siunitx error: "invalid-number"

Question

Very reduced example:

\documentclass[a4paper]{article}
\usepackage{amsmath, amsthm, amssymb, mathtools}
\usepackage{siunitx}

\begin{document}
\begin{equation}\begin{aligned}
   n(O2)&=\SI{\frac{0,3}{2}}{\mol}\qquad\qquad &n(Fe3O4)&=\SI{0,3}{\mol} % <- this line
\end{aligned}\end{equation}
\end{document}

However I end up with

siunitx error: "invalid-token-in-number"
n(O2)&=\SI{\frac{0,3}{2}}{\mol}
                               \qquad\qquad &n(Fe3O4)&=\SI{0,3}{\mol}

Any clue on what's my problem here?

Answer 1

For anyone wondering: Either use

\sisetup{parse-numbers = false}

(thanks to Skillmon) or

\sisetup{quotient-mode = fraction}

and input the number as \SI{3/4}{\mol}.

Answer 2

The error message indicates that siunitx means a number written in decimal notation and not fractional.

\documentclass[a4paper]{article}
\usepackage{amsmath, amsthm, amssymb, mathtools}
\usepackage{siunitx}

\begin{document}
\begin{equation}
\begin{aligned}
   n(O2)&=\SI{.15}{\mol}\qquad\qquad &n(Fe3O4)&=\SI{0.3}{\mol} % <- this line
\end{aligned}
\end{equation}
\end{document}