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  4. Ion exchange resin can replace Ca2 + ions in hard water with H+ ions: RH2+Ca2 + arrow RCa+2H+ 1L of hard water sample after passing through the resin shows pH=2 . What is ppm of Ca2 + ions in water sample? [Atomic weight: Ca=40 ].

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Q. Ion exchange resin can replace $Ca^{2 +}$ ions in hard water with $H^{+}$ ions :
$RH_{2}+Ca^{2 +} \rightarrow RCa+2H^{+}$
$1L$ of hard water sample after passing through the resin shows $pH=2$ . What is ppm of $Ca^{2 +}$ ions in water sample? [Atomic weight: $Ca=40$ ].

NTA AbhyasNTA Abhyas 2020

Solution:

$\left[H^{+}\right]=10^{- 2}M$
mol of $H^{+}=10^{- 2}$ mol
mol of $Ca^{2 +}=\frac{10^{- 2}}{2}$ mol
ppm of $Ca^{2 +}=\frac{\frac{10^{- 2}}{2} \times 40}{1000}\times 10^{6}=200$