Given the very low value of Ksp for Cr(OH)3, a precipitate of Cr(OH)3 would be e

Question

Given the very low value of Ksp for Cr(OH)3, a precipitate of Cr(OH)3 would be expected if only 6 M NaOH were added to the mixture of Group Ill cations in the first step of the procedure. Explain how and why the chromium remains in solution 1. A solution may contain one or more of the Group IIl cations. When this solution is combined with NaOH (ag), NaOCI (aq) and NH3 (aq) only a colorless solution is obtained with no precipitate evident. Indicate whether each of the following cations is present, absent or undetermined. 2. Cr3 Fe3- Ni2 Explain.

Explanation / Answer

Q1

recall that

Cr(OH)3(s) is formed when some basic media is present, such as NH3 which forms NH4OH in solution

OH- is present so Cr(OH)3 will form solid precipitate

when more base is added, for instanc eNaOH

then

OH- is in excess

Cr(OH)6-3 is formed

this is in aqueous media, i.e. a complex

therefore, no solid will be seen since the solid goes towards more complex formation

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