1.3 chemical calculations Flashcards
Relative atomic mass
Average mass of 2 atom relative to the mass of an atom of Carbon 12
Relative formula mass
The sum of the relative atomic masses of the elements as given in the formula for any non-molecular compound.
Relative isotopic mass
The mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12
Relative molecular mass
The weighted average mass of a molecule compared with one-twelfth of the mass of an atom of carbon-12.
Stages in mass spec
Vaporisation
Ionisation
Acceleration
Deflection
Detection
Vaporisation
Sample is heated and turned into a gas before entering mass spectrometer
Ionisation
The gaseous sample is bombarded with high energy electrons which form positive ions
Acceleration
Positive ions are accelerated through an electric field.
How can you use mass spec to deduce the relative molecular mass of a sample of a compound
The peak with the highest m/z value is caused by the whole molecule therefore m/z value = molecular mass.
Deflection
Ions are deflected through magnetic field according to mass and charge (heavy - deflect least)(light - deflect most)
Detection
Some ions pass through a slit and are detected by the detector and only those ions that have correct mass/charge ratio can pass through
Calculate relative atomic mass
(% of isotope a x mass of isotope a) + (% of isotope b x mass of isotope b) /100
Mass Spec Chlorine
parent peaks have a 3:1 ratio
avrogadro’s constant to moles
Number of particles = moles x avrogadros constang
Concentration
Amount of moles per unit volume
Concentration equation
mass/volume
PV=nRT
pV=nRT
Pressure x Volume = moles x gas constant x temp (k)
Percentage yield
actual yield/theoretical yield x 100
why may % yield be less than 100%
Incomplete reaction
Unwanted side reactions
Practical losses (solid may get lost when transferring beakers)
Atom economy equation
Mr of desired product/Mr of total reactants x100
% error equation
Absolute uncertainty/calculated value x100
Titre volume is recorded as 11.30cm3 the accuracy of he burette is ±0.05cm3 calculate the maximum percentage error
0.05/11.30 x100 = 0.442%
