2.2 Relative Mass

Question 1

Definition of relative isotopic mass

Answer 1

the mass of an isotope relative to 1/12th the mass of an atom of carbon-12

Question 2

Definition of relative atomic mass

Answer 2

the weighted mean mass of an atom of an element relative to 1/12th the mass of an atom of an element relative to 1/12th the mass of an atom of carbon-12

Question 3

What does the weighted mean mass take into account of

Answer 3

-the percentage abundance of each isotope
-the relative isotopic mass of each isotope

Question 4

Why is mass spectrometry used

Answer 4

to determine the relative isotopic masses and relative abundances of an isotopes

Question 5

How does a mass spectrometer work?

Answer 5

1. a sample is placed into the mass spectrometer
2. the sample is vaporised
3. an electron gun knocks off an electron from the sample, the sample has now been ionised to form positive ions
4. ions are accelerated using magnets, heavier ions move slower and are more difficult to detect, this allows the ions of each isotope to be separated
5. the ions are detected on a mass spectrum as a mass-to-charge ration m/z. each ion reaching the detector adds a signal so the greater the abundance the larger the signal

Question 6

how to calculate the mass-to-charge ration

Answer 6

m/z = relative mass of ion/ relative charge of ion