Vinay K. Chaudhri wrote:

>>- Bruce, you said Acid and Base were objects, rather than roles. I think 
>>	that's wrong: If I remember right, I think Acid and Base are actually 
>>	reaction-specific, that is the same chemical can play the role of an 
>>	acid in one reaction, but a base in another. Pedro can clarify.
>>    
>>
>
>Let us defer to Pedro, and see what he has to say.
>  
>
Well, both ideas are true, depending on the context. I didn't want to 
interrupt Bruce's presenation, so I thought I would talk about this in 
mine, but the opportunity did not arise, and the discussion would have 
extended the presentation.

In some contexts, acid and base are a class of objects -ionic compounds- 
(I think in Chapter 4 there is a place in which the student is told to 
recognize acids as compounds whose "formula starts with H"). So, there 
are some compounds that can be classified as, say, acids, regardless of 
the roles they may play in some situations. In this group we would have 
all the strong and weak acids and bases listed in different tables 
throughout the book.

On the other hand, we have the concepts of Bronsted-Lowry and Lewis 
acids/bases, which are better though of as roles. So, in acid/base 
equilibria, when we are asked which species are acting as acids/bases, 
this is asked in the Bronsted-Lowry sense. (We can say that an acid is 
an ionic compond that acts as a Bronsted-Lowry acid when reacting with 
water in an aqueous solution).

I think we can have a class of ionic compounds for each acids, bases and 
salts. This will help a lot towards defining types of reactions (like 
"oxidation of metals by acids and salts" or "acid-base reactions with 
gas formation"). The definition of a role as a Bronsted acid or base 
would be independent of that classification and dependent on the studied 
equilibrium reaction. I believe which concept we are deling with will 
depend on the question's definition and context.

We could name the classes "acid" and "base", and the roles 
"Bronsted-Lowry acid" or base (or simply Bronsted acid/base). Lewis 
acids and bases can be also thought as roles.

This are my two cents...

Pedro