Chemistry Flashcards
what is the trend in melting point down group 1?
melting point decreases down group 1
+ve metal ions increase in size & less charge dense
so delocalised e-s less strongly attracted to +ve metal ions
so less te needed to overcome the weak electrostatic attraction
which group 1 elements float on water?
Li, Na, K
properties of group 1 metals that I missed
low density
low mp
ductile
malleable
properties of transition metals that I missed
can form different ions
form coloured compounds
not very reactive
what is the trend in boiling point down group 7?
boiling point increases
molecules increase in size
so stronger forces b/w molecules
more te needed to overcome them
why are group 8 elements unreactive?
do not need to lose, gain or share e-s to gain full outer shell
already have full outer shell of e-s
colourless gases
what are the limitations of:
dot & cross diagrams
ball & stick models
2d & 3d representations?
d&c: do not show how ions are arranged in space
b&s: cannot see position of e-s / lone pairs
2d: cannot see where ions are located on different layers
3d: not to scale
no information about the forces of attraction b/w ions or the movement of e-s to form the ions
what are the limitations of the particle model in relation to changes of state?
it does not show the size and shape of particles or the space b/w particles
it is not to scale
it does not take into account the forces between particles
it shows particles as same size & inelastic
it assumes particles are spheres
what are nanoparticles?
particles that are 1nm-100nm in diameter
smaller than typical particles
how does the size of nanoparticles compare with the typical dimensions of atoms & molecules?
nanoparticles: 1nm-100nm
typical atoms & molecules:
fine particles >100nm
coarse particles 2500nm-10,000nm
sa:v of nanoparticles?
large
what are the uses of nanoparticles?
as catalysts
in nanomedicine
in electrical circuits
silver nanoparticles have antibiotic properties
how do properties of nanoparticles relate to their uses?
as catalysts: high sa:v ratio
so large area exposed in reaction
so for the same effect, a smaller amount of nanoparticles is needed than larger particles
in nanomedicine: fullerenes (nanoparticles) are v small so can deliver drugs to the inside of cells
in electrical circuits: some conduct electricity so can make tiny components e.g. computer chips
silver nanoparticles have antibiotic properties so are used to make surgical masks & wound dressings
what are the possible risks associated with some nanoparticulate materials?
relatively new so effects on our bodies aren’t fully understood
currently not regulated strictly
nanoparticles in sun cream could damage our cells or damage environment when washed into sea
what is the order of elements in the reactivity series?
potassium
sodium
lithium
calcium
magnesium
aluminium
carbon
zinc
iron
hydrogen
copper
silver
gold
platinum
reactivity of metals with water or dilute acids is related to
the tendency of the metal to form its +ve ion
what is the preparation for testing metal cations?
clean metal loop with HCl
heat with Bunsen burner roaring flame
charge of anode vs cathode
anode = +ve
cathode = -ve
what is a fuel cell?
continually produce a voltage if supplied with:
- constant fuel supply
- oxygen
fuel oxidised electrochemically not by being burned
so the reaction takes place at a lower temp. than combustion
energy is released as electrical energy
describe hydrogen-oxygen fuel cell
hydrogen-oxygen fuel cell, hydrogen and oxygen are used to produce a voltage
water is product
overall reaction: hydrogen + oxygen → water
2H2(g) + O2(g) → 2H2O(l)
what are the advantages & disadvantages of fuel cells?
advantages:
use of hydrogen-oxygen fuel cells reduces
- carbon dioxide emissions
- air pollution where the car is being driven
- reliance on fossil fuels
disadvantages:
- hydrogen is gaseous at rtp so difficult to store in the car
- fuel cells & electric motors are less durable than petrol engines and diesel engines so not long-lasting
- expensive
- no countrywide network of refuelling stations
- some methods of producing hydrogen fuel release CO2
what is a chemical cell?
they use chemical reactions to transfer energy by electricity
the voltage of the cell depends on factors e.g. material electrodes are made from, the substance used as the electrolyte
how can a simple cell be made?
by connecting two different metals in contact with an electrolyte
rechargeable vs non-rechargeable cells
non-rechargeable: voltage produced until the reactants are used up
rechargeable: chemical reactions can be reversed when an external circuit is supplied
describe the simple electric cell (electrodes coated in 2 different metals)
more reactive metal undergoes oxidation bc it loses electrons readily
= it becomes the anode
less reactive metal = cathode bc less likely to lose electrons
the further apart the metals are in the reactivity series, the greater the voltage of the cell
table of steel properties & uses
see camera roll 19/10/24
examples of exothermic & endothermic reactions
exothermic:
combustion
thermite
hydration of anhydrous compounds
respiration
neutralisation
displacement
metals + acids
endothermic:
photosynthesis
thermal decomposition
acid + carbonate reactions
electrical decomposition
what are the stages that are analysed as part of a life-cycle assessment?
- making materials for the product from raw materials
- manufacture the product
- transporting the product
- using the product
- disposing of the product
what is analysed at each stage of LCA?
use of raw materials inc. water
use of energy
release of waste substances into environment
what is the impact of each type of disposal on the environment?
landfill - using up land
incineration - release of waste gases = pollution
recycling - use of energy & production of waste
reusing - reduces impact on environment
what factors must be considered to evaluate whether recycling is viable?
balancing the use of the raw materials such as finite resources & need to conserve them
availability of the material to be recycled
issues with collecting the material
removal of impurities (economical & practical)
energy use for transport & processing
environmental impact of the processes
level of demand for the recycled material
describe steps needed to recycle a metal
collect used items & transport to a recycling centre
break up items & sort different metals
melt metal & remove impurities
solidify the metal in ingots (slabs of metal)
advantages & disadvantages of recycling
advantages:
fewer quarries & mines
less noise, traffic & air pollution
fewer habitats destroyed
metal ores conserved
disadvantages:
collection & transport of item needs fuel, workers, vehicles
difficult to sort metals
sorted metals might need to be transported
how are polymers disposed of?
incineration - releasing CO2 & toxic gas
most ores are
metal oxides
so all extraction reaction reduce the metal
copper oxide + carbon →
copper + carbon dioxide
iron(III) oxide + carbon →
Fe2O3(s) + 3CO(g) →
iron + carbon monoxide
2Fe(l) + 3CO2(g)
what are the stages of phytoextraction?
plants grown in soil contain low-grade ore (low % metal)
plant absorbs metal ions & concentrate them in cells
plants harvested & burnt
ash contains metal compounds
what are the benefits of phytoextraction?
although slow, it
reduces mining to obtain ore
conserves high-grade ores
reduces rock waste
describe the process of bioleaching & 1 advantage & disadvantages
bacteria can break down low-grade ores to form acidic solution containing copper ions
the solution is called a leachate
bioleaching does not need high temperatures but it:
produces toxic substances, including sulfuric acid, which damage the environment
how are metal compounds produced by bioleaching processed?
iron more reactive than copper so iron displaces copper from the leachate
iron + copper sulfate → iron(II) sulfate + copper
or
copper compounds can be dissolved & solution electrolysed to produce Cu
conditions that cause corrosion & product of corrosion
presence of water & oxygen
hydrated metal oxide
e.g. rusting
iron + oxygen + water → hydrated iron(III) oxide
how can rusting & corrosion be prevented?
barrier to oxygen & water:
painting
coat in grease/oil
sacrificial protection:
galvanisation
coat with more reactive metal so it corrodes instead of the protected metal
equation of Haber process
N2 + 3H2 ⇌ 2NH3
describe the steps in the Haber process
N2 (from air) & H2 (from natural gas) are pumped through pipes
the pressure = 200atm
temp. = 450°C
iron catalyst
mixture is cooled so that ammonia liquefies & removed
unreacted nitrogen & hydrogen are recycled
how are nitrogen, phosphorus & potassium compounds important in agriculture?
in fertilisers to promote plant growth
how is ammonia used to make fertilisers?
it is oxidised to make nitric acid, which is the source of nitrate ions (NO3-)
it can be neutralised by nitric acid to make the salt ammonium nitrate (NH4NO3)
NH3 + HNO3 → NH4NO3
when this happens in aqueous solution, the equation is:
ammonium hydroxide + nitric acid → ammonium nitrate + water
NH4OH + HNO3 → NH4NO3 + H2O
what are the raw materials used in the industrial production of fertilisers?
raw materials
mining
potassium chloride & potassium sulfate = fertilisers
phosphate rock cannot be used as a fertiliser because it is insoluble but it can be used to make fertilisers
or lab synthesis
how does phosphate rock react with acids to form useful soluble compounds?
with nitric acid –> calcium nitrate & phosphoric acid –> ammonium phosphate
with sulfuric acid –> single superphosphate (calcium sulphate & calcium phosphate)
with phosphoric acid –> triple super phosphate (calcium phosphate)
how is sulfuric acid synthesised & what are the conditions of its reaction with ammonia?
sulfur + oxygen → sulfur dioxide
sulfur dioxide + oxygen ⇌ sulfur trioxide (at 450°C)
sulfur trioxide + water → sulfuric acid
ammonia gas + sulfuric acid is continuous process that happens at 60°C, to form ammonium sulfate on a very large scale
ammonia sulfate in lab is made by reacting measured vol of ammonia solution & sulfuric acid solution - process?
- 25cm^3 ammonia –> pipette –> conical flask
- methyl orange indicator (yellow in alkaline ammonia)
- add dilute sulfuric acid from burette until methyl orange = orange
- record vol. sulfuric acid added
- repeat without indicator
compare 2 methods of making ammonia sulfate (industrial vs lab)
see camera roll 21/10/24
desulfurisation equation
CaO + SO2 –> CaSO3
where did the atmosphere come from?
one theory: from intense volcanic activity, releasing gases which have lots of CO2, little or no O2, small amounts of ammonia & methane
how did oxygen concentration in the atmosphere increase over time?
photosynthesis by primitive plants & algae released oxygen, gradually building up over time
how did CO2 concentration in the atmosphere decrease over time?
formation of sedimentary rocks - CO2 dissolves in water to form carbonate compounds
uptake by living organisms - organisms’ food chains turned into fossil fuels billions of years ago, which contain carbon
how is the availability of potable water increased?
from freshwater:
passing water through filter beds to remove insoluble particles
sterilising water to kill microbes (chlorine, ozone, UV light)
describe desalinisation
= obtaining potable water from sea water
distillation
reverse osmosis: water put under high pressure & passed through partially permeable membrane
how is waste water treated?
screening & grit removal removes large particles
sedimentation settles tiny particles from still water
sewage sludge is digested anaerobically by bacteria
effluent (liquid on top) is treated with aerobic bacteria to reduce volume of solid waste
enthalpy change of reaction =
= energy required to break bonds - energy required to form bonds
= break - make
