1.3 Chemical Calculations Flashcards
The relative atomic mass (Ar) of an element
the average mass of one atom relative to one-twelfth of the mass of one atom of carbon-12.
The relative isotopic mass of an isotope of an element
the average mass of an isotope relative to one-twelfth of the mass of one atom of carbon-12.
Relative atomic mass is calculated using the equation below.
The percentage by mass of an element in a compound can be determined in the way shown below.
In the mass spectrometer the sample undergoes the following processes.
Vaporisation: the sample is heated and turned into a gas before it enters the spectrometer.
Ionisation: the gaseous sample is bombarded with high energy electrons from an electron gun. This knocks electrons off the particles to form positive ions.
Acceleration: the positive ions are accelerated using an electric field and a vacuum pump.
Deflection: the ions are deflected by a magnetic field. The amount of deflection depends on the mass and charge of the ion. Lighter ions are deflected more than the heavier ones.
Detection: the abundance and mass/charge (m/z) ratio of the ions is read, and a mass spectrum graph is produced.
The inside of the spectrometer is a vacuum so that air molecules do not interfere with the movement of the ions.
mass spectrometer diagram
Mass spectrometry can be used to analyse samples of substances.
Calculating number of particles
The number of particles of carbon dioxide gas in 0.200 moles is:
0.200 x 6.02 x 1023 = 1.20 × 1023
