AP Chemistry : Acid-Base Reactions
Study concepts, example questions & explanations for AP Chemistry
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Example Questions
Example Question #153 : Reactions And Equilibrium
Put the following in order of INCREASING acid strength: H2Se, KH, AsH3, HBr.
AsH3, H2Se, HBr, KH
AsH3, H2Se, KH, HBr
HBr, H2Se, AsH3, KH
KH, AsH3, H2Se, HBr
KH, H2Se, AsH3, HBr
KH, AsH3, H2Se, HBr
Acid strength increases going across a period.
Example Question #1 : Ph And Pka
If you have a solution that consist of a weak monoprotic acid (HA), with a pKA of 5.3 and a pH of 3.2, what is the predominant species present?
HA
A-
Equal amounts of acid and conjugate base are present.
H2A+
H3O+
HA
Since pH < pKa the undissociated acid is the predominant form.
Example Question #1 : Ph And Pka
If you have a solution that consists of a monoprotic acid (HA), with a pKa of 4.1 and at a pH of 5.8, what is the predominant species present?
H3O+
HA
Equal amounts of acid and conjugate base are present.
H2A+
A-
A-
Since pH > pKA, the deprotonated form of the acid is predominant.
Example Question #1 : Ph And Pka
Carbonic acid as a pKa1 = 6.35 and a pKa2=10.33. If the pH is 3.52, what is the predominant species present.
H2CO3
H3O+
HCO3-
CO32-
Can not be determined.
H2CO3
Since pH < pKa1, the undissociated form of carbonic acid (H2CO3) is predominant.
Example Question #1 : Ph And Pka
Sulphurous acid (H2SO3) has a pKa1 = 1.92 and a pKa2 = 7.18, if the pH = 5.3, what is the predominant species present?
Can not be determined
H2SO3
H3O+
SO32-
HSO3-
HSO3-
Since pH > pKa1 but pH < pKa2 the predominant form is one with a single hydrogen dissociated.
Example Question #2 : Ph And Pka
Phosphoric acid has a pKa1 = 2.15, a pKa2 = 7.20, and a pKa3 = 12.35. If the pH = 13.0, what is the predominant species present?
PO43-
HPO42-
H3PO4
Can not be determined
H2PO4-
PO43-
Since pH > pKa1, pKa2, and pKa3 the predominant form of the acid is the fully deprotonated form.
Example Question #1 : P H And Poh Of Strong Acids And Bases
Which of the following is a Lewis base?
NH3
BF3
B2H6
Me3B
NH3
NH3 should be the clear correct choice, since it is the only one having a pair of electrons that are available. The rest of the answer choices are all Lewis acids.
Example Question #2 : P H And Poh Of Strong Acids And Bases
What is the defining characteristic of Bronsted-Lowry bases?
Electron pair acceptor
Proton (H+) acceptor
Dissociates in solution to give the H+ ion
Proton (H+) donor
Dissociates in solution to give the OH– ion
Proton (H+) acceptor
The definition of a Bronsted-Lowry base is a species that has the ability to gain, or accept a proton (H+). Dissociating in solution is part of the Arrhenius definition of acids and bases, and Lewis acid are electron pair acceptors.
Example Question #3 : P H And Poh Of Strong Acids And Bases
Which of the following can act as a Lewis base?
NH2NH2
HF
CH3COOH
BF3
NH2NH2
A Lewis base is an electron-pair donor. N atoms have a valence of 5, and in the NH2NH2 compound, it is only bonded to another N atom and 2 H, so it's only using 3 of its 5 valence electrons to form these bonds. Thus, each nitrogen has a pair of unbonded electrons and can act as a Lewis base.
Example Question #4 : P H And Poh Of Strong Acids And Bases
In the following equation, which is the conjugate base of HClO4?
HClO4 + H2O → ClO4– + H3O+
none of the above
HClO4
H2O
H3O+
ClO4–
ClO4–
The conjugate base of an acid will be the same compound, short one H atom. ClO4– is the only one that meets this criterion.
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