Question #fa00c

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Question #fa00c

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Answer 1 · 2015-05-04T09:38:08

Yes, a precipitate will form.

A solution with pH 8.5 has a pOH of 14-8.5 = 5.5, therefore $[O H^{-}]$ $[OH^-]$ = $3.16 \cdot 10^{- 6}$ $3.16*10^-6$ . The dilution of 12.5 ml to 25 ml brings this concentration to $[O H^{-}]$ $[OH^-]$ = $1.58 \cdot 10^{- 6}$ $1.58*10^-6$ .
$[A l^{3 +}] \cdot {[O H^{-}]}^{3}$ $[Al^(3+)]*[OH^-]^3$ = $\frac{3.5 \cdot 10^{- 8}}{2} \cdot {(1.58 \cdot 10^{- 6})}^{3}$ $(3.5*10^-8)/2*(1.58*10^-6)^3$ = $1.75 \cdot 10^{- 8} \cdot 4.74 \cdot 10^{- 18}$ $1.75*10^-8*4.74*10^-18$ = $8.29 \cdot 10^{- 26}$ $8.29*10^-26$
This value exceeds the ksp of $3.1 \cdot 10^{- 34}$ $3.1*10^-34$ , and a precipitation will occur.

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