Which of these follows the Arrhenius definition?
#a)# Dissociates in water to produce #"OH"^(-)# in solution.
#b)# Donates a proton
#c)# Releases protons into aqueous solution
#d)# A proton acceptor
1 Answer
I got only (c), because it follow the Arrhenius definition 100% with no ambiguity or vagueness.
ARRHENIUS DEFINITION
The Arrhenius definition of acids and bases states that:
- An acid releases protons (
#"H"^(+)# , or hydrogen ions) into aqueous solution, or increases hydrogen ion concentration in aqueous solution. - A base releases hydroxide ions (
#"OH"^(-)# ) into aqueous solution, or increases hydroxide concentration in aqueous solution.
Unfortunately, the Arrhenius definition does not include acid/base behavior in acids/bases that do not obey the above classifications.
Other acid/base classifications that should be familiar are the Bronsted-Lowry and Lewis definitions.
BRONSTED-LOWRY DEFINITION
- A Bronsted acid donates protons to a Bronsted base.
- A Bronsted base accepts protons from a Bronsted acid.
LEWIS DEFINITION
- A Lewis acid accepts electron pairs from a Lewis base.
- A Lewis base donates electron pairs to a Lewis acid.
How I keep this straight is that I use ammonia (
From here, I recall that when you donate electrons, you do so with a purpose: to make a bond. You can bond with either
When a Lewis base donates an electron pair to get
Then I associate Lewis acids with Bronsted acids by process of elimination! :)
So, I think we have enough context now.
a) By definition, this describes an Arrhenius base, not an acid. Example:
#color(red)(stackrel("Arrhenius Base")overbrace("KOH"(s)) stackrel("H"_2"O"(l)" ")(->) "K"^(+)(aq) + stackrel("Released hydroxide")overbrace("OH"^(-)(aq)))#
b) Donating a proton describes a Bronsted acid, not an Arrhenius acid, unless a proton is donated to water (in which case it actually increases the hydrogen ion concentration in aqueous solution as a result).
#color(red)(stackrel("Arrhenius Acid")stackrel("Lewis Acid")(stackrel("Bronsted Acid")overbrace("HA"(aq))) + stackrel("Lewis Base")(stackrel("Bronsted Base")overbrace("H"_2"O"(l))) -> stackrel("Conjugate acid")overbrace("H"_3"O"^(+)(aq)) + stackrel("Conjugate base")overbrace("A"^(-)(aq)))# where
#"H"_3"O"^(+)# is another way to represent#"H"^(+)# .
But since this is not specific enough of a wording, we cannot say that (b) is always true, so we cannot accept (b).
c) !This is an Arrhenius acid! It releases protons into aqueous solution, increasing the
#color(blue)(stackrel("Bronsted Acid")stackrel("Lewis Acid")stackrel("Arrhenius Acid")overbrace("HCl"(aq)))# #color(blue)(+ stackrel("Lewis Base")stackrel("Bronsted Base")(overbrace("H"_2"O"(l)) -> )# #color(blue)(stackrel("Released protons")stackrel("written here as H"_3"O"^(+))overbrace("H"_3"O"^(+)(aq)) + "Cl"^(-)(aq))#
d) A proton acceptor is similar to (b): it is not specific enough, and it instead defines a Bronsted base. Example:
#color(red)(stackrel("Lewis Base")(stackrel("Bronsted Base")overbrace("A"^(-))) + stackrel("Arrhenius Base")stackrel("Lewis Acid")(stackrel("Bronsted Acid")overbrace("H"_2"O")) -> stackrel("Conjugate base")overbrace("OH"^(-)) + stackrel("Conjugate acid")overbrace("HA"))#
In this case, the Bronsted base turned out to not also be an Arrhenius base. Instead, the Arrhenius base was water, because it was the source for the increase in