Determine what affects the rate of reaction when magnesium and hydrochloric acid are combined to form a solution.

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Magnesium and Hydrochloric Acid Coursework

Aim

The aim of this investigation is to determine what affects the rate of reaction when magnesium and hydrochloric acid are combined to form a solution.

The variable that I am going to change shall be the concentration of acid (the acid used in this experiment is going to be hydrochloric acid). We are going to control the temperature, the amount of acid and the amount of magnesium. We are going to measure the amount of hydrogen given off from the experiment.

Prediction

I expect that the magnesium will displace the hydrogen in hydrochloric acid, to form magnesium chloride.

I expect this to happen because magnesium is higher in the reactivity series than hydrogen. If an element is higher in the reactivity series than an element from a compound, it will displace it. In this case, magnesium will be displacing hydrogen. This is called a displacement reaction. Magnesium is an element and hydrochloric acid is a compound, made up of hydrogen and chlorine. The hydrogen will be displaced, and the magnesium will connect with the chlorine to form the compound, magnesium chloride.

This is the formula for the reaction:

Mg + 2HCl MgCl2 + H2

magnesium hydrochloric acid magnesium chloride hydrogen

There are several factors that could possibly affect the rate of reaction between magnesium and hydrochloric acid. It depends on the surface area of the magnesium used, the mass of the magnesium, the temperature of the hydrochloric acid and the concentration of the hydrochloric acid.

Particles need to collide with enough velocity so that they react. As the temperature is increased the particles move faster; because they have more energy. This means that they are colliding more frequently and more of the collisions have enough velocity to cause a reaction. Since there are more collisions the chemical reaction takes place faster; therefore increasing the rate of reaction.

I will also be expecting the time taken for 100cm³ of hydrogen given off to decrease as the concentration of acid is increased. I also predict that all of the experiments within this investigation will gradually slow down after a rapid beginning to the reaction.

This is because of the collision theory. This theory states that reactions should slow down because towards the end of a reaction there are fewer particles to collide. At the beginning of a reaction, none of the particles have reacted. This means that all of the particles at the beginning of the reaction are available to react; so there is more of a chance that the particles will collide and therefore increase the speed of the rate of reaction. Towards the end of the reaction, most of the particles will have already collided, making collisions more infrequent; which resultantly slows down the rate of reaction.
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Method

Before I begin the main experiment, I am going to perform a smaller preliminary experiment first. In my preliminary work I am going to measure the speed at which gas is produced at three different concentrations molar acid when reacted with 0.1g magnesium. The concentrations that I am going to use will be 2.0, 1.6 and 1.2 molar acid. I am doing this to check that the volume of acid that I have chosen (100cm³) will be sufficient for the experiment.

Concentration of acid (molar)

Time taken to release 100cm³ gas (seconds)

2.0
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