Chem 1612008 Homework 8
th
Week
Chapter 7 problems: 5,23,27,29,31,35,37,41,45,47,53,69,74,89,90,97
SelfAssessment Questions
5.
Which property of waves is not mathematically related to the other three?
(a) wavelength
(b) frequency
(c) speed
(d) amplitude
In the equations below, wavelength of light is related to the frequency and speed of light, frequency of
light is related to the wavelength and speed of light, and speed of light is related to the wavelength and
frequency of light.
None of these parameters is related to amplitude.
Amplitude is the intensity of light,
which is related to the number of atoms or molecules undergoing the transition.
E
photon
= hυ
υ = c/λ
E = hc/λ
Subatomic Particles
23.
The masstocharge ratio of the proton is 1.044 x 10
8
kg/C.
What is the charge on a proton?
What is
its mass?
The charge on a proton is +1.
Since, according to Millikan, the charge on one proton is 1.602 x 10
19
coulomb, then:
1.044 x 10
8
kg/C x (1.602 x 10
19
coulomb/proton) = 1.67 x 10
27
kg/proton.
27.
Determine appropriate masstocharge ratios for the following ions.
(a)
80
Br

(b)
18
O
2
(c)
40
Ar
+
Why are these values only approximate?
(Hint: What are the masses of these ions?)
Note to students: Look at “b” for a thorough explanation.
(a) The masstocharge ratio is 80:1.
We don’t have to write this in SI units, because that wasn’t requested.
However, the Solutions Manual
wrote the answer in SI units.
Writing this in SI units, as kg Br atom/Coulomb, and considering that there
are 1.602x10
19
C/electron charge:
(80g x (1kg/1000g)/(6.022x10
23
))/(1.602x10
19
C) = 8.29x10
7
kg/C
(b)
It seems to me that an acceptable answer should be that the masstocharge ratio is 18:2 = 9:1, i.e., the
mass of a particular isotope of oxygen divided by the charge.
However, the convention for most problems
in the quantum mechanics area is to deal with atoms (not moles) and SI units, i.e., kg (not grams).
In
addition, although you and I would refer to the charge as “2” or “2“, the official unit of charge is
“Coulombs”, in which the charge of one electron is 1.602 x 10
19
Coulombs.
In summary, divide the mass
(in kg) of 1 atom of the substance by the number of coulombs.
1