- Megan Andrews - Mrs. Ball - Chemistry Coursework - 09/04 - 11 Alpha -
-Investigation: Find the concentration of the unknown acid using Mg strips-
It is necessary that all these factors be applied to my results. For instance, the length of magnesium strips should be taken into consideration, because if the length is 5 cm, then it may take a very long time for the whole thing to dissolve in a weak solution, which will be waste of lesson time.
Using this theory, I predict that the higher the concentration, the faster the magnesium strips will dissolve.
Temperature can affect this research, and affect the results of preliminary and final experiments. Therefore it is very important that the room or working area is kept at the same temperature, with no windows being opened half way through a trial, or near a draught. This could affect the results because, as said previously, it could slow down and quicken the rate at which the reaction takes place, therefore making it an unfair test.
Apparatus:
- Conical Flask
- 8 lengths of 2cm Magnesium Ribbon
- Solution X
- Stopwatch
- Solutions of 20cm3 – 0.5 mol/dm3, 0.75 mol/dm3, 1 mol/dm3, 1.25 mol/dm3, 1.5 mol/dm3, 1.75 mol/dm3 and 2 mol/dm3.
- Tweezers
- Goggles
- Apron
- Water
- Measuring Cylinders
Method
- Put on safety goggles, tie back hair, put on apron
- Collect measuring cylinders, water, hydrochloric acid, magnesium strips, conical flask, stopwatch and tweezers.
- Measure out 20cm of 0.5 mol/dm3 of solution with the measuring cylinder (method shown in Outline section)
- Pour concentration into flask
- Measure 2cm of magnesium strip
- Make sure surface of ribbon is clean
- Drop the magnesium ribbon into flask
- Quickly start the stopwatch
- Measure the time it takes for the magnesium to have completely dissolved and stopped having giving off gas
- Repeat steps 3 – 9,changing the concentration of the acid and comparing time with solution X, make sure results are reliable and reproducible.
- Megan Andrews - Mrs. Ball - Chemistry Coursework - 09/04 - 11 Alpha -
-Investigation: Find the concentration of the unknown acid using Mg strips-
Diagram
Preliminary Work
Unfortunately, I have no preliminary work recorded, but my first method consisted of Magnesium the length of 5cm. However I changed my mind after that because I discovered that using that length took up a lot of class time and then decreased the length to 2cm.
I also discovered that my first concentrations, which were only 0.5 mol/dm3, 1 mol/dm3, 1/5 mol/dm3 and 2 mol/dm3, was not enough to make a decent conclusion as to the concentration of chemical x, therefore I added more concentrations.
Explanation
Once I have done my experiment, I am going to use my results to determine the unknown concentration of solution X.
I will do this by recording my results, and the time taken for the magnesium strip to dissolve in the unknown solution. Then we are to compare our results to all the other times taken, when magnesium is dissolved in the different known concentrations. If two times are very identical, then we will know that the concentrations are similar.
- Megan Andrews - Mrs. Ball - Chemistry Coursework - 09/04 - 11 Alpha -
-Investigation: Find the concentration of the unknown acid using Mg strips-
Table Of Results
Graph Of Results
Key: Green Line - – Experiment 1 Results
Blue Line - – Experiment 2 Results
- Megan Andrews - Mrs. Ball - Chemistry Coursework - 09/04 - 11 Alpha -
-Investigation: Find the concentration of the unknown acid using Mg strips-
Analysis
As the concentration decreases, so does the rate of reaction. Increasing the concentration of solution increases the number of the particles. The more particles there are, the greater the number of collisions, and therefore the rate of the reaction increases.
Chemical reactions take place by chance. Particles need to collide with enough velocity so that they react. As the concentration is increased the particles move faster since they have more energy from more energy. This means that they are colliding more often and more of the collisions have enough velocity to cause a reaction. Since there are more collisions the chemical reaction takes place faster.
This graph shows the results I recorded when dissolving the magnesium strip in the solution of unknown concentration. When comparing the results to table, in the picture shown below, shows how I can apply this to my graph and attempt to estimate the concentration of the Unknown Acid.
I believe the unknown acid to have a concentration of 1.27 – 1.32 mol/dm3.
I believe this because, When following the line along the graph, it ends up at that point on the concentration line.
After having done the experiment, we were told that the actual concentration was 1.3 mol/dm3. I think that my estimate was very close to the real concentration and applied my information to my research quite well.
Evaluating Evidence
I believe that the experiment was successful but some of the results were unexpected/unreliable. The lines on the graphs for 1.0 mol/dm3 and 1.25 mol/dm3 in Experiment 2 do not follow the steady decrease line, this doesn't affect my results since I am only concerned with the initial rate or reaction but it was unexpected.
- Megan Andrews - Mrs. Ball - Chemistry Coursework - 09/04 - 11 Alpha -
-Investigation: Find the concentration of the unknown acid using Mg strips-
I believe that the experiment was designed well but there were a few problems. The initial rate of reaction (which is what I am concerned with in this investigation) seemed to fit a trend, and the rate of reaction curves on the results on the graph do not cross. However, if this had occurred it would have been because some of the magnesium had corroded forming a magnesium oxide layer which would have affected the rate of reaction.
Another factor which could have given me unreliable results could have been that when waiting for the magnesium to completely dissolve, the timing may not have been perfect. Also, some results may have been affected because they may have been stirred more, or with an increased speed, than others. Temperature could also have affected my results, but I don’t think it did, because I was very careful to stay in the same part of the room, out of drafts and making sure that temperature could not affect my results.
I conducted the two experiments for each concentration at the same time to save time. An error in my graphs (plotting, drawing curves or calculating gradients) could have also affected the calculated moles per decimetre cubed.
To improve the experiment I would find a way of attaching and releasing the magnesium inside the side arm tube above the acid (with a bung at the top of the side arm tube) so that the magnesium could be dropped into the acid without any gas or time being lost.
Additional work, which could be carried out, is to repeat the experiment using, a wider range of concentrations. The investigation could also be extended to investigate other factors affecting the rate of reaction such as catalysts, temperature of the acid or particle size of the magnesium.
In conclusion, I think that I applied my information to my results well, and reached an appropriate answer and conclusion.