AP Chemistry : Reactions and Equilibrium

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #3 : Molecular Structure Of Acids And Bases

Put the following acids in order of their DECREASING acid strength:  HOCl, HOBr, HOI, H2O.

Possible Answers:

HOCl, HOBr, HOI, H2O

H2O, HOCl, HOBr, HOI

HOCl, H2O, HOBr, HOI

H2O, HOI, HOBr, HOCl

HOI, HOBr, HOCl, H2O

Correct answer:

HOCl, HOBr, HOI, H2O

Explanation:

Acid strength of an oxy acid increases with increasing electronegativity on the halogen.

Example Question #1 : Molecular Structure Of Acids And Bases

Put the following acids in order of their DECREASING acid strength:  HOCl, HO2Cl, HO3Cl, HO4Cl.

Possible Answers:

HOCL, HO2Cl, HO3Cl, HO4Cl

HO2Cl, HOCl, HO3Cl, HO4Cl

HO4Cl, HO3Cl, HO2Cl, HOCl

HO4Cl, HOCl, HO2Cl, HO3Cl

HOCl, HO4Cl, HO2Cl, HO3Cl

Correct answer:

HOCL, HO2Cl, HO3Cl, HO4Cl

Explanation:

For an oxyacid, the acid strength increases as the number of oxygens increase.

Example Question #1 : Molecular Structure Of Acids And Bases

Put the following in order of INCREASING acid strength:  H2Se, KH, AsH3, HBr.

Possible Answers:

KH, AsH3, H2Se, HBr

KH, H2Se, AsH3, HBr

HBr, H2Se, AsH3, KH

AsH3, H2Se, HBr, KH

AsH3, H2Se, KH, HBr

Correct answer:

KH, AsH3, H2Se, HBr

Explanation:

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?

Possible Answers:

H3O+

Equal amounts of acid and conjugate base are present.

H2A+

A­-

HA

Correct answer:

HA

Explanation:

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?

Possible Answers:

H2A+

A­-

HA

H3O+

Equal amounts of acid and conjugate base are present.

Correct answer:

A­-

Explanation:

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.

Possible Answers:

HCO3-

H2CO3

CO32-

H3O+

Can not be determined.

Correct answer:

H2CO3

Explanation:

Since pH < pKa1, the undissociated form of carbonic acid (H2CO3) is predominant.

Example Question #2 : 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?

Possible Answers:

H2SO3

Can not be determined

H3O+

HSO3-

SO32-

Correct answer:

HSO3-

Explanation:

Since pH > pKa1 but pH < pKa2 the predominant form is one with a single hydrogen dissociated.

Example Question #1 : 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?

Possible Answers:

H2PO4-

HPO42-

H3PO4

PO43-

Can not be determined

Correct answer:

PO43-

Explanation:

Since pH > pKa1, pKa2, and pKa3 the predominant form of the acid is the fully deprotonated form.

Example Question #151 : Reactions And Equilibrium

Which of the following is a Lewis base?

Possible Answers:

Me3B

NH3

B2H6

BF3

Correct answer:

NH3

Explanation:

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 #152 : Reactions And Equilibrium

What is the defining characteristic of Bronsted-Lowry bases?

Possible Answers:

Electron pair acceptor

Dissociates in solution to give the H+ ion

Proton (H+) acceptor

Dissociates in solution to give the OH– ion

Proton (H+) donor

Correct answer:

Proton (H+) acceptor

Explanation:

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. 

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