A few days ago the question came up how to draw Hägg diagrams with 
.
Well for these kinds of diagrams there is an obvious choice: pgfplots.
.
Well for these kinds of diagrams there is an obvious choice: pgfplots.
\documentclass{scrartcl}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
\def\Ka{10^(-4.75)}% the equilibrium constant
\def\co{1}% the starting concentration
\begin{axis}[ymode=log,domain=0:14]
\addplot[red] { \co*10^(-x)/(\Ka+10^(-x)) };
\addplot[blue] { \co*\Ka/(10^(-x)+\Ka) };
\end{axis}
\end{tikzpicture}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
\def\Ka{10^(-4.75)}% the equilibrium constant
\def\co{1}% the starting concentration
\begin{axis}[ymode=log,domain=0:14]
\addplot[red] { \co*10^(-x)/(\Ka+10^(-x)) };
\addplot[blue] { \co*\Ka/(10^(-x)+\Ka) };
\end{axis}
\end{tikzpicture}
