Pretest 2.2
Part 2
8. Two isotopes of boron, B, are found in nature. The relative abundance of Boron 11 is 80.22 %. The second isotope of boron has one less neutron than Boron 11.
Calculate the average atomic mass of boron.
9. Richard recorded data on the three stable isotopes of a newly discovered element. Unfortunately, a coffee spill in the late hours of the night resulted in smudged data. Richard was able to recover data on the average atomic mass (24.72 a.m.u.), as well as data on the first two isotopes in the chart below.
|
Isotope |
Natural abundance (%) |
|
24W |
78.99 |
|
26W |
11.01 |
|
?W |
? |
What is the
atomic mass of the missing isotope?
Solutions
8. Determine atomic mass of
second isotope of boron
11 m – 1 neutron = 10 m
Determine relative abundance
of boron 10
100 % – 80.22 % = 19.78 %
Calculate average atomic mass
of boron
Average atomic mass =
= 
= 10.80 m
9. let x = is the
atomic mass of the missing isotope
0.7899(24) +
0.1101(26) + (1- 0.7899 - 0.1101)x = 24.72
X = 29 atomic mass units