A 49.9 g sample of barium hydroxide octahydrate $\mathrm{Ba}(\mathrm{OH}{)}_2\cdot 8{\mathrm{H}}_2\mathrm{O}$ is dissolved in water and the solution is diluted to give a final volume of 2.50 L What is the concentration of the hydroxide ion in this solution?

$\text{ Molar mass ( }\mathrm{g}{\mathrm{mol}}^{-1}\text{ ) }$
$\mathrm{Ba}(\mathrm{OH}{)}_2\cdot 8{\mathrm{H}}_2\mathrm{O}$	315