubed measuring cylinder, a set of scales, a beaker, a stop watch, hydrochloric acid and medium size marble chips. The experiment will be set up in this way:

I will weigh out exactly or as close as possible to 2 grams of medium sized marble chips. Using a burette I will measure out exactly 5 cm cubed of hydrochloric acid in a chronicle flask. I will put the chips into the flask with the acid and immediately place the gas syringe bung over it so as to lose as little gas as possible. I will then take readings at intervals of ten seconds. I will do the same but with 4cm cubed of acid and 1cm cubed of water thus decreasing the concentration. I will carry on like this to 1cm cubed of acid and 4cm cubed of water. I will then do exactly the same again for the second time.

Whilst carrying out the investigation I will of course wear safety spectacles to protect my eyes from harmful acids. I will also stand up whilst carrying out the experiment in case I spill acid and it goes onto my lap.

The rate of reaction depends on how often and how hard the reacting particles collide with each other. Particles have to collide in order to react, and the have to collide hard enough as well. This is called the collision theory. When the temperature is increased the particles all move quicker. If they are moving quicker then they are going to have more collisions. Higher temperature also increases the energy of the collisions, because it makes all the particles move faster. Faster collisions are only caused by increasing the temperature. Reactions only happen if the particles collide with enough energy. Ata higher temperature there will be more particles colliding with enough energy to make the reaction happen. This initial energy is known as the activation energy, and it is needed to break the initial bonds. If one of the reactants is a solid then breaking it up into smaller pieces will increase its surface area. This means the particles around it in the solution will have more area to work on so there will be more useful collisions. A catalyst works by giving the reacting particles something to stick to where they can bump into each other. This obviously increases the number of collisions too. If the solution is made more concentrated it means that there are more particles of reactant knocking about between the water molecules which makes collisions between the important particles more likely. Because of this I expect the reaction rate to be quicker when the concentration of the acid is higher. The reaction should however, end on the same amount of gas given off.

I did a number of trial experiments. Firstly, I took 5g of marble chips and 20 cm cubed of hydrochloric acid. However, the gas given off was too much for the gas syringe so I changed it to 2g of marble chips and 5cm cubed of hydrochloric acid. This turned out to be fine.

Analysing Evidence According to my graph, the higher the concentration of the acid, the more gas given off. The 2M concentration of acid started and ended with the most gas given off (by thirty seconds the 2M of concentration had reached 36.5cm3 of gas collected). Whereas the 0.4M of acid started and ended with the least gas collected (by thirty seconds only 8.5cm3 of gas had been collected). However, according to my prediction these results should have shown that the higher the concentration of acid should give a steeper graph with the reaction finishing much quicker. Despite, my results I still think that my prediction was a correct one. I think that it is not the prediction but the results that are incorrect. Results First experiment:

Time (seconds)Gas given off (in cm cubed) from 5cm cubed HCl, 0 H3O, 2.004g chipsGas given off (in cm cubed) from 4cm cubed HCl, 1cm cubed H3O, 2.000g chipsGas given off (in cm cubed) from 3cm cubed of HCl, 2cm cubed H3O, 2.003g chipsGas given off (in cm cubed) from 2cm cubed HCl, 3cm cubed H3O, 1.999g chipsGas given off (in cm cubed) from 1cm cubed HCl, 4cm cubed H30, 2.007g chips























Second experiment:

Time (seconds)Gas given off (in cm cubed) from 5cm cubed HCl, 0 H3O, 2.002g chipsGas given off (in cm cubed) from 4cm cubed HCl, 1cm cubed H3O, 1.999g chipsGas given off (in cm cubed) from 3cm cubed of HCl, 2cm cubed H3O, 2.000g chipsGas given off (in cm cubed) from 2cm cubed HCl, 3cm cubed H3O, 1.997g chipsGas given off (in cm cubed) from 1cm cubed HCl, 4cm cubed H30, 1.996g chips























Average of first and second experiment:

Time (seconds)Gas given off (in cm cubed) from 5cm cubed HCl, 0 H3O, 2.004g chipsGas given off (in cm cubed) from 4cm cubed HCl, 1cm cubed H3O, 2.000g chipsGas given off (in cm cubed) from 3cm cubed of HCl, 2cm cubed H3O, 2.003g chipsGas given off (in cm cubed) from 2cm cubed HCl, 3cm cubed H3O, 1.999g chipsGas given off (in cm cubed) from 1cm cubed HCl, 4cm cubed H30, 2.007g chips























Evaluating Results In my opinion the investigation went OK. I think I did take a sufficient amount of readings but of course it would have helped if I had another set of results. I am not entirely convinced that my results were accurate enough because each concentration should have ended on the same amount of gas but in the higher it should have only taken a shorter time than the lower concentrations. I think his happened because I used too much carbonate for the acid, which meant it could not reach its maximum capacity of collected gas. I also could not get the carbonate into the acid and put the bung on without losing any gas. This evaluation point is perhaps the most important. Also, I could never get exactly the same amount of marble chips each time.

There were a number of anomalous points (these are circled on the graph). These can be explained by simply a poor reading.

If I had to do the investigation again I would change the amount of marble chips I put in from 2grams to 1gram.

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