For the reaction between magnesium and hydrochloric acid, if the temperature is increased, the particles each substance move faster and causing more collisions thereby increasing the rate of the reaction.
- Add a catalyst: a catalyst is any substance that speeds up the rate of the reaction but doesn’t take part in it or still remains unchanged after the experiment has taken place. A catalyst reduces the activation energy of a reaction (energy needed to start a reaction is the activation energy). Catalysts are used in cars (catalytic converters) to convert harmful gasses produced in the exhaust to harmless gasses before being released into the atmosphere. Tiny amounts of catalysts can bring about great changes in the rate of the reaction. As the amount of catalyst used is increased, the rate of the reaction increases until it reaches a point where it cannot go any faster.
I have decided to leave the surface area and temperature the same and unchanged. I am going to be changing the concentration in my experiment because the change in concentration allows me to find out how the rate of the reaction can be affected by different molarities.
EQUIPMENT
For my experiment, the following equipment will be used;
- a gas syringe that has 0-100 mile-litres (ml) calibrations
- a clamp to hold the gas syringe
- a stopper to prevent the loss of gas
- a dropping pipette to allow my measurements to be accurate
- a test tube rack to hold the test tube
- a measuring cylinder that is calibrated and can measure small volumes of acid
- a beaker to pour acid in to the measuring cylinder
- a stopwatch to time the experiment
- a scale that can measure up to two decimal places to measure the magnesium I use for the experiment
I have chosen the following equipment because the measurements and readings gotten from this experiment are very accurate and they are very easy to use. They also help to make my experiment fair.
FAIR TEST
I will make my experiment fair by doing the following things
- always use test tubes of the same size
- use the same mass of magnesium and volume of hydrochloric acid
- make sure the temperature is always the same by covering it with a sock
- Not changing the surface of the magnesium, but this is out of my control because the magnesium has already been cut by the industry it was manufactured in and we cannot increase or reduce the surface area of the magnesium.
PREDICTION
In my experiment, I predict that if I change the concentration of the hydrochloric acid (by adding water to make it dilute) the rate of the reaction will be slowed down. This is because by adding water to the acid, the number of particles that will react with the magnesium has been reduced, therefore reducing the amounts of collisions taking place. The reaction will be slower than using a concentrated hydrochloric acid.
PRELIMINARY EXPERIMENT
I have carried out a preliminary experiment (s) and I have gotten the following results;
Before I got the results, I had to perform my experiment.
Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g)
I set up the experiment using the right equipment. During my experiment, I found out the following things;
- I can measure how quickly the magnesium disappears in the hydrochloric acid
- I can also measure how much product is formed (the hydrogen gas given off)
From these two points, I chose to measure the hydrogen gas given off at the end of the experiment because it is easy to collect and the readings are very accurate and precise because you can measure the gas with the calibrations on the gas syringe, unlike when you are measuring the magnesium because I am relying on when the magnesium disappears and forms the new substance.
During my experiment, I found out that if a large amount of magnesium reacted with a large amount of hydrochloric acid, the reaction will go over the top and the hydrogen produced cannot be recorded. But, if the amount of magnesium is reduced (from 10 to 0.09) and the acid is kept constant or is also reduced (from 20 to 16) the reaction would not go over the top and the amount of hydrogen produced can be documented.
Therefore, from this preliminary experiment, I have decided to do the following things for my real experiment:
- The amount of magnesium to be used will be reduced to 0.06gramms. I have decided to use this amount because if a lower amount is used (like 0.05) there would not be much of a difference with when I use 0.06, and if a higher amount is used (like 0.09), there is a big tendency that the reaction will go over the top. So because of this, I feel that 0.06 is the right amount to use.
- Also, for my experiment I have decided to change the amount of acid I use from 20millilitres (ml) to 16millilitres (ml). I have done this because when I want tot reduce the molarity by diluting the acid, 16ml would be easy to use and find the accurate measures of the water and acid to be used for the reaction. The amount used has to add up to 16ml.
(Note: the amount of magnesium and hydrochloric acid has to be kept constant throughout the whole experiment. The only variable to be changed is the concentration of the acid)
- I am going to take the reading of the hydrogen gas and I intend to do this every 20 seconds. This time I feel is very appropriate because it allows a change but not a very big change and it will also allow the readings on my graph to look stable. And for each acid molarity/concentration I use, I will take the readings three times and these readings will have to be between 10 percent (%) range of the first reading to give an accurate graph. I am not going to do less or more than three (3) readings because if less than three readings are taken, it does not give a definite result that the readings are accurate and if more than three readings are taken, the readings become very monotonous. So three readings for each molarity is the best to use.
- For my experiment to take place, I need five different concentrations of acid. I have decided to do this because this shows me how the rate increases/decreases per different concentration. To find out the different amounts of acid and water I use for each molarity, I will multiply the molarity by the volume and divide by the original concentration of the acid used in the preliminary experiment like I have done below:
OBTAINING EVIDENCE
As I was carrying out my experiment, I made sure I carried out all the safety measures I listed before.
I have used a table for recording my results because when data is put on a table, it puts the data into different boxes and each result can be easily and quickly found on a table. When I carried out my experiment, I had to repeat some of the readings because they were not within the 10% range and due to that, I had to repeat the experiment.
The first readings I took had the concentration of 1molar.
I noticed that my third set of results were wrong because they were not within the 10% range. I knew this was an error. I had put the stopper in and some of the gas had come off. So due to this, I had to re-take my readings.
The second set of readings was with the concentration of 1.5molar of acid
The third reading was wrong because too much gas was let out before the cork was put in and the magnesium used for this reaction was less than 0.06gramms.the readings were not within the 10% range.
The third readings I took were with the concentration of 0.5 molar of acid.
At the end of this experiment, I did not have re-do any of my experiments because I did all the procedures accurately and did not let too much hydrogen gas escape. I also made sure all the readings were in the 10%range.
The forth set of readings I took were with the concentration of 1.25molar of acid.
Just like the readings before this one, I did not have to repeat any of the readings because to me, they seemed correct. Also because, they were within the 10% range I mentioned. So I had no problems with these.
The last readings I had to take for my investigation had a concentration of 0.75 molar of acid.
These are all the readings for my experiment. I followed all the necessary procedures and safety measures needed.
I included all the units of measurements used in the course of this experiment. All the readings I had to repeat were repeated with enough cause.
For my investigation, I need to regroup my information in order to draw a suitable chart and even if I was able, the chart will not be a general chart; it will be for the different readings taken.
So in order to re-group my information, I will have to take the three readings for each concentration and find the average gas produced. The information will still be in tabular form.
ANALYSIS
From theses results I am going to draw a graph to show the movement of the volume of the gas given out against the time. I have chosen the line graph to draw because they bring out the information and make it easier to understand when comparing results.
On my graph, I have decided to use different colours to show the different molarities. This will make it easier for me to read and compare the results. No line of best fit is needed to be drawn because it was a curved graph.
I have noticed that all my graphs move I the same trend; they start at the same point and move upwards, then they curve and then level out (move in a straight line). This shows that the graphs show how much hydrogen gas is obtained and it continues to get more gas, and at the end of the reaction, the points remain unchanged to show/mark the end of the reaction.
What happens in these reactions is that the hydrochloric acid is put into the magnesium, the molecules start reacting by colliding with each other to form a new compound. When water is put into the hydrochloric acid which is then put into the magnesium, the reaction still takes place but it would not be as fast as when the acid was undiluted. It takes some time before the molecules collide with each other, thereby taking a longer time for the reaction to end. Therefore the more the water, the slower the reaction.
In terms of graph. The curves with the steeper lines are the reactions that went fairly fast, but after about 60 seconds, the graphs begin to loose their steepness. There fore these graphs had little amounts of water.
1 Molar
1.50 Molar
1.25 Molar.
The other curves are not as steep as the first few curves but are really long because they had a high percentage of water in them and because of that, it slowed down the reaction.
0.50 Molar
0.75 Molar
At the beginning of the reaction the test tube was quite cold. It was cold because bonds (metallic and covalent) were being broken, but as the reaction progressed, the test tube began to warm up, even hot in some of the reactions. Therefore this reaction is exothermic because energy in the form of heat was given out during the reaction.
Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g)
EVALUATION
The prediction I made was right. The rate of the reaction did slow down as the reaction progressed. I also found out the hydrogen gas took longer to be given off when the hydrochloric acid was given off. The reason why this happened, like I had mentioned before, was because the acid had been diluted by the water, the molecules were very slow to collide with each other giving rise to the slow rate. All my results support this decision because all my results which were later plotted on the graph moved in the same trend; started fast for those with a high percentage of acid and ending slow for those which had a high percentage of water. Some of my results did not follow this trend. They were anomalous results. These must have occurred either because my variables were not as accurate or there was a mistake in the recording of my results. I made sure my results were accurate so it had to have occurred with the variables.
My results are not very accurate because I had some anomalous results but my results were taken three times per molarity, so this proves that my results have a degree of accuracy. Also, they were all within a 10% range so this proves that the results can be used.
IMPROVEMENTS
If I had a chance to repeat my experiment, I would change the apparatus used. I would have also included a thermometer to make sure the temperature in the laboratory remains constant. I would also need a scale that can measure up to four decimal places to allow all my results to be very accurate. I would want to add more concentrations to the experiment, to have a better knowledge of how the reaction takes place. These points would not only make my results very accurate, it will allow my evidence to be more reliable because the more accurate my measurements are, the more accurate my results are leading to better graphs and less anomalous results.
My test was not fair because the temperature was not constant. Also the measurement of the magnesium was not very accurate because two decimal places are not the best of measurements. The mass could be 0.061 or 0.064 and it will be measured as 0.06 when the second mass is heavier.
I did experience some difficulty in the experiment. I did not know how to prevent the plentiful loss of hydrogen during the experiment. I experienced this because as I was pouring in the hydrochloric acid into the test tube, it had started reacting with the magnesium giving off hydrogen gas.
IMPROVEMENTS TO THE EXPERIMENT
I could use a thistle funnel and a two holed stopper. The experiment setup will look like this;
The funnel will be used to pour the hydrochloric acid into the test tube instead of pouring the acid into the test tube directly. It is better than the first method because it is safer and it also prevents/reduces the loss of hydrogen gas.
