Investigating the rate of reaction between Magnesium Ribbon and Hydrochloric Acid.

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Chemistry Coursework                George Hiner

Investigating the rate of reaction between Magnesium Ribbon and Hydrochloric Acid.

Aim:

        The aim of my project is to investigate the reaction between Magnesium Ribbon and 2M Hydrochloric Acid by measuring the rate of reaction as the concentration of the acid is varied.

Magnesium is in the second group of the periodic table which means it is an alkaline earth metal with an atomic number of 12, that means that there are two spare electrons on the outer shell of the atom. This is why it’s only fourth in the reactivity series because the three above it are in the first group and so only have one spare electron, where as magnesium has two spare electrons.

The reaction between an acid and a metal can be shown as: 

Acid + Metal             Metal Salt + Hydrogen

Therefore I’d expect the reaction between Hydrochloric acid and Magnesium ribbon to react together as shown in the equation below:

        

Hydrochloric acid +         Magnesium                        Magnesium Chloride + Hydrogen

 

     2HCl (aq)          +             Mg(s)                                   MgCl2 (aq)             +     H2 (g)

Scientific Theory: 

In my experiment in order that the magnesium and the Hydrochloric acid react together:

  • A Magnesium atom and an acid atom must collide with each other.
  • The collision between the two atoms must have enough energy. The minimum amount of energy needed for the reaction to occurs called the Activation Energy.

This is also known as the collision theory. When there’s a successful collision old bonds between the magnesium atoms are broken and then new bonds are formed which will be the magnesium chloride. If there are a lot of these collisions, then the reaction is going very quickly and so the rate of reaction is high, but if there are not very many collisions the rate of reaction is low. In other words the rate of reaction depends on how many successful collisions there are in a given unit of time. 

The rate of reaction can be measured two ways:

  • Measure the rate at which the reactant is used up
  • Measure the rate at which the products are formed.

In this experiment I’ll be using the second method where I Measure the rate at which the products are formed, this will mean that I measure the rate at which hydrogen is given off as it is the only gas being given off. I will be measuring it in a 100 cm3 measuring cylinder.

Prediction

        I predict that as the concentration of the Hydrochloric Acid increases the rate of the reaction will also increase. I believe this to be the case because in my scientific theory I state that for the reaction to take place a magnesium atom and an acid atom have to collide with each other. Therefore increasing the concentration of the hydrochloric acid then the number of acid atoms will be greater and so the chance of one of these atoms colliding with a magnesium atom will be higher and so the rate of reaction should be higher. But then as the magnesium starts to run out the rate of reaction will decrease because there aren’t as many magnesium atoms and so the chance that the acid atoms collide with the magnesium atoms will be less. If I was to show it on a graph I predict that it would look like:

 

An example of rate against concentration graph.

Preliminary Experiment:

        While planning my experiment I decided to carry out a preliminary experiment to try and discover and foresee different aspects of my experiment that might go wrong and find out how I can overcome the problems to achieve the most accurate and reliable results. To do this I set up the apparatus and I put in the magnesium ribbon of different lengths, where the concentration of the hydrochloric acid was 2 Mol. The first time I did the experiment I took readings every ten seconds but all the magnesium had been used up within this time and so when I did the experiment again I thought that taking a reading every 5 seconds was a more sensible time, because every ten seconds was too longer time and anything less than five seconds wouldn’t be enough time to read off a result from the measuring cylinder accurately. The results of my second preliminary experiment are shown below:

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From my preliminary I learnt a few things that, in order that I can obtain the best and most reliable results, I will have to enforce. Firstly I realised that the length of the magnesium I should use in the main experiment should be ten cm and that the time interval between the readings should be five seconds. Secondly, I realised that when I was measuring out the solutions, and when I was reading off the results, I would have to be careful of the meniscus. So in the real experiment I will have to be very careful ...

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