Method: Tip a small amount of a base into the pestle and mortar, grinding it to remove any larger lumps. Now place the base onto the balance and add, remove a small amount of the substance as necessary until it weighs 0.2g. Place this into the conical flask. Place the white tile onto the base of the burette stand. Using the glass pipette, measure 25ml of water and add it to the conical flask containing the base and ensure that as much as possible is dissolved. Now add 5 drops of methyl orange to the solution. Place the burette funnel into the top of the burette and pour in 50ml of hydrochloric acid so that the bottom of the meniscus is level with the appropriate marking. Now place the glass beaker on the white tile and open the burette tap in order to clear it of any air bubbles thus removing any inaccuracies. Top up the burette as appropriate with HCl. Now place the conical flask containing the base onto the base of the stand and, open the tap of the burette slightly whilst ‘swirling’ the conical flask using the other hand. You will observe that the solution will change colour from orange to pink (caused by the methyl orange indicator). As this occurs, it will normally return to orange as you continue to add the acid. When it becomes clear that the solution is neutralised (ie. is pink and does not appear to change back to orange within a reasonable period of time for example, after having stood for 5 minutes), put it to one side and record the amount of acid that it neutralised (ie. the reading on the burette).
Discard the neutralised base and rinse the conical flask using distilled water. Repeat the experiment with each base three times if time allows and repeat for each of the available bases.
The known medical side affects of the chemicals available for testing include:
Magnesium hydroxide (Mg(OH)2), milk of magnesia is relatively insoluble and is therefore an antacid of greater gastric longevity and usefulness. It is fast reacting and only a small amount of ionic magnesium is absorbed into the blood stream. Magnesium salts remain in the intestines and can have a laxative effect. Magnesium and aluminium containing antacids often combined in commercial products to offset their individual effects on bowel function.
Calcium carbonate (CaCO3) is a very effective antacid and reacts more slowly than Sodium bicarbonate. Some of the ionic calcium is absorbed and may infrequently cause hypercalcemia (high calcium in the blood) which can cause kidney failure. It is also used as an antidote to corrosive acid poisoning.
Sodium bicarbonate (NaHCO3) is very soluble, fast reacting and the active ingredient in baking soda. Because it is readily soluble, it is rapidly removed from the gut by absorption. Therefore, sodium bicarbonate not useful for long term use as it can cause fluid retention.
Magnesium oxide (MgO) and Magnesium carbonate (MgCO3) can have a laxative effect, which can interfere with absorption of vitamins from your diet.
The magnesium based antacids neutralised the most acid on average because they had the highest formula mass compared to the amount of HCl being neutralised. This allowed for a greater amount of HCl to be neutralised compared to the other bases (in particular NaHCO3) and confirms my prediction.
In conclusion, in using a base for the production of an antacid drug, I would consider the use of MgO or Mg(OH)2 because they neutralised the most HCl, the acid that is present in our stomachs. Despite their possible laxative effects, it is unlikely that such a drug would be used continuously over a longer period of time. It is also to be remembered that many medicines contain laxative compounds and, as such, this is not a great problem if used infrequently for short periods of time, as and when necessary, as with many medicines that have side effects.
Alternatively, CaCO3 may be used as its side effects are extremely rare yet my results show it to be reasonably effective, with an average of 9.6ml of HCl neutralised during the titrations. In order to make a full judgement for the use of a base in an antacid drug, this experiment would have to be repeated many more times before use in human trials in addition to assistance from knowledgeable medical staff, obviously beyond the scope of our own work.
Evaluation: This experiment was designed with the aim of being able to make a judgement on both medical and chemical grounds for the most suitable out of a given range of bases for use as a human antacid drug. Whilst providing me with a set of clearly distinguishable results, there were a few difficulties encountered when taking and subsequently evaluating the figures.
We were using balances for the weighing of each base with the ability to display to 1 decimal place. Whilst normally enough for most experiments, the differences between the relative formula masses was so small that I have had to use more than this in order to differentiate between them. If I were to carry out this experiment again for a medical firm, I would ensure the use of more accurate equipment in order to obtain more reliable results with a smaller percentage error.
In addition, the indicator during the titration would often continually revert to ‘orange’ as more and more of the acid was neutralised, meaning that we had to eventually decide to terminate the experiment after a certain length of time, and that not all of the neutralisation was complete. If I were to carry out this experiment ‘for real’, I would probably use a calibrated digital pH meter to allow me to precisely ascertain the point at which the neutralisation was complete, eliminating any inaccuracies due to the indicator.
I could also extend the enquiry by cross-checking my original results with those of a back titration whereby they are dissolved in acid of an exact known concentration and then calculating the amount of acid each base neutralised. One would expect these results to match, confirming the data taken and allowing a more complete judgement to be made.
In conclusion, I believe that the experiment was completely adequate given the resources available and that we were preparing an initial study for further investigation by a specialist team (ie. there would be extensive further testing before any product was used in human trials). It was clearly possible to distinguish between the bases and I was able to confirm my prediction. Further study would only be necessary for a ‘real’ test.