I am going to investigate how temperature affects the rate of reaction between magnesium and hydrochloric acid. The procedure for the experiment is as follows;
* Using a measuring cylinder, measure 10cm3 of water and pour it into the side arm tube.
* Measure 10cm3 of hydrochloric acid (1 mol/ dm3) and add it to the water.
* Place the side arm tube in a water bath at 20OC, set up the apparatus below.
* Measure 10.9 cm of magnesium ribbon and check on the balance that it weighs 0.1g.
* Coil the ribbon around a pencil and then drop it into the side arm tube and quickly put a bung on the side arm tube (this must be done quickly to prevent gas escaping).
* Every 15 seconds measure the volume of gas produced until less than 1cm3 of gas is produced every 15 seconds.
* Repeat experiment two more times (for accuracy) and record all results in a table.
* Repeat the experiment for temperatures of 0.5M, 1.0M, 1.5M and 2.0M (1mole/dm)
It is important that only the temperature is changed since this is what is being investigated.
Method
* Apparatus
I have chosen to use a 10cm3 measuring cylinder to measure the volumes of substances used since it is more accurate than a pipette. I will use an electronic water bath for maintaining the mixture at a temperature since the temperature is more accurate than a water bath above a Bunsen burner.
A 100cm3 gas syringe should be appropriately accurate for measuring the gas produced since it is accurate to 1cm3 of gas. I will use a three figure balance to measure the mass of magnesium to be used since it is vital that as close to 0.1g of magnesium is used as possible.
* Variables
After deciding how to approach all of the variables in the experiment I decided how to carry out my experiment. I decided to use different concentrations of HCl in 0.5M, 1.0M, 1.5M and 2.0M (1mole/dm ). To obtain these different concentrations I used a solution of 1.0M which was already prepared and the same with a 2.0M solution. However in order to create a 0.5M and 1.5M solution I had to mix different solutions. The 0.5M solution was made using 10cm of deionised water and 10cm of 1.0M solution, this was then stirred with a glass rod. To make 1.5M solution the same concept was used, I mixed 10cm of 2.0M solution with 10cm of 1.0M solution.
I then measured and recorded how much volume of gas (cm ) was given off each 10sec using a stopwatch. Finally the gas syringe is an excellent piece of apparatus as it is very accurate, however I will have to make sure that the clamp does not hold on to it too tightly as this could effect the results.
To help obtain the best possible results I will repeat each experiment twice and then find an average set of data.
I predict that the high molarity concentration solution will have a much faster rate of reaction than the weaker solution. I have predicted this from my knowledge of a previous experiment and scientific knowledge. I think that this happened because the more HCl in the solution the greater the concentration and there will be more particles colliding and more energy and therefore a faster rate of reaction. The reason I think that the rate of reaction will increase is that the experiment is exothermic, this means that it will give itself more energy and therefore more collisions and faster collisions. Also in the 2.0M solution compared with the 0.5M solution there are much more HCl particles in the same volume so the are going to collide with each other more often
Therefore I predict that the rate of reaction will increase with the concentration of the HCl solutions.
* Rates of Reaction
Increasing the temperature increases the speed of the particles. The faster the particles move, the greater the number of collisions, and therefore the rate of the reaction increases. A 10OC rise in temperature almost doubles the rate of most reactions.
Chemical reactions take place by chance. Particles need to collide with enough velocity so that they react. As the temperature is increased the particles move faster since they have more energy. This means that they are colliding more often and more of the collisions have enough velocity to cause a reaction. Since there are more collisions the chemical reaction takes place faster.
Conclusion
My results prove my hypothesis. The higher the concentration of acid the faster the rate of the reaction. The results also show that the research that I did also showed a valid pattern, as the concentration doubled so does the rate of reaction. Between 0.5 and 1.0 mols the amount of time roughly halves as the concentration is doubled, this is also true for the 1.0 and 2.0 mol gap. If my results had been more accurate I think the results would show the concentration of the acid and the rate of reaction to be proportional. The graph also supports my prediction. On the graph the steeper the curve, the faster the rate of reaction. Also from the graph I was able to work out the average rate of reaction for the gas produced.
Evaluation
Overall I am pleased with my results and the way the experiment was carried out. I think my results were fairly accurate and proved my hypothesis. To make the overall experiment results more accurate we repeated it three times and then took the averageIf I was to do this experiment again I would probably make it more accurate by using a Burette to measure the amount of gas given off, this would measure a lot more accurately the amount of gas given off. And also using smaller particles of marble chip so I could match up surface area and weight more accurately each time. I would like to then see if the concentration of acid is proportional to the rate of the reaction.I had only one anomalous result due to the simplicity of the experiment, this is why I chose this factor to show the effect on the rate of reaction. The only odd result that I had was the third time I repeated the experiment on the 1.5 mol solution, the reaction took place a lot faster then the previous two. I think this was due to the marble chips that we were using. At first there was a large selection of marble chips available, so finding three to match the weight that I had set was pretty easy, by the time I had to repeat the experiment for the third time it was a lot harder, so in that instance instead of three chips being used I had to use five to make up the weight, this altered the surface area giving a larger area for it to react, which is why I think the reaction went a lot faster then expected..Also other things that I would like to investigate would be the experiment of time against amount of gas produced to show at which points the rate of reaction was at best and the curve/line of reaction. I would like to also investigate other factors, which affect the rate of a reaction like temperature and surface area to see how they affect the rate of a reaction. Some other areas in the experiment that I feel I could have improved on were factors like, controlling the stopwatch. There is lots of room for human error here. But the inaccuracies due to them were negligible because I paid close attention to these during the experiment.
