paper 2 mock Flashcards
(48 cards)
what is the current gas composition of the atmosphere
nitrogen - 78% oxygen 21% carbon dioxide 0.04% argon 0.9% other less than 1%
the early gas composition of the atmosphere
lots of carbon dioxide
little to no oxygen
some water vapour
not much nitrogen
why did the atmosphere change
the earth’s surface cooled and a thin crust formed but volcanoes kept erupting releasing gases from inside the earth. This degassing released mainly carbon dioxide but also steam, methane and ammonia
when things settled down the atmosphere was mainly CO2 and water vapour and little oxygen. the water vapour condensed to form the oceans which absorbed the CO2
Nitrogen gas was then put into the atmosphere by ammonia reacting with nitrogen and by denitrifying bacteria. N2 isn’t very reactive so the amount of N2 in the atmosphere increased because it was being made but not broken down. Next green plants evolved over most of the Earth as they photosynthesised they removed CO2 and produced O2 (say increased and decreased … )
the amount of O2 in the air gradually built up and much of the CO2 got locked up in fossil fuels and sedimentary rocks
the build up of oxygen in the atmosphere killed off early organisms and allowed the evolution of more complex organisms that made use of the oxygen
the oxygen also made the ozone layer which blocked harmful rays from the sun and enabled more complex organisms to evolve
virtually no CO2 left now
what is the test for chlorine
damp blue litmus paper turns red then bleach white
what is the test for ammonia
red litmus paper turns blue
ionic bonding
electron transfer / attraction of ions
covalent bonding
shared pairs of electrons
what should you always do when drawing an ionic bond diagram and covalent diagram
ionic - all shells and square brackets
covalent - dots and cross and only outer shell
discuss covalent bonding
strong covalent bonds but a weak intermolecular force between these pairs of covalent bonds meaning it has a low mp and bp
discuss ionic bonding
high mp and bp as it has lots of bonds and needs lots of energy to break every bond and the forces between the positive and negative ions
discuss fractions at the top of the fractional distillation column
- short chains
- most useful
- highly flammable
- less viscous
how do we make the longer chains more useful
crack them over an aluminium catalyst into shorter chains
word equation for complete combustion
oxygen + methane -> CO2 + water
blue flame
word equation for incomplete combustion
methane -> carbon + carbon monoxide + water + carbon
yellow flame
soot from carbon
carbon monoxide binds to haemoglobin so you can’t carry oxygen
what things speed up the rate of reaction and why
- catalyst (lowers the activation energy and balances out the use of low temperatures)
- pressure increase (means a smaller space so more collisions take place)
- increase in surface area (more surface for reactions to take place on)
- increases in temperature for more energy
- increase in concentration means more particles to collide
Endothermic
Bond breaking
Exothermic
Bond making
Which are the most reactive in group 7
The elements at the top because it is easier to attract an electron because there isn’t as many shells between the other electron shell and the nucleus
But as you go down there is more shielding and the atoms become less reactive because it gets harder to attract the electron - larger atomic radius
What happens to the reactivity of the atoms in group 1
As you go down group 1 the alkali metals get more reactive. The outer electron is more easily lost because it’s further from the nucleus - large atomic radius - so its less strongly attracted to the nucleus and less energy is needed to remove it
homologous series
- same functional groups
- similar properties
- same general formula
5 alkanes and alkenes
my enormous penguin bounces pretty high methane ethane propane butane pentane
methane ethene propene butene pentene
what colour do these go in the flame test lithium sodium potassium calcium copper
Li + red Na+ yellow K+ lilac Ca2+ orange-red Cu2+ blue-green
what colour do metal hydroxides go that are insoluble and precipitate in reaction when you add sodium hydroxide solution aluminium calcium copper iron II iron III
Al3+ white then a colourless solution in excess Ca2+ white Cu2+ blue Fe2+ green Fe3+ brown
test for the halide ions
dilute nitric acid and silver nitrate 2ml each
chlorine - white
bromine - cream
iodine - yellow
