The Effect of Concentration on the initial rate of a chemical reaction

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Matthew Jaroszewicz

Investigation: The Effect of Concentration on the initial rate of a chemical reaction

The Reaction:

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

Equipment                                                Chemicals

  • Graduated gas syringe (+/- 0.5cm3)                Magnesium Ribbon
  • Conical Flask                                        2 Molar hydrochloric acid
  • Thermometer
  • Stopwatch
  • Clamp/Stand
  • Burettes (+/- 0.05cm3)

Diagram

The Magnesium ribbon is to be put into the conical flask of Hydrochloric Acid and every 10 seconds the total amount of Hydrogen produced is read for a total of 2 minutes.

I will make the test as fair as possible by making sure that the controlled variables are very much controlled.

Controlled Variables

Volume of acid – I have chosen to use 20cm3 of acid.  I came to this decision because in preliminary experiments I used less acid and found that the reaction was too slow but too much acid would be a waste.  20cm3 would be perfect and it divides easily, therefore calculating how to dilute the acid precisely will be easier.

Temperature of acid – if the temperature is increased; the rate of reaction shall also increase due to an increase of kinetic energy in the particles (greater frequency of collisions).  The experiment will be done at room temperature because it is the most convenient temperature and the easiest to keep constant.

Apparatus – the apparatus must be used, other this could effect the reaction.

Stirring?  – I have decided not to stir the mixture because manual stirring is difficult to keep at a steady rate, it is easier and more accurate if no stirring occurs because it is definite that it shall be the same.

Amount of Mg ribbon – I decided to use 10cm3 of magnesium ribbon because it means that the reaction will take longer to complete than 5cm3 and if a pattern occurs it will be easier to see.  In preliminary experiments, a small amount of Mg took to shorter time at 2M, and a large piece took too long at a low concentration.  The ribbon shall be spiralled.

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Changed Variables

The concentration of the acid shall be changed.  I shall be given 2M Hydrochloric Acid and to decrease the concentration, the solution will be diluted accurately by using burettes.  To change 20cm3 of 2M acid to 20cm3 of 1M acid, the ratio of acid to water would be 1:1 - 10cm3 of water + 10cm3 of 2M hydrochloric acid.  These measurements shall be accurately measured by using burettes.  The burettes are very accurate (+/-0.05cm3), this making the results more reliable.  The concentration shall range from 0.5M to 2.0M to ensure a wide range of results.

Measured Variables

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