The tablets should be crushed using the pestle and mortar, so they resemble a fine powder. Measure out 100ml of distilled water into a measuring cylinder and then add to the first tablet in the beaker.
Set up the apparatus as shown, and calibrate the pH probe using the buffer solution.
Turn on the magnetic stirrer to an appropriate speed. Most tablets will dissolve in this time, however, if they don’t dissolve, continue with the experiment, as the neutralisation reaction will still occur once the acid is adding, however it may take longer to react.
Check the solubility of each in the table below
After about 50 seconds of stirring the solution, begin to titrate the dilute Hydrochloric acid. The first will be a trial titration to work out the rough value for the equivalent point (“end point”) which I am trying to achieve. On the second titration follow the same procedure, and as you approach the equivalent point titration value, begin to add the acid one-drop at a time. The equivalent point will be the value of pH 5 on the probe, as that is a safe value of acidity in the stomach. pH 7 could have been used, however, as this is testing the tablet, in the stomach it would only raise the value not neutralise the acid, therefore, I will use pH 5.
Record the amount of HCl titrated in the table below. Continue until the titrations for each tablet are within 0.1cm3 of each other. Then record the average value in the table. Save the results from the pH probe.
There are a number of variables that can be altered, but most must stay the same to make it a fair test.
Independent variable(s) : Ingredients in indigestion tablets
Dependent variable(s): pH value
Controlled variable(s) : amount and concentration of acid, amount of antacids, temperature
The amount of antacid may be kept constant or the recommended adult dose could be used. As it is a scientific experiment to test the effectiveness of the tablet, it is more important as to the ingredients, rather that the amount. Therefore the recommended adult dose will be used, and in each case if 1-2 tablets is specified, 1.5 tablets will be used where appropriate.
Fair test Precautions
1. The indigestion tablets should be crushed into fine powders, each tablet, to approximately the same sediment size.
2. The solution should be kept stirred to ensure that the powder is not floating on the surface. The magnetic stirrer is used, as this would mean that each solution was stirred at the same speed.
3. The set-up should not be moved during the experiment.
The main ingredient, for example calcium carbonate in the case of Rennie, must be soluble in the hydrochloric acid. The most effective tablet will be the one that neutralises the acid to a safe level in the quickest time.
Some of the tablets are soluble, and thus form in solution with the water solvent. Non-soluble alkalises do not have polarity within the molecules, and thus do not form hydrogen bonds with the delta negative oxygen in the water. If they are insoluble, the small particles will jus be stirred until they form a cloudy suspension.
Sodium Hydrogencarbonate will be added to the dilute hydrochloric acid to give carbon dioxide, water and sodium chloride. As carbon dioxide is a product of some tablets, this could be measured, and thus, calculate a rate of reaction. I can measure how quickly the tablets work by recording the loss in mass as the tablets react. But this of course tells you how fast it is dissolving, but not necessarily neutralising the acid. Some tablets do not produce CO2 as a by-product, so this method would not be useful.
Each tablet is alkaline e.g [H+] < [OH-]
The HCl is acidic e.g [H+] > [OH-]
Although they will not be neutralised, a neutral solution is [H+] = [OH-] = 10-7 dm-3 (where the number of protonated waters equals the number of hydroxyl anions.)
The pH is defined as the negative of the logarithm of the hydrogen ion concentration.
H+ + OH- -> H2O
Or more correctly
H3O+ + OH- -> 2H2O
The alkaline solution/suspension contains millions of hydroxide ions, this number will gradually decrease as the acid containing hydronium ions are added. Eventually, a point will be reached when the number of hydronium ions is proportional to the number of hydroxide ions originally present, at this point the pH value will be five, and the end point will have been reached.
Rennie 2HCl + CaCO3 → H2O + CO2 + CaCl2
Andrews Antacid 2HCl + CaCO3 → H2O + CO2 + CaCl2
Asilone Antacid 3HCl + Al(OH)3 → 3H2O + AlCl3
Bisodol 2HCl + CaCO3 → H2O + CO2 + CaCl2
Remegel HCl + CaHCO3 →
Milk of Magnesia 3HCl + Mg(OH)3 → 3H2O + MgCl3
