An Investigation to show how concentration changes the speed of reaction between magnesium and hydrochloric acid.

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An Investigation to show how concentration changes the speed of reaction between magnesium and hydrochloric acid.

Planning 1:

The aim of this investigation is to find out the effect of acid concentration in the reaction between dilute hydrochloric acid and magnesium ribbon. The rate of a chemical reaction is a measure of how fast the reaction takes place. A high concentration of hydrochloric acid could mean a fast reaction whereas as a low concentration could mean a slow long reaction. I will be testing different concentrations of acid reacting with magnesium in two separate experiments, which will hopefully prove this initial prediction.

        During my science lesson I have learnt the following information that has enabled me to plan my investigation. Using my science book as evidence, I feel that as I continue to add water to the hydrochloric acid, its concentration decreases. Therefore the less acid molecules there are the smaller the chance of them colliding with the solid magnesium ribbon. This means decreasing the concentration of hydrochloric acid slows down the rate of the reaction between the magnesium ribbon and hydrochloric acid.

                         

                                     The diagram shows how fast acid molecules are colliding in a  

                                     concentration of 50cm3 hydrochloric acid.      

                         There are less collisions with the magnesium ribbon (mg) in a                    

                                     concentration of 40cm3 acid and 10cm3 water than a

                                     concentration of 50cm3 acid and 0cm3 water. This is because

                         the 10cm3 of water has replaced 10cm3 of acid molecules, so

                         now there are less acid molecules to collide with the Mg

                         ribbon.          

        = Magnesium molecule

        = Hydrochloric acid molecule

        = Movement

Planning 2:

Magnesium + Hydrochloric Acid              Magnesium Chloride + Hydrogen

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

The information in the paragraph that follows was researched from a secondary source, which enabled me to further plan my investigation. According to the collision theory, the more concentrated the reaction the greater the number of collisions between reactant molecules. This explains why the rate of reaction is highest when the reactants are initially mixed together (as their concentration are the highest at this time). As the reaction progresses the amount of each of the reactants decreases, hence the concentration decreases also. As a lower concentration means fewer molecules this means on average ...

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