V
b
= 
V
a

C
a
1+[
+
H
]
K
a
 -  [
+
H
] + 
K
w
[
+
H
]
C
b
1+
K
w
[
+
H
]
K
b
 + [
+
H
] -  
K
w
[
+
H
]

In[]:=
ClearAll[gridLinesF]​​gridLinesF[style1_:Directive[Thickness[.003],GrayLevel[.7]],style2_:Directive[Thin,GrayLevel[.9]],divs_:{6,6}]:=Join[Thread[{#,style1}],Thread[{DeleteCases[DeleteDuplicates[Join@@#2],Alternatives@@#],style2}]]&@@FindDivisions[{##},divs]&
In[]:=
Labeled[%,{"pH","Vb"},{Left,Bottom}];
In[]:=
ListLinePlot[{Reverse[dataPairs1,2],Reverse[dataPairs2,2]},PlotRange->{{0,20},{0,14}},PlotLabel->Style["Titration of weak acids with sodium hydroxide",16,Italic,Bold,FontFamily->"Courier",FontColor->Red],PlotLegends->Placed[LineLegend[{"Acetic acid","2-chloroaniline"},LegendFunction->"Frame",LegendMarkerSize->{{10,10}},LabelStyle->{FontSize->10}],{Center,Below}],Frame->True,FrameLabel->{Style["Vb/
3
cm
",16],Style["pH",16]},RotateLabel->False,ImageSize->550,PlotStyle->{Red,Blue},PlotMarkers->{{,20},{,20}},GridLines->{gridLinesF[],gridLinesF[]}]
Out[]=