alkanes Flashcards
(32 cards)
why do branched molecules have lower boiling points
there are weaker forces of attraction between branched molecules - prevents closer approach to neighbouring molecules.
what happens when you add an alkane to water
forms 2 layers (insoluble)
what conditions are needed for cracking
Over 400°c
moderate pressure
zeolite catalyst
% error =
error on equipment x times used
———————————————- x 100
measurement taken
which equipment has an error x 2
balance
burette
define hydrocarbon
compounds containing hydrogen and carbon only
what does an empirical formula show
simplest whole number ratio of atoms present in the molecule
what does a molecular formula show
number of each type of atom present in the molecule
what does structural formula show
functional groups and how the atoms are bonded together
what does displayed formula show
shows all the bonds and all the atoms and how they are bonded
what does skeletal formula show
does not show C atoms or C-H bonds
define structural isomerism
occurs when two or more compounds have the same molecular formula but different structural formulae
define chain isomers
a type of structural isomer
they have a different arrangement of the carbon chain but the same molecular formula
why does boiling point increase with increasing chain length
more carbon atoms more electrons so stronger london forces
require more energy to overcome
how does branching affect boiling point
branching reduces the boiling point
how does fractional distillation work
crude oil vapourised at base of column
this temperature < the bp of the longest molecules which liquefy/solidify as tar
others remain as vapours and they rise up to the next layer
pass through bubble traps and condense
shorter molecules may revapourise and continue to rise to the next layer where they condense
define cracking
the breakdown of molecules into shorter ones by heating with a catalyst
what happens during cracking
fresh feedstock and zeolite flow into the vertical reactor
cracked products pass to a fractionating column
catalyst flows to a regenarator
what is reforming
the conversion of straight chained hydrocarbons intto branched and cyclic hydrocarbons by heating with a platinum catalyst
what is crude oil used for
fuel and lubricants
manufacture of paints and polymers
what is the purpose of cracking
increases our supply of gasoline
produces short chain alkanes that are used to manufacture polymers
what do alkanes produce when burned in excess 02
CO2 and H2
what pollutants are formed from combustion of fuels
carbon (soot)
CO
sulfur dioxide
nitrogen dioxide
unburnt hydrocarbons
method to find solubility of alkanes in water
add 10 drops of each to a half a test tube of water and shake
