An ion exchange resin, RH_2 , can replace Ca^ 2+ in hard water as...

An ion exchange resin, $\mathrm{RH}_2$, can replace $\mathrm{Ca}^{2+}$ in hard water as $\mathrm{RH}_2+\mathrm{Ca}^{2+} \rightarrow \mathrm{RCa}^{2+}+2 \mathrm{H}^{+}$ When a 1.0 L hard water sample was passed through the resin, all $\mathrm{H}^{+}$ions were replaced by $\mathrm{Ca}^{2+}$ ions and the pH of eluted water was found to be 2.0 . The hardness of water (as ppm of $\mathrm{Ca}^{2+}$ ) in the sample of water treated is