The analysis of a water sample produces the following results Ionmilligram per milli-equivalnet for the ionConcentration $(m g / L)$

$C a^{2 +}$ 20.0 60

$M g^{2 +}$ 12.2 36.6

$N a^{+}$ 23.0 92

$K^{+}$ 39.1 78.2

$C l^{-}$ 35.5 71

$S O_{4}^{2 -}$ 48.0 72

$H C O_{3}^{-}$ 61.0 122

The total hardness (in mg/L as $C a C O_{3}$ ) of the water sample is
300

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Solution

The correct option is A 300
Hardness will be due to multivalent cations only
$C a^{2 +} = 60 m g / L \to$
equivalent weight =20 (given)

$M g^{2 +} = 36.6 m g / L \to$
equivalent wight $= 12.2$ (given)

milliequivalent of
$C a^{2 +} = \frac{60}{20} = 3$
$M g^{2 +} = \frac{36.6}{12.2} = 3$

$T o t a l h a r d n e s s m g / L a s (C a C O_{3})$
$=$ (milliequivalent of $C a^{2 +} +$ milliequivalent of
$m g^{2 +}) \times$ equivalent weight of $C a C O_{3}$

$= (3 + 3) \times \frac{100}{2}$

$= 300 m g / L a s C a C O_{3}$

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