Safety
As I conduct the experiment I will have to follow a number of safety regulations that are:
- Keeping bags and coats under tables or away from the place that the experiment is being conducted. This is because, as we are collecting apparatus or during the experiment, we could trip over them and could lead to an accident, especially as we are dealing with acid.
- Wearing safety goggles. These will protect my eyes from any acid getting in them during the experiment.
Variables
For my experiment I will have to consider the following variables in order to carry out the investigation fairly and successfully.
Control Variables I will have to keep the following variables the same:
- The volume of solution (water and hydrochloric acid)
- The size (surface area) of magnesium
- The temperature of the surroundings/ water
- The beaker
Independent Variable I am going to change the volume of acid in water.
Dependent Variable This is the variable which will automatically change due to the independent variable. I will be measuring the time it takes for the magnesium to totally react in different volumes of acid and water.
Apparatus
In order to perform the experiment efficiently I will need the following apparatus:
- hydrochloric acid
- water
- magnesium
- ruler – to measure the correct length of magnesium
- scissors – to cut the magnesium
- sandpaper – to sand down the magnesium which may have become oxidised
- measuring cylinder – to measure the correct volumes of hydrochloric acid and water
- stop clock – to record the time it takes for the magnesium to react totally in the solution of hydrochloric acid and water
Plan
These are the steps I have to follow to perform the experiment:
- Put on safety goggles so no acid can get in my eyes
- Ensure all bags and coats are out of the way so nobody can fall over them
- Collect all of the apparatus
- Measure out the volume of hydrochloric acid and water in a measuring cylinder. Firstly measuring 100% acid and 0% water, then 80% acid and 20% water and so on.
- Cut the magnesium measuring 2cm
- Sand down the magnesium to remove the oxides
- Get someone to hold the stop clock to record the time taken for the magnesium to totally react
- Repeat the experiment three times with the same solution and work out an average time.
- Record all of the results in a table.
Results
The figures in bold were anomalous results. I can tell this by looking at the previous results for the different solutions. As they were anomalous, I repeated the test to get a more accurate result.
Pre – Test
The reason I chose to use 25cm3 of acid for the 100% concentration is because, firstly I tested how long the magnesium would take to react in 10cm3 of acid, and it took an average of 150 seconds. If I had used 10cm3 as the 100% concentration, then as we decreased the concentration throughout the investigation, the time taken for the magnesium to react in a 20% concentration would be hours.
When I tested 25cm3 of acid to use for the experiment, it only took 15 – 16 seconds for the magnesium to react, so when I tested 20% concentration, it wouldn’t take hours to react, just a couple of minutes. This is why I chose 25cm3 of acid to use in the experiment.
Analysis
I found out that as the concentration was decreased, the time taken for the magnesium to react totally increased, so what I predicted would happen earlier on, did actually happen.
I predicted that as the concentration of the acid is decreased, the rate of a chemical reaction on the magnesium is increased.
I predicted this because as you decrease the concentration, you are decreasing the amount of acid particles. Because there were less particles in the solutions as the concentration decreased, there was less chance of them colliding with the magnesium, making the rate of the chemical reaction slower.
Trend
The trend is that as X (concentration) increased, y (time taken for magnesium to dissolve) decreased.
Between the 20% and 40% concentration of acid, there is a 269.55s decreased difference, between 60% and 80% concentration the decreased difference is 12.22s and between 80% and 100% concentration the decreased difference is only 3.28s. So we know that as the concentration is increased, the difference of the time taken for the magnesium to react decreases.
Evaluation
I thought that the majority of my results were accurate. This is because I followed the steps on my plan very carefully, measuring the solution as accurately as I could and measuring the length of the magnesium to 2cm too.
Although, even though I measured everything as closely as I could I did have two anomalous results, which proves that, other possibilities could have made the results inaccurate because if the control variables were perfectly controlled in my experiment then all of the results should have been the same. I may have not pressed the stop clock exactly on time and may have been a few milliseconds out. Also when I dropped the magnesium into the solution, it may not have been fully immersed so I had to use a spoon to totally immerse it. This may have slightly affected the results.
When I conducted the experiment and found two anomalous results, I repeated the test again for each concentration to get a more accurate result. I then used this result to work out the average time taken for the magnesium to react in the hydrochloric acid.
As I look back on the experiment I have realized that there are a number of things which I could have done to improve the accuracy of the results. Firstly I could have repeated the experiment more than three times for each concentration and then worked out an average to give a more accurate result. I could have also measured the mass of the magnesium and not the length, because even though it may show to be the same length, the magnesium may have been slightly thicker or thinner and this would mean a different mass.
Overall, I think the experiment showed very good and accurate results. It showed the results which we had expected and the experiment wasn’t hard to conduct because there weren’t any extremely difficult measurements to find.
I can now say without a doubt that this experiment proves that concentration affects chemical reactions. The results table and graph show you that as you increase the solutions concentration, the time taken for the magnesium to react totally decreases.
