Document 6wGYKaZk0pLYOzdXJDrojk5b4
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Object: determination of the Ka of the tiration
acid by means of
The determination of the Ka of the
has been made
titrating with NaOH 0.1N a 0.165% aqueous solution of the product. It
has been worked on this acid because it is the only one of the series, with
surfactant characteristics, to having a water solubility to allow the
acidimetric titration
The titration has been carried out very slowly in order to allow the
electrode to stabilize after every adding.
In the strong acid case, in fact, it is absolutely necessary a very precise measurement of the potential, point-to-point, from which [H+] is
obtained.
The integral formula of Henderson we used, sets as denominator the
difference: [residual acid]-[H+ ]. If the electrode is not at the the stability point, [ H + ], that decreases during the titration, is overestimated and the
difference turns out negative like, consequently, the K a: Ka = [ H + ] * ([ A - ]+[H + ])/([ HA ] - [ H + ])
In comparison it has been calculated also the K a of hydrochloric acid.
From the results, it can be concluded that the two acids have a similar
acid power (within the analytical error)
HCl Ka (average value) = 0.1162
Ka (average value) = 0.1633
Ka=H*(A+H)/(HA-H)
Fitting curve mV=389,28-56,29pH
HCl 0.1N ( 5 ml in 150 ml of H2O)
ml
mv
pH
Ka
pKa
0 246,5 2,537 0,0177 1,7508
0,31 245,9 2,547 0,0259 1,5869
0,61 244,7 2,568 0,0318 1,4977
0,91 243,4 2,592 0,0407 1,3903
1,21 241,8 2,620 0,0487 1,3121
1,51
240 2,652 0,0577 1,2391
1,81
238 2,688 0,0684 1,1649
2,11 235,8 2,727 0,0843 1,0744
2,41 233,4 2,769 0,1175 0,9299
2,71 230,6 2,819 0,1573 0,8031
3,01 227,4 2,876 0,2338 0,6312
3,31 223,7 2,942 0,5105 0,292
3,61 219,2 3,021 1,4282 -0,1548
3,91 213,6 3,121 9,4478 -0,9753
Ka (Vm) Taratura mV=388,468-56,6289pH
0,1162
n2 (g.0.2475 in 150 ml of H2O)
ml
mv
pH
Ka
pKa
0
249 2,4628 0,1091 0,9622
0,31 248,5 2,501 0,0574 1,2411
0,61 247,2 2,5241 0,0714 1,1464
0,91 245,9 2,5472 0,1058 0,9757
1,21 244,3 2,5756 0,1355 0,8679
1,51 242,6 2,6058 0,2009 0,697
1,81 240,6 2,6413 0,227 0,644
2,11 238,4 2,6804 0,2439 0,6128
2,41 235,9 2,7248 0,2064 0,6853
2,71 233,3 2,771 0,2726 0,5644
3,01 230,3 2,8243 0,2918 0,5348
3,31 226,8 2,8865 0,2357 0,6277
3,61 222,7 2,9593 0,1744 0,7584
3,91 217,8 3,0464 0,1284 0,8915
4,21 211,8 3,153 0,1034 0,9853
4,51 203,3 3,304 0,0495 1,3054
Ka (Vm) 0,1633