TWA Lab Summary - Titration of a weak acid PDF

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Lauren Murphy Anthony Mba Emma Maddox CH 263, Section 21, Group 5 TWA Lab Summary Summary Questions 1) The concentration for phosphoric acid in our experiment was 0 H 3PO4 mol M= L mol 0 NaOH= 0 L NaOH mol=0 NaOH 0 mol H 3 PO 4 M= 0 L M= 0 M H3PO4 2) The Ka1 and Ka2 for phosphoric acid in our group ...

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Lauren Murphy Anthony Mba Emma Maddox CH 263, Section 21, Group 5

TWA Lab Summary Summary Questions

1) The concentration for phosphoric acid in our experiment was 0.088M H3PO4 mol M= L mol 0.1109M NaOH= 0.02 L NaOH mol=0.00218 NaOH 0.00218mol H 3 PO 4 M= 0.025 L M= 0.088 M H3PO4 2) The Ka1 and Ka2 for phosphoric acid in our group was 0.0245, and 1.44x10-9 respectively. 3) Literature values for Ka1 and Ka2: 7.5x10-3 and 6.2x10-8. The percent error value for Ka1 is 226% error and for Ka2 it is 97% error. 4) A value for Ka3 could not be determined because after the second equilibrium point all of the H3PO4 is consumed, and we wouldn’t get another equilibrium point on the graph for us to calculate Ka3. 5) (34−19.5 )mL (0.1109) M =0.064 M H 3 PO 4 25 mL 19.5−(34−19.5)mL(0.1109)M 6) =0.0222 M HCl 25 mL Summary of Experimental Procedures:

To begin the pH meter was connected to the computer and logger pro was turned on. Then “Chemistry with vinier” and “24a titrate acid and base” were opened. The pH meter was calibrated in a pH 7.0 buffer and a pH 4.0 buffer by placing it in each solution for 30 seconds. Obtained 25 mL of H3PO4 put it into a 150 mL beaker with a stir rod and then it was placed on the stir plate. The burette was filled with NaOH. Then the pH meter was placed into the H3PO4 solution and the stir plate was turned on. The solution was titrated in 1 mL increments until 17 mL, while data points for each mL were collected. After 17 mL, the solution was titrated in 0.5 mL increments to the first equilibrium point (about 22mL). The method of titration previously used was repeated until 37 mL were titrated, and 0.5 mL to second equilibrium point. The titration was used again 1 mL increments to 55 mL to finish titrating. Next, the titration of the mixture of

HCl and H3PO4 (25 mL) was performed using the exact same method as the previous titration. The data was recorded and saved on logger pro. Finally, the concentration and Ka values were calculated for H3PO4 in the first titration and the concentration of HCl and H3PO4 were calculated for the second titration. The materials were cleaned and waste was disposed of. Specific Results

First titration using NaOH and H3PO4

Second titration using NaOH and mixture of H3PO4/HCl

H3PO4 titration Concentration: .088 M Ka1: 0.0245 Ka2: 1.44x10-9 H3PO4 and HCl titration H3PO4 concentration: 0.064 M HCl concentration: 0.0222 M

Brief Conclusions The titration using NaOH and H3PO4 resulted in the findings of the concentration of H3PO4 . The concentration calculated was .088 M by using the pH graph’s equilibrium points and the volume of NaOH used to titrate. The concentration was then used to calculate the two Ka values for each equivalence point. The second titrations data was used to calculate the concentration of the H3PO4 and HCl. The volumes of NaOH used to titrate between equilibrium points were used to determine these concentrations. In conclusion, titrations, and pH meter data allows the concentrations and Ka values to be determined. Ka values represent acid dissociation for H3PO4 in this experiment. The Ka1 value was 2.45E-2 which resulted in a 226% error and Ka2 was 1.44E-9 and a 97% percent error....