-A measuring cylinder was then filled to its maximum capacity with water. It was then covered by hand and tipped upside down and placed under the bowl’s water, the water all remains in the tube and allowed us to measure the gas given off (same as for temperature experiment).
-The tablet was dropped in and immediately I sealed the bung onto the conical flask. At the same time a stopwatch was started to record the time taken. When all signs of the carbon dioxide being given had stopped (no more fizzing and the tablet being no-longer visible in solution) I stopped timing and then recorded our results.
As you can see from the graph the preliminary results are very good, there is only one anomaly at 50% otherwise this would almost be a straight line graph. Because of this I decided that I should use concentration because the preliminary experiment worked well and so with improvements to the equipment and method and I would be able to produce some hopefully accurate results (like now). The changes I decided I wanted to the equipment will be mentioned later in the method.
Make sure no stirring takes place in any experiments, as this will increase the rate of reaction due to the ‘collision theory’. This would be ok to do however, there is no way to ensure that you have stirred each conical flask the same – making it an unfair test.
Variables,
Concentration,
The variable I am going to vary is concentration; the advantage of this is it can be varied accurately by simply adding water. However, there are also other variables as well that will affect the experiment if not considered.
With a higher concentration there is more particles per volume of substance. This means the more concentrated the acid is, the more particles there are ready to collide with the tablet particles (which are the same in all experiment). This means that as the concentration is raised the more particles there are that are free to react. If there is more particles than the other reactant then not all the particles will be used up and it will mean there will be more particles to collide so a smaller distance would have to be travelled by the particle to find a particle it wants to react with, therefore increasing the rate of reaction by taking less time.
Temperature,
When heat is applied to anything the particles of the heated thing will be vibrating a lot harder and therefore if in a liquid will move faster. If the temperature is increased, the particles in the newly made solution will collide a lot quicker as the particles are travelling faster and so meet reactant particles faster. This means that the heat supplied will vastly increase the rate of reaction.
Size of substance (surface area),
The surface area of the indigestion tablet is very important, if it is in one large piece the places that particles can collide will only be reachable at the sides, not in the inside. This means that for the acid particles to collide with the tablet, the side of the tablet has to react first before the layer underneath can. This really affects the rate of reaction and so must be controlled by using the same shape of tablet. The easiest way to ensure that the tablets surface area is the same is by using whole tablets (so this has been changed for our real experiment)
Catalysts,
A catalyst provides a surface for the particles to stick to and therefore come into contact with more particles to react with. This speeds up the rate of reaction however I shall not use any catalysts in my experiment.
Prediction,
I can predict what will happen by the collision theory. The collision theory says that a reaction occurs when the particles of one reactant collides with the particles of the other.
This means that the more concentrated the acid is in the solution, the faster the rate of reaction will be because there will be more particles available to collide with the tablet particles. As you increase the concentration more particles will be contained in the same volume of solution. This means that there will be more acid particles to indigestion tablet particles, so the particles will have to travel shorter distance to collide and will be easier to find so the same amount of reactions will happen but quicker (quicker rate of reaction). This also means that there will be an even bigger excess of acid particles in the solution as not all the acid particles will be reacted with (but this is the same for all of these experiments otherwise the tablet would not completely dissolve).
I predict that at the beginning of the experiment (at 20%) there may not actually be enough acid to react with all the tablet and if there is enough, it will be in the same volume of the others, so particles will have to travel further to collide as the particles are more spread out in the solution (so the rate of reaction will be very slow). However, if you take a more concentrated acid like 60% then there will be more particles in the same volume of acid. This means there may be a left over amount of particles after the acid and indigestion tablet have reacted. It also means that the particles will have to travel less far for a collision and it will be easier to find another particle (from the tablet particles view) to react with as there are so many more at less spaced out distances therefore making the rate of reaction faster.
Although very hard to predict the actual rate of the reaction it is not too hard to predict the gradient of a graph produced from this type of experiment.
Method,
For the real experiment I decided to collect the gas given off up to 70ml, although our preliminary results didn’t reach 70ml given off I knew that when the experiment was done accurately with the right amounts of the substance (100 ml of acid and a full tablet) all of the results would be able to reach 70ml (I also knew this as others using full tablets were all getting in excess of 70ml). In the preliminary experiment only half tablets were used and only 50 ml of the acid were added which may not have produced all the gas required to reach 70ml although the tablet had dissolved indicating all tablet was used up. I changed it so 100 ml of acid were added not 50ml and a whole tablet was used this meant the variable of surface area can be kept constant through out the experiment as cutting may result in either 2 lumps of tablet being used as a half. Or simply the cut may go in a different angle revealing more tablet area to the acid. Also through the preliminary experiment I discovered that a measuring cylinder was not very accurate as the markings are not as accurate as the burette. I therefore, used a burette for both water and acid in the experiments to create the concentrations.
- Take a burette and fill it up with acid, make sure it fills up to the zero (if not drain until at zero), otherwise extra or not enough acid may be filled into the beaker.
- Measure 5 different amounts of acid into 5 separate beakers (20ml, 30ml, 40ml, 50ml and 60ml) by slowly letting the acid go drain into the beaker from the burette (stopping the acid when it reaches the desired amount released). These concentrations were used in the preliminary experiment and provided a good range of results (a quite low concentration – 20% and a reasonably high concentration – 60%).
- Using a different burette fill it with water to zero, and then measure off 5 different concentrations of water that will equal 100ml when added to the correct beaker of acid. This will make it so the acid concentration (in %) is exactly the amount of acid added in ml into the solution.
- Take a water bowl and fill it with water.
- Get a stopwatch, a conical flask, a measuring cylinder and a delivery tube. Add the acid in to the conical flask (only one beaker at a time, start with the highest or lowest concentration, so you do not confuse concentrations) before you start.
- Fill the measuring cylinder to the top with tap water (so it is completely filled with water) and cover it so it is watertight. Insert it hole first (still covered watertight) into the bowl of water and release your hand.
- Put the delivery tube’s end under the measuring cylinder ready to collect gas given off.
- Keep the stopwatch ready to start, drop the tablet into the acid and simultaneously fasten the bung onto the conical flask. Start the stopwatch as soon as the tablet hits the water. When all traces of the tablet have been removed in the solution stop the stopwatch (traces being – stopping of carbon dioxide being released, tablet no longer being visible)
- Repeat this action for the remaining concentrations and record the results.
I wanted to make sure that the results obtained in the first experiment were reliable and so I repeated it in exactly the same way.
To make sure that our results were accurate I used our experience from our preliminary experiment to change a few instruments used. To make the experiment accurate I:
- Replaced the measuring cylinder to measure acid and water quantities with a burette in to a beaker, this allowed the quantities of acid to water to be almost exact; therefore the concentration of acid will be almost exact.
- Replaced tap water with distilled water to make sure that all impurities in the water would be removed in case these impurities in anyway alter the rate of reaction.
- Used the same stopwatch for every experiment done.
- Use the same measuring cylinder to collect the gas in case the measuring cylinder is slightly out it will be the same for each experiment.
- Ensure that all equipment is cleaned before and after.
- Use full tablets, this way the surface area will be the same for each experiment. If the tablet has to be cut in half there will be variations in what angle the cut is at and to get a half tablet may involve using smaller pieces. This means the surface area may vary from in each different experiment – which would make it an unfair test (not very accurate).
Make sure no stirring takes place whilst doing the experiment as this will increase the rate of reaction due to the ‘collision theory’. This would be ok to do if the same was done to each part of the experiment (at 20% 30% etc) however, there is no way to ensure that you have stirred each conical flask the same – making it an unfair test.
Obtaining Evidence,
I believe that I obtained our evidence quite well. Obviously the equipment provided to use was not of an excessive accuracy, as it is not really needed. This is why results cannot be taken to too many points of accuracy, for example, when you stop the stopwatch it is hard to find the exact time when it finishes reacting. This means you certainly will not be able to see the split second it finishes reacting, so time should be recorded to the second not the split second.
Results,
Graphs are printed on single pages in the next pages.
Analysis of Results,
The graphs that have been produced from the experiment and the repeat experiment are very similar; this suggests that the results are reliable because the experiments were both done in the same way.
The data that I have been able to get from the experiments can be explained by the effect the concentration has on the ‘collision theory’. As mentioned before the ‘collision theory’ says that substances react together when their particles collide with the other reactants particles. I see that at 20% concentration it takes the longest time to react in both experiments. This is because the particles will all have to travel quite far to collide, however, at the beginning of this experiment (using 20%) when the tablet is dropped into the acid fizzing occurred almost immediately but after the tablet has begun reacting soon it’s rate of reaction slows down. The rest of the time on this experiment is the time it takes for the other particles that have not reacted to find each other and collide together because at 20% there is five water particles for every 1 acid particle.
However when you look at 60% concentration it is very different. There is a complete abundance of acid particles to tablet particles (the fact that 20% does use up all the tablet suggests that there is at least a 3:1 ratio of acid to tablet). This means that the tablet particles have to travel a much shorter distance to encounter an acid particle to react with. This means that the same amount of collisions will happen but in a much shorter time. If you look at the first experiment, I can see that the 20% experiment took almost double what it took to react 60% because 20% was 368 seconds and 60% took only 198 seconds.
My prediction was quite accurate; although the tablet did entirely dissolve at 20 % it took a very long time. The 20% acid took in one experiment 368 seconds, which is just over 6 minutes, this means I was right in my prediction. My prediction says that 20% would take a very long time to react, as there were a small amount of acid particles in a large volume. The ‘collision theory’ says for the indigestion tablet particles and acid particles to react they have to collide together. If you have a 100 ml volume and a large concentration compared to a low concentration, it will react a lot faster because there are more particles to collide with, as a tablet particle is moving through the solution. At 60% I said that the volume of solution would not change but the amount of particles of acid. This meant that acid was at a ratio of at least 3:1 (as 20% used up the whole tablet) compared to tablet, so a travelling tablet particle would have 3 particles to collide with not 1 and it would be in the same volume (so obviously the travelled collision distance will be shorter for 60% and so have a faster rate of reaction.
Evaluation,
I believe that my results were quite accurate; this is because the changes made to my experiment from the preliminary were quite useful. Looking at my results of all 3 graphs I can see that they all have basically the same gradient give or take a few anomalies. There was one anomaly that happened per experiment, however these are quite strange as they are all between 50% and 60%. If you look at the graph for the repeat set of results the graph starts to level off, the anomaly here is 60% because it interrupts the graphs almost straight line. This may be explained by looking at the volume, as you increase the concentration this stays the same. Eventually increasing the concentration will not make a difference as the tablet particles are reacting whenever they collide with an acid particle an the acid particles will be so close hardly any distance will need to be travelled. However, if you look at the 1st experiment’s graph the graph seems as if the straight line could continue. If I were to extend my investigation I would like to investigate the area from about 50% concentration acid to 90% (each interval being every 5%). This would allow us to see where the point at which concentration no longer carries on the increase in rate of reaction (if this exists).
I think my results have been quite accurate however; there is a limit to the amount of accuracy available. This down through human error, there is no way you will be able to say for example stop the stopwatch as soon as the reaction has finished because the signs I look for a quite inaccurate – observe the stopping of carbon dioxide being release and the tablet no longer being visible therefore, to use split seconds for times accuracy would be ridiculous.
I am pleased with my method and believe that it was definitely sufficient to obtain the evidence I needed to prove my prediction right. It allowed me to make concentrations that were of a good accuracy that is essential to this investigation.
The reliability of my results I would say is extremely good; when I compare all 3 graphs I can see that the gradient for each one is basically exactly the same. The quality of the real experiment and the repeats was I think, very good, I can see that in both experiments they reached almost exactly the same rate for each point (even the preliminary results show good correlation with the 2).
A variable that affects quite a lot was not considered enough during my experiments. I can see that from my very first preliminary test (on temperature) that temperature is very significant to the rate of reaction. Although I completed each experiment on the same day (1st experiment one day repeats another) at the same time the temperature may have varied per concentration due to a sudden change in temperature. However this would probably not have been enough to affect our results considerably but taking the temperature before each concentration test would have been good as it might have explained so anomalous results or at least may show you if the temperature has an affect on the rate when it is varied within a few degrees.
So in conclusion if I were to extend my investigation I would use a thermometer to measure the temperature in future before the reaction takes place and I would also vary the temperatures from 50% to 90% at 5% intervals to see what happens around this area in more detail.
