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

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How Concentration Affects the Rate of Reaction


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. Collision theory states that the rate of reaction increases depending on how often and how hard the particles collide with each other in order to react. Therefore more collisions increase the rate of reaction because the number of collisions between the reactants increases. So, if there is a greater concentration (more particles between the water molecules) there is a greater chance of collisions. There are other factors that need to be controlled. The temperature can also increase the number of collisions because the particle energy is increased so there is a greater chance of collisions. Therefore we must make sure the surrounding temperature is kept constant throughout the experiment. The use of a catalyst also speeds up the reaction rate because it provides a “surface” for the reactants to collide with each other. A catalyst will not be used in this experiment.

Collision theory states that particles more collisions increase the rate of reaction. Basically, rate of reaction depends upon how often and how hard the reacting particles collide with each other. A substance with a higher concentration would have more chance of colliding with other particles. The diagrams below show particles dissolved in water.

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Low Concentration                                         High Concentration

From the diagrams, we can see that it would be very hard to collide with a particle in the first diagram because there are not many to do it with. In the second diagram we can see that it is harder not to collide with particles because there are so many (highly concentrated). This shows that it would be quicker to react in a substance that has a high concentration like the second diagram than the first diagram.

        

The following is a step-by-step guide towards the procedure used

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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.

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).

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.