Investigating the rate of a chemical reaction

Apparatus

Conical flask with gas syringe attached / Bunsen burner / Gorse / Tripod / Thermometer / Stop watch / Magnesium ribbon / Hydrochloric acid (0.25 mol) / protective goggles.

Plan

? Make sure that you have all of your equipment ready before you start the experiment.

? Set up the apparatus ready to carry out experiment and put protective goggles on.

? Measure out 30ml3 of Hydrochloric acid into a conical flask

? Heat acid to one of the five different temperatures that you are testing, by using thermometer.

? Add the magnesium ribbon, attach bung to the conical flask and start the clock.

? Observe reaction and wait for the designated amount of gas (40cm3) to be produced and then stop watch and record results.

? Repeat experiment for five different temperatures.

Diagram

To Make Test Fair

In order to make each of the tests fair I will use 30cm3 of Hydrochloric acid / one piece of magnesium ribbon, 7cm in length / wait till the amount of gas in the gas syringe reaches 40cm3 before recording result.

Results

Temperature (0 C)

Time (seconds)

Rate of Reaction (1/time)

25

19

0.01

35

47

0.02

45

24

0.04

55

5

0.06

65

9

0.08

75

4

0.07

(Find graphs attached)

Analysis

The two graphs, which I have devised to show my results in the best possible way, are scatter graphs.

From the scatter graphs attached I can see that the data entered into the first graph (A Graph to Show the Rate of Reaction at Different Temperatures) shows that as the temperature was increased so did the rate of reaction, although at 75oc a freak result occurred (highlighted in green) and the freak result is not on the line of best fit, where as the other results are as they are all on the same curve

In the second graph that I devised (A Graph to Show the Time it Take's for 40cm3 of Hydrogen to be Produced at Different rates of Reaction) I can see that as the rate of reaction increased, the time that it takes for hydrogen to be produced decreased. In this graph the freak result is not as obvious, but it still is not part of the curve in which the normal results produced.

So from my graphs in can say that my prediction for Temperature was correct, so as the temperature of the acid is increased, the rate of reaction increases as well, therefore the 40cm3 of hydrogen is produced quicker.

Evaluation

I feel that I was precise and accurate in recording measurements. I measured the acid accurately by measuring the acid when the bottom of the liquid meniscus just touched the line on the measuring cylinder. I accurately cut the magnesium ribbon to the nearest millimetre with the ruler provided. I measured the starting and the end temperature accurately with a thermometer to the nearest 10C. I accurately measured the volume of gas evolved to the nearest 1cm3. I accurately measured the time that had elapsed to the nearest second with the stop clock.

Improvements to my experiment are that I could also use a monometer to be sure that the atmospheric pressure inside the syringe is the same as the pressure outside. To be sure that the pressure is the same inside the syringe as outside the syringe the water levels in the monometer must be level. The last improvement to my procedure is that I should check for gas leakages where the bung is placed into the conical flask, a smear of Vaseline would help me do this.

There are several things that I could do for further work. The first is to find out what the initial rate of reaction would be for concentrations 1.25M hydrochloric acid and 1.75M hydrochloric acid as it would be interesting to see how the rate increases compared to 1M hydrochloric acid.

I could repeat the experiment a further four times and I could either use all of the results or find the average rate, and time for each temperature. I could also experiment with different temperatures e.g 20oc, 30oc 40oc etc.

Another experiment that I could do is change the type of acid that I use. I could use sulphuric acid. This is a dibasic acid and its molecular build-up is H2SO4 and hydrochloric acid is 2HCL, because of this I would obtain different results. I could also use phosphoric acid, which is a tribasic acid, and its molecular build-up is H3PO4, I would also obtain different results if I used this type of acid. Nitric acid is a monobasic acid but its molecular build-up is HNO3, which is very similar to the molecular build-up of hydrochloric acid so the results that I would obtain from using this acid would be similar to the ones I already have, so I would not use this for any further experiments. The reason I could use a different type of acid for any further work is to find if the is a difference between them if their molecular build up is different. I could also use the less reactive metals of the reactivity series (zinc, aluminium, iron and lead) that way I could find the initial rate of reaction at 5 seconds for the higher concentrations of acid like 3.0M or 3.5M and I could find there relative activity. I obtained most of the information that I needed for my experiment form my teacher and exercise book. I also obtained information from several science textbooks and computer encyclopaedias. I obtained a small amount of information from the Internet.

During the test a freak result occurred, this is a result that goes against the pattern and flow of the other results. We know that this result differs from the others, as for all of the previous results, either the rate increased as the temperature increased, or the time increased as the rate also increased; but on this occasion the freak results temperature increased as its rate decreased. The scientific reasoning behind this result is that because the acids temperature became higher it released gas a lot quicker, so when the acid reached 750c the acid was letting off that much gas that the strip of magnesium ribbon had been raised from the surface of the acid, the affect of this was that the top of the magnesium could not be reached by the acid, so there was a smaller surface area for the acid to react with, so as I stated in my third prediction, the larger the surface area the greater the rate of reaction, but if this is reversed it means that if the surface area is decreased then the rate of reaction will become less. So that is why this freak result occurred in the experiment. A way to overcome this happening again is to find out at what temperature this kind of result occurs, so in future experiments I will know the limits of the acid and what temperature not to exceed.

As I only did an experiment for my first prediction, I can only evaluate that prediction and results. In my prediction I predicted that the rate of reaction would double if the temperature (oc) were to increase by 10. I can conclude that my prediction was partly true; as the rate did double s the temperature was increased by 10 for the first three results ( 25oc = 0.01 / 35oc = 0.02 / 45oc = 0.04 ) after these three the rate began to go up in twos. So therefore I can finally conclude that to a certain temperature the rate of reaction will double as the temperature increases by 10oc.