Could you please help me set up this problem... How many moles cations
are in 1.45 mol of K2SO4? I am not sure how to set this problem up...
Thank you

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Clarification of Question by lilgreeny-ga on 02 Mar 2006 16:22 PST

Sorry How many moles of cations

One approach is to look at what items are mentioned and what you know
(or can look up) about them:

* cation
A cation is a positive ion. (If you couldn't remember this, the index
in your book would probably lead you to its definition.)

* ionic compound
A compound made of a metal(s) and a non-metal(s) is likely to be made
of ions (cations and anions).

* K2SO4
K is potassium, a metal in Group I; S is sulfur, a non-metal; and O is
oxygen, also a non-metal. (The non-metals are often combined in one
unit, the sulfate ion in this case.)

* metals and cations
Metals tend to lose electrons; in the process, they become positive
ions, or cations.

* cations in K2SO4
From the formula, you see that there are two potassiums, or two
cations. You should be able to finish the problem now.

Other information: Although not strictly necessary here, you should be
able to figure out that K has one positive charge since it is in group
I (and so has one electron that can be removed fairly readily). With
two K+ ions, the sulfate ion must have two negative charges, SO4-2.
(You could also get the charges by a google search using "cation ion K
SO4.")

thanx

the dissociation occurs as follows:
K2SO4->2K+ + SO4(2-)
ie. for every mole of K2SO4 you produce 2 moles of K+ (a cation).
Hence, if you start with 1.45 mol of K2SO4 then you will get 2.9 mol
of cations.
This is a result of the equation needing to be balanced. As you have 2
potassium atoms on the left then you need to have 2 on the right.
Also, charge must be balanced so as the SO4 provides 2 negative
charges the potassiums must provide 2 positive charges. The two
options here are as shown or K2 (2+). You know the 1st is formed
because potassium is in group one so it wants to lose one electron to
get to a Noble gas electronic configuartion and the formation of K2
(2+) is less favourable than forming 2K+.
Hope this helps.