Analysis of antacid By titration Hawler Medical University

Analysis of antacid By titration Hawler Medical University College of Medicine Department of Biochemistry 1st year Medical Students Presented by Fargeen. E. Abdullah M. Sc. in Clinical Biochemistry Titration: A titration also known as titrimetry, is a technique where a

solution of known concentration is used to determine the concentration of an unknown solution. The titrant or titrator (the know solution) is added from a buret to a known quantity of the analyte (the unknown solution) until the reaction is complete. An indicator is used to detect the end of the reaction, or the endpoint. Titrations can be classified as: 1. Acid-base titrations or acidimetry and alkalimetry.

2. Oxidation-reduction titrations or redox titrations. 3. Precipitation titrations. 4. Complexometric titrations. 1. Acid-base titrations : Both acid and base titrations involve neutralization. In these titrations H+ ions of the acid combine with OH ions of the alkali to form unionized molecules of water.

HA + BOH BA + H2O Acid Alkali Salt Water or H+ + OH H2O The end point in these titrations is determined by the use of organic dyes, which are either weak acids or weak bases. These change their colours within a limited range of hydrogen ion concentrations,

Phenolphthalein is a suitable indicator in the titrations of strong alkalis against strong acids or weak acids, Methyl orange is used as an indicator in the titrations of strong acids against strong or weak alkalis. 2. Oxidation-reduction titrations : The titrations based on oxidation-reduction reactions are called redox titrations. The chemical reaction proceed with transfer of electrons (simultaneous loss or gain of electrons) among the

reacting ions in aqueous solutions. The reduction of free iodine to iodide ions, and oxidation of iodide ions to free occurs in these titrations. I2 +2e 2I (reduction) 2I I2 + 2e (oxidation) Free iodine is titrated against a standard reducing agent usually with sodium thiosulphate. can be estimate by this method. I2 +2Na2S2O3 2NaI+ Na2S4O6

In iodimetric titrations, such solution is used as an indicator. Starch solution gives blue or violet colour with free iodine. At the end point the blue or violet colour disappears when iodine is completely change to iodide. 3. Precipitation titrations: The titration which are based on the formation of insoluble precipitates. For example, when a solution of silver nitrate is added to a

solution of sodium chloride, a white precipitate of silver chloride is formed. AgNO3 + NaCl AgCl+ NaNO3 4. Complexometric titrations: A titration, in which an undissociated complex is formed at the equivalence point. EDTA (ethylenediamine tetra-acetic acid) is a useful reagent which forms complexes with metals. In the form of disodium salt, it is used to estimate Ca 2+

and Mg2+ ions in presence of erichrome black-T as an indicator. Analysis of antacid By titration The natural environment of our stomach is quite acidic, which is mostly hydrochloric acid has a pH of 1.0 such a strong acidic environment denatures, proteins and helps with their digestion by enzymes such as pepsin. The acidic environment helps to activate pepsin, by converting pepsinogen(inactive form) to pepsin

(active form), This can only occur in an acidic environment and pepsin molecules catalyze this reaction (autocatalysis). But too much acid in the stomach is not good, in the absence of food, the strong acid HCL, denatures the proteins in the stomach wall, If this goes on unchecked, it may cause stomach or duodenal ulcers. we feel the excess acidity in our stomach. Such

sensations are called heartburn or sour stomach to relieve it we take antacids in tablet or liquid form. Active ingredient of some antacid drugs 1- sodium bicarbonate 2- calcium carbonate 3- aluminum hydroxide and magnesium hydroxide NaHCO3+HCl CaCO3+2HCl Al(OH)3+3HCl

Mg(OH)2+2HCl NaCl+H2O+CO2 CaCl2+H2O+CO2 AlCl3+3H2O

MgCl2+2H2O Procedure 1- Fill the buret with the standard (0.1N) HCl solution. 2- Dissolve one tablet antacid in 100 ml distil water. 3- Pipette out 10ml of the (antacid tablet solution) into the conical flask. 4- Add 3 drops of phenolphthalein as indicator. 4- Titrate the antacid solution with HCl until the color changes at the end point from pink to colorless, repeat

the titration to ensure the end point and measure the volume of HCl (V1) which is required to neutralize the total alkality. Calculations: (Na x Va) HCl = (Nb x Vb) Antacid 0.1x V1 = 10 x N antacid