Method
I will carry out the experiment by, firstly filling the trough half full with water, then fill a 25ml measuring cylinder full with water, using my thumb put it over the top of the measuring cylinder full with water and place it into the trough making sure no air bubbles escape into the measuring cylinder (meaning it’s a fair and accurate test). I will then place the delivery tube into the trough, again making sure no air bubbles escape into the measuring cylinder I will lift the measuring cylinder onto the delivery tube. Then I will place one piece of magnesium which is 1cm long into a boiling tube and pour in 15ml of HCL I will use different strength acids for each experiment, so using 15ml of 0.2m, 0.4m, 0.7m and 1m. Lastly I will place the bung on top of the test tube making sure it is secure so no gas escapes and start the stop watch. The variable that I will control is the strength of the hydrochloric acid, my reasons for doing this is to vary the results and see what acid is best to use to produce 10ml of gas in the fastest time, I predict that the 0.2m will take the longest and 1m will be the quickest.
Range of values
The values that I am looking to collect are the time taken for the magnesium and HCL reaction to produce 10ml of Hydrogen gas.
How many times will I carry out the experiments?
I will carry out each experiment once; I choose to do this as doing each experiment more than once would mean over running the lesson, so due to time constraints I only had opportunity to do each of the four experiments only once. However the whole classes results were collected and from that I could see weather the results that I had produced were accurate, also another reason for collecting the classes results is that if I find the results that I had produced were corrupt in anyway I could comment on this, but also use other results, which are accurate to complete the full experiment and write up.
Preliminary Investigation
I can justify my prediction by carrying out preliminary investigations which is exactly what I did.
My reasons for carry out preliminary investigations is to notice any improvements that can be made when carrying out the proper experiment to make sure the results are accurate and fair.
I carried out several preliminary investigations. This allowed me to choose what strength acids would be best to use, because if the acid is too weak and take too long to fully dissolve then that is not an acid which I would consider appropriate to use in the investigation.
Below is the results table from my preliminary investigations.
I was unable to complete the experiment due to the time constraints of a 1 hour lesson; therefore I was unable to establish how long it took for all the magnesium ribbon to dissolve. Therefore it wasn’t a fair test and they were inaccurate so I decided to change that experiment in favour of seeing how long it took the acids to produce 10ml of hydrogen gas.
What I learnt from the Preliminary work
The preliminary work showed me that using 0.1m hydrochloric acid was inappropriate, so I decide to not use it. To compensate and still use four strength acids I decided to use 0.7m as this was a realistic strength acid to be able to use in the experiment as it should react quite quickly and be achievable during one lesson.
Using the equipment safely
When carrying out the experiments I kept my goggles on at all times, I did this so the acid couldn’t spit out of the boiling tube when it was reacting with the magnesium and to generally stop any acid getting into my eyes. The only other safety precautions that were necessary was just to be aware of the dangers and to known what to do if you or somebody else is injured through-out the investigations.
I observed the experiment and recorded the results as I took them from the stopwatch. There are as follows in the table below.
My results show that the weaker the acid is the longer it took for the 10ml of hydrogen gas to be produced.
I also recorded the whole classes results, to back up my own results and to see weather the results that I took are accurate.
From these results I can see that the results I recorded where reasonable close to that of the class average this leading me to believe that the results I recorded are sufficient enough to use, as they were accurate. Also looking at these I can again and by using my own results I can justify my prediction.
Conclusion
My aim was to see how the different strengths of HCL affect the time taken to produce 10ml of gas. From my results and my observations and graphs I can prove that, the stronger the acid is the less time it takes for 10ml of gas to be produced. This is because the higher strength acid has more h+ Ions, therefore it has more to donate and if an acid has more h+ Ions the more hydrogen gas it will produce and in a shorter amount of time.
My prediction is supported to a sufficient extent as it proves that the higher the strength acid the faster 10ml of gas will be produced, which is exactly what I said in my prediction.
The method that I used, I felt was sufficient, as it was simple with few complications meant that here was little room for thing to go wrong. I feel this as my results showed no anomalies, although I carried out the experiment only once which is the only let down, but I rectified this by collecting the classes results which when compared with my results gave similar results. Also I feel that the quality of the experiments was high, as there were no strange results (anomalies), nothing that stopped me from obtaining accurate and reliable results. The suitability of the method was good as it was simple and uncomplicated meaning little could go wrong which would results in anomalies in my results, I can say that the method was good as that is justified by my results.
The accuracy of my observations again I feel was high, this can be backed up by my results as they returned no anomalies and they were very similar in cases when compared to the rest of the classes. Only minor things let the accuracy down, when stopping the stopwatch it is hard to stop it at the precise point when exactly 10ml of gas has been produced, so lowering the accuracy.
Improvements which I could do to the method are to take more time when carrying out the experiment. As I had to stay within the time constraints of one lesson I couldn’t spend as much time on being as accurate as I would have liked, although they were still accurate to a certain mark and are still very reliable.
The reliability of my evidence is again as they are similar to others results from other experiments which were carried out in the same class, so they can be used without fear of them being in accurate or unreliable. The evidence I recorded is more than sufficient to firmly support my conclusion, as the conclusion states that as the strength of the acid increases the time taken to produce 10ml of hydrogen gas de-creases, which when compared to the evidence is exactly the same. So the evidence is more than sufficient so support a firm conclusion.