Determination of Pka

Topics: Titration, Acid dissociation constant, PH Pages: 2 (435 words) Published: April 24, 2013
Determination of pKa

James McDuffie

ABSTRACT: In this lab, the pKa of unknown solution #4 was measured

Introduction:

This lab focused on the equilibrium constant, Ka. Ka is associated with chemical properties of acids. The equivalence point will be reached once the moles of OH- equal the moles of HA and once this point is reached, the PH changes very quickly. With the results, a titration curve should be produced.

Experimental Section

Materials and Methods: A buret with NaOH solution was used to ensure an accurate measure of NaOH could be taken. A PH recording machine was used to measure the PH. To make sure 25.0 ml of the unknown was measured, we used a 25.0 ml pipet.

The buret was primed and filled with NaOH. The measured 25.0 ml of the unknown solution was placed into a beaker and the PH was measured. At this point, different amounts of NaOH (varying from 0.5 ml to 2.0 ml) were added to the solution, each PH and new amount of NaOH being recorded until the equivalence point was reached.

Results and Discussion:

Each time completed, PH, and ml of NaOH solution left was recorded in the following table:

Time |PH |NaOH (ml) |Time |PH |NaOH (ml) |Time |PH |NaOH (ml) | |1 |3.17 |1.27 |21 |4.64 |26 |41 |5.47 |49 | |2 |3.77 |3.62 |22 |4.70 |28 |42 |5.54 |50 | |3 |3.61 |4 |23 |4.75 |30 |43 |5.64 |1 | |4 |3.64 |4.5 |24 |4.81 |32 |44 |5.71 |2 | |5 |3.70 |5 |25 |4.88 |34 |45 |5.81 |3 | |6 |3.86 |6 |26 |4.95 |36 |46 |5.94 |4 | |7 |3.95 |7 |27 |5.01 |38 |47 |6.08 |5 | |8 |4.06 |8 |28 |5.04 |39 |48 |6.21 |5.5 | |9 |4.12 |9 |29 |5.07 |40 |49 |6.32 |6 | |10 |4.19 |10 |30 |5.12 |41 |50 |6.52 |6.5 | |11 |4.20 |11 |31 |5.17 |42 |51 |6.78 |7 | |12 |4.22 |12 |32 |5.17 |42.5 |52 |8.60 |7.5 | |13 |4.29 |13 |33 |5.21 |43.5 | | | | |14 |4.30 |14 |34 |5.25 |44.5 | | | | |15 |4.31 |15 |35 |5.30 |45.5 | | | | |16 |4.38 |16 |36 |5.31 |46 | | | | |17 |4.43 |18 |37 |5.34 |46.5 | | | | |18 |4.51 |20 |38 |5.36 |47 | | | | |19 |4.56 |22 |39 |5.40 |47.5 | | | | |20...
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