In this experiment we are going to change the concentration of the acid and we will measure the hydrogen given off when the two reactants react. We will change the concentration of the acid by reducing the amount of acid and adding water. Another way to change the concentration of the acid is to use a different strength for example instead of using 1M acids we can use 0.50M.
Equipment
For this experiment we will need
- Gas Syringe
- Clamp
- Side Arm Flask
- Measuring Cylinder
- Stop clock
- Safety Goggles
In this experiment we will need to take at least five readings to produced a sufficient graph and results table. We will try to do as many repeats as possible as we want the results to be accurate.
We will change the concentration of the acid by having
- 50ml of acid and 0ml of water
- 45ml of acid and 5ml of water
- 40ml of acid and 10ml of water
- 35ml of acid and 15ml of water
- 30ml of acid and 20ml of water
Diagram
Here is an example table where I am going to record my results.
We are going to make and keep this experiment safe by
- Tucking tie into trousers if hanging out
- Tie back long hair
- Handle the acid with care as it can burn you
- Watch the Magnesium as it is sharp
For this experiment I predict that the less acid and more water we react with the Magnesium, the slower the reaction will go. This is because we will be diluting the acid. The stronger the acid is the better it reacts with the Magnesium because Magnesium is very high in the reactivity scale. The reaction will slow down when we add water because Magnesium doesn’t react with water as well as it does with Hydrochloric acid. So I predict that the more water we add the slower the reaction will go and the longer the time it will take to collect enough gas for the stated amount.
Before we attempted the real experiment we went into the computer room on Crocodile Chemistry and performed and experiment on there. This was our preliminary work. We simulated the experiment so we could get a taste of what we were going t do in the real experiment.
Here is the experiment that we simulated.
Obtaining Evidence
Preliminary Work
Here is a table of results that I obtained from using Crocodile Chemistry
For this table I predicted that each time I halved the strength of the acid the time would have doubled, but this is not the case, and I do not know why this has happened.
In this table I can see that it is taking far too long to reach 100cm3 on these strengths of acid, so now I will attempt the experiment again but with different strengths of acid.
This is the table of results I obtained from the second experiment on Crocodile Chemistry
In this table you can see that with the new strengths of acid have worked well and produced me with some good adequate results.
Real Experiment
This is the table of results that I obtained from the real experiment.
We first tried this experiment with 3cm of Magnesium (above) and we found that it wasn’t enough to react with the acid and produce enough Hydrogen. So we then tried it with 6cm of Magnesium, and could then obtain some results, as there was enough Magnesium to react with the Hydrochloric acid.
We then drew up another table to show our new readings.
As you can see the new amount of Magnesium reacted well with the acid and produced enough hydrogen for us to collect. It also was strong enough for us to accumulate the time it took to collect the gas.
I think these results are quite reliable because if you look back at the results we obtained from Crocodile Chemistry you can see that those results and these ones are quite similar and the time taken both rise in a similar pattern.
As we had time left in the lesson we performed some repeats for the results we acquired.
Here is what we got.
In this table you can see that the repeated results times’ took over twice as long to collect the gas produced as the first attempt. This is because we did this experiment over two days and we attempted the repeats on the second day, and on the second day we used and new batch of Magnesium and Hydrochloric acid. So with using new Magnesium and Hydrochloric acid the test was not fair so the results were different. Also we used a different Gas Syringes and the one we used on the second day might have jumped a little, giving us unfair results.
Analysis
In doing this experiment I have found that the more water we add to the acid to decrease it’s concentration, the longer the reaction takes to occur. I also found that on the second day when we used a new batch of Hydrochloric acid and Magnesium to do repeats of the experiment, the results that we got from the reaction were different to the ones that we got in the first experiment. Also that the graphs produced from my results is what I expected because the line is slightly curved and ascending.
Here is the graph that was produced from the real experiment results.
Here is the graph that was produced from the repeats of the experiment.
As you can see the repeats graph is different to the first experiment graph, the main reason for this is because we used a different batch of Hydrochloric acid and Magnesium on the two days.
I conclude that when I added more water to the acid and decreased the concentration of it, the longer the reaction took to occur and the longer time it took to reach 100cm3. This is because decreasing the concentration of the acid makes it less strong and weaker and when you have weaker acid the reaction takes longer to occur. This is also because there are less acid molecules and particles to collide with the Magnesium ones so less energy is produced from the reaction thus being less gas given off. Before weakening the acid I knew that the reaction with the Magnesium was going to be quick because Magnesium is very high in the reactivity series so it will react very fast.
The results that I received from the experiment support my predicted as in my prediction I said. The more water we add to the acid and the more we dilute it, the slower the reaction will go and the longer the time it will take to collect enough gas for the stated amount, and that is exactly what happened in my experiment. My results were good because they supported my prediction well.
Evaluation
I think my experiment went well because I stuck to what I was supposed to do, and because of this achieved what I wanted to achieve. The evidence that I obtained was very supportive of my prediction, so I think my experiment went well.
I think my measurements are very accurate as on my graph the stick very close to the line of best fit, be it a straight or curved line.
In my experiment I did not get any anomalous results as you can see on my graph. This shows us that the experiment went well and was fair. It was fair because no gas escaped from one experiment and not from another.
If I were to endeavour the experiment again I would.
- Try to be a bit quicker getting the bung onto the side-arm flask as a little bit of gas was escaping from the top of the flask.
- Clean the gas syringe before and after every time it is used, so it will be clean and be able to slide in and out easily to make the test even fairer.
- Remember to start the stop clock at the exact time of the Hydrochloric acid and Magnesium combining and reacting.
To improve the reliability of my results I would attempt the whole experiment again a few times to see if I could get the same results, and make them become more reliable. Also I would try to find a textbook with this experiment and some results in it, either at school, in the library or on the Internet. I would then copy and paste the results in a table on to my work to make my results more reliable.
