Mass Number And Isotopes

Question 1

Mass number (description and letter used to represent it)

Answer 1

Sum of protons and neutrons

Represented by letter A

Question 2

Atomic number (description and letter used to represent it)

Answer 2

Number of protons

Z

Question 3

Isotopes

Answer 3

Atoms of the same element which have the same atomic number but different mass number ( different number of neutrons)

Question 4

Neutral atoms of isotopes

Answer 4

React chemically in the same way (proton number and electron configuration is the same ) they have different physical properties (due to different mass number)

Question 5

Ions

Answer 5

Formed when an atom loses or gains electrons therefore the atom is no longer neutral and has an overall charge

Question 6

Mass spectrometry

Answer 6

Analytical technique used to identify different isotopes and find the overall relative atomic mass of an element

Question 7

Relative atomic mass

Answer 7

The average mass of an atom of an element compared to 12C on a scale where an atom of 12C has a mass of exactly 12.

Question 8

Time of flight (TOF) mass spectrometry

Answer 8

A form of mass spectrometry which record the time it takes for ions of each isotope to reach a detector. Using this spectra can be produced showing each isotope present

Question 9

What are the steps of TOP mass spectrometry

Answer 9

1. Ionisation
2. acceleration
3. ion drift
4. detection
5. analysis

Question 10

Describe electrospray ionisation

Give equation

Answer 10

-sample(X) dissolved in a polar volatile solvent (water or methanol or both)
-solution pumped through hypodermic capillary needle where converted to fine mist(nebulized)
-high voltage applied to tip of capillary, sample emerges dispersed in an aerosol of highly charged droplets
-solvent evaporates(desolvation) esch particle ionised by gaining a proton from the solvent producing XH+(g)
Equation X(g) + H^+ -> XH^+(g)

Question 11

Electron impact ionisation with equation

Answer 11

Sample vaporised
High energy electrons fired at sample from electron gun
Electron knocked off from each particle forming 1+ ion
Equation X(g) -> X^+(g) + e^-

Question 12

Acceleration

Answer 12

Positively charged ions are accelerated (to five all ions constant kinetic energy) towards a negatively charged detection plate

Question 13

Ion drift

Answer 13

Ions are deflected by a magnetic field into a curved path (the radius of their path is dependent on the charge and mass of the ion

Question 14

Detection

Answer 14

Positive ion hits negatively charged detection plate they gain an electron producing a flow of charge the greater the abundance the greater the current produced

Question 15

Analysis

Answer 15

Current values used in combination with flight times to produce a spectra print out with relative abundance of each isotope displayed

Question 16

During ionisation a 2+ charged ion may be produced what happens to its m/z ratio

Answer 16

It is halved

Question 17

Which ionisation method causes less fragmentation and is often used for substances with high Mr

Answer 17

Electrospray ionisation