Prediction: – My prediction is that the higher the concentration of the acid, the faster the magnesium strips will dissolve. The higher the concentration means, the more Hydrochloric acid particles for Magnesium particles to react with, increasing the chance of successful collision.
Safe and Fair test
To ensure that our experiment is safe, one of the first procedures that took place before starting the experiment was to wear goggles. This way our eyes were protected against any HCL acid.
While doing the experiment, we made sure that if we spill any acid on ourselves to wash it away under cold water immediately, to stop getting burned.
We always kept the lid of the HCL acid bottle closed, in case of a spill.
We also kept our ties out of reach of any acid, and had our hair tied back.
We used the same volume of acid for the first and the second experiments.
We ensured that we used same sizes of Mg strip and the same stop watch for both experiments.
We repeated each concentrated reaction more than once, (twice each in the first experiment and three times in the second experiment).
We put both the acid and water at the same time in the second experiment, and placed the Mg strip afterwards to make certain that the reaction hadn’t started only with the HCL acid or water.
We started the stopwatch just as the Mg strip was put in, to be certain of the time.
For the first experiment
1. First of all I will gather all my apparatus in to one place.
2. Then I will place the conical flask on top of a white paper, this will make the image clearer.
3. I will then use emary paper to take away all impurities from the magnesium strips, and then cut them in to 3cm strips.
4. I will then measure the correct amount (10cm3) of HCL with different molarities.
5. I will fill the conical flask with HCL acid, and get the stop watch ready.
6. Then I will put the Magnesium strip inside and start the stop watch.
7. When all signs of Magnesium disappear, I will stop the stopwatch, and record the time on to a table.
8. I will repeat the same procedure as before again with the same molarity. This id done to determine fair testing.
9. I will then start another test with a different molarity and repeat the same procedures as stated above. This will be done with all the different, molarities, twice each.
10. I will record all times on to a table and find an average time for each molarity.
Volume of acid
Size of Magnesium
0.5m Time taken for molarities to dissolve.
1m Time taken for molarities to dissolve
1.5m Time taken for molarities to dissolve
1.75m Time taken for molarities to dissolve
2m Time taken for molarities to dissolve
For the second experiment
1. My colleagues and I will gather all our equipment together, along with the goggles to protect our eyes.
2. Then we will divide our jobs so each one of us has our own duty. I will first fill a test tube with 20ml of HCL acid, and then we will put the acid into the conical flask.
3. We will then put the Mg strip into the flask and would start the stopwatch.
4. After the Mg strip has completely disappeared, we will stop the stopwatch and would record the time on to a table.
5. We will repeat the same procedures as shown on my result table, and would record the time down.
6. We will work out the average time, and then the 1/t.
Time for Mg to dissolve (minutes)
Factors that affect the rates of reaction are;
; The surface Area
; The Concentration (pressure if gas)
Surface area affects the rates of reaction due to the size or the area exposed in a solid. If the solid is small, then more surfaces are exposed and can react faster than a larger surface.
Temperature gives particles ‘kinetic energy’. This means they will move faster and will collide faster with other particles.
Catalysts enable substances to break up and form bonds easily. The atoms need less energy and the catalyst remain unchanged and can be re-used.
The only factor that was imperative to the experiment we have done was the concentration of the acid. This will increase the number of particles present and will increase the chance of collision between them.
Solids have a high density, volume and a definite shape. They are usually tightly packed together and have high inter-molecular forces holding them. They are arranged in a certain pattern. These particles are unable to move around from place to place. But they are able to vibrate, and kinetic energy (usually from heat) enable them to do so, and sometimes even break apart if the level of energy is high. This information is relevant to my experiment because the Magnesium strip is a solid whilst the Hydrochloric acid is a liquid.
Liquids have more kinetic energy as the bonds between its particles are weaker than the solid’s, allowing them to move about. Because of this ability Hydrochloric acid is able to break into the Magnesium solid and weaken its forces. There is activation energy to start the process; this initial amount of energy is what is required to start breaking the bonds to allow the reaction to proceed. This energy along with the high concentration starts off the experiment, allowing the particles to react with each other.
As the concentration of HCL acid increases the chance of successful collision between HCL particles and Mg particles increases. This leads to breaking the bonds between Hydrogen and Chlorine particles (intra-molecular bonds) resulting in an exothermic reaction.
When the Hydrogen and Chlorine bonds are broken, the Chlorine particles make new bonds with Magnesium particles, forming a new substance; MgCl2, giving out Hydrogen as gas.
Mg + 2HCL ï¿½ MgCl2 + H2
We know that this is an exothermic reaction because, while doing the experiment, I noticed that the reaction between HCL and Mg was giving out heat and gas. It is a well known fact that in an exothermic reaction heat is given out as the bonds are broken, unlike in endothermic reaction where energy is taken in, thus the heat and gas. As there is exothermic energy, the activation energy in the experiment is high, allowing the particles to react faster with each other.
First of all I’d like to look at my prediction. I have predicted that the higher the molarity of HCL, the faster the magnesium strips would dissolve. After doing a preliminary test and an added experiment, I have come to a conclusion that my prediction is true; the higher the concentration, the faster the rates of reaction.
This is because increasing the concentration of liquid reactants also increase the frequency of collisions; therefore, chance of successful collision between HCL acid and Mg strips increase. Particles in solids are held together by strong forces of attraction, whereas particles in a liquid are held together by weak forces of attraction. This allows the bonds between Hydrogen and Chlorine to break; exothermic reaction, and new bonds to make between Magnesium and Hydrogen particles.
This can be shown by this equation:
Mg + HCL Mgcl2 + H2
The results I got from my experiment support my prediction. As there’s high concentration of acid the reaction time is much faster, than a concentration that is low. My graph is able to support these claims, (see graph 2), 20ml of HCL dissolve in 0.37 minutes, and 10ml of HCL dissolves in 3.93 minutes. Another example of this can be found in my first graph for the first experiment; 0.5 molarities of acid dissolve in 11.46 minutes, and 2 molarities of HCL acid dissolve in 29.55 minutes.
As I have stated previously, my prediction was accurate as my results proved that the rate of reaction would go faster, if the concentration is high.
Although, most of my results were acceptable, there was an anomalous result in the first experiment. The results of 1.75 molarities (see graph one), indicates that it takes 30 to 40 minutes for Magnesium strip to dissolve in HCL acid. This of course cannot be true, as the rest of my results show that the higher the molarity, the faster the time taken; (0.5m and 1.5m in graph one), my prediction and my results can be backed up by a theory which shows that increasing the rate of collision, (this is done by increasing concentration), the reaction would take place faster. This particular molarity gave us and the other groups anomalous results due to the fact that the technicians have gotten the molarities mixed up. This meant that what we thought was 1.75m was actually a much lower molarity. Before knowing the cause of this problem, my colleagues and I repeated the experiment three to four times, just to make sure that these anomalous results were not caused by our faults.
Graph two however, seems free of any anomalous results, even though the 2ml reaction made things difficult. The time taken for the 2ml of HCL and 18ml of water, ranged from 49 minutes to 51 minutes. The reaction was extremely slow; this meant that one of us (my colleagues and I) had to stay beside the experiment, examining it carefully to make sure that the Mg strip hasn’t dissolved without us knowing. Even though the time difference between 4ml and 2ml is very large, it clearly shows the variation between solvent with a high concentration, and the same solvent with a low concentration. The possible reason for such high timing could be because that we have measured that acids or liquids incorrectly, or because the sizes of the Mg strips were not the accurate size.
I think we could have improved our experiment by spending more time ensuring that we have the correct equipment, and measuring the solvents. Instead of using test tubes to measure the solvents, we could have used syringes, as they are more accurate and effective.
In some of the concentrations, we made mistakes such as pressing the start button on stop watch few seconds delayed; we could have avoided these problems if we were better prepared.
I could also extend my investigation by using various other acids, such as Sulphuric acid (H2SO4), Nitric acid (HNO3), etc.
Overall, I am happy with the results, although we could have done better,