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# URGENT help with precipitation exercise? watch

1. It goes as follows:

>Knowing Ks = 6*10^-38 for Fe(OH)3in neutral solutions, calculate the minimum hydronium ion concentration of an acidic solution in order to completely dissolve 10 mg of Fe(OH)3. Data: Volume = 0.1 L.

Edit:
My idea was to calculate the amount of iron and hydroxide ions, and then add enough acid containing hydronium ions in order to neutralise the hydroxide. To do this I used the equilibrium constant leaving the hydroxide ions as the unknown. Then I calculated the difference between the initial hydroxide concentration (corresponding to 10 mg of salt) and the needed concentration to reach Ks. This corresponds to the concentration of hydronium ions in the acidic solution, and I can calculate pH.

Doing this I get pH= 3.03. Is this how it should be done?

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Updated: January 17, 2017
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