Cliffs AP Chemistry, 3rd Edition

7. Which of the following statements is true of the critical temperature of a pure substance?

A. The critical temperature is the temperature above which the liquid phase of a pure

substance can exist.

B. The critical temperature is the temperature above which the liquid phase of a pure

substance cannot exist.

C. The critical temperature is the temperature below which the liquid phase of a pure

substance cannot exist.

D. The critical temperature is the temperature at which all three phases can coexist.

E. The critical temperature is the temperature at which the pure substance reaches, but

cannot go beyond, the critical pressure.

Answer:B

This is the definition of critical temperature.

8. A certain metal crystallizes in a face-centered cube measuring 4.00 × 102 picometers on
   each edge. What is the radius of the atom? (1 picometer (pm) = 1 × 10 –12meter)

A. 141 pm

B. 173 pm

C. 200. pm

D. 282 pm

E. 565 pm

Answer: A

The formula which relates the radius of an atom (r) to the length of the side (s) of the unit cell
for a face-centered cubic cell is 4r= s 2.

.
r ..
pm
4 pm

400 2

===100 1 414^h 141

400. pm
     s

r

Liquids and Solids