[Catalist] Acidic/ Basic Salts

[Leon Harris]

Hi Andrew, it is definitely acidic. You can buy some at Bunnings 
(pHDown) to lower the pH in your pool !

You can tell from a table of Ka s, it's Ka is larger than the Ka for 
SO_4 ^2-

I teach this in this way to make it easy for my kids to remember: By 
definition, the first ionisation of an acid will occur more readily and 
be more complete than the second - the first is the more likely (that is 
why it happens *first*). So in strength of acid H_3 PO_4 > H_2 PO_4 ^- > 
HPO_4^2-

Ditto H_3 ASO_4
The one that dissociates most easily will dissociate first_. (I use 
dissociate in exactly the sense that WACE likes our kids not to here, I 
want to focus on the splitting up, not on the formation of a charged 
species.  I am talking about the hydrogen dissociating from an acid (H_2 
PO_4 ^- , HPO_4 ^2- ) _.
_
_
Another way to look at it is that all these reactions are happening 
simultaneously in water:_
_
H_2 SO_4   + H_2 O <--> HSO_4 ^- + H_3 O+
HSO_4 ^- + H_2 O <--> SO_4 ^2- + H_3 O+
The actual reaction that predominates depends on the Ka for each 
reaction and the concentration of H+.  So, at very high [H+], formation 
of H_2 SO_4   will occur, whereas at high pH, formation of sulfate will 
occur. It is the interplay of Ka s and [H+] that determines which actual 
reaction predominates. Because the Kb of HSO4- is relatively small, 
little  H_2 SO_4   is formed except at vey low pH.

Hope this helps,
Cheers,
Leon
>
> Question for the chemists:
>
> Q: Is NaHSO4 and acidic or basic salt and why? Or in other words when 
> HSO4- ion reacts with water, does it produce H2SO4 and H+ or SO42- and 
> OH-? Why is one reaction favoured over the other?
>
> Thanks
>
> Andrew.
>
>
> Andrew Bland
> Head of Year 10 and Head of Geographe House
>
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