Number of indigestion tablets
After conducting a test experiment I have chosen to use one tablet. Combined with the acid this produces sufficient, but not too much, gas for the 100cm3 measuring cylinder. This could also be a dosage for somebody trying to relieve indigestion.
Type of indigestion tablets
I will be using "Boots Soda-mint Indigestion Tablets" for all my experiments.
I will not be using other indigestion tablets because they will have different active agents and varying amounts of the active agent.
Prior to conducting this investigation I went into a Boots Pharmacy and found that the tablets contain the following active ingredients
- Calcium Carbonate (PhEur 200mg)
- Magnesium Carbonate (PhEur 200mg)
- Magnesium Trisilicate (PhEur 60mg)
- Sodium Bicarbonate (PhEur 60mg)
Mass/size/shape of indigestion tablet
I will be using one indigestion tablet because manufacturers (Boots) have to make tablets as identical as possible because they are made in a mould.
So therefore the masses of the tablet used should be virtually identical. It is important to keep the masses the same so that the number of molecules of active agents is the same for each experiment.
Also, the surface area should be the same because the tablets are made in a mould. The reactions between the acid and tablet occur on the surface of the tablet where the acid is in contact with the tablet. A reaction will therefore occur more quickly if there is a larger surface area because there are more acid and tablet molecules in contact with each other at the beginning of the experiment. The diagrams below illustrate this point.
Same mass... ...extra surface area
Agitation given to boiling tube
No agitation will be given to any of the experiments, as this will induce more collisions and a faster reaction. The acid and tablet particles are moving around randomly and so will eventually collide and react. If they are stirred or shaken (agitated) then the particles are given more energy and so are more likely to collide. I will not be stirring because I could not guarantee that the agitation given would be identical for all the experiments.
Prediction
I predict several things will happen
-
There will be a reaction between the acid and indigestion tablet causing carbon dioxide to be produced
- Each tablet will give off roughly the same amount of gas, whatever temperature of acid
- When the results are plotted on a graph they will produce a curved line of decreasing rate, similar to the one to the left of these bullet points
- The higher the temperature the shorter the time it takes for the tablet to completely react with the acid.
Justification
1. There will be a reaction between the acid and the indigestion tablet because indigestion tablets are designed to neutralise stomach acid. The hydrochloric acid that I am using is very similar to the acid that is in the stomach.
Carbonates “…all react with acids to give off carbon dioxide.” (page 169) will react with an acid to produce a salt + water + carbon dioxide.
The formula for the reaction of Calcium Carbonate and Magnesium Carbonate are the similar because calcium and magnesium have the same electrovalencies. This is shown below.
calcium + hydrochloric → calcium + water + carbon
carbonate acid chloride dioxide
“CaCO3 + 2HCl → CaCl2 + H2O + CO2”(page 216)
hydrochloric Acid + Magnesium → Magnesium + water + carbon
carbonate chloride dioxide
Sodium bicarbonate is also know as sodium hydrocarbonate
“Sodium hydrocarbonate is used in baking. The carbon dioxide gas it gives off when heated makes dough rise. It is also used as an antacid to relieve indigestion” (page 169)
Therefore, as the sodium bicarbonate is warmed by being in hot acid it could break down into sodium carbonate, water and carbon dioxide. This carbon dioxide will add to the volume of gas being produced.
“2NaHCO3 → Na2CO3 + H2O + CO2” (page 169)
This sodium carbonate would then react with the acid to form sodium chloride, water and carbon dioxide.
2HCl + Na2CO3 → 2NaCl + H2O + CO2
Alternatively the sodium bicarbonate could react directly with the acid -
HCl + NaHCO3 → NaCl + H2O + CO3
The other active ingredient is magnesium Trisilicate. This does not contain any carbon atoms so will not produce carbon dioxide when it reacts with the acid.
2. Each tablet will give off roughly the same amount of gas, whatever temperature of acid. This is because each tablet will have the same mass – refer to “Ensuring a fair test”. Therefore they should have the same number of active agent molecules so should produce the same number of product molecules. This means that the volume of carbon dioxide produced should be the same.
3. When the results are plotted on a graph they will produce a curved line of decreasing rate. This is because at the start of each test the tablet will have a greater surface area and therefore have more tablet and acid particles in contact with each other. As the experiment progresses there is a smaller surface area as the products move away from the remaining tablet.
The acid becomes more dilute as water is one of the products of this reaction. Also the number of acid particles is decreasing because they are reacting and being used up. Therefore the reaction rate slows down, as there is less chance of acid and tablet particles colliding.
4. The higher the temperature the shorter the time it takes for the tablet to completely react with the acid. This is because, according to collision theory, molecules with more energy will move about quicker and therefore the particles are more likely to collide so the reaction will occur more quickly. This means the reactants are used up more quickly in a hotter experiment so the same amounts of products are formed but at a greater rate. At low temperatures the time taken for the experiment should be significantly different to the time taken at higher temperatures.
Bibliography
All quotes are taken from
The Usborne Illustrated Dictionary of Science by C. Stockley, C. Oxlade and J. Wertheim. Pages 169, 179 and 216.
Obtaining Evidence
1 2 3
Analysing Evidence
As I predicted, a gas was produced. This gas put out a lit splint and so I assumed that this was carbon dioxide. Had I had additional equipment and time I would have tested the gas using limewater. See ‘Justification’ for scientific theory to support this.
The three graphs on the previous page show the results from the 3 tables in the obtaining evidence section.
The first graph shows the reactions of the tablet with acid of different temperatures.
Each tablet (except that tested at 35oC) produced between 57cm3 and 65cm3, a range of just 8cm3. This supports my prediction that all the tablets would produce similar amounts of gas but the range is on the limits of acceptability (see ‘Justification’ for theory). I believe this difference comes from two reasons, firstly because there was a very brief time lapse between dropping the tablet into the acid and replacing the bung and secondly because the very hot acid would have produced CO2 of a higher temperature. When gases are heated up they gain more energy and so the particles move around more quickly. This means the gas particles exert a higher pressure on their surroundings so they tend to expand and therefore their volume increases.
The shape of all the graphs showed that the reaction was fastest at the beginning of the experiment, decreasing towards the end. This is the same as what I predicted (see ‘Justification’ for theory).
Not including the 350C line, the lowest temperature experiment lasted the longest time (24oC, for 6mins), decreasing in time until the highest temperature (72oC, for 1min 45secs). I also predicted that this would happen (see ‘Justification’ for theory).
The second graph has been used to check the reliability of my results. For this I carried out repeat experiments using acid of 22oC and 55oC. Both repeat experiments, when superimposed over the other experiment of the same temperature, are very close together. I have used a highlighter to show that throughout their curves their respective results were very close. The two 55oC lines fall within the width of a relatively narrow band (highlighted in orange) for the complete curve. The 22/24oC graph line band has been coloured in yellow between the points to show that again the results are very similar. Even though the second reading lasted 1½ minutes longer it only produced 2cm3 more carbon dioxide, a negligible amount. This suggests that my results are reliable.
The third graph shows two anomalous results (acid at 24oC marked as black x and acid at 71oC marked as blue x). These are compared against the results for 24oC and 72oC respectively that follow the general pattern for graph 1. During the time that I took my results these 2 experiments that produced anomalous results, went quite wrong because of equipment problems. The first (black x) results was from my first experiment. I had been supplied with a short delivery tube. The experiment was fine until the 2-minute mark when the delivery tube came out of the measuring cylinder. The result of this was that the gas produced by the reaction escaped rather than being collected in the measuring cylinder. From this point on I used 2 delivery tubes carefully put together and sealed at the joint. This provided ample length for the rest of my experiments and from that point on I did not have any problems with the length of the delivery tube. The second line, from column 7 in ‘Obtaining Evidence’ (blue x) started very slowly, compared with the other equivalent, then only produced 4cm3 of CO2 between 30secs and 1min 45secs. This was because I was using a smaller bung on the end of my delivery tube that did not create a good enough seal with the boiling tube. The effect of this was that the gas escaped rather than being collected in the measuring cylinder. After this I replaced the bung with one that gave a better fit.
When the room temperature experiment had finished I noticed that the boiling tube had become warm. This means that the reaction was exothermic (heat was given out). This happens when more energy is given out in making the new chemical bonds than is needed to break the original bonds of the acid molecules and indigestion tablet molecules.
Evaluation
As I have already said in the Analysing Evidence section I feel that the results I have taken are reliable. I think I have taken enough results to support all my conclusions.
If I were to do this experiment again in a perfect environment I would make changes to increase the accuracy of the results. The most notable problem with my experiment was the reliability of my bung and delivery tube. In future I would start with a new delivery tube that has a longer tube to reduce the risk of the tube coming out of the measuring cylinder. I also found that I would have preferred to use a more accurate measuring cylinder as at times the reading was between two points and so there was a slight margin for error. This margin of error was small and did not have much of a noticeable affect on any of my experiments. For the hotter acid tests, the CO2 in the measuring cylinder had more energy (was hotter) and so had a greater volume than CO2 from the room temperature test. To see that exactly the same amount of gas is produced each experiment regardless of temperature I would have to wait for the gas to cool to give a fairer reading.
The mass of each tablet should have only varied slightly from tablet to tablet. To check that each indigestion tablet was the same I could weigh the tablets using a digital scale that is accurate to at least 100th of a gram.
Air pressure exerts a force on the water and gas in the measuring cylinder. From day to day this changes with the weather. Because of time constraints I was forced to carry out my experiments on two separate days. This means that the pressure exerted on the measuring cylinder could have changed and could have affected the readings. To improve the experiment I would have to carry out all the experiments on the same day or take into account the change in barometric pressure.
To improve the reliability of my experiments I would repeat each temperature test 3 times to find an average. As I showed with the second graph, the results are very similar for each temperature but not identical.
I was limited on the number of boiling tubes that I could use and so had to wash out the ones I was using when I ran out. This meant that there was some water left in the tubes, as I was unable to dry it properly. This would have affected the concentration of the acid slightly as the remaining water would have diluted it slightly. To avoid this I would have to use clean and dry boiling tubes to improve the reliability.
Another way of carrying out this experiment would be to measure the mass change as the tablet reacted with the acid. This is because the mass of the boiling tube and its contents would decrease as carbon dioxide is given off.
To further this investigation I would like to test different indigestion tablets to see how different brands and strengths affect:
- The speed of the reaction.
- The amount of acid that can be neutralised.
-
The amount of CO2 produced, affecting the amount of burping after taking a tablet
This would allow me to suggest which varieties are best for quick relief or relieving heavy indigestion problems.
Another way of extending the investigation would be to test whether the shape of the tablet made any effect on the speed of the reaction. For example a ‘Polo’ shaped tablet would have a greater surface area than a traditional tablet shape.
There were some anomalous results other than the “anomalous results” table. I have not included the 35oC line in points 1 and 3 of my Analysing Evidence section because I feel that this is an anomalous result. This is because it produced noticeably less than any of the other results and lasted less time than two of the experiments which started at higher temperatures. This graph only fits the shape pattern, producing a good curve. Because of the good curve I do not believe that this anomaly came from faulty apparatus. Instead the acid could have been, for some reason, weaker than the other experiments and so was completely used up in the experiment. This would explain why the reaction started at an acceptable rate then tailed off prematurely. There are no specific points that seem anomalous. All the points either closely fit the curved line of best fit or, as in the case of the graph lines on graph 2, between them form the curve of best fit.
To improve this experiment and make my results more accurate I could use a thermostatically regulated water bath which keeps the water and so the acid at the same temperature. This would ensure that throughout the experiment the temperature would remain constant. In my experiments the temperature of the acid in the very hot water was much lower than at the start but the room temperature acid, because the reaction is exothermic, was hotter at the end of the experiment. Regulating the temperature of the acid would improve the reliability of my results. The reaction between the indigestion tablet and acid is exothermic which means keeping the experiment at the same temperature is more difficult especially at room temperature. Keeping the reaction as close as possible to the starting temperature is important because it will improve the reliability of my results.
