1.3 (pt2) Flashcards
Avogadro’s law applies to…
only gases or liquid that’s formed as steam
STP
0 degrees
1 atm pressure
molar volume = 22.4 dm3
RTP
25 degrees
1 atm pressure
molar volume = 24.5 dm3
Equation to work out number of moles of gas
n = V0 (volume of gas)
Vm (molar volume)
Ratio e.e 3:2
rhannu gyda 3, lluosi 2
Gas equation
pV=nRT
Mr
p=pascals
V=volume M3
R=gas constant (on data sheet)
T= Kelvin temperature (if indegrees +273)
Reorganising the gas equation
pV=nRT
n=pxv/RT
V=nRT/p
Mass Spectrometer
used to calculate the Mr of an element
Mass Spectrometry theory
> Knowing the speed and force you can calculate mass - less the deflection, the heavier the object
Full diagram of a mass spectrometer
.
5 main stages of the mass spectrometer
- Vapourisation
- Ionisation
- Acceleration
- Deflection
Vapourisation
Gases, liquids, volatile solids injected into the instrument.
volatile solids must be pre-heated to vaporise them.
Ionisation
Vapourised sample passed into ionisation chamber.
>atom are bombarded with high energy electrons.
>some collision energetic enough to remove 1 or more electrons to make positive ions.
M(g) + e- –> M+(g) + e- +e-
Acceleration
+ions are accelerated so they have the same kinetic energy.
+ions pass through three slits.
Deflection
+ions enter the analyser tube (curved, surrounded by a powerful electromagnet)
>evacuated to a high vaccum so +ions don’t collide with background gas molecules.
Amount of deflection depends on :
mass of object - lighter ions are deflected more
charge of ion - ions with 2+ charges are deflected more than ions with 1+
these combine into the mass/charge ratio (m/z)
Detection
only +ions that have not been deflected will be detected.
other ions will be removed by the vacuum pump.
Summary of mass spectrometry
V-sample vaporised
I- +ions are obtained from vapour
A- _ions are accelerated by an electric field
D- Deflected using a magnetic field
D- ions detected and recorded
A mass spectrum tells you
> The atomic mass of all the isotopes
The relative abundances of each of the isotopes
How to read a mass spectrum
> sizes/height of the peaks gives a measure of the relative abundances of the isotopes
Number of peaks shows the number of isotopes and their relative atomic masses
Calculating Ar using the mass spectrum
Ar= (mass x abundance) + (massxabundance) / total of abundances
