A comparison of various proprieary antacids

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Ebrahim Palkhi, IB1

Lab 14: A Comparison Of Various Proprietary Antacids

Planning A:

Research Question:  How to determine and compare between a set of antacids( Eno powder, Tums Tablets and  Zolicid gel), which antacid neutralizes the most moles of stomach acid( Hydrochloric acid, HCl), by conducting back-titration reactions using standardized hydrochloric acid(0.5M) and standardized sodium hydroxide(0.5M).

Hypothesis:

In this experiment I plan to compare between a set of antacids, which antacid neutralizes the most moles of Hydrochloric acid(0.5 M), as this will help me to establish their relative effectiveness in helping to reduce excess stomach acidity.

 I am going to use back titration reactions whereby I will place a fixed volume, 25 cm3 of standardized hydrochloric acid, 0,5M, in a conical flask. Then, I shall add the maximum daily dosages of each individual antacid to the hydrochloric acid in the flask.  The antacid which is supposed to neutralize some of the excess hydrochloric acid of the stomach, will neutralize some of the excess hydrochloric acid in the  conical flask. The number of moles of hydrochloric acid to be neutralized would be 0.0125 moles.

I will then neutralize the unreacted hydrochloric acid, if any,  using standardized aqueous sodium hydroxide(0.5 M) from a 50 cm3 burette. In order to clearly note the point of neutralization( the equivalence point), I will use phenolphthalein indicator which experiences a colour change from colourless to pink, from acid to base. Using the volume of base needed to neutralize the excess acid, I will be able to calculate the amount of acid neutralized by the individual antacids, hence enabling me to compare their relative effectiveness.

The antacids have differing chemical compositions which are shown in the lists below:

Eno powder contains sodium bicarbonate which is a weak base. This is the main component which makes the Eno an antacid, however, there is also citric acid in the Eno sachets. Even though Sodium Bicarbonate will neutralize some of the hydrochloric acid in the flask and hence reduce the acidity of the mixture, the high percentage composition of 43.41% in the Eno will reduce the effect of neutralization caused by the Sodium Bicarbonate Base. The equation for the reaction between sodium bicarbonate and Hydrochloric acid is as follows:

Na2CO3(s) + 2HCl(aq)→ 2NaCl(s) + H2O(l) + CO2(g)

Even though each mole of Sodium bicarbonate will neutralize 2 moles of hydrochloric acid as seen from the mole ratio in the above reaction, I predict that the citric acid will act against neutralization. This in my view, will make the Eno powder very ineffective.

On the other hand, Actal Tums contain Calcium carbonate powder. Although we are not notified about the percentage composition of calcium carbonate powder in the tablets, there are no other ingredients mentioned which work against the action of the antacid. The equation for the reaction between calcium carbonate and hydrochloric acid is:

CaCO3(s) + 2HCl(aq)→ CaCl2(s) + H2O(l) + CO2(g)

As seen from the above chemical equation, the mole ratio of calcium carbonate to hydrochloric acid is 2:1. The mole ratio is also the same as that of sodium bicarbonate and hydrochloric acid. However I predict that the Tums will neutralize a greater number of moles of hydrochloric acid compared to Eno powder, because unlike Eno there is no other acid ingredient to counteract the neutralizing effect of the antacid. I therefore predict that the sodium hydroxide will have to neutralize less excess acid to reach the equivalence point when using Actal Tums, as compared to the maximum dosage of Eno.

On the other hand Zolicid, powder contains 6 g of aluminium hydroxide and 80mg of magnesium hydroxide. Magnesium hydroxide and aluminium hydroxide are generally stronger bases than calcium carbonate and sodium bicarbonate. The chemical equations for the reaction of aluminium hydroxide and magnesium hydroxide are given below:

Al(OH)3(s) + 3HCl(aq)→ AlCl3(s) + 3H2O(l)

Mg(OH)2(s) + 2HCl(aq)→ MgCl2(s) + 2H2O(l)

Each mole of aluminium hydroxide neutralizes three moles of hydrochloric acid, that is to say the mole ratio is 3:1. On the other hand each mole of magnesium hydroxide neutralizes 2 moles of Hydrochloric acid, that is to say the mole ratio is 2:1. In all, a mole of aluminium hydroxide and magnesium hydroxide neutralize a net number of 5 hydrochloric acid moles. This is far more than the 2 net moles neutralized by one mole of sodium bicarbonate in Eno , or, the two net moles of HCl neutralized by one mole of calcium carbonate powder in Actal Tums. I therefore predict that the Zolicid will neutralize relatively more moles of hydrochloric acid, in comparison to Actal Tums and Eno powder. The fact that it has two strong antacids working together will certainly make it more effective is terms of the number of moles of HCl neutralized. As a result, very little standardized sodium hydroxide will be needed to neutralize the remaining acid in the conical flask.

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Variables:

Independent variables:

  • The tablets/ Sachets/ Syrup of antacids( Eno powder, Tums Tablets, Zolicid gel)

Dependent Variables:

  •  The moles of HCl neutralized by each antacid
  • The moles of HCl neutralized by the sodium hydroxide base
  • The volume of sodium hydroxide needed to neutralize the excess hydrochloric acid

Controlled Variables:

  • The concentration of Hydrochloric acid ( HCl)
  • The volume of Hydrochloric acid (HCl) to which each antacid is added
  • Amount/ dosage of each antacid( e.g. 2 tablets, I sachet, 2 teaspoons..)
  • The concentration Of aqueous sodium hydroxide base( NaOH ...

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