AP Chemistry : pH and POH of Strong Acids and Bases
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Example Questions
Example Question #1 : P H And Poh Of Strong Acids And Bases
Which of the following is a Lewis base?
BF3
B2H6
Me3B
NH3
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 #1 : P H And Poh Of Strong Acids And Bases
What is the defining characteristic of Bronsted-Lowry bases?
Dissociates in solution to give the H+ ion
Proton (H+) donor
Dissociates in solution to give the OH– ion
Proton (H+) acceptor
Electron pair acceptor
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 #2 : P H And Poh Of Strong Acids And Bases
Which of the following can act as a Lewis base?
HF
NH2NH2
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 #3 : P H And Poh Of Strong Acids And Bases
In the following equation, which is the conjugate base of HClO4?
HClO4 + H2O → ClO4– + H3O+
ClO4–
HClO4
H2O
H3O+
none of the above
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.
Example Question #1 : P H And Poh Of Strong Acids And Bases
Which of the following is a Lewis base?
PH3
CH3CH2CH2CH3
CH2COOH
NH4+
PH3
A Lewis base is an electron-pair donor. Only PH3 has a pair of nonbonding electrons and can act as a donor.
Example Question #4 : P H And Poh Of Strong Acids And Bases
Which of the following is the conjugate base of oxalic acid (H2C2O4)?
HC2O4+
HC2O4–
H2C2O4
(C2O4) 2–
HC2O4–
The conjugate base has one less H atoms and one unit greater negative charge because of this. Thus, the correct answer is HC2O4–
Example Question #7 : P H And Poh Of Strong Acids And Bases
Which of the following solutions will have a pH greater than 7?
HCN, HCl, CH3COOH, and NH4Cl are all acids (NH4+ is the ammonium ion). That only leaves KCN as the correct answer.
Example Question #4 : P H And Poh Of Strong Acids And Bases
BCl3 is a .
Arrhenius acid
Lewis base
Lewis acid
Bronsted-Lowry base
Bronsted-Lowry acid
Lewis acid
A Lewis acid is a species that can accept an electron pair. In the BCl3 molecule, B does not have a complete octet (3 covalent bonds, thus 6 electrons around it rather than 8). Thus, it can accept another electron pair, making it a Lewis acid.
Example Question #1 : P H And Poh Of Strong Acids And Bases
Which of the following compounds is a Lewis acid: 
A Lewis acid is a 2-electron acceptor, and a Lewis base is a 2-electron donor.
Example Question #10 : P H And Poh Of Strong Acids And Bases
Which of the following salts will result in an acidic solution?
All of the listed salts will dissolve into ions when in water. When the ions are in solution, they can act as acids or bases by donating or accepting protons. Chloride, bromide, and iodide ions are all conjugate bases of strong acids, so they will not accept protons. Sodium and potassium ions are the conjugate acids of strong bases, which dissociate completely, so they will not accept hydroxide ions.
Ammonium is the conjugate acid of ammonia, a weak base. The ammonium ion can donate a proton to the solution. This will make the solution slightly acidic. As a result, ammonium bromide is a salt that will make an acidic solution.
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