5 Steps to a 5 AP Chemistry

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

 Answers and Explanations

4. What is the missing product in the following
   nuclear reaction?


5. Which of the following statements are correct
   concerning βparticles?
   I. They have a mass number of zero and a
   charge of –1.
   II. They are electrons.
   III. They are less penetrating than αparticles.
   (A) I and II
   (B) I and III
   (C) II and III
   (D) I only
   (E) II only


6. An atom of undergoes radioactive decay by
   αemission. What is the product nuclide?


7. If 75% of a sample of pure decays in
   24.6 years, what is the half-life of?
   (A) 24.6 yr
   (B) 18.4 yr
   (C) 12.3 yr
   (D) 6.15 yr
   (E) 3.07 yr

1

(^31) H
(^3) H
(E) 238230 Pu
(D)^23091 Pa

(C)^23092 U

(B)^23490 Th

(A)^23090 Th

92

(^238) U
(E) Nb 4198
(D) Zr 4098

(C) Y^9639

(B) Sr 3896

(A) Y^9039

92

236

0

1

53

UnI→++ 4 136 _____

1. D—The mass should be 226 −(4 + 4 + 0 +4) =
   214. The atomic number should be 88 −(2 + 2 −
   1 +2) =83.


2. B—Mass difference = 234 − 230 =4, and atomic
   number difference = 92 − 90 =2. These corre-
   spond to an αparticle.


3. C—Alpha particles are the least penetrating, and
   gamma rays are the most penetrating.


4. C—Mass difference = 236 −4(1) − 136 =96.
   Atomic number difference = 92 −4(0) − 53 =39.
   5. A—In nuclear reactions the mass of a βparticle
   is treated as 0, with a charge of −1. Electrons and
   βparticles are the same thing.
   6. B—Mass number = 238 − 4 =234, and atomic
   number = 92 − 2 =90.
   7. C—After one half-life, 50% would remain.
   After another half-life this would be reduced by
   one-half to 25%. The total amount decayed is
   75%. Thus, 24.6 yr must be two half-lives of
   12.3 yr each.