During each experiment I will observe the rate of reaction by closely monitoring and timing how long it takes for all of the magnesium to disappear. I know already that when magnesium and hydrochloric acid react there is effervescence. I will record the time from when the magnesium is added to the acid (effervescence starts) until the all the magnesium has reacted (effervescence stops). I will also notice that hydrogen gas is given off which has an unpleasant smell.
I will use a range of temperatures for each reaction. I am going to investigate the effect of 7 different temperatures in total. I will start at room temperature, which I will measure before I start, and I will finish at 80˚C. I will not be investigating the effects of any temperatures over 90˚C, as I do not want the water to boil.
To make sure that my results are as accurate as possible I am going to do 3 replicates of each temperature and then take an average, as we can’t rely on one result alone. An average will take into consideration all of the results however high or low they may be and it gives a better overall result.
Prediction
From my own background knowledge and from the theory I learnt in class I know that as the temperature increases the rate of reaction will increase.
This will happen due to an increase in the effects of the Collision Theory. In both the magnesium and the hydrochloric acid there are a number of particles waiting to react. In order for a particle to react two things must happen:
- It must collide with another particle.
- The collision must have enough energy.
Therefore the rate of a reaction depends on how many successful collisions there are in a given unit of time. In a successful collision between particles, bonds are broken which needs energy and new bonds are formed which releases energy.
So at a low temperature particles of reacting substances do not have much energy. However, when the substances are heated, the particles take in energy. This causes them to move faster and collide more often. The collisions have more energy, so more of them are successful. Therefore the rate of the reaction increases. Faster collisions increase the rate of reaction and these faster collisions are only caused by increasing the temperature.
Practical procedures.
List of Apparatus:
*Bunsen burner
*Heatproof mat
*Tripod stand
*Gauze
*Thermometer
*250ml Beaker
*Measuring cylinder
*Boiling Tube
*Water
*Test tube rack
*Stopwatch
*Top pan balance
*Tongs
*Safety goggles
*21 lots of 0.1grams of magnesium.
*21 amounts of 20ml of hydrochloric acid.
*Water
*Weighing boat
Diagram of Apparatus:
Safety precautions:
As we are carrying out a chemical reaction involving acid we need to wear safety goggles to protect our eyes. The boiling tube, which contains the hydrochloric acid, will become very hot as we increase the temperature so we will have to use tongs when lifting the tube away from the heat; this is to insure that we do not burn our hands. We are also working with a Bunsen burner; we need to be aware of it and to make sure that we leave it with an orange flame so that others can see it. We also need to take into consideration all of the other basic lab safety precautions.
Method
- Measure out 20ml of acid and put into the boiling tube.
- Set-up apparatus as above and heat the beaker and its contents to the desired temperature.
- When the acid is at the correct temperature lift it from the water and place into the test tube rack. Carefully weight out 0.1grams of magnesium using the weighing boat and the top ban balance.
- Add the magnesium into the boiling tube containing the acid.
- Start the stopwatch and watch until all the effervescence has stopped.
- Stop the stopwatch when the effervescence has stopped.
- Record result.
- Repeat another two times at the same temperature, and then move on to the next temperature.
Results
As we do the investigation the results table, which we will draw out before we start, will be filled in as we collect the data. Appropriate graphs will be drawn later on as a way of analysing our data. The rate =1/ time in seconds. The units of rate in S .
A sample results table has been included below:
Obtaining evidence
Below is a table of my results.
We carried out the experiment in the chemistry lab at school under supervision. We took our time to record results properly and worked in pairs, as there would not be enough apparatus for everyone in the class to use.
Interpreting and evaluating
Interpreting.
I have found that yes the temperature has an impact on the rate of the reaction, in that as the temperature increases so does the rate of reactions. I can see this clearly from my results table, by looking at the column of the average time we can see that as the temperature increases the average time decreases therefore the rate becomes quicker.
To analyse my data and results I have drawn two graphs to show the patterns that occur between the rate, temperature and average time. Graphs were draw on the computer, as they were more accurate and were more consistent at giving the lines through the results.
From the first graph there is a negative relationship showing that as the temperature increases the average time decreases.
From the second graph we see a positive relationship in that as the temperature increases the rate of the reaction between hydrochloric acid and magnesium increases.
Both graphs fit in with my prediction, showing that the rate increases with the temperature.
From both graphs I can also see that there are no residuals.
On the basis of what the graphs have shown me I can say that my conclusion fits in with my prediction.
When two chemicals react their molecules have to collide with each other with sufficient energy for the reaction to take place. This is the collision theory, which I mentioned in my prediction. The two molecules will only react if they have enough energy. So by heating the mixture, I have raised the energy levels of the molecules involved in the reaction. Increasing the temperature means the molecules move faster. This is Kinetic theory. Since temperature is a measure of the motion of particles, as I increased the temperature the particles of magnesium and hydrochloric acid moved faster. When these particles moved faster there were more collisions, which were also more violent. This is why the rate of reaction increased. A rise of 10˚C approximately doubles the rate of reaction. I can also say that since the particles moved faster they travelled a greater distance in the given time which also meant they were involved in more collisions. Again because these particles were moving very quickly a larger proportion of the collisions exceeded the activation energy so the rate of reaction increases. The activation energy is the fixed amount of energy, which must be reached so that the reaction between magnesium and the acid can take place.
If there are lots of successful collisions in a given time, then a lot of hydrogen is produced, which I also found to be true.
Evaluation
My method was accurate and I feel that the experiments were carried out well. Instructions were followed carefully and time was taken to ensure that everything went well. The results are reliable and accurate as they were always double-checked by both group members before they were recorded. Steps in the method such as making sure readings were read correctly from the thermometer or measuring cylinder prevented miss readings and allowed further dependable results to be obtained. Each test-tube was washed and dried to prevent contamination from earlier use. This was the best way of carrying out this investigation for GCSE level but further small changes could have lead to the results to be more accurate. We could have used more advanced equipment, but we only had the knowledge of how to use certain and limited equipment, which we used.
If I were to do the experiment again I would have made a few changes as below:
*Control the temperature of the surrounding by encasing each experiment to prevent any changes in temperature at the start of the reaction to the end of the reaction from affecting the experiment.
*Use a water bath, which has a thermostat, which would have been easier to keep the acid at a constant temperature.
*We could also use a larger boiling tube because as we added the magnesium some of it got stuck to the sides of the tube, therefore not reaching the acid. Because of this sometimes not all the magnesium reacted with the acid.
*More repeats could be carried out to qualify the findings. These could be done under different conditions to see how the reactions react under a colder or hotter environment.
*I could also use a different form of magnesium i.e.) powdered magnesium, which would have a different surface area.
*I could also investigate whether or not the rate of reaction will decrease as the temperature decreases.
*I could also investigate whether the same patterns occur if I used a different acid and a different metal.
I could further my investigation by investigating how other factors influence the rate of reaction i.e.) Concentration, catalysts etc.
I found that all of my results were accurate and I found that all of the results fitted in with the patterns shown by the graphs.
In conclusion from this experiment I have found that the rate of a reaction increases as the temperature increases.
