Revision for 21/9/22 Flashcards
alkane general formula
CnH2n+2
homologous series
a ‘family’ of organic compounds with the same functional group and similar chemical properties
hyrdocarbons
compounds that contain only hydrogen and carbon atoms
alkene general formula
CnH2n
Fractional distillation
Oil is heated to about 350°C and pumped into the bottom of a tall tower called a fractionating column, where it vaporises.
The column is hotter at the bottom and cooler at the top. As the vaporised oil rises, it cools and condenses.
The heavy fractions (containing large molecules) have a high boiling point and condense near the bottom of the column (where they flow out through a pipe).
The lighter fractions (containing small molecules) have a low boiling point and condense near the top of the column (where they flow out through a pipe).
Order of fractional distillation:
Liquid Petroleum Gas (LPG) - Short Chain Hydrocarbons
Petrol
Kerosene
Diesel Oil
Heavy Fuel Oil
Bitumen - Long chain hydrocarbons
How is crude oil formed?
Crude oil is formed over millions of years from the remains of plankton, which decayed anaerobically in mud under high pressure and temperature.
The mud stopped them from rotting away.
This organic matter turned into crude oil and was stored within rocks.
Formulation
A formulation is a mixture that is a useful product (e.g. toothpaste)
Carbon monoxide cause + effects
C: insufficient oxygen during combustion
E: carbon monoxide poisoning
Carbon dioxide cause + effect:
C: complete combustion of fuels with carbon atoms
E: contributes to global warming (greenhouse gas)
Carbon dioxide cause + effect:
C: complete combustion of fuels with carbon atoms
E: contributes to global warming (greenhouse gas)
Nitrogen oxide cause + effect:
C: oxidation of atmospheric nitrogen in cars + lorries
E: acid rain
Particulates cause + effect:
C: incomplete combustion of fuels containing carbon atoms
E: global dimming
Water vapour cause + effects:
C: complete combustion of hydrocarbons
E: greenhouse gas that radiates heat back onto the Earth’s surface
Sulphur dioxide cause + effect:
C: combustion of fuels containing sulfur impurities
E: acid rain
Trend in the boiling point of alkanes
The boiling point increases as the number of carbon atoms increase
This causes the intermolecular forces to increase as the size of molecules increase
alkene + hydrogen —> ….
alkane
(reaction requires a catalyst)
addition reaction
when 1 molecule combines with another molecule to form a chain or a long molecule
alkene + water (or steam) —> ….
alcohol
(reaction requires high temperatures + a catalyst)
Alkene + bromine —> …..
Alkene + bromine —> dibromoalkane
Order of alkanes
Methane - my
ethane - energetic
propane - parents
butane - bought
pentane - popsicles
Steam cracking
Heat alkanes to vaporize them and mix with steam and then heat to a very high temperature - causes them to split
Catalytic Cracking
Heat alkanes to vaporise them then pass over a hot (600–700°C) catalyst - causes it to split
Cracking
Thermal decomposition of long chain alkanes into shorter alkanes and alkenes (which are more useful)
Properties of hydrocarbons
- long chain hydrocarbons are extremely viscous
- short chain hydrocarbons are extremely flammable
- short chain hydrocarbons have a low boiling point
- short chain hydrocarbons have a higher volatility (tendency to turn into a gas)
Test for alkenes:
add bromine water to a solution of alkenes
(will turn from orange to colourless in the presence of alkenes)
Polymer
a large, long chain made from many monomers joined together
monomer
small molecule that bonds with other small molecules to form a larger molecule (polymer)
Features of alkenes
unsaturated hydrocarbons
more reactive than alkanes (double bond)
can join together to form polymers
Features of alkanes
saturated hydrocarbons
form a homologous series
general formula - CnH2n+2
Complete combustion
when there are sufficient amounts of oxygen
reaction produces carbon dioxide and water
Describe why sulfur should be removed from petrol
burning sulfur produces sulfur dioxide
causes acid rain
how to name poylmers
poly(alkene)
how to name polymers
poly(alkene)
endothermic reaction
gains energy from surroundings
exothermic reaction
transfers energy to the surroundings
Why is sulfur dioxide produced in petrol engines
petrol contains sulfur impurities (that react with oxygen)
How are nitrogen oxides produced in petrol engines?
nitrogen and oxygen react
at high temperatures (inside a petrol engine)
Why is biodiesel carbon neutral
CO2 released when burning biodiesel
CO2 is absorbed by crops to grow and produce biodiesel
Ethical + Economic concerns related to biodiesel
ethical: uses land that could be used to grow food
economic: causes cost of food to rise
Fermentation of yeast cells
glucose —> ethanol + carbon dioxide
Why shouldn’t we use plastic bags?
made from crude oil
not biodegradable
use non-renewable resources
litter (could go to landfill)
Explain how different dyes are separated by paper chromatography.
solvent moves through the paper
different dyes have different solubilities in the solvent
the different dyes also have different attractions to the paper
so the dyes each move up the paper a certain distance
How does an energy level diagram show that a reaction is exothermic?
the products are at a lower energy level than the reactants
How does an energy level diagram show that a reaction is endothermic?
the products are at a higher energy level than the reactants
Explain how a catalyst increases the rate of the reaction.
a catalyst provides an alternative pathway
with lower activation energy
which increases the number of successful collisions
increases the rate of reaction
(it is also not used up in reaction)
Compound
2 or more different elements
mixture
2 or more different substances not chemically combined
(use filtration to separate)
molecule
2 or more atoms chemically bonded together
law of conservation of mass
total mass of products = total mass of reactants
bond breaking = …
endothermic (energy is required to break bonds)
bond making = …
exothermic (energy is given out when bonds are made)
Energy change equation:
energy in - energy out
or
bonds broken - bonds made
energy values
kJ/mol
How would you explain an overall reaction is exothermic?
overall the reaction is exothermic
as more energy is given out when new bonds are made
than energy needed to break bonds
How would you explain an overall reaction is endothermic?
overall the reaction is endothermic
as more energy is taken in when bonds are broken
than the energy given out when new bonds are made
enthalpy change =
change in energy
How would you separate ethanol, water and unreacted ethene?
ethene (low boiling point): so cool the mixture to separate it
ethanol and water: place mixture in a round bottom flask and heat with a bunsen burner, the ethanol will boil first (has a lower boiling point), and evaporate up the fractionating column, it then condenses, and is then collected in another tube
difference between a smart polymer and a regular polymer
a smart polymer can return to its original shape
pros of nanoparticles in sun cream
better coverage
more protection from the sun’s UV rays
cons of nanoparticles in suncream
could damage cells in our body
could have harmful effects on the environment
why are nanoparticles useful?
they have a high SA:V
Equation for heat energy
Q (in J) = m (in g) x c (j/kg °C) x change in temperature ( °C)
Q = mcΔT
How to test for water:
use anhydrous cobalt(II) chloride (which is blue)
it turns pink in the presence of water
or
use anhydrous copper (II) sulphate (which is white)
it turns blue in the presence of water
collision theory states:
in order for particles to react, they have to collide with sufficient energy
activation energy
the minimum amount of energy needed for a reaction to take place
rate of reaction is dependent on
frequency of collisions
amount of energy the particles have
Greater surface area: volume ratio increases rate of reaction because…
increases the frequency of collisions between reacting particles
Effect of temperature on rate of reaction:
temperature increases
particles gain more energy and move faster
increases the frequency of collisions and particles collide with more energy
increases the number of successful collisions
Effects of concentration and pressure on rate of reaction:
increased concentration or pressure
results in more particles per unit of volume
increases the frequency of collisions
increases the rate of reaction
Required practical: Rate of reaction (black cross)
measure out 10cm3 of sodium thiosulphate into a conical flask
place onto a printed black cross
add 10cm3 of hydrochloric acid and swirl the solution
start the stopwatch and look down
stop the stopwatch when you can no longer see the cross
repeat this experiment to calculate a mean
then repeat this experiment for different concentrations of sodium thiosulphate
(PROBLEM: PEOPLE WILL SEE THE CROSS DISAPPEAR AT DIFFERENT TIMES)
Required practical: rate of reaction
place 50cm3 of hydrochloric acid into a conical flask
attach a bung and gas syringe to the conical flask
then add 3cm strip of magnesium to the acid
start the stopwatch
record the volume of hydrogen gas collected every 10 seconds
repeat this experiment for different concentrations of hydrochloric acid
sharing electrons =… bonding
covalent bonding
(between non-metals)
transferring electrons = … bonding
ionic bonding
(usually between metals + non-metals)
Properties of ionic compounds
high melting and boiling points - lots of energy required to break strong ionic bonds
conduct electricity when molten or dissolved in water - electrons are free to move around
Half equations
Na —> Na+ + e-
(losing electrons)
Cl- + e- —> Cl
(gaining electrons)
oppositely charged ions are attracted to each other by…
electrostatic forces
Covalent bonds have:
strong covalent bonds
weak intermolecular forces
Simple molecular substances:
small molecules with strong covalent bonds + weak intermolecular forces
e.g. methane, water, ammonia
giant covalent structures:
graphite
diamond
sulfur dioxide
giant covalent structures:
graphite
diamond
sulfur dioxide
properties of simple molecular substances:
low melting and boiling points due to weak intermolecular forces
(these increase as molecules get larger)
don’t conduct electricity - no free electrons
Properties of giant covalent structures:
atoms are arranged in regular repeating lattices
high melting and boiling points
don’t conduct electricity - don’t have charged particles
Explain how a covalent bond holds two atoms together.
electrostatic forces of attraction between negative electrons
and the positive charge of the nuclei
when you measure gas you measure the…
volume of the gas
Why may people not want to be near an ammonia factory?
risk of explosions - due to the high pressures
risk of fire - due to high temperatures
Why is the best yield of ammonia at equilibrium obtained at low temperatures?
the reaction is exothermic
Why is the best yield of ammonia at equilibrium obtained at high pressure?
there are fewer molecules of product than there are
reactants
Haber process:
take nitrogen from the air and hydrogen from natural gas
pump it into a reactor at 200 atmospheres and 450 degrees celsius and pass over an iron catalyst
some of the gases will react to form ammonia
ammonia has a low bp
so to separate it from the gases
pump the mixture into the condenser
the ammonia will cool down and condense into liquid ammonia
Why do we not use pressures higher than 200 atmospheres?
expensive to maintain high pressures
high pressures can lead to explosions
What happens at dynamic equilibrium:
only reactants at the start
forward reaction is really fast - backwards reaction hasn’t started
some products are formed
forward reaction is greater than backwards reaction
forward reaction begins to slows down - backwards reaction speeds up
eventually the rates of the forward reaction = to the rate of the backward reaction
this is dynamic equilibrium
Equilibrium
when the concentration of products and reactants are constant
Use of ammonia:
fertiliser
explosives
nylon
nitric acid
if the forward reaction is endothermic
increases in temperature = increase in products
if the forward reaction is exothermic
decrease in temperature = increase in products
increasing the concentration of the reactants =
equilibrium shift in favour of products - to decrease the concentration of reactants
decreased pressure favours:
side with most gas particles (molecules)
increased pressure favours:
side with fewer gas particles (molecules)
Catalyst and equilibrium
catalyst speeds up time taken to reach equilibrium
does not change position of equilibrium
dynamic equilibrium takes place in:
a closed system - otherwise the products would escape
in certain conditions
reversible reaction
reaction that can go forwards and backwards
allotropes
different structural forms of the same element in the same physical state
Allotropes of carbon
diamond
graphite
fullerene
graphene
diamond
each carbon atom is covalently bonded to 4 other carbon atoms
strong - giant covalent structure
high melting point
Graphite
each carbon atom is covalently bonded to 3 other carbon atoms - forms large flat sheets
no covalent bonds between layers - layers can slide over each other - weak forces between layers - hence graphite is soft
have a free delocalised electron - as each atom has one free electron - which can move through the structure - therefore can conduct electricity and heat
high melting point
graphene
is a single layer of graphite - one cell thick
able to conduct electricity - can be used in electronics
fullerenes
large cage-like structures
can form cages around drugs and be delivered to specific sites in the body
can be used as industrial catalysts - large SA:V
can be used to strengthen composite material
metallic bonding
metal-metal
consists of a giant structure of atoms
in a metal, the outer shell electrons on each atom are free to move around - creates a sea of delocalised electrons
the atoms become positive ions and form a strong electrostatic attraction with the negative electrons
Properties of giant metallic structures
high melting and boiling point - lots of energy needed to overcome strong metallic bonds
good conductors of heat and electricity - the sea of delocalised electrons can carry electrical current + thermal energy
strong
malleable - layers of metal atoms can slide over each other
Alloys
2 or more different elements
made by mixing together 2 different metals (or non-metal + metal)
usually use metals with different size atoms
Properties of alloys
harder - the combination of different sized atoms disrupts the regular structure + distorts the layers so layers can no longer slide over each other
ammonium nitrate is made from
crystallisation
Problems with the ball + stick model
there are no gaps between ions
no sticks between ions
Explain how electricity is conducted in a metal.
metal is made up of a giant structure of atoms
with free electrons
that are free to move
so can carry charge
Copper alloys
Brass (made of copper + zinc)
harder than copper (pure copper is too soft)
used in door fittings and fixtures
Bronze (made of copper + tin)
used in decorative items and ship propellers
tough + resistant to erosion
Gold alloys
alloyed with copper - for jewellery
can get different shades of ‘gold’
pure gold is soft
Reasons why instrumental methods of analysis are used to detect impurities in metals.
rapid
accurate
negative electrode =
cathode
positive electrode =
anode
elements contain
1 type of atom
Explain how a covalent bond holds 2 atoms together.
the electrostatic force of attraction
between a shared pair of negative electrons
and both positive charged nuclei
electrolysis
break down of ionic compounds using an electric current
Electrolyte
liquid that contains free to move ions - which is broken by electricity in electrolysis
Process of electrolysis:
positive ions move to the cathode
negative ions move to the anode
when the ions reach the electrodes
they lose their charge and become elements
at the electrodes, gases may be given off or a metal is deposited
why is it difficult to electroplate plastic?
it does not conduct electricity (insulator)
Why are spoons electroplated?
to prevent corrosion (improve lifespan)
to improve appearance
Describe the bonding in a metal, and explain why metals conduct electricity.
metal is a lattice of positive ions
with negative delocalised electrons
electrostatic force of attraction between positive ions and electrons
electrons are free to move through the metal
Why do aluminium ions collect at the negative electrode?
they are positively charged
so are attracted to the negative electrode
gases covalently bonded together are …
simple molecules
by lowering the melting point…
less energy is needed
