# Calculations

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## Working out Relative Ar from the Mass Spectrum

Step 1; For each peak, read the % relative isotopc adundance from the y-axis and the relative isotopic mass from the x-axis. Multiply them together to get the total mass for each isotope

Step 2; Add up these totals

Step 3; Divid by 100

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## Working out the Molecular Formula

Its a ratio that gives you actual nubers of the atoms in the molecule. The molecular formula is made up of a whole number of empical units which builds up on your knowledge from the empirical formula

• Step 1; Mass/Mr for the reactants to work out the moles for each element
• Step 2; Number of moles x Mass = mass of each element altogether that will equal product
• Step 3; Get molar ratio
• Step 4; Compare empirical to molecular
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## Octane Numbers

• Octane number= the tendancy of a petrol based fuel to auto ignite (knocking)
• If it has a low tendancy to auto ignite it has a score of 100
• High tendancy to auto ignite score 0
• In both petrol and diesel engines the fuel-air mixture has to ignite at the right time, usually just before the piston reaches the top of the cylinder.
• The shorter the hydrocarbon the less likey it is to ignite
• As the fuel-air mixture is compressed it heats up and the more it gets compressed the, the hotter it gets. Modren cars achieve greater effiiciency than in the past by using high compression ratios. Often compressing the gases in the cylinder by about factor 10
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## Mass Spectrometry

It is a process which the atomic mass of the atoms/ molecules is determined which can be used to find the relative isotopic abundance, atomic and molecular masses and structure of a compound

Time of Flight

• Sample is ionised by bombarding it withe lectrons, also causes fragmentation to form smaller groups of atoms all positively charged
• The ions are accelerated by electromagnectic field and travel through a vaccum area called the drift region before being detected by an ion dector
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## Oxidation and Reduction

Oxidation States of;

• atoms of elements= 0
• compounds=0
• ions= same as charge                         n
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