ANALYTICAL CHEMISTRY
EXPERIMENT 3:
NEUTRALISATION CAPA CA PACITY CITY OF COMMERCIAL ANTACID ANTACID TABLET TABLET
ABSTRACT
This experiment is to determine the neutralisation capacity of commercial antacid tablet. Firstly, dissolve the tablet in an excess amount of acid of known concentration. Some of the HCl will be neutralized by the carbonate, but there will be some remainin. Continue with a titration with !a"H solution from experiment # to fiure out the amount of excess acid. Then, from this, calculate how much acid reacted with the antacid. This method of analysis is called a back$titration. The reactions above are reversible, which means that C"# dissolved in water will produce some carbonic acid. This acid will react with the !a"H solution and the titratin and ive us inaccurate results. Therefore it is important to boil the solution when the carbonate reacts with acid, to remove C"# as a as.
OBJECTIVE
%. To prepare Hydrochloric &cid Solution. #. To standardise the &cid aainst Sodium Hydroxide. '. To determine !eutralisation Capacity of a Commercial &ntacid Tablet.
INTRODUCTION
This experiment is about neutralisation capacity of commercial antacid tablet. Firstly, preparin an approximate concentration of hydrochloric acid solution and standardise aainst standard sodium hydroxide solution from experiment #. Hydrochloric acid is also not a primary standard because its concentrated solution vaporises rapidly at room temperature. "nce the accurate molarity of the hydrochloric acid solution is known, t is referred as standard solution.
The neutralisin capacity of the tablet is the amount of hydrochloric acid that it can neutralise. The antacid tablet does not dissolve in water alone but re(uires the presence of HCl. Since the HCl is excess, only some of the added HCl will react with the base present in the tablet. The remainin amount of HCl is then analysed with the standard !a"H solution from experiment #. The difference in the amount of HCl added initially in excess and the remainin HCl ives the amount of HCl that reacts with the antacid and thus the neutralisation capacity of the antacid tablet. The calculated amount of HCl that reacts ives the mass and percentae of hydroxide in the tablet.
PROCEDURE
This experiment starts with preparation of the HCl solution. Firstly, volume of ).* + HCl is calculated as #%.**m. Then, poured -* of distilled water into /**m conical flask. 0sin raduated cylinder, the volume of ).* + HCl is been measured and transferred to the conical flask. #/*m of distilled water is added to the mark of the conical flask. Covered the conical flask with parafilm and mix the solution well. The solution is labelled. !ext step is to standardisation of the the acid aainst sodium hydroxide. First, /*m of burette is rinsed and filled with !a"H solution from previous experiment. The initial readin is recorded. 1ipette and transferred %*.* m of prepared HCl into a clean conical flask. Then, #*m of distilled water is added followed by ' drops of phenolphthalein indicator to the flask and titrate to the end$point with standard !a"H solution. The final readin is recorded. The titration is been repeated two times. ast procedure is determination of neutralisation capacity of an antacid tablet. Starts with refilled the burette with !a"H solution and the initial readin is recorded. !ext, antacid
tablet is weihed without touchin by hands. The mass is recorded and the tablet is crushed usin mortar and pestle. Split the crush tablet into two or three samples and reweihed each of samples to the nearest milliram. The mass of each crushed samples is recorded and transferred to a clean #/*m conical flask. +easured #/m of distilled water and poured to the flask. 2ispense usin a volumetric pipette, #/.* ml of standard acid into the flask containin the crush tablet. The content is heated usin hot plate until boil ently for / minutes. Check the litmus paper only contains the remainin acid solution. The solution is cooled down to room temperature and then carefully placed the flask to beaker of tap water. Then, / drops of phenolphthalein indicator is added to the solution. The indicator chanes colour from colourless to red and titrated aain usin standard base. The experiments is repeated with the two other samples.
QUESTIONS
%. &cid is always added to water, and never the reverse. 3hy4 & lare amount of heat is released when stron acids are mixed with • water by addin more acid releases more heat. 5f add water to acid, it will form an extremely concentrated solution of acid initially. The solution that forms is very dilute and the small amount of heat released is not enouh to vaporize and spatter it. #. 3rite a balanced chemical e(uation for the reaction of the antacid tablet with HCl if the antacid contains hydroxide ion. HCl6a(7remainin 8 !a"H6a(7 9 !aCl6a(7 8 H#"6l7 •
'. 3rite a balanced chemical e(uation for the reaction if the antacid contains carbonate ion. •
C"' #$6a(7 8 H#"6l 7 HC"' $6a(7 8 "H$6a(7
DISCUSSION
This experiment is about neutralisation capacity of commercial antacid tablet. Firstly is to do a preparation of the hydrochloric acid solution. The volume of ).* + HCl is calculated as #%.**m. The volume is taken from preparation of #/*m of *./+ HCl. Then, the volume is mixed with water to the conical flask. !ext is to standardise the acid aainst sodium hydroxide. This step needs to use !a"H solution from previous experiment. The volume of the acid used is %*.*m. &s for !a"H solution, the initial readin is *.** and for the final readin is #:.#* for the first time titration. &s for second time, the final readin is also #:.#* and the last titration is #:.'* which for all volume of the acid used and initial readins are the same. For the last step is determination of neutralisation capacity of an antacid tablet. This last step is used antacid tablet. First weihed one antacid tablet without touchin by hands and the mass recorded is *.)*:*. Crushed the tablet by usin mortar and pestle and then divided the crushed tablet into two samples. The samples is reweihed resulted sample % is *.'** while sample # is *.#)//. The samples is transferred into a flask.Then, distilled water is added into a flask followed by #/m of HCl. The solution is been titrated with !a"H solution. The initial readin of !a"H solution for both samples solution is *.**m. Final readin for the first sample is )*.#*m while the second sample is )*.**m.
CONCLUSION
The molarity of HCl solution aainst sodium hydroxide is #%.**m. For the first samples, resultin )*.#*m of !a"H solution need to be titrated to the HCl solution. For the second samples, resultin )*.**m of !a"H solution need to be titrated to the HCl solution.
REFERENCE
;
!elson, <., Chemistry= The Central Science, 'rd edition, 1rentice$Hall, %>-/
