Dot point (1 Viewer)

[Faera]

One of the dot points I have to research on for an assessment is:

- Gather and process information from secondary sources to trace developments in understanding and describing acid/base reactions.

...and I, and the majority of my grade don't really know what it's actually asking us to do- At first, i thought it was acid/base reactions as in acids actually reacting with bases... but there's not really that much information you can get regarding that- at all, so, yeah... and then I asked my tutor and he went through all this stuff with me- limitations of the definitions of davy, lavoisier, ahrrenius, etc etc... but they're definitions, right?... to understanding the properties and stuff of acids and bases... not reactions.... 0.o unless they're refferring to acids reacting with something else, and not bases...
bah
but yeah, anyway
if anyone could sort of help me out (and quite possibly half the grade) and tell me what exactly the point's after, then it'd be greatly appreciated!

thanksssss!

 

[CM_Tutor]

Your tutor is correct. The dot point is taking about developments in understanding - the development of understanding of acids and bases went Lavoisier - Davy - Arrhenius - Lowry-Bronsted. Each described these reactions in a different way. Consider, for example, the reaction of HCl and NaOH:

Lavoisier would have said HCl isn't an acid, as acids must contain oxygen.

Davy would have said it was an acid base reaction, as HCl as its H can be replaced by a metal, like Na. He would have described as a reaction

HCl + NaOH ---> NaCl + H2O

Arrhenius would have said it was an acid base reaction, as HCl produces hydrogen ions in water:

HCl ---> H+ + Cl-

and bases produce hydroxide ions:

NaOH ---> Na+ + OH-

The reaction is then a simple neutralisation:

H+ + OH- ---> H2O

or in complete ionic form:

H+ + Cl- + Na+ + OH- ---> Na+ + Cl- + H2O

Remember that it was Arrhenius who developed the theory of ionic solutions.

Lowry-Bronsted would have improved on the Arrhenius description, by recognising the role played by the solvent. HCl is acidic because of:

HCl (g) + H2O (l) ---> H3O+ (aq) + Cl- (aq)

which involves the transfer of a proton from the acid (HCl) to the base (H2O).

NaOH dissociates in water:

NaOH (s) ---H2O---> Na+ (aq) + OH- (aq)

and can then undergo an acid base reaction with hydronium:

H3O+ (aq) + OH- (aq) ---> 2 H2O (l)

which is again a proton transfer reaction, in keeping with Lowry-Bronsted theory.

Do you now see how the historical developments in our understanding alter how we describe acid/base reactions?

 

[Faera]

wow- thanks. That helped a lot!
Yeah, I see it now. The thing was my tutor explained it in terms of properties and understanding definitions, not reactions, so I got a little confused with that- but now it's all good- thanks for the help!
ahh... enlightenment...

(yay for passing!)

 

[CM_Tutor]

This sort of question is usually asked with a definitions focus, but you do need to understand it both ways. I'm glad I could help

 

[xiao1985]

lolz... luckie us 03ers, lewis is taken out of syllabus... ^^

but further on the contribution of arrhennius, i fink he also realised the difference between strong acids n weak acids being the difference in degree of ionisation... however, he did not mention the role of the solvent tho... =(

 

[CM_Tutor]

xiao1985, you're right. Arrhenius was aware of the concept of strength, although it's easier understood (and therefore usually taught) in the context of L-B theory.

As for Lewis theory, it is really important in a number of areas of chemistry, but the way it was covered in the syllabus really didn't show why it matters. It was a good change to take it out - you need to spend a while if you're going to really appreciate it.

 

[xiao1985]

lolz... but like, my teacher didn't really give a damn... he briefly taught us any way... n my tutor is like, full on "u gotta learn this" etc etc... =p blehz