5 Steps to a 5 AP Chemistry

 Free-Response Questions

First Free-Response Question

Answer the following questions. You have 15 minutes, and you may not use a calculator.

You may use the tables at the back of the book.

Answer each of the following with respect to chemical bonding and structure.

a. The nitrite ion, NO 2 – , and the nitrate ion, NO 3 – , both play a role in nitrogen chemistry.

i.Draw the Lewis (electron-dot) structure for the nitrite ion and the nitrate ion.

ii.Predict which ion will have the shorter bond length and justify your prediction.

b.Using Lewis (electron-dot) structures, explain why the ClF 3 molecule is polar and the

BF 3 molecule is not polar.

c. Consider the following substances and their melting points:

Substance Melting point (°C)

SrS > 2000

KCl 770

H 2 O 0.00

H 2 S −85.5

CH 4 − 182

Explain the relative values of the melting points of these substances.

Second Free-Response Question

Answer the following questions. You have 15 minutes, and you may not use a

calculator.You may use the tables in the back of the book.

Answer the following questions about structure and bonding.

a.Which of the following tetrafluorides is nonpolar? Use Lewis electron-dot structures

to explain your conclusions.

SiF 4 SF 4 XeF 4

b.Rank the following compounds in order of increasing melting point. Explain your

answer. Lewis electron-dot structures may aid you.

SnF 2 SeF 2 KrF 2

c.Use Lewis electron-dot structures to show why the carbon–oxygen bonds in the

oxalate ion (C 2 O 42 −)are all equal.

d.When PCl 5 is dissolved in a polar solvent, the solution conducts electricity. Explain

why. Use an appropriate chemical equation to illustrate your answer.

 Answers and Explanations

First Free-Response Question

a.

i.Nitrite ion: Nitrate ion: ONO

O

ONO

162  Step 4. Review the Knowledge You Need to Score High