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September 4, 2015

Homework Help: Chem- follow up question

Posted by Joe on Sunday, February 28, 2010 at 2:03pm.

Sorry i posted this as an answer after my question had been answered, this is continued from the qualitative analysis question:

That reallly cleared some things up, but I do still have a few questions. Umm im not completely clear on the hyrogen peroxide subject. its added to a solution containing aluminum chloride and iron chloride, and you said it is ther eto make sure the ion is Al3+, can you please explain that bit. Also is it assumed that the chloride ions dissociate in the solution on their own, and can hydrogen peroxide not contribute to making Al ions into Al(OH)3.

Also in the experiment excess NaOH was added like you said, and the precipitate which formed was treated with a little bit of water and H2SO4, before being treated with KSCN. Im wondering whether theprecipitate was treated with H2SO4 simply to dissolve hte precipitate , or whether it had another function also.

Lastly, the liquid portion of teh solution, from the step where hydrogen peroxide and excess NaOH were added, is suposed to contain the Al(OH)3 like you said. This is then made acidic by the addition of HNO3 before being boiled and treated with NH3. i understand it would precipitate when NH3 was added, but im not totaly clear about why the solution was made acidic first as it was already in liquid form.

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