Respuesta :
Explanation:
It is known that,
Molar mass of Cd = 112.41 g/mol
Standard concentration of Cd = 0.005 mg/L = [tex]0.005 \times 10^{-3}[/tex] g/L
Hence, we will calculate the molarity as follows.
Molarity = [tex]\frac{0.005 \times 10^{-3}}{112.41} mol/L[/tex]
= [tex]4.45 \times 10^{-8}[/tex] M
Equation for the reaction is as follows.
[tex]Cd(OH)_{2} \rightleftharpoons Cd^{2+} + 2OH^{-}[/tex]
[tex]K_{sp} = [Cd^{2+}][OH^{-}]^{2}][/tex]
[tex]2 \times 10^{-34} = 4.45 \times 10^{-8} \times [OH^{-}]^{2}[/tex]
[tex][OH^{-}] = 6.7 \times 10^{-4}[/tex] M
Also,
[tex][H^{+}] = \frac{10^{-14}}{[OH^{-}]}[/tex]
= [tex]\frac{10^{-14}}{6.7 \times 10^{-4}}[/tex]
= [tex]1.49 \times 10^{-11} M[/tex]
Relation between pH and concentration of hydrogen ions is as follows.
pH = [tex]-log [H^{+}][/tex]
= [tex]-log (1.49 \times 10^{-11} M)[/tex]
= 10.82
Thus, we can conclude that a minimum pH of 10.82 is necessary to reduce the dissolved cadmium ion concentration to the standard.
