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AS - Mass Spectrometry
AQA AS Chemistry Unit1
9
Chemistry
11th Grade
02/25/2014

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Cards

Term

 

 

 

Mass Spectrometry

Definition

Accurately determines relative atomic masses.

Can be used to identify an element.

Drawing:

Term

 

 

 

Mass Spectormeter Conditions

 

 

 

Definition

 

 

Kept under a high vacuum.

-So Ions do not collide wth air molecules.

The sample is is a gaseos state

Term

 

 

 

Mass Spectrometry Stages

Definition

 

 

Ionisation

Acceleration

Deflection

Detection

Term

 

 

 

Ionisation

Definition

 

A beam of Electrons form an 'Electron Gun' to knock of an electron to form a possitive Ion.

Nearly all Electrons lose 1 electron to form 1+ Charge.

Around 5% lose 2 electrons to for a 2+ Charge.

Term

 

 

 

Acceleration

Definition

 

 

Positive Ions are attracted towards negatively charged plates and accelerated at high speed.

The speed they reach depends on mass.

Term

 

 

 

Deflection

Definition

 

The beam of ions move into an electromagnetic field.

The heavier the ion, the less it is deflected.

The lighter the ion, the more it is deflected more.

Th strength of the electromagnet can be changed to direct the ions onto the detecter.

Term

 

 

 

Deflection

Definition

The ions hit the detector, accept electrons (causeing them tio lose their charge) and create a current proportional to the abundence of each ion.

From the strength of the feild at which it hits the detector, a computer works out the mass to charge ratio (m/z).

This is normaly presented as a graph.

Term

 

 

 

Calculating Relative Atomic Mass

Definition

 

(mass1x Abundance1)+(mass2x Abundance2)+...


Total Abundance

 

 

Abundance can be amounts or %.

 

Term

 

 

 

Doubly Charged Ions

Definition

 

Durng ionisation a small number of ions with a 2+ Charge are formed. These are deflected more than singly charged ions.

They behave like ions with half the mass.

Therefore there is sometimes a small peak on a mass spectra graph.

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