Chemistry, 02.09.2019 22:10 alexandraparava

How many moles of ni(oh)2 are soluble in 1l of sodium hydroxide (naoh) when the ph is 12.34?
pksp of ni(oh)2 = 15.8

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Answer from: ana2896

$[Ni^{2+} ]=3.31x10^{-13} M$

Therefore there is $3.31x10^{-13}$ moles of $[Ni^{2+} ]$

in one liter of this solution.

Explanation:

This is a problem of common ion effect. In an equilibrium, by the Le Chatelier's principle, when the concentration of a given species rises the equilibrium shifts to the direction that consumes the species that increased in concentration.

Therefore, if a common ion is present in a solubility equilibrium the molar solubility shall decrease.

1) First of all, calculate Ksp and molar solubility in pure solvent

Ksp

The problem states that pKsp=15.8. The 'p' is the '-log' function, so 'pKsp' expresses '-log(Ksp)'. Isolating for 'Ksp' gives:

$-Log_{10} K_{sp}=15.8$

$Log_{10} K_{sp}=-15.8$

$K_{sp}=10^{-15.8}$

$K_{sp}=1.58x10^{-16}$

Molar solubility in pure solvent

$K_{sp}=[Ni^{2+}][OH^{-}]^{2}$

$S=[Ni^{2+}]$ and $[OH^{-}]=2S$ , where 'S' stands for molar solubility.

Then Ksp expression can be expressed as:

$K_{sp}=S*(2S)^{2}$

$K_{sp}=4S^{3}$

Isolating for 'S' gives us the molar solubility in pure water:

$S=\sqrt[3]{\frac{K_{sp} }{4} }$

$S=3.4x10^{-6}$

We only calculate the pure solvent molar solubility to compare with the solubility with the common ion and make sure the first is grater, witch confirms the Le Chatelier's principle.

2) Calculate the molar solubility with the common ion

First we calculate the $OH^{-}$ concentration from the pH value

In a solution with a pH of 12.34 the pOH is 1.66 (14=pH+pOH)

$-Log_{10} [OH^{-} ]=1.66$

$Log_{10} [OH^{-} ]=-1.66$

$[OH^{-} ]=10^{-1.66}$

$[OH^{-} ]=0.0219$

Then we input this value in the Ksp expression

$K_{sp}=[Ni^{2+}][OH^{-}]^{2}$

$[Ni^{2+}]=\frac{K_{sp}}{[OH^{-}]^{2}}$

$[Ni^{2+}]=\frac{1.58x10^{-16}}{0.0219^{2}}$

$[Ni^{2+}]=3.31x10^{-13}$

The molar solubility of Ni(OH)2 when there is excess OH- in solution is lower than when the solvent is pure, which indicates that the Le Chatelier's principle has been obeyed.

Answer from: Quest

wanahton purified a portion of water with 900 grams of contaminants. each hour, a third of the contaminants was filtered out.

let g(n) be the amount of contaminants (in grams) that remained by the beginning of the nth hour. g is a sequence, what kind of sequence is it, arithmetic or geometric? then, write an explicit formula for the sequence, g(n)=

wanahton purified a portion of water with 900 grams of contaminants. each hour, a third of the contaminants was filtered out.

explanation:

Answer from: Quest

The correct answer would be 1. precipitation

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How many moles of ni(oh)2 are soluble in 1l of sodium hydroxide (naoh) when the ph is 12.34?
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