[tex][tex]C_{m} = \frac{\frac{m_{s}}{M}}V_{r}} /* V_{r} \\ C_{m} * V_{r} = \frac{m_{s}}{M} /*M \\ m_{s} = C_{m} * V_{r} * M \\ M = 2 * 23 + 12 + 3*16 = 106 \frac{g}{mol}[/tex]
[tex]m_{s} = 0,25\frac{mol}{dm^3} * 0,45dm^3 * 106\frac{g}{mol} \\ m_{s} = 12g[/tex]