Everything is constructed of particles. For a chemical reaction to take place there must be a collision between these particles. However, a simple collision is not sufficient for a reaction to occur; the particles must collide with sufficient energy to break and make chemical bonds, an amount known as the activation energy.
Due to this, as the concentration increases, so should the rate of reaction because there are more particles in a given volume (in this investigation HCL), so therefore, it is more likely that a higher number of effective collisions will occur at any given time – giving a higher rate of reaction.
Apparatus: The apparatus required for this experiment are:
- Three measuring cylinders (1 small, 2 large)
- Timer
- Conical flask
- Bung with collecting pipe connected
- Water bowl
- Safety glasses
Method:
- Collect apparatus, as listed above
- Place on safety goggles.
- Fill bowl with water (enough to cover the end of the pipe by 3cm)
- Fill one of the large measuring cylinders with water and with holding hand across end place into bowl and over pipe without any air getting into the measuring cylinder.
- Remove bung from flask and place correct amount of magnesium into the conical flask.
- Measure the first amount of hydrochloric acid with the correct amount of distilled water, as in the dilution series below.
- Pour diluted hydrochloric acid into the conical flask and start timer while simultaneously placing the bung back into the neck of the flask.
- Record result.
- Clean apparatus with distilled water.
- Continue doing the above steps for each of the dilutions in the series
- Repeat each dilution at least twice, preferably three times, to gain a good scientific average.
Fair test: In order to keep the experiment a fair test the variables, except for the concentration must remain constant because if the conditions alter between temperatures, two results cannot be compared because it cannot be determined if the changed variable has affected the results gained.
Safety: In order to keep the conditions for the experiment safe I will wear safety goggles and take care to immediately wipe up any spillages and follow general laboratory practical rules so as to limit the risk of potential injury.
Results:
Conclusion: As I predicted, as the concentration decreases, so does the rate of reaction.
The reason for this is because when the concentration is 1M of HCl there are 6 x 1023 atoms in 1000cm3 with which the magnesium ribbon particles can react; however, when the concentration decreases to 0.8 M there are only 4.8 x 1023 atoms in 1000cm3 with which the magnesium particles could collide, so therefore is stands to reason that with less atoms there will be less effective collisions and do less hydrogen given off in a given time (or a slower rate of reaction). This links directly with my prediction from my understanding of the collision theory; as the concentration of HCl particles decreases so does the rate of reaction.
Evaluation: The results, although fairly basic, do link in with scientific theory. The curves on the graph seem fairly reliable as they show a decrease in the gradient when the molarity decreases. However, there are errors in the results as a great deal relies on human-eye for the reading of the Hydrogen collection. Using a gas syringe instead of a measuring cylinder could have lessened this problem. If this particular piece of equipment had been available, I may have been able to gather a more reliable and accurate set of results.
