AP Mass Spec and Atomic Mass Concepts

Question 1

What is atomic mass?

Answer 1

(for our purposes) number of protons plus neutrons (weighted average of an element’s isotopes)

Question 2

Why do multiple atoms of one element have different weights?

Answer 2

isotopes

Question 3

What is the number of protons in the nucleus called?

Answer 3

atomic number

Question 4

What is the mass number?

Answer 4

element’s protons + neutrons

Question 5

How to find average atomic mass

Answer 5

atomic mass x percent (of each isotope then added together)

Question 6

What is mass spec?

Answer 6

technique for determining the abundance of isotopes

Question 7

How to read mass spec graph

Answer 7

x-axis is atomic mass (protons + neutrons) y-axis the relative abundance/intensity

Question 8

What is relative abundance?

Answer 8

ratio of less abundant isotopes to more abundant isotopes

Question 9

How to find average atomic mass given ratios

Ex: chlorine- 35 is three times as abundant as chlorine-37

Answer 9

1) add the ratios and divide one ratio by total (multiplying by 100 to get percent abundance)
2) multiply atomic masses by their percents and add them

Question 10

What happens the graphs of diatomic elements?

Answer 10

their atomic masses are added together

Question 11

True/False: Absorbance and transmittance are unitless

Answer 11

true

Question 12

Why should you use absorbance instead of transmittance?

Answer 12

because absorbance is a linear function (transmittance is not)

Question 13

What does a colorimeter show you?

Answer 13

shows you how much light you started with vs how much you ended with

Question 14

What color light should you shine through the solution?

Answer 14

the color that is complementary to that color

Question 15

What are the x and y axes on the colrimeter graph?

Answer 15

x-axis: concentration

y-axis: absorbance

Question 16

What is interference?

Answer 16

a color can be recognized by multiple things in the solution (on the graph multiple peaks of the same color on top of each other)

Question 17

How to avoid interference?

Answer 17

pick a peak absorbance that only reacts with one element

Question 18

What is Beer’s Law?

Answer 18

A = e x b x c
A- absorbance (unitless)
e- molar absorbtivity (constant for substance)
b- path length (usually 1 cm)
c- concentration (mol/L)

Question 19

Electromagnetic spectrum
high energy –> low
high frequency –> low
short wavelength –> long

Answer 19

gamma
x-rays
UV
visible
IR
microwave
radio

Question 20

What to do if you have an unknown concentration of a sample?

Answer 20

dilute it and use M1V1 = M2V2 to find concentration

Question 21

What is photoelectron spectroscopy (PES)?

Answer 21

atoms are shot with photons (particles of light) and the leftover energy used to remove electrons is measured

Question 22

True/False: the more farther away the electrons are from the nucleus the more energy it takes to remove it

Answer 22

False

Question 23

How to read PES graph

Answer 23

x-axis is the amount of energy it takes to remove electron from shell
y-axis is number of electrons in that shell

Question 24

True/False: shells that are completely full are going to take more energy to remove an electron

Answer 24

True

Question 25

How to read longer PES charts

Answer 25

bottom to top, left to right

Question 26

Why would an element that has more protons have a higher ionization energy?

Answer 26

because there are more protons pulling on the electrons

Question 27

What to do when trying to see if a photon with wavelength “x” nanometers will remove an electron

Answer 27

1) convert nm into m (1 m = 1e9 nm)
2) use c = lambda*v and find frequency
3) plug frequency into E = hv to find energy (in J)
4) convert J into MJ/mol by using (1 MJ = 1e6 J and avagdro’s number)