Solving for pH with diprotic/triprotic acids

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To calculate the pH of diprotic (H2SO4) or triprotic (H3PO4) acids, the concentration of the acid must be multiplied by 2 or 3, respectively, to determine the total [H+] before applying the -log function. For bases like Mg(OH)2, which do not fully ionize, the calculation may vary; one can either assume complete dissociation or consider dissociation equilibrium based on educational level. The discussion emphasizes the importance of understanding the dissociation behavior of polyprotic acids and bases for accurate pH and pOH calculations. Additional resources are provided for further clarification on these calculations. Accurate pH determination is crucial for various chemical applications.
dnt
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i know if you have an acid, say .0001 M HCl, to get the pH you simply take the -log of the acid concentration (which is the same as [H+]), but what if you have a diprotic (H2SO4) or triprotic (H3PO4) acid...do you need to multiply the acid contentration by 2 or 3 to get the new H+ concentration BEFORE plugging it into -log[H+]?

and the same goes for pOH? eg. Mg(OH)2 needs to be multiplied by 2?
 
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Check out these links. They should help in answering your question.

http://www.science.uwaterloo.ca/~cchieh/cact/c123/polyprot.html"
http://www.sparknotes.com/chemistry/acidsbases/phcalc/section1.html"
 
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Mg(OH)2 do not completely ionise in water as do for instance NaOH or KOH.
 
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