Test 4: 2 Molar hydrochloric acid. 1-gram marble chips
Analysising my preliminary tests and decisions
‘The more concentrated the hydrochloric acid, the more collisions that will take place’. This would mean, the faster the reaction. From my preliminary tests, I have decided to use 1gram of marble chips and 10ml of hydrochloric acid. I have decided to change the concentration of the acid (molar) I use. The reason I chose the 2nd experiment as my actual measurements was because it seemed most accurate and the speed of the reaction gradually slowed down. This was because the amount of collisions had decreased amounting to a more steady reaction because the concentration was getting less. However, the other experiments didn’t seem to show this in the amount of time I tested each experiment (100 seconds). Maybe, if I’d have used more than a hundred-second’s to carry out each experiment, my results may have been different.
So, in my actual experiments, I’ll be using 5 different concentrations of hydrochloric acid (in molar). The reason I have chosen 5 different measurements is because, if I had done 1, I wouldn’t have realised which concentration of hydrochloric acid worked best. By doing 5 experiments, I’ll get a more accurate answer at the end.
The 5 different measurements I’ll be experimenting on, of hydrochloric acid are:
- 1m
- 1.25m
- 1.5m
- 1.75m and
- 2m
Molar: the units I’ll be measuring in.
My plan
Firstly, I will have to set out the apparatus I’ll be using, as shown on my diagram. Then I’ll be accurately measuring the concentration of hydrochloric acid into a measuring tube and 1gram of marble chips using the electric scales. . After pouring each of the ingredients into a flask (the amount of acid 1st), I’ll seal the rubber bung on top. Immediately, I’ll start the stopwatch. Every 10 seconds, I’ll be taking the reading of the volume in the tube. I will do this experiment 5 times. Each time, with a different concentration of hydrochloric acid. When I have completed each experiment, I’ll be retaking each one again. This will mean my results will be more accurate and I can work out an average for each one.
Fair test
In order for my results to be as accurate as possible, I’ll have to make sure all my experiments are fair. This will mean;
- I will always be using 10ml of hydrochloric acid and 1 gram of marble chips
- The input variables will always be accurately measured too (1m, 1.25m, 1.5m, 1.75m and 2m)
- I will have to be as accurate as possible when measuring the volume using a stopwatch.
- I will always use marble ‘chips’. I won’t be using powdered calcium carbonate, as this will change the surface area and my results would be unfair.
- I will always work at room temperature.
- I’ll always set up the apparatus as I have done in my diagram.
Calcium Carbonate
Calcium carbonate (named marble chips) also comes in three different varieties;
- Powder
- Small chips or
- Large chips
In order for my experiment to be fair, I’ll have to use the same type of chips. If I had used power for one experiment and large chips for the second, my results would probably be inaccurate. This is because, it would take a longer time for large chips to break down than it would for powder.
Safety
I’m working in a science lab with a class full of people. Therefore, I must work sensibly. I will set up my experiments properly, so that no one can get hurt from unstable apparatus. I will have to be careful with the way I handle the acids to prevent spillage. If so, I will have to clear it up straight away as I’m dealing with acids. There will be glass objects in my experiment, so I will have to be extra careful with them. I’ll be using a clamp to hold the measuring tube (which has water in it) in case of a spillage.
Prediction
My prediction is that, the higher the concentration of hydrochloric acid, the faster the rate of reaction. This is due to the fact that they’ll be more particles in the acid colliding with other particles causing chemical reactions to take place at a faster rate than it would be if there was less acid. This is called a successful collision. Putting this theory into my actual experiments, I predict that 2m of hydrochloric acid will work twice as fast as 1m of acid because the amount of acid has been doubled.
As I already know through previous lessons on this, If my diagram is accurate, it should look something like this:
As the reaction reaches its highest point, its starts to curve. This is because the amount of chemical reactions has decreased because there are fewer ions. Hence, fewer collisions taking place.
My Actual experiments
I completed my experiments successfully and kept to my plan, safety precautions and fair test.
I took re-takes of my test as I had said, and then I worked out the averages: I used 10 ml of hydrochloric acid, 1 gram or marble chips, and changed the amount of acid I used, 1, 1.25, 1.5, 1.75, 2 Molar:
1 molar experiment:
1.25 Molar experiment
1.5 Molar experiment
1.75 Molar experiment
Note: Test 2 seems to be a little lower in comparison to Test 1. It may not have been as fair as the other tests or maybe a slight change in room temperature could have meant a little lower set of results. The size of the marble chips, the slight change of concentration could have also made a difference.
2 Molar experiment
From my results, I was able to plot a graph of my results:
Note: I’ve plotted the averages from test 1 and 2.
Conclusion of my results
The collision theory proved to work in my experiments. As I’d predicted, the more concentration of hydrochloric acid, the faster the rate of reaction. This theory worked in all of my experiments and because of the successful collisions, the reactions were faster when a higher molar concentration was added.
From the ‘chemistry for you’ book, it had shown a diagram for the rate of reactions. It showed a diagram in which the reaction was at its fastest at the beginning and began to slow down later. This is what happened from the experiments I had taken.
However, the first set of experiments I had taken seemed to work faster than the second (repeated experiments, which I have shown- then averaged). So my repeated results seemed quite anomalous because I thought they should have been very similar to the first set of results. This may have been because of the room temperature, which may have been different. It may have also been because the size of the marble chips I used were bigger than the first tests. The sizes of marble chips do make a difference in my experiments, and I can’t control this fully because they don’t come in exact sizes. Hence, the surface area of the marble chips may have been the factor for slightly slowing down the repeated tests I did.
From the graph, I can see the reaction is at it’s fastest at the beginning and starts to slow down during the end leaving less particles left to collide and react. The reactions get faster as the concentrations rise.
I predicted that the higher the concentration, the faster the rate of reaction. I also predicted that if the concentration was double, so would the rate of reaction. I have calculated the rates and put them onto a diagram. Here is a table of the results:
My predictions were quite accurate. When I doubled the amount of concentration (from 1 molar to 2), the rate of reaction also doubled. However, there is some kind of anomaly with the 1.75 molar concentration of hydrochloric acid. I’d have expected the rate of reaction to be around 0.9/1 (cm³/sec) because the 1.25 concentration had the same rate of reaction. Looking back at my experiment results using 1.75 concentration of hydrochloric acid, I realised this set of results were a little lower. This could have been for a number of reasons, including room temperature or was it as fair a test? Nevertheless, my results are still quite accurate and my predictions were also fairly accurate.
Evaluations
I thought I had worked to my targets by doing what I had said I’d have done in my plan and so my results were reasonably reliable. I tried to keep the rules to a fair test, however, some were beyond my control. For instance, maybe if I could have used more hi- tech equipment. For instance, it would have been more accurate if I’d use a gas-measuring device rather than the equipment I had used.
The surface area of the marble chips could have made a difference as to how fair my experiment was. I’ve realised that if I used powder, my results could have been more accurate. This is because the surface area would have been exactly the same. However, I used medium sized marble chips, and these were all different sizes. Some were much larger than others were. Even though I always measured out the correct amount of chips onto the scales, I couldn’t have controlled the surface area as much as if I’d have used powder. Therefore, my results weren’t as accurate as they could have been.
I had planned each experiment to be taken in 100 seconds, each to be measured in 10-second intervals. This was because I believe I would have been enough time for the reactions to work. Maybe if I had spent longer experimenting each one, I could have found out if any of my experiments actually stopped producing carbon dioxide.
My results worked just as I’d put it in my prediction however. As I can see from the graph, the reactions started out very fast and gradually slowed down.
My results are fairly reliable because I kept to my fair test and my plan. However, they may have been more reliable if I’d have used calcium carbonate in the form or powder, rather than chips. Even though there were a few liabilities in my experiments, I believe they were more reliable than not.
Before I had started my experiments, I already had a rough picture in my mind of what type of results I was looking for. From chemistry books like ‘Chemistry for you’ I was able to find information on the collision theory and activation energy. I also found some information about these types of experiment’s off www.bbc.co.uk.
Overall, I am pleased with my results and I think most of them are fairly accurate. However, next time it would be a more accurate if I had had longer time to test each experiment. I spent 100 seconds on each test, but it would have been more accurate if I had spent about 150-200 seconds on each experiment. I could have also used powered calcium carbonate instead of marble chips. Marble chips come in all shapes and sizes so its not as fair a test.
