3.1.1.2 Mass number and isotopes- Mass spectrometry

Question 1

how Cu atoms are converted into Cu+ ions in a mass spectrometer

Answer 1

high speed/energy electron from electronic gun

knocks electron off Cu atom

Question 2

How ions are detected in a mass spectrometer

Answer 2

Positive ions collide with the detector;

causing current to flow and electricity or voltage to be generated;

Question 3

How abundance is measured in a mass spectrometer

Answer 3

current depends on abundance/number of ions hitting detector

Question 4

The device used to ionise ions in a mass spectrometer

Answer 4

electron gun

Question 5

Why it is necessary to ionise atoms before acceleration

Answer 5

only ions can be attracted or accelerated by an electric field
or converse; if not charge not attracted to electric field

Question 6

What deflects the ions in a mass spectrometer

Answer 6

magnetic field (or magnet)

Question 7

What is adjusted in order to direct ions of different mass to charge ratio onto the detector in a mass spectrometer

Answer 7

magnetic field

accelerating potential or strength of magnet

Question 8

the shapes and directions of the paths traced by the fundamental particles as they pass through the electric field

Answer 8

• neutron has no charge so is undeflected
• proton and electron attracted to –ve and +ve plates respectively
• mass of proton>mass of electron so deflected less

Question 9

Purpose of an electron gun in a mass spectrometer

Answer 9

to produce high speed electrons / stream of electrons or to fire electrons or to bombard with electrons
which remove electrons from species cause formation of positive ions

Question 10

Purpose of the electric field in a mass spectrometer

Answer 10

to accelerate / speed up positive ions / ions / fragments

Question 11

Purpose of the magnet in a mass spectrometer

Answer 11

to deflect / bend ions / ion stream

OR separate ions accordingly to mass

Question 12

Purpose of the detector in a mass spectrometer

Answer 12

to detect positive ions / ions / particles / fragments / molecular ion

Question 13

an instrument which is used to measure the relative abundance of isotopes

Answer 13

mass spectrometer

Question 14

e device, in a mass spectrometer, which causes particles to become ionised

Answer 14

electron gun

Question 15

What happens to these particles immediately after they are ionised in a mass spectrometer

Answer 15

accelerated

Question 16

The factor, other than the mass to charge ratio of an ionised particle, determines how much that particle is deflected in a magnetic field of a given strength

Answer 16

Speed

Question 17

what is adjusted in a mass spectrometer in order to direct ions with different m/z values onto the detector

Answer 17

Magnet/electromagnet/magnetic field / electric field/charge on negative/accelerator plate

Question 18

the process by which particles are ionised in a mass spectrometer

Answer 18

Electron gun

knocks out electron(s) from the particle

Question 19

Reasons why particles must be ionised before being analysed in a mass spectrometer

Answer 19

Acceleration

Deflection

Question 20

Ionisation is the first of the four main stages involved in obtaining the mass spectrum of a sample of gaseous titanium atoms. Explain how ionisation is achieved. Name the remaining three stages and, in each case, state how each stage is achieved

Answer 20

Ionisation
High speed or high energy electrons or electron gun
Knocks out (outer) electron
Forming positive ion
Acceleration
By electric field or attraction to negative plate or electrostatic attraction
Deflection
By magnetic field or magnet or electromagnet
Detection
Idea that ions collected at detector and generate current

Question 21

why it would be difficult to distinguish between 48Ti2+ and 24Mg+ ions using a mass spectrometer

Answer 21

Both ions have the same m / z value (of 24) or valid arguments in terms of the doubled charge on 48Ti2+ exactly counteracting its doubled mass
Deflected equally (so detected together) or deflection dependent on m / z value

Question 22

how the gaseous atoms of rubidium are ionised in a mass spectrometer

Answer 22

Electron gun / high speed/high energy electrons

Knock out electron(s)

Question 23

In a mass spectrometer how the abundance of an isotope in a sample is determined

Answer 23

Detector

Current / digital pulses / electrical signal related to abundance

Question 24

a fundamental particle that would not be deflected by an electric field

Answer 24

Neutron

Question 25

Why the sample of isotopes must be ionised in mass spectrometry

Answer 25

To accelerate/ make go faster

To deflect/ to bend the beam

Question 26

what can be adjusted in the mass spectrometer to enable ions formed by the different isotopes to be directed onto the detector

Answer 26

Electromagnet / magnet / electric field /accelerating potential or voltage

Question 27

an instrument which is used to measure the relative abundance of isotopes

Answer 27

Mass spectrometer

Question 28

What is used in a mass spectrometer to accelerate the positive ions

Answer 28

Magnetic field or electric field or electromagnet

Question 29

What is used in a mass spectrometer to deflect the positive ions

Answer 29

Deflection depends on mass or m/z

Question 30

How isotopes can be separated in a mass spectrometer

Answer 30

sample introduced at low pressure (or gas or vapour or vacuum)
electron gun (or bombarded with electrons)
which knocks out an electron (or removes an electron)
producing a positive ion
the ions are accelerated
and focused (or made into a beam)
by an electric field (or negative plates or electric plates)
magnetic field (or magnet)
ions are deflected
deflection depends on m/z of each ion
lightest (or smallest m/z) deflected most
ions go to a detector
a small current is produced (or abundance counted)
which is fed to a computer (or recorder or display or chart etc)
electric field (or magnet) adjusted to collect ions of different mass
Note: a picture of a spectrum can score the chart mark and the abundance mark (if the ‘y’axis is labelled ‘abundance’ or ‘%’.