Discussion of Back Titration Report

2024 Words May 2nd, 2011 9 Pages
The acid neutralising capacity (ANC) of 3 brands of calcium carbonate (CaCO3) tablets was determined by reacting the tablets in excess standardized hydrochloric acid (HCl) and then back-titrating with a standardized sodium hydroxide (NaOH) solution. Back titration was required for two reasons. Firstly, CaCO3 tablets are poorly water-soluble but dissolve rapidly in acid. Secondly, CaCO3 is a weak base so it is difficult to determine the end point of the reaction if titrated directly.

Assuming good manufacturing practice, the amount of active ingredient described on the product label should conform to quality control standards and accurately reflect the experimentally determined content of CaCO3 in each tablet. Titralac antacid
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This is how effective the antacid is at neutralizing HCl (based on number of moles) relative to the tablet’s mass. A higher value for mass effectiveness is desirable. For Titralac the value was 11.8(mmol/g). This was greater than that of Tums with a value of 6.4(mmol/g). However, Quick-eze had the lowest mass effectiveness with a result of 3(mmol/g). Therefore Titralac would be the best choice although, Tums would be favoured over Quick-eze, a different result to that of cost effectiveness.

To mimic the action of the antacid being dissolved by stomach acid, the time taken for the tablets to react with 5-10 ml of HCl was assessed. This allowed for an indication of the speed of action of the tablets, which ranged from 3-6 mins. Titralac dissolved in 151 sec, Tums took 492 seconds and Quick-eze dissolved in 327 seconds. For a fair comparison the reaction time was corrected for the moles of CaCO3 in each tablet. In this case Titralac, Tums and Quick-eze were able to neutralise 3.45, 1.04 and 2.81mmol of acid per min respectively. Since the molarity of stomach acid is about 0.1M, this would neutralise about 10-30mL of stomach acid/min. Titralac therefore was marginally quicker than Quick-eze in neutralizing HCl, perhaps due to Titralac’s concentrated formulation giving it a small size and greater tablet surface area. In real life, the chewing of the tablets before swallowing may alter this brand difference.

A summary of the results is