An Experiment to study the affect of changing the concentration of hydrochloric acid on the rate of reaction between hydrochloric acid and magnesium.

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Russell Robertson         Chemistry coursework        11MM

An Experiment to study the affect of changing the concentration of hydrochloric acid on the rate of reaction between hydrochloric acid and magnesium.

Aim To study the affect of changing the concentration of hydrochloric acid on the rate of reaction between hydrochloric acid and magnesium.

Background- The speed of a reaction is based on four factors, temperature, concentration, catalysts and surface area. The faster the particles of each substance collide, the faster the reaction will take place. This is due to the collision theory. If you heat up the two or more reactants, then the particles will gain more energy and will collide with other particles more frequently and harder.  When I say harder I mean with a lot more kinetic energy that would have been transferred from the thermal energy applied.

A catalyst will lower the activation energy, needed for a reaction to take place. This means less energy is needed for the reaction to start taking place.

A larger surface area makes the reaction speed up because there is more area for the particles available to have a collision with the large surface area.. This is because there are more sides of the solid particles to collide against so the probability of collisions and therefore the speed of the reaction is increased.

This diagram shows that the smaller particles have more surface area for the reactants to collide with whereas the large particle has most of the substance inside the particle walls

The last aspect is increased concentration. If there are more reactant particles, there are more chances of collisions than if there were less particles. This will speed up the reaction as the particles have more chance of colliding.

Here you can see in the first diagram the acid particles would collide with the magnesium, but they would need a lot more energy to react with all of the magnesium particles, as most of the energy would have been absorbed by the magnesium particles at the beginning of the reaction. This means that there is less energy to meet the reaction energy ( the energy required for the reaction to start). Eventually the acid particles will run out as the amount of acid is disproportionate to the magnesium. The hydrochloric would have broken down into hydrogen and magnesium chloride. The second diagram shows an increase in concentration of acid. This will mean that there are more acid particles to collide with the magnesium particles. This means that there will be more collisions a lot more frequently.

The experiment that I will do is reacting magnesium in hydrochloric acid. There is no known catalyst, and the surface area will be hard to measure so in this experiment the only realistic choices of variables is whether to vary the concentration of hydrochloric acid or the temperature. The variable, which I will choose, is the concentration of the Hydrochloric acid. In this case, I predict that the higher the concentration the faster the reaction will be. This is because there is more chance of the hydrochloric acid particles colliding with the magnesium than if there weren’t many particles. This is because more particles is the same space would mean a larger probability that there will be more collisions between the particles. Because of the larger probability, the reaction should speed up with a higher concentration of acid in the reaction.

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Preliminary experiment

In the preliminary experiment we started by timing how long the 2 cm of magnesium took to react with the hydrochloric acid. But although we found that the reaction occurred quicker with the higher concentration of acid we realised that this method was very unreliable because we had to rely on our eyesight and reflexes to find out the speed of the reaction. We needed to trust our reflexes but as the speed was too fast we weren’t sure at which point the reaction was over. When we saw that there was no more action (no ...

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