Rates Of Reaction

Planning

In this experiment I am going to observe and record the reaction between Magnesium and Hydrochloric Acid. My aim is to find out how the rate of this reaction will be affected if we change the concentration of the Hydrochloric Acid.

The rate of a chemical reaction is a measure of how fast the reaction takes place. It is important to remember that a rapid reaction is completed in a short period of time. An example of a fast reaction is an explosion, and an example of a slow reaction is rusting.

In the experiment, the Magnesium reacts with the hydrochloric acid to create Magnesium chloride and Hydrogen. The balanced formula for this is:

Mg(s) + 2HCL(aq) = MgCl2(aq) + H2(g)

Magnesium + Hydrochloric Acid => Magnesium Chloride + Hydrogen

Magnesium will react with Hydrochloric acid, because it is higher in the reactivity series than Hydrogen. The Magnesium displaces the Hydrogen in the acid, so it forms Magnesium Chloride and Hydrogen gas.

For a reaction to occur, the reactant particles (Magnesium and Hydrochloric Acid) must collide. Only a certain fraction of the total collisions are actually successful collisions though. The successful collisions have enough energy at the moment of impact to break the existing bonds and form new bonds, resulting in the products of the reaction. Increasing the concentration of the reactants bring about more collisions, and therefore more successful collisions, increasing the rate of reaction.

Equipment

* Magnesium Ribbon

* Different concentrations of Hydrochloric acid (0.25, 0.5, 1.0, 1.5 and 2.0M)

* Beaker

* Measuring cylinder

* Tube to carry the hydrogen into the measuring cylinder and a bung

* A container full of water

* Safety goggles

* Stopwatch

Method

First, I will pour 50cl of 0.25M Hydrochloric acid into my beaker. I will then fill my container and measuring cylinder full with water, and put the measuring cylinder in the container of water upside down, with my finger over the end so that the water will stay in the cylinder, when it is put in the upside down position. I will then put one end of the hydrogen collecting tube in the upturned measuring cylinder, where the end is still submerged into the water, keeping the pressure so that the water stays inside it. Next, I will put the strip of Magnesium Ribbon inside the beaker with the Hydrochloric Acid in, and put the end of the tube with the bung, into the top of the beaker to collect the hydrogen. When the hydrogen created by the reaction goes through the collecting tube and into the measuring cylinder, it will bring the water level down, and then we will be able to observe and record how much hydrogen has been produced in the reaction. I will record the amount of hydrogen produced every 30 seconds up to 2 minutes and 30 seconds, in a table. I plan to repeat this in order to get three sets of readings.

Once I have completed the experiment for all of the concentrations of acid, I will carry it all out again, to get a second set of results. From these, I make an averages table and draw a suitable graph to show my results. I will do the experiment again to get a second set of results to cover for anomalies, and to ensure that my results are as accurate as possible.

For my results to be of any use, I must ensure that the investigation is carried out impartially; therefore it is important to control the variables so that only one variable changes.

Therefore I must:

* Use the same volume of hydrochloric acid throughout (50cl)

* Use the same mass of Magnesium for each test

* Use the same lengths of Magnesium ribbon for each test

* Always start the timer as soon as the acid is poured onto the Magnesium

* Make sure that the reaction always takes place at the same room temperature.

The only one variable will be the concentration levels of the hydrochloric acid, which I have already said, will be 0.25, 0.5, 1.0, 1.5 and 2.0M.

The factors that could affect the rate of reaction of are:

Concentration of acid - This could affect the rate of reaction because the higher the concentration of the acid, then the more acid particles there are per volume of acid. Therefore, more collisions per second will occur and then there will be more successful collisions per second.

Temperature of the acid - Rates of reaction increase with a higher temperature because the particles involved in the reaction have more energy to move (from the heat) so they collide more rapidly. This will give more successful collisions per second, and therefore it is essential to keep the temperature the same.

Surface area of the Magnesium - If the Magnesium had a bigger surface area each time the experiment was repeated, then the acid particles will have a bigger area to collide with, so more collisions will occur every second, which would mean there are more successful collisions per second, and therefore it is essential to keep the surface area the same throughout the experiment.

Prediction

From my own knowledge I can predict that as the concentration of the hydrochloric acid increases, the rate of reaction will also increase/speed up. I have based this upon the collision theory. The higher the concentration of acid, then the higher the concentration of acid particles there will be in a certain volume. This will mean that the higher the concentration of acid, the more the successful collisions there will be in 1 second. Therefore, the rate of reaction increases. I predict that if I double the concentration of hydrochloric acid the rate will also double, because there will be double the number of particles and therefore double the chance of collision.

Preliminary work

I did the same experiment, but on a smaller scale, as preliminary work. This enabled me to discover the best time to record the amount of Hydrogen produced at regular intervals, which I found to be every 30 seconds. I needed to choose a measuring cylinder of a sufficient size