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Topic: Dissolving Processes and Formulas  (Read 1417 times)

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Offline Cheistrynoob768

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Dissolving Processes and Formulas
« on: April 07, 2013, 09:28:10 PM »
http://puu.sh/2vZMM

I know that acidic compounds dissociate and basics do not, and I think the 2 other dissolving processes are dispersion and ionization, but I don't know to tell which one of dissolving types a compound is just by looking at what the question gave me. If someone could tell me how to tell what a compound's dissolving type is by looking at the chemical formula, that would be great.

You can also see my attempt in that screenshot, and I tried to do the formula for dispersion for the ones I thought dissociate (they have OH), I'm not sure if I did that correctly as well...

Thanks in advance!

Offline Big-Daddy

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Re: Dissolving Processes and Formulas
« Reply #1 on: April 08, 2013, 07:29:34 AM »
Dissolution and dissociation are different. Dissolution refers to your species having its state changed from, say, "(s)" to "(aq)" (i.e. from solid to aqueous), assuming the solvent is H2O (l). The issue with salts is that we often assume they are broken into respective ions in solution; this is a decent approximation for many salts at low concentrations but not for sparingly soluble or insoluble ones. Ksp equilibria take care of this (if you want to look up more).

THEN we have dissociation. One the acid/base is in water, it can gain protons/lose hydroxides (if it's a base) or gain hydroxides/lose protons (if it's an acid). The second option is more common in each case.

I'm not entirely sure what you mean by "dissolving type" but it's very easy to explain how to tell the difference between an acid and base: an acid will generally have the formula HnA, where n is any integer number of protons it can lose. It might also be an ion in solution which you recognize as capable of gaining a hydroxide (e.g. Ca2+ is acidic - it can gain 2 hydroxides, Ca(OH)- and Ca(OH)2). A base either has the formula B(OH)m (i.e. it can dissociate OH- ions) or is an anion A- which can gain protons, e.g PO43- can gain protons to become HPO42-, then H2PO4- and then finally H3PO43-. Though we're forming an acid, because each step involves taking H+ out of the solution, PO43- is actually a base.

If there's anything I'm unclear on or if I've failed to address your question just ask back :)

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