To determine the effectiveness of an indigestion tablet at neutralising acid

The stomach produces Hydrochloric acid, which provides a medium for the digestion of protein by the enzyme protease. An excess of acid can lead to indigestion, many tablets are on the market to help neutralise this excess acid, but all have different ingredients.

I am to find out which commercially available indigestion tablet is most effective;

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Brand Name

Dosage

Active Ingredient

Other Ingredients (non-active)

Do not exceed…

Rennie

2 tablets

Calcium Carbonate 680mg

Heavy magnesium carbonate 80mg

Sucrose, glucose and saccharin

16/day

Andrews

Antacid

1-2 tablets

Calcium Carbonate 600mg

Heavy magnesium carbonate 125mg

Malic Acid, sugar, magnesium stearate, talc, saccharin, sodium (22mg), sodium bicarbonate

12/day

Tums Antacid

Calcium carbonate 500mg

Sugar, glucose, starch. Talc, magnesium stearate

Setlers Antacid

Calcium Carbonate 500mg

Sucrose, dextrose, maize starch, talc, magnesium stearate, adipic acid

Asilone Antacid

1-2 tablets

Dimeticone 270mg

Aluminium hydroxide 500mg

Sucrose, sorbitol, French chalk, menthol

Bisodol

1-2 tablets

Sodium bicarbonate 64mg

Calcium carbonate 522mg

Light magnesium carbonate 68mg

Saccharin, maize starch, sucrose, calcium stearate

Remegel

1 tablets

Calcium Carbohydrate 800mg

Glucose, butylated hydroxyanisole, methanol

Milk of Magnesia

2 tablets

Magnesium Hydroxide 300mg

The brands in bold are the six that I have chosen to investigate

Equipment

As there are six different brands available, the equipment list below may need to be multiplied by 5.

250ml beaker

Pestle and Mortar

Magnetic stirrer

Burette

2x Stand, Clamp and Boss

Distilled water

pH 7 buffer solution

Pipette

Top-pan balance

PH probe

Laptop with appropriate software

Method

There are many ways of doing this experiment, but titrating 1 molar acid onto the tablet, is by far the simplest, as well as being effective and time efficient. 1 molar acid is usually available; however, it can simply be made by diluting more concentrated acids with distilled water. The burette should be thourgherly cleaned out, using distilled water. Then the acid (“titrant”) should carefully be filled into the burette using a funnel. It should be filled to the zero level, pipetting (at eye level) if necessary to reach the value accurately. Check for bubbles in the valve of the burette, and if necessary refill after releasing the bubbles.

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

Chemical

Solubility

Extra Time needed?

Calcium Carbonate CaCO3

4.8×10-9

Yes

Magnesium Carbonate MgCO3

Yes

Dimeticone

Aluminium Hydroxide Al(OH)2

1.0×10-33

Magnesium Hydroxide Mg(OH)2

1.1×10-11

Calcium Carbohydrate Ca

Sodium Bicarbonate Na

Yes

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.

1st tablet

2nd tablet

3rd tablet

4th tablet

5th tablet

6th tablet

Brand

1

Initial value (cm3)

Final value (cm3)

(Final-Initial)

Titre (cm3)

2

Initial value (cm3)

Final value (cm3)

(Final-Initial)

Titre (cm3)

3

Initial value (cm3)

Final value (cm3)

(Final-Initial)

Titre (cm3)

FINAL AVERAGE TITRATION cm3

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 ilone Antacid he pH value will be five, and the end point will have been reached.number of hydrogenium as the hydonium ions a

Chemistry Practice Plan March 2003

Camilla Marcus-Dew 12.7 Dr. Pratt

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