1.3 Chemical calculations

What is the definition of relative atomic mass (Ar)

The average mass of an element (taking into account all possible isotopes) relative to 1/12 the mass of one atom of carbon-12

What is the definition of relative isotopic mass

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

What is the definition of relative formula mass

The average mass of a molecule relative to 1/12 the mass of an atom of carbon-12 (sum of all the relative atomic mass in a formula)

How to calculate relative atomic mass using isotopes

(Mass of isotope 1 x abundance) + (mass of isotope 2 x abundance) /100

What is mass spectrometry used to find

-abundance of different isotopes for an element

-relative isotopic mass of a particular element

-relative atomic mass for an element overall

What happens in mass spectrometry

1.Ionisation - the atom or molecule is ionised to give a positive ion using an electron gun which bombards the sample with high energy electrons to knock an electron off the sample. A vacuum is used so the ions don’t hit any molecules in the air

2.Acceleration - the ions are accelerated through an electric field so that they all have the same kinetic energy

3.Deflection - the ions are deflected by a magnetic field according to their masses. The lighter they are the more they are deflected. The more the ion is charged the more it gets deflected

4.Detection - the beam of ions passing through the machine is detected electrically and amplified