2.1.4 Determining masses using mass spectrometry

Question 1

what is a mass spectrometer?

Answer 1

a piece of apparatus that can be used to find out about molecules

Question 2

what can a mass spectrometer be used to find out?

Answer 2

-identify a new compound
-find the relative abundance of each isotope of an element
-determine structural information about molecules

Question 3

how does a mass spectrometer determine the mass of a molecule/isotope?

Answer 3

it causes substances to become positive ions and then measures the mass-to-charge ratio.

Question 4

what is a mass spectrum similar to?

Answer 4

a complex bar graph

Question 5

what does the mass spectrum give info of?

Answer 5

of the abundance of ions present in sample

Question 6

what is on the y axis on a mass spectrum?

Answer 6

percentage abundance

Question 7

what is on the x axis on a mass spectrum?

Answer 7

mass to charge ratio

Question 8

how is the mass to charge ratio labelled on the mass spectrum?

Answer 8

m/z

Question 9

what are the three steps in analysing a mass spectrum?

Answer 9

-the number of bars represents the number of isotopes
-the number under the bar represents the isotopic mass
-the number above the bar represents the relative abundance

Question 10

how to work out the relative abundance if there isn’t any values or no scale on the y axis?

Answer 10

measure each line and use the formula height of singular isotope/ heights of the isotopes x100

Question 11

what can the relative abundance and individual isotopic masses be used to find out?

Answer 11

the relative atomic mass of the sample

Question 12

what is the formula for relative atomic mass?

Answer 12

(isotopic mass of A x abundance)(‘B”) (“C”) / 100

Question 13

in A level mass spectrometry, what is charge always?

Answer 13

1

Question 14

as charge is always 1, what is mass + charge equal to?

Answer 14

mass

Question 15

what are the four steps of mass spectrometry?

Answer 15

-ionisation
-acceleration
-deflection
-detection

Question 16

what is the ionisation step of mass spectrometry?

Answer 16

molecules/isotopes become positive ions (after being placed in a volatile substance)

Question 17

what is the acceleration step of mass spectrometry?

Answer 17

the ions are accelerated so they have the same kinetic energy

Question 18

what is the deflection step of mass spectrometry?

Answer 18

the ions are then deflected by a magnetic field, depending on their masses and their charges

Question 19

in the deflection stage, how are the ions deflected?

Answer 19

the lighter they are, the more they are deflected and the more charge they have (the electrons they lost), the more they are deflected

Question 20

what happens in the detection stage?

Answer 20

The beam of ions passing through the machine is detected electrically and a mass spectrum is produced

Question 21

how does a mass spectrometer determine the mass of a molecule/isotope?

Answer 21

by measuring mass-to-charge ratio

Question 22

why is there a need for a vacuum?

Answer 22

the ions produced in the ionisation chamber must have a free run through the machine without hitting air molecules.