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LABORATORY REPORTExperiment 8Finding the Acid Ionization Constant from pH and Acid-Base TitrationName:____________________________________________Date: ___________________Lab Partner’s Name:_ ________________________________Score:_________________I.IntroductionAn acid can be defined as a substance that produces H+ ions in a solution (Tro, 2017). Acids arealso regarded as a proton donor because they give out their H+ ion in a solution. An example of thiswould be the reaction between hydrochloric acid and water:HCl (aq) + H2O(l)H3O+(aq) + Cl-(aq). Inthis reaction, HCl donates it H+ion to water to form a hydronium ion (H3O+) (Tro, 2017). Acids can eitherbe strong or weak. A strong acid is an acid that completely ionizes in solution while a weak acid is an acidthat partially ionizes. The strength of an acid can be measured by looking at the attraction between theanion of the acid and the hydrogen ion with respect to their attractions to water (Tro, 2017). In a strongacid, there is a weak attraction between the H+and the A-which results in complete ionization. In aweak acid, there is strong attraction between the H+ and A-, resulting in a partial ionization. Besides that,the strength of an acid can be measured by measuring the size of the equilibrium constant when it reactswith water (Tro, 2017).The Acid Ionization constant represented as (Ka), is the equilibrium constant used to measure thestrength of a weak acid in an ionization reaction (Tro, 2017).The generic equilibrium expression for theionization reaction is−¿A¿¿+¿H3O¿¿¿Ka=¿(Tro, 2017). The Kaof an acid can be obtained using two methods: Theacid-base titration method and the pH and ICE table method. In an acid-base titration, a weak acid istitrated with a strong base until the equivalence point is reached (Wargniez, n.d.). At the equivalencepoint the number of moles of the weak acid is equal to the number of moles of the weak base in thereaction (Wargniez, n.d.). This relationship is used to calculate the molarity of the weak acidby dividingthe number ofmoles of the acid (titrant) against the volume of the base at equivalent point (base). Thehalf equivalence point of a weak acid allows for one to determine PKa. Since the Pka= -logKa, Kacan bedetermined by solving for the antilog of -pKa(Wargniez, n.d.).In the pH and ICE table method, the pH of
the weak acid solution coupled with the obtained molarity from the equivalence point of the titration isused to calculate the concentration of H3O+and the acid ionization with water at equilibrium. Thisequilibrium concentrations will be used in the ICE table to calculate the Kaof the weak acid (Wargniez,n.d.).The objectives of this experiment were as follows: To perform a titration using the solution of aweak acid and sodium hydroxide, to understand the half equivalence point concept in acid-basereactions, to be able to determine their pH and understand its importance in acid base equilibria, tocalculate the pKaand Kaof an unknown weak acid using the half equivalence titration method and theICE table method and lastly, to compare the Ka values of the two different concentrations of a weak acid(Wargniez, n.d.).