Weak Acid Lab.pdf - Lab 5: Weak Acid Group 1: Thessaly...

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Lab 5: Weak AcidGroup 1:Thessaly AlexanderAlly DeimekeNick HumphreysSathana SelvamCHM 116(section), Tuesday 8:30 am-10:20 pm, PSH-136
What is the Weak Acid?IntroductionWeak acids are known to dissociate significantly less than strong acids in water. When a weakacid dissociates in water, it does not completely dissociate like strong acids. The dissociationreaction for a weak Bronsted Lowry acid is reversible as shown in the following equation,HA (aq)+ H2O(l)H3O+(aq)+ A-(aq). The ionization rate of a weak acid is usually under10%. The acid dissociation constant at equilibrium is known as Kawhich is defined as .Thepurpose of this lab was to find the concentration and identity of the weak acid as well understandconcepts including titration, titration curves, equivalence points, endpoints, pH, pKa, and Kavalues.This experiment was separated into two parts, including the standardization of the NaOH and thetitration of an unknown weak Acid. Standardization is the practice of finding the concentrationof a solution. Titration, a type of standardization, is when a known solution’s concentration isused to find another unknown solution’s concentration. In order to standardize the NaOH, firstthe KHP samples were mixed with 40 ml of boiled distilled water as well as 2-3 drops ofphenolphthalein indicator. NaOH was added from a burette slowly until the mixture turned pink.Once the color changed pink for 30 seconds, the team assumed that the reaction reached itsendpoint. The reaction between Na and KHP (also known as KHC8H4O4) is described as thefollowing equation, KHC8H4O4(aq) + NaOH(aq) --> KNaC8H4O4(aq) + H2O(l).The grams ofKHP were used to calculate the moles of KHP and the moles of NaOH. The moles of NaOHwere divided by the liters of NaOH to calculate the molarity of the NaOH. For part 2, thetitration of an Unknown Monoprotic Weak Acid, the team used a pH meter to monitor the pHand the titration data of the weak acid and the standardized NaOH. The lab team documented 30- 60 points of data documenting the change in pH. Once the pH changed drastically (usually byan increase of 4 to 5 in pH) the team presumed that was the endpoint of the titration of the weakacid and the standardized NaOH. Part two of the lab was run twice. By standardizing the NaOHand titrating the unknown weak acid, the team was able to identify both the concentration andidentity of the weak acid.Experimental

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