I
CALCULATING AVERAGE ATOMIC MASS
1. There are five naturally occurring isotopes of the element zinc. The relative abundance and mass
of each are as follows. Calculate the average atomic mass of zinc.
k GS 92 G) f (o.oyl/ X &4,927)
Zn-64 = 48.89%, 63.929 amu c~gPq X /r 3.929) f ~A 27,'/
Zn-66 =27.81%, 65.926 amu
Zn-67= 4.11%, 66.927 amu
Zn-68= 18.57%, 67.925 amu
Zn-70 =0.62%, 69.925 amu
+- ~.457~67,125) +
2. An element has three naturally occuriing isotopes with the following masses and abundances.
Calculate the atomic weight of this element. What is the identity of the element.
Isotopic Mass (amu)
(0,g32(v x 31.9toy) +(O.O0000 l x 3g•116,41~
38.964
39.964
+ (0,0006?3 x 40.91o2) =~
40.962
% abundance
93.26%
0.0001%
0.0673%
3. Calculate the atomic weight of boron, B, from the following data:
Isotope
Isotopic Mass (amu)
Percent Abundance
B-10
B-11
10.013
11.009
19.78%
80.22%
4. An element has two naturally occurring isotopes with the following masses and abundances.
What is the atomic weight of this element? What is the identity of the element?
Isotopic Mass (amu)
Percent abundance
84.9118
86.9092
70.15%
70.85%
C~~•9o~2 t o, 7~~s~ = ~
5~ o
5. An element has three naturally occurring isotopes with the following masses and abundances.
Calculate the atomic weight of this element. What is the identity of the element..
Isotopic Mass (amu)
Percent Abundance
27.977
28.976
29.974
6.6 q -70)
92.21°x° /Z~. !~1 ~0-g2Z1) ~" ~2~•93~o x
4.70%
3.09%~ (2 J.171/ X 0.03b Xi
,~ 9,054.m,5i
~