SC9: separate chemistry 2 Flashcards
flame test method
1) dip a clean wire loop into a solid sample of the compound being tested
2) put the loop into the edge of the blue flame from a bunsen burner
3) observe and record the flame colour produced
(sterilise by dipping into acid and putting into flame)
each metal ion produces a …
flame test colour
different
flame test: lithium
red
flame test: sodium
yellow
flame test: potassium
lilac
flame test: calcium
orange-red
flame test: barium
green
flame test: copper
blue-green
precipitate test for positive ions (steps)
1) add sodium hydroxide to the metal ion solution
2) look at the colour
precipitate test for positive ions: aluminium
white
precipitate test for positive ions: calcium
white
precipitate test for positive ions: copper
blue
precipitate test for positive ions: iron (II)
green
precipitate test for positive ions: iron (IIII)
brown
how to distinguish between aluminium and calcium ions
if excess is added to aluminium hydroxide, a colourless solution forms
test for ammonium ions
1) add dilute sodium hydroxide solution to the sample
2) warm the mixture over a bunsen burner
3) ammonia gas is given off if ammonium ions are present
4) damp red litmus turns blue is ammonia is present
testing for carbonate ions (negatively charged ions)
-an acid, such as dilute hydrochloric acid, is added to the test compound
-bubbles are given off due to carbon dioxide
-limewater is used to confirm that the gas is carbon dioxide, it turns milky when carbon dioxide is bubbled through it
testing for sulfate ions (negatively charged ions)
-add a few drops of dilute hydrochloric to the sample
-add a few drops of dilute barium chloride solution
-a white precipitate forms if sulfate ions are present
why is hydrochloric acid added before barium chloride solution in testing for sulfate ions?
to remove carbonate ions, which also forms a white precipitate with barium chloride solution, this way no false positive result is made
testing for halide ions (negative ions)
- add a few drops of dilute nitric acid to the sample
- add a few drops of dilute silver nitrate solution (silver reacts with halide ions to form precipitates)
negative ion test for halide ions: chloride
white
negative ion test for halide ions: bromide
cream
negative ion test for halide ions: iodide
yellow
why, in a test for halide ions, is the sample acidified with dilUte nitric acid first?
-carbonate ions also produce a white precipitate with silver nitrate solution
-the acid reacts with any carbonate ions present
-removing silver nitrate solutions stops them giving an incorrect positive result for chloride ions
why, in a test for halide ions, can’t dilute hydrochloric acid be used to acidify the sample?
-hydrochloric acid, contains chloride ions these would react with silver ions in the test, giving a false positive result
how to identify the ions in unknown salts
-flame tests (observe the flame colour)
-hydroxide precipitate tests (add a few drops of dilute sodium hydroxide solution & observe the colour of the precipitate formed)
-test for ammonium ions (add a few drops of dilute sodium hydroxide solution, then warm gently, ammonia gas is produced if ammonium ions are present; tested with litmus)
-test for carbonate ions (few drops of dilute hydrochloric acid, bubbles prod if carbonate ions are present; limewater turns milky)
-test for sulfate ions (few drops of dilute hydrochloric acid, then barium chloride solution, white precipitate formed if sulfate ions are present)
-test for halide ions (few drops of dilute nitric acid, few drops of silver nitrate solution, observe colour of precipitate)
instrumental methods of analysis
-faster, more accurate and more sensitive than simple chemical tests
-some are suitable for detecting and identifying elements, while others are better suited to compounds
the flame photometer
a scientific instrument based on flame testing
what can data from a flame photometer be used to do?
-identify metal ions in a sample
-determine the concentration of metal ions in dilute solutions
each metal ion produces a…
unique emission spectrum
emission spectrum
light given off by a substance, split into its component colours or wavelengths
how is the metal present in a sample identified?
by comparing its spectrum with reference spectra
what does it mean if two spectra match?
they must be from the same metal ion
what is an addition reaction?
one molecule combines with another molecule, forming one larger molecule and no other products
alkanes: homologous series
-saturated hydrocarbon
-have the same general formula
-differ by CH2 in molecular formulae from neighbouring members of the series
-show a gradual variation in physical properties, such as their boiling points
-have similar chemical properties
alkenes: homologous series
-unsaturated hydrocarbons
-have the same general formula
-differ by CH2 in molecular formulae from neighbouring compounds
-show a gradual variation in physical properties, such as their boiling points
-have similar chemical properties
general formula for alkenes
CnH2n
(where n is the number of carbon atoms in the molecule)
functional group of alkenes
C=C
functional groups of alkanes
C-C
what are functional groups responsible for?
the typical reactions of the homologous series
which reactions can alkanes vs alkenes go through
alkanes
-combustion
alkenes
-combustion
-addition reactions
distinguishing between alkanes and alkenes
-there is no change when bromine water is mixed with an alkane
-the bromine water becomes colourless when it is mixed with an alkene
polymer
a large molecule formed from many identical, repeating smaller molecules known as monomers
poly(ethene)
-a polymer made from a very large number of ethene molecules combined together
polymerisation reaction:
-ethene is the monomer
-poly (ethene) is the polymer
polymerisation reaction
many monomers combine together to form a polymer
how can you model addition polymers
-show the structure of its repeating unit
1) draw the structure of the monomer but use C–C instead of C=C
2) draw brackets around the structure with a long bond passing through each bracket
3) put an n next to the bracket on the right side
properties and uses of poly(ethene) / polythene
-flexible, cheap, can be made into thin films
-carrier bags, shampoo bottles, food wrap
properties of poly (propene) / polypropylene
-flexible, strong, resists shattering
-buckets, bowls, crates, ropes, carpets
properties of poly (chloroethene)/PVC
-tough, electrical insulator, can be made hard or flexible
-insulation for electrical wires, windows, gutters, pipes
properties of
poly(tetrafluoroethene)/PFTE
-slippery, chemically unreactive
-non-stick coatings for pans, containers for laboratory substances
polymers & biodegradability
-not biodegradable, microorganisms can’t break them down
-they cause a litter problem if disposed of carelessly
-last for many years in landfill sites
-space in landfill sites is wasted if it is filled with non-biodegradable polymers
polymers & combustion
-waste polymers can be incinerated, this involves combustion at very high temperatures
problems with combustion
-carbon dioxide is produced (greenhouse gas)
toxic gases are produced eg: sulfur dioxide
benefits of combustion
-incineration releases a lot of energy which can be used to heat homes or generate electricity
polymers & recycling
-the use of landfill and incineration wastes valuable resources
-crude oil is the raw material for making most polymers, it is finite
-recycling reduces the problems of disposal & reduces the volume of crude oil used
what does recycling of polymers include
-melting the waste polymer
-forming the polymer into a new product
benefits of recycling polymers
problems of recycling polymers
-different polymers must be separated from each other before recycling, this can be difficult and expensive to do
biological polymers
made naturally by living organisms
DNA
-a polymer made from four different monomers, called nucleotides
-these join together in different combinations to make long strands
-in a DNA molecule, two strands wrap around each other to form a double helix structure
starch
-polymer made from sugar monomers
-starch molecules contain many glucose molecules, joined together in long chains with branches
protein
-polymers made from different monomers, called amino acids
-these join together in different combinations to make long strands, which then fold into complex shapes
condensation polymers
-long molecules produced during condensation polymerisation
-form in a different way to addition polymers
-instead of forming just the polymer molecule, a polymer molecule and a small molecule (often water) form
forming esters
an ester forms when an alcohol reacts with a carboxylic acid
what two monomers are formed by polyester?
-a ‘dicarboxylic acid’ which contains two carboxylic acid groups (–COOH)
-a ‘diol’ which contains two alcohol groups, –OH
addition polymerisation vs condensation polymerisation
-addition polymerisation needs one type of monomer and forms one product
-to form polyesters, condensation polymerisation needs two types of monomer and forms two products
what do the alcohols form
a homologous series
homologous series’s…
-have the same general formula
-differ by CH2 in molecular formulae from neighbouring compounds
-show a gradual variation in physical properties, such as their boiling points
-have similar chemical properties
functional group of the alcohols
-the hydroxyl group, –OH.
-It is responsible for the typical reactions of alcohols
general formula for the alcohols
CnH2n+1OH
(where n is the number of carbon atoms in the molecule)
complete combustion of alcohols
alcohol + oxygen → carbon dioxide + water
chemical oxidisation of alcohols
-alcohols can also be chemically oxidised, without combustion in oxygen (with an oxidising agent), to produce carboxylic acids
how are oxidising agents shown?
[O]
ethanol + oxidising agent → ethanoic acid + water
CH3CH2OH + 2[O] → CH3COOH + H2O
how to name a carboxylic acid
-oic acid
where is ethanol found?
-alcoholic drinks
-used as a fuel for vehicles, either on its own or mixed with petrol
how can ethanol be produced?
fermentation
how can ethanol be concentrated?
using fractional distillation
what type of process is fermentation
anaerobic
fermentation equation
glucose → ethanol + carbon dioxide
yeast for fermentation
-yeast is a type of single-celled fungus, -it provides the enzymes needed for fermentation
-if the yeast cells become too cold, fermentation happens very slowly, or may not happen at all
-if the yeast cells become too hot, their enzymes become denatured and fermentation stops
typical conditions needed for fermentation
-sugars dissolved in water, and mixed with yeast
-an air lock to allow carbon dioxide out, while stopping air getting in
-warm temperature, 25-35°C
when does yeast die in fermentation?
when the ethanol concentration reaches about 15%
how long does fermentation take to finish?
several days or weeks (slow process)
what happens if air is present in fermentation?
the oxygen causes the ethanol to oxidise to ethanoic acid, so the drink tastes of vinegar
test for carbon dioxide
the gas is bubbles through limewater and the limewater turns cloudy
what does the fermentation mixture contain once fermentation has finished?
yeast cells and insoluble substances, which are separated from the impure ethanol solution by filtration
ethanol from fractional distillation
-fractional distillation is used to produce a concentrated solution of ethanol from the filtrate
-this works because ethanol and water have different boiling points
-when the mixture is heated, ethanol evaporates more readily
steps of ethanol’s fractional distillation
- water and ethanol solution is heated
- the ethanol evaporates first, cools, then condenses after being led out
- the water left evaporates, cools, then condenses
why is is better to use an electric heater than bunsen burner in fractional distillation?
ethanol liquid and vapour are highly flammable, and could be set on fire by accident
what are carboxylic acids
a homologous series
what is the functional group in the carboxylic acids?
-the carboxyl group, –COOH
-it is responsible for the typical reactions of carboxylic acids
what strength are carboxylic acids?
weak
carboxylic acid properties
-dissolve in water to form acidic solutions
-react with metals to form a salt and hydrogen
-react with bases to form a salt and water
-react with carbonates to form a salt, water and carbon dioxide
core practical: investigate the combustion of alcohols (aim)
-to investigate the temperature rise produced in a known mass of water by the combustion of ethanol, propanol, butanol and pentanol
-these alcohols can be supplied in spirit burners that have a wick and a lid
core practical: investigate the combustion of alcohols (steps)
- use a stand, boss and clamp to secure a conical flask over a spirit burner. adjust the height of the can so that the lid of the burner can be removed and replaced safely
- measure and record the mass of a spirit burner with its lid
- use a measuring cylinder to add 100 cm³ of cold water to the conical flask. measure and record its temperature
- place the spirit burner underneath the conical flask, remove the lid and light the wick
- stir the water carefully with the thermometer. when the temperature has increased by about 20°C, replace the lid to put the flame out
- measure and record the mass of the spirit burner with its lid, and the maximum temperature of the water
- repeat steps 2 to 6 with different alcohols, starting with fresh water each time
how to calculate the change in temperature per gram of each alcohol burned
change in temperature/mass of fuel burned
why should the height of the can
above the wick be kept the same for each experiment?
-the distance between the bottom of the can and the wick affects the amount of energy transferred to the water by heating
-it would affect the temperature rise if it was not kept the same
core practical: investigate the combustion of alcohols (hazards, risks & precautions)
hazard: alcohols are highly flammable liquids, and produce highly flammable vapours
risks: this can cause: burns to the skin, damage by fire
precautions: light the wick with a lighted splint; do not move a spirit burner while it is alight; keep the lab well ventilated
2.
hazard: methanol is toxic in contact with the skin
risks: damage to health
precautions: avoid skin contact
nanoparticles
tiny particles which are between 1 and 100 nanometres (nm) in size
the ____ it’s particles, the greater it’s surface area to volume ratios
smaller
how to calculate surface area to volume ratio
surface area divided by volume
what is a nanoparticulate substance?
a substance that consists of nanoparticles
nanoparticulate substances in sunscreen
-titanium dioxide blocks ultraviolet light, so it is used in sunscreens
-in bulk titanium dioxide is white -however, nanoparticulate titanium dioxide has no colour and cannot be seen when it is spread on the skin
-many people prefer nanoparticulate sunscreen because it is not obvious that they are wearing it
disadvantages of nanoparticulate sunscreen
-tend to clump together, making them difficult to apply
-it may be more difficult to tell where you have applied the sunscreen if you can’t see it on your skin
why can nanoparticulate substances act as catalysts
-they have large surface area to volume ratios
nanoparticulate catalysts compared to normal catalysts
-catalyse reactions more efficiently
-catalyse different reactions
-produce different products
-more expensive
nanoparticulate substances & self cleaning windows
-self-cleaning window panes have nanoparticulate coatings
-these catalyse the breakdown of dirt in the presence of sunlight
nanoparticulate substances for wound dressings
-silver has antibacterial properties
-nanoparticulate silver is used in some dressings for wounds
hazards of nanoparticulate silver
could harm or kill useful bacteria in the environment when these dressings are thrown away after use
possible risks of nanoparticles
-small size of nanoparticles makes it possible to breathe them in, or for them to pass into cells, once inside the body, they might catalyse reactions that are harmful
-toxic substances could bind to them because of their large surface area to volume ratios, harming health if the nanoparticles do get into the body
-modern nanoparticulate materials have only become common recently, so it is difficult for scientists to determine their risks
appearance of glass, clay & metals
glass: transparent
clay: opaque
metal: shiny
melting point of glass, clay & metals
glass: high
clay: high
metal: high
shapeability of glass, clay & metals
glass: brittle
clay: brittle
metal: malleable
electric conduction of glass, clay & metals
glass:poor
clay: poor
metal: good
thermal conduction of glass, clay & metals
glass: poor
clay: poor
metal: good
composite materials
-consists of two or more materials with different properties
-they are combined to produce a material with improved properties
what do most composite materials consist of?
-the reinforcement (fibres that make up the bulk of a composite material)
-the matrix, which binds the reinforcement together
examples of composite materials:
reinforced steel:
steel (r) & concrete (m)
fibreglass:
glass fibres (r) & polymer resin (m)
carbon fibre reinforced polymer:
carbon fibres (r) & polymer resin (m)
chipboard
wood chips (r) & resin glue (m)
separation of composite materials
-it is often possible to separate the reinforcement from the matrix by physical processes
fibreglass and carbon fibre
-the fibres in these composite materials have a low density
-strong in tension, but they are flexible
-polymer resin which binds the fibres together is not strong, but it is stiff
-the composite materials show a combination of these properties: they are strong, stiff and lightweight
chipboard
-wood itself is a natural composite material (it consists of a reinforcement of cellulose fibres bonded together by a matrix of lignin, the fibres are aligned alongside each other, so wood is stronger in one direction than it is in the other)
-chipboard contains randomly arranged wood chips bonded together by a glue, so it is strong in all directions
chipboard may be supplied with a thin polymer layer glued to its surfaces. suggest reasons that explain why this material is more suitable than chipboard alone for making self-assembly furniture
-the polymer can be coloured or patterned to look like wood
-it makes the surface waterproof so it protected from spills and can be cleaned more easily
reinforced concrete
-properties of concrete can be improved by reinforcing it with steel rods or mesh
-compressive strength of concrete is higher than its tensile strength
-the tensile strength of steel is higher than its compressive strength
-the combination of the two materials is strong in tension and in compression
-reinforced concrete is strong and slightly flexible, which is important when constructing large buildings and structures
