Lab 7C: Determining Concentration in Acids and BasesPurposeIn this experiment you will use a volumetric titration to determine theconcentration of hydrochloric acid found in a contaminated river water. You willrepeat the titration on two sites on the river in the Simulation or activities, andthen use the data to determine an average amount of the acidic River water thatwas used to reach neutralization of the known concentration of NaOH. Thisamount of the known base can be used to calculate the concentration of thehydrochloric acid in the River water sample.IntroductionAcids and bases are two related types of substances that are part of our everydaylife. They are found in foods, beverages, medicines, and cleaning products. Acidsand bases are very reactive with each other. When a base is added to an acid, itwill eventually neutralize the acid. The concentration of an acid or a base can bedetermined by doing a volumetric titration.Volumetric TitrationWhen an acid reacts with a base in a neutralization reaction, the products arewater and an ionic compound called a salt. The amount of base needed toneutralize the salt depends on the balanced reaction. For example, for the reactionof HCl with NaOH, 1 mole of HCl reacts with 1 mole of NaOH.HCl(aq)NaOH(aq)NaCl(aq)H2O(l)For the reaction of H2SO4with NaOH, though, the balanced equation tells us that1 mole of H2SO4reacts with 2 moles of NaOH.H2SO4(aq)2NaOH(aq)Na2SO4(aq)2H2O(l)In a volumetric titration, a base or acid of known concentration is added to an acidor base of unknown concentration. An acid-base indicator is a dye used todistinguish between acidic and basic solutions by means of a color change. In thisexperiment an acid-base indicator is used to determine when neutralization isreached. In this experiment, phenolphthalein is used as the indicator. It will becolorless before the reaction but pink after the completion. You will start to seepink as you add NaOH, but then upon mixing, it will turn colorless again. Thepoint at which the color stays pink is called theendpoint. This is when you stopthe titration and determine the volume of NaOH that was added.
