The Collision Theory
The collision theory is how a reaction happens. The particles need to collide for a reaction to happen. These particles also have to collide with enough energy. This is because if the particles move too slow they just pass each other and it less likely for a collision to happen. The higher the temperature the faster the particles move.
Tasneem Husain
20o 40o
Prediction
I predict that the higher the concentration the faster the rate of reaction will be. I can support my predictions by using the collision theory. If there were 2 beakers, 1 has 5M and the other has 1M, then you put something into each test-tube to react with it. The 5M is more concentrated that 1M, therefore I think 5M will react much faster than 1M will. This is because 5M will have many more particles than 1M. So the magnesium that I have put into each test -tube will have a higher chance of colliding with 5M than in 1M.
Equipment List
This is all of the equipment that I have used in the experiment:-
- Magnesium
- 5 different types of concentrated acid: 3M, 2.5M, 2M, 1.5M and 1M
- 3 Test-tubes
- Test-tube rack
- Measuring cylinder
- Pipette
- Scissors
- Ruler
- Paper towel
Method
Step 1: Pour 25cm3 of 3M of hydrochloric acid into a test-tube using a measuring
cylinder.
Step 2: Pour the same amount and same concentration into two other test tubes.
Step 3: Cut 15 pieces of magnesium. Each piece must be 1cm long
Step 4: Drop 1 piece of magnesium into 1 of the test tubes. As soon as the magnesium touches the hydrochloric acid, press start on the stopwatch.
Step 5: Press stop when the reaction is complete (when the magnesium has disappeared completely).
Step 6: Repeat this in the other two test tubes.
Step 7: Record all three results.
Step 8: Rinse out all 3 test tubes and measuring cylinder. Then dry the test tubes with paper towels.
Step 9: Repeat all of these steps, in exactly the same way, except changing the concentration each time. Do these steps for the other contractions of 2.5M, 2M, 1.5M and 1 M.
Fair and Accuracy
This experiment was a fair test. Each time 25cm3 of acid and 1cm of magnesium was used. Also we started the timer exactly when it hit the acid and stopped it as soon as the
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reaction was completed. As the reaction took place, we observed it at eye level. We did not shake the test tube as the reaction took place. Here are some extra things that we kept the same: it was on the same day, the magnesium was cut from the same strip (therefore the magnesium had the same surface area) and the same test tubes were used each time. If I were to get an odd result, while carrying out this experiment, I shall check whether or not I followed the method properly. I would still record the result(s) in my table. However I would note down which step, in the method, I missed out or incorrectly followed. In order to make my results more accurate, I would repeat this experiment at least three times.
Safety
As we were doing this experiment we wore safety goggles because we were using acid.
Result
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Conclusion
From looking at Graph 1, we can instantly see that the more concentrated the acid is, the less time it took for the reaction to take place. We can also see from Graph 2 that the more concentrated the acid, the faster the rate of reaction. These are the obvious trends and patterns, which occur in the graphs. This conclusion fits the information from my scientific knowledge. The scientific knowledge states: ‘the more concentrated the solvent, the faster the rate of reaction.’ The explanation for this is also stated in the scientific knowledge: ‘the more concentrated the solvent the more particles there will be. This means the particles are squashed in a certain amount of space. Therefore the particles are more likely to collide more often with the solute.’ In this experiment the solvent would be the hydrochloric acid (HCl) and the solute would be the magnesium (Mg). We can also see that the conclusion is true from looking at the table of results. My conclusion and my results agree with the prediction I made earlier: ‘I predict that the higher the concentration, the faster the rate of reaction will be.’ This is exactly what my conclusion stated.
Evaluation
In my opinion, although overall the investigation went pretty well, I think it could still have been better. This is because none of the individual experiments were 100% accurate. The timings in the 2.5 molar and the 1 molar experiment didn’t have similar results. There was one odd result in the 1 molar experiment. This was in the second experiment. We think this was an odd result because when we came to this experiment we had to get a new strip of magnesium. From this strip we had cut a 1cm piece off, but we hadn’t cut the beginning edge straight. Therefore the acid had more magnesium to react with and took longer to finish the reaction.
We used the same method for each experiment. The equipment that we used was reasonable, but we could have used a graduated pipette rather than a measuring cylinder, just to make the volume of acid more accurate. There were many ways in which we could have improved our method to make our results more accurate. We could have used a water bath to control the temperature of the acid and to ensure that it is the same each time. In our experiment the test tube got hotter as the experiment started because it’s an exothermic reaction. The heat would have given the particles more energy. As the temperature increased, the kinetic energy of the particles also increased. Due to the fact that the particles were moving around more quickly, the collisions are likely to take place more often and therefore making the reaction faster. Another way that we could have made the results more accurate is by weighing the magnesium to make sure that it is the same mass each time.
We could have used a wider variety of concentrations to see by how much the rate of reaction changes. For example we could have used concentrations like 0.5 molar, going up in half a molar, all the way up to 7 molar. Also we could have repeated the same experiment, say 5 or 6 times, to make the results more accurate. Another way that we could have made our investigation more accurate is by using different metals and substances in the acid to see whether it makes any difference to the rate of reaction. Other
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than these points that I have made, I feel that these results are quite reliable. On Graph 1, only one of the results was odd. We know that the result was odd because it did not fit on the curve.
