Catalysts:
The rate of reaction ought to increases when a catalyst is added because if a catalyst is present, a collision needs less energy in order to be successful. This increases the chance of collisions being successful.
Concentration:
When the concentration of the acid is increased the rate of reaction ought to also increases. This is because there are a greater amount of acid particles increasing the chance of collision.
Plan
I have decided to investigate how temperature affects the rate of the reaction between Hydrochloric acid and Magnesium. I will observe and measure the rate of reaction at 20, 30, 40, 50 and 60 degrees Celsius. I will test the rate of reaction for each of these temperatures three times so that there is less chance of my results being affected by experimental error.
The highest temperature I am testing is 60 degrees because I want my experiment to be safe. I am also making my experiment safe by indirectly heating the acid. This means I will put the test tube of acid in a beaker of water and use a Bunsen burner to heat the beaker of water which will in turn heat the test tube of acid. Water will also maintain the temperatures I am testing for longer than acid. Other safety precautions I will be taking are to wear safety goggles and to place the Bunsen burner on a safety mat.
I have decided to use 5 ml of Hydrochloric acid (measured to the bottom of the meniscus) and 0.013 grams of Magnesium. I was originally going to use 0.026 grams of Magnesium but discovered during preliminary work that the reaction took quite a long time with this so I decided to halve the amount used. My investigation will be fair, as I will only use these amounts of Hydrochloric acid and Magnesium for each test.
I will need Hydrochloric acid, magnesium and the following apparatus:
Safety mat, Bunsen burner, tripod, beaker, test tube, stopwatch, thermometer and a measuring cylinder.
Method:
- I will fill the beaker with water and put the test tube with 5 ml of acid in the beaker
- I will indirectly heat the acid (as explained above) to whichever temperature I am testing
- When the acid reaches the appropriate temperature I will remove the Bunsen burner
- I will add the Magnesium and immediately start my stopwatch
- When all the Magnesium has reacted to form Magnesium Chloride I will stop my stopwatch and make a record of the time taken for the Magnesium to finish reacting.
I predict that as temperature increases, the rate of reaction will increase also.
Results
See fig. 1 for graph.
Conclusion
My set of results has led me to the conclusion that temperature does affect the rate of reaction between Magnesium and Hydrochloric acid. When the temperature of the acid is increased, the rate of reaction also increases.
Four of the points on the graph have a line of best fit with positive correlation. This clearly shows that as I predicted, there is a direct relationship between temperature and the rate of reaction - they are proportional to each other. However, the result for the rate of reaction at 60 degrees Celsius is not close to the line of best fit and is therefore anomalous. Despite this, it still agrees with the four other results that if temperature is increased, the rate of reaction will increase also.
The rate of reaction increases with temperature because at low temperatures, particles of reacting substances do not have much energy. However, at higher temperatures, particles take in more energy and thus move around faster. This results in the particles colliding more often and because they have taken in more energy, they are more likely to react. This means that the reaction occurs faster. This is why milk will keep for a few days if kept in a refrigerator, but it will sour within hours if left out on a hot, sunny, day.
Evaluation
I think the method I chose to investigate how temperature affects the rate of reaction between Magnesium and Hydrochloric acid worked well as most of my results would seem to suggest that my experiment was very accurate.
However, I do have one anomalous result. As my other results were either on or very close to the line, I do not think this anomalous result can be blamed on a poor method but it is possible that it was due to experimental error. It may be possible that although I took three lots of readings in order to rule out any such mistake; I may have repeatedly heated the acid to a temperature above 60 degrees or stopped my stopwatch too early.
Another possibility is that Hydrochloric acid or Magnesium begins to behave differently at 60 degrees Celsius. I would have to carry out further experiments in order to confirm or dismiss this theory. This would be dangerous however, as it would involve heating the acid to temperatures above 60 degree Celsius.
I said in my introduction that when temperature is increased by 10 degrees Celsius, the rate of reaction should double. However, in my experiment this was not the case. This was probably because I had no means of maintaining the temperature I was testing, which resulted in a steady fall in temperature. This would slow down the rate of reaction. This is also another possible explanation as to why my result for 60 degrees Celsius is anomalous. In the other tests, the water may have cooled more quickly than in the test for 60 degrees.
My test would have been better if I had been able to maintain the temperature that I was testing, as water was obviously not very good at retaining heat. My test may have been better if I had measured how much Hydrogen was produced in each reaction rather than just how long the reaction lasted for. I could have done this by putting a bung with a delivery tube in the test tube which contained the Hydrochloric acid and Magnesium and put the other end of the delivery tube in an upturned measuring cylinder full of water in a beaker full of water. I would have then been able to record how long it took for a certain amount of Hydrogen to be produced by the reaction. This would have been more accurate than my method as the method I used was based on me using something visual which was dependant on my judgement so there was a possibility of experimental error rather than simply taking down a measurement.
