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The Effect of Concentration on the Rate of Reaction when you React Hydrochloric Acid with Marble Chips

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Introduction To observe how concentration affects the rate of reaction I will be doing an experiment involving an acid, hydrochloric acid (HCl) and marble chips, Calcium Carbonate (CaCO3). This experiment requires the following apparatus: * Conical flask * Thistle tube * Rubber stop cork * Delivery tube * Burette * Plastic container In this experiment some factors must be varied and others controlled. The concentration of the acid needs to vary. This is because the experiment involves measuring the affect of concentration on the rate of reaction. The volume of the acid used in the experiment needs to be the same because this will make it a fair test. Preliminary work has shown that 25cm3 of acid is a good amount to use. The mass of marble chips (calcium carbonate) needs to be kept constant. Preliminary work has also shown that an appropriate mass of chips to be used is 1.5 grams. The size of the marble chips must be kept relatively the same because the surface area affects the rate of reaction. It affects the rate of reaction because finer particles cause the surface area to increase as they take up more space than larger chips and therefore the extra surface area leads to a quicker reaction because there are more collisions. ...read more.


3.5 45secs 42secs 33secs 40secs 4 29secs 22secs 27secs 26secs The table above gives the rate of reaction time in minutes and seconds for all attempts for all the different molars. For every attempt, looking down the column we can see that the rate of reaction decreases because the concentration increases. This is a trend present throughout all the attempts. The average time has been calculated in the last column. This gives the results in a more reliable way. The results can be relied upon, but there is an instance where the reaction rate increases instead of decreasing in the average section. The time has gone up by 2 seconds for 2.5 moles concentration. The following graph shows the affect of concentration on the rate of reaction. From the graph I have come to the conclusion that the more concentrated a substance is, the quicker the reaction will occur. So the rate of reaction will be increased if the substance is more concentrated. The graph shows a decreasing time. There is a reasonable negative correlation here. This is because all the points aren't so close to a straight line but this is probably due to some minor flaws in the procedure, which will be analysed in the evaluation. The only anomaly here is the reaction using a 2.5 mole concentration. ...read more.


It could be sealed using a cork-screw that is the same size as the flask top. This could be the improvement to the current method. I think the evidence obtained is enough to support the conclusion, but I don't think that it proves collision theory, just supports it. The evidence does support the theory of collision but with these results and this experiment, you cannot prove that this theory actually exists. The evidence that I have obtained here is quite reliable, but further work could be done to make the results more reliable and prove other things. Further work could include measuring the rate of reaction. There are 2 ways in which this could be done: 1. This reaction produces a gas (CO2). If we place the flask on top of a mass balance then we can observe the change in mass and see how long it takes for it to disappear. 2. Another method is to use a gas syringe and observe the volume of gas that is given off when there is a reaction. Note the change in volume and how long it has taken. For both of these methods you would need to vary the concentration each time and then see what the effect is on the rate of reaction. How Concentration Affects the Rate of Reaction ...read more.

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Response to the question

Although the essay provides a good idea about this investigation, it contains some practical and theoretical errors. The method of approach to the question is good and it contains most of the information needed. However the essay is not properly ...

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Response to the question

Although the essay provides a good idea about this investigation, it contains some practical and theoretical errors. The method of approach to the question is good and it contains most of the information needed. However the essay is not properly organized and there are lots of scattered information all over the essay. There are many extra information provided to explain the basics of the experiment which is a useful method however the usage and explanations are not totally consistent.

Level of analysis

Although the method of approach is good, the biggest problem with the experiment, is the apparatus used which is not completely suitable and would not produce a reliable result. Carbon Dioxide is a partially soluble gas which should not be collected using the water displacement method since some of the gas would get dissolved in the water. Therefore a gas syringe would be required to measure the volume of the gas produced. Since the apparatus is not suitable completely, some of the steps in the experiment should be modified. The assumptions are correct but the explanations are not reasonable and consistent. Some details are also missing including the method of handling and carrying the acid. There are some incorrect information in the essay including the function of catalyst which is providing an alternative route with a lower activation energy, and the definition of concentration which is the ratio of the no. of moles of solute over the volume of solvent(dm^3).

Quality of writing

There are not many grammatical or spelling errors to point out but the author has not made use of technical terms correctly. There are some silly mistakes that could had been avoided by double checking before submitting the essay for example in the conclusion, the writer has written "...as the concentration of acid increases, the rate of reaction will decrease." and then stated that higher concentration results in faster rate of reaction. The writer knows that the higher concentration results in higher rate but like any human, he/she has made a mistake but such mistakes should be avoided when writing such informative essays.

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Reviewed by alireza.parpaei 09/02/2012

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