What is the molarity of $\mathrm{SO}_{4}^{2-}$ ion in aqueous solution that contain $34.2 \mathrm{ppm}$ of…

What is the molarity of $\mathrm{SO}_{4}^{2-}$ ion in aqueous solution that contain $34.2 \mathrm{ppm}$ of $\mathrm{Al}_{2}\left(\mathrm{SO}_{4}ight)_{3} ?$
(Assume complete dissociation and density of solution $1 \mathrm{~g} / \mathrm{mL}$)
  1. $3 \times 10^{-4} \mathrm{M}$
  2. $2 \times 10^{-4} \mathrm{M}$
  3. $10^{-4} \mathrm{M}$
  4. None of these

Solution

$\frac{\text { mass of } \mathrm{Al}_{2}\left(\mathrm{SO}_{4}ight)_{3}}{\mathrm{r} \text { water }} \times 10^{6}=34.2$
mass of water
litre solution contains $1000 \mathrm{~g}$ of water $\Rightarrow$ In 1 litre solution, mass of
$\mathrm{Al}_{2}\left(\mathrm{SO}_{4}ight)_{3}=\frac{34.2 \times 1000}{10^{6}}=34.2 \mathrm{mg}$
molarity of
$\mathrm{Al}_{2}\left(\mathrm{SO}_{4}ight)_{3}=\frac{34.2 \times 10^{-3}}{342} \mathrm{M}=10^{-4} \mathrm{M}$
$\mathrm{Al}_{2}\left(\mathrm{SO}_{4}ight)_{3}(\mathrm{aq}) \longrightarrow 2 \mathrm{Al}^{3+}(\mathrm{aq})+3 \mathrm{SO}_{4}^{2-}(\mathrm{aq})$
$10^{-4} \mathrm{M}$ $\quad$$\quad$$\quad$$\quad$$2 \times 10^{-4} \mathrm{M} \quad 3 \times 10^{-4} \mathrm{M}$
$\left[\mathrm{SO}_{4}^{2-}ight]=3 \times 10^{-4} \mathrm{M}$ ,

Asked in: JEE-TOPICTESTS-CHEMISTRY

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