Identify the Br0nsted-Lowry acid-base pairs in each of the following: A.) H 3 PO
ID: 978617 • Letter: I
Question
Identify the Br0nsted-Lowry acid-base pairs in each of the following:
A.) H3PO4(aq) + H2O(l) <-->H3O+(aq) + H2PO4-(aq)
B.) CO32- (aq) +H2O (l) <--> OH-(aq) + HCO3-(aq)
C.) HBr(aq) + H2O(l) ->H3O+(aq) + Br-(aq)
D.) HNO2(aq) +CH3 - CH2 - NH2(aq) <--> NO2-(aq) + CH3 - CH2 - NH3+(aq)
I need help identifying which of these would be the base and conjugate base, and the conjugate acid and acid. If it could be explained how to identify each of these for the above probelms, it would help me immensly.
Explanation / Answer
According to bronsted-lowry concept acids are defined as being able to donate protons in the form of hydrogen ions; whereas bases are defined as being able to accept protons.
H3PO4 (aq) + H2O(l) <-->H3O+ (aq) + H2PO4 - (aq)
H3PO4 - acid because it donates proton
H2PO4 - base because it can accept proton
CO3 2- (aq) +H2O (l) <--> OH- (aq) + HCO3 - (aq)
CO3 2-/HCO3 - base/acid
H2O/OH- acid/base
HBr(aq) + H2O(l) ->H3O+ (aq) + Br-(aq)
HBr/ Br- -acid/base
H2O/H3O+ base/acid
HNO2 (aq) +CH3 - CH2 - NH2 (aq) <--> NO2 - (aq) + CH3 - CH2 - NH3 + (aq)
HNO2/NO2 - - acid/base
CH3 - CH2 - NH2/CH3 - CH2 - NH3+ - base/acid
Conjugate acid base pairs
A conjugate pair refers to acids and bases with common features. These common features include the equal loss/gain of protons between the pairs. Conjugate acids and conjugate bases are characterized as the acids and bases that gain or lose protons, respectively. In an acid-base reaction, an acid plus a base reacts to form a conjugate base plus a conjugate acid.
Acid + Base Conjugate Base + Conjugate Acid
The conjugate acid of a base is formed when the base gains a proton. Refer to the following equation:
NH3(g)+H2O(l)NH+4(aq)+OH(aq)NH3(g)+H2O(l)NH4+(aq)+OH(aq)
We say that NH4+ is the conjugate acid to the base NH3 because NH3 gained a hydrogen ion to form NH4+, the conjugate acid. Theconjugate base of an acid is formed when the acid donates a proton. In the equation, OH- is the conjugate base to the acid H2O because H2O donates a hydrogen ion to form OH-, the conjugate base. Note: The stronger the acid or base, the weaker the conjugate. The weaker the acid or base, the stronger the conjugate.
An excellent reference for the concept:
http://chemwiki.ucdavis.edu/Core/Physical_Chemistry/Acids_and_Bases/Acid%2F%2FBase_Reactions/Conjugate_Acids-base_Pairs