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Topic: Enviro Chem Question about pH  (Read 4529 times)

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Offline flaren5

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Enviro Chem Question about pH
« on: November 03, 2012, 09:25:11 PM »
It is known that Fe3+ can be strongly hydrolyzed in water according to the reaction: Fe3+ + H2O → Fe(OH)3 ↓ + 3H+ to form a sparingly soluble iron hydroxide.  When 1.01 grams of Fe(NO3)3·9H2O is dissolved in 100.0 mL of degassed distilled water (i.e., remove dissolved CO2 from the atmosphere), theoretically what is the pH of the solution?  Ignoring the dissolution of Fe(OH)3, what is the mass of Fe(OH)3 formed in the solution?

...Any insight on this question would be greatly appreciated...

Thank you.
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Offline Borek

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Re: Enviro Chem Question about pH
« Reply #1 on: November 04, 2012, 03:45:42 AM »
Simple stoichiometry. Take a look at the reaction equation - what is being produced? What is pH definition?
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Offline flaren5

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Re: Enviro Chem Question about pH
« Reply #2 on: November 04, 2012, 03:41:52 PM »
OH is being produced, therefore I'm assuming that the pH is going to be more basic..
14 = pH + pOH is the equation that I believe I'll have to use, but I'm not sure how to get to that point. Nor am I sure how to obtain the mass of Fe(OH)3 formed in the solution?

I just need assitance getting on the right track and then I should be able to figure it out from there....
Thank you...

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Offline Borek

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Re: Enviro Chem Question about pH
« Reply #3 on: November 04, 2012, 03:52:52 PM »
Quote from: flaren5 on November 04, 2012, 03:41:52 PM
OH is being produced

Are we talking about the same reaction equation?

Quote from: flaren5 on November 03, 2012, 09:25:11 PM
Fe3+ + H2O → Fe(OH)3 ↓ + 3H+

I don't see OH- between the products.

Quote from: flaren5 on November 04, 2012, 03:41:52 PM
Nor am I sure how to obtain the mass of Fe(OH)3 formed in the solution?

Simply assume all Fe3+ put into the solution reacts according to the reaction equation.
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Offline flaren5

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Re: Enviro Chem Question about pH
« Reply #4 on: November 04, 2012, 04:01:12 PM »
Oops...I realize now that it's actually H+ being produced....so the pH should be more acidic.

But i obviously don't have the understanding of how to proceed with the equation(s).

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Offline Borek

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Re: Enviro Chem Question about pH
« Reply #5 on: November 04, 2012, 04:23:55 PM »
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Offline flaren5

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Re: Enviro Chem Question about pH
« Reply #6 on: November 04, 2012, 04:58:18 PM »
Fe3+ + 3H2O → Fe(OH)3 ↓ + 6H+

...not sure if this is the proper stoichiometry...but if there is anything that I have a little understand about from the whole question it's how to balance the equation...it's the rest of it that I'm not sure of...
Thanks anyhow for the selected input and the reference for the stoichiometry website, but I'm obviously not going to figure out how to approach the question.
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Offline Borek

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Re: Enviro Chem Question about pH
« Reply #7 on: November 04, 2012, 05:03:47 PM »
The reaction is not balanced now - count hydrogens on both sides, check the charge on both sides. It was much better before.

Assuming 1 mole of Fe3+ was put into the solution, how many moles of H+ would be produced?
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