Analysing chemicals has many uses:
- to check general health or diagnose diseases by doing blood tests to check iron levels or cholesterol level to check for heart disease
- used by police on drunk drivers to findd the amount of alcohol in their blood. if it is more than 80mg per 100ml of blood then they can be prosecuted.
QUALITATIVE- to find out what substances are in a compund
QUANTITATIVE- to find out how much of each substance is in a compound
it has to have a unique result for each substance so that they you have a definite answer for what the compound contains and not what it might be,
Analysing Substances- positive ions
You can check for positive ions by mixing the mystery solution with a sodium hydroxide solution and the substance would form and insoluble metal hydroxide that would pprecipitate out of the solution. The colour of the preicipitate would determine what metal the mystery solution contained.
Calcium ions - white
copper II - blue
iron II- green
iron III - brown
aluminium - white preicipate which redissolves bakc into NaOH solution forming colourless solution
Ammonium - no precipitate but releases amonia when heated which turns universal indicator purple and has a distinctive smell
Analysing Substances - Negative ions
Testing for halides such as chloride, bromide or iodide in a solution add nitric acid then silver nitrate
Chloride forms a white precipitate of silver chloride
Bromide forms cream precipitate of silver bromide
Iodide forms yellow precipitate of silver iodide
(the acid is to get rid of the carbonate ions before the test)
Sodium - yellow
Potassium - lilac
Calcium - brick red
Copper - bluey green
testing for carbonates, sulfates and chloride ions
Carbonates- test for carbon dioxide by bubbling through limewater. mix with acid as carbonatess react with acid to form carbon dioxide
Sulfates- add dilute hydrhloric acid then barium chloride solution and if sulfate is present then it will form white precipitate of insoluble barium sulfate
Chloride- add dilute nitric acid then silver nitrate solution and if chloride is present it will form white precipitate of silver chloride which is insoluble
6.023 x 10(23)
one mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass for that substance.
MASS OF ELEMENT OR COMPOUND = NUMBER OF MOLES x RFM
NUMBER OF MOLES= MASS IN G / RFM
MASS CONCENTRATION= MASS (g) / VOLUME (dm3)
convert between mass concentration and mole concentration:
MOLE CONCENTRATION (mol/dm3) = MASS CONCENTRATION (g/dm3) / RFM
MASS CONCENTRATION (g/dm3) = MOLE CONCENTRATION (mol/dm3) x RFM
hard water wont easily form a lather with soap it reacts with the soap to form a precipitate called scum.
hard water contains magnesium and calcium ions when the water flows over rocks and through soils containing calcium and magnesium compounds
Magnesium sulfate dissolves in water so does calcium sulfate but only a little bit
Calcium carbonates commonly exists as chalk, limestone or marble. It reacts with acid rain to form calcium hydrogencarbonate which is soluble ad dissolves in water releasing calcium ions.
Hard water continued
temporary hardness can be removed by boiling as the calcium hydrogen carbonate decomposes to form insoluble calcium carbonates which is limescale. heating sulfate ions doesnt do anything though.
hardness can be removed using an ion exchange resin: water supplycan be fed through it. the resin contains lots of sodium ions or hydrogen ions ad exchanges them for calcium or magnesiuim ions in the water.
used to find out concentrations
- an acid base titration is a neutralisation reaction where hydrogen ions from an acid react with hydroxide ions from a soluble base
allows you to find out exactly how much acid is needed to neutralise a quantity of alkali
1. using a pipette and pipette filler add some alkali to a conical flask with 2 or 3 drops of indicator
the indicator used depends on the strength of the acid and alkali
2. fill a burette with the acid a
4. using the burette add the acid to the alkali a bit at a time giving the conical flask a regular swirl go slowly when you think the end point is near
5. indicator changes colour when all the alkali is neutralised. record volume of acid used to neutralise
first carry out rough titration. repeat 2 or 3 times if you get same answer results reliable.
Preparing soluble salts
make soluble saltsby reacting an acid with an insoluble base eg. a metal oxide or metal carbonate.
add the base to the acid and the solid will dissolve as it reacts
acid has been neutralised when excess solid sinks to the bottom
filter out solid to get solution containing only salt and water-
heat gently so water evaporates leaving salt to crystallise
making soluble salt using a soluble reactant
reacting acid with alkali
cant tell nif reaction has finished so have to add exaclty the right amount of acid so have to do a titration first
evaporate off water
one mole of any gas occupies 24dm3 = 24000cm3
volume of gas dm3 = mass / rfm of gas x 24
= moles x 24
when products of a reactant can react together to return to original reactants
closed system nothing can escape
dynamic equilibrium will be reached reaction occurring still but no overall effect as forward and reverse cancel each other out
pusition of equilibrium depends on temperature and pressure
temp: all reactions are exothermic in one direction and endothermic in the other
raise the temp endo thermic take in heat more
lower exothermic give out heat more
raise pressre will favour the side which produces less volume
lower pressure favours side which prodces more volume
catalyst speeds up both just reaches equilibrium faster
nitrogen and hydrogen reacted to make ammonia but reversible so not all will react to form ammonia dynamic equilibrium
manufacture ammonia: pressure 200 atmospheres temp 450 oC catalyst iron
higher pressures favour forward reactions so set as high as possible to give best % yield
high temp favours back reaction but low temps slow rate of reaction so have high temps to reach equilibrium faster
ammonia forms as gas but condenses and liquefies then removed
iron catalyst makes reaction go faster
used in nitrogenous fertilisers. increase plant growth
if fertilisers enter rivers or lakes eutrophication occurs. stimulate excess growth of algae on top which blocks sunlight so plants cant photosynthesise and decomposers feed on dead animals which use up oxygen so animals die
a group of compounds with the same general formula
all have similar chemical properties as have same lements and similar stricture
alkanes and alkenes
alcohols Cn H2n+1 OH
carboxylic acid have same formula Cn H2n+1 COOH end in -anoic acid
production of ethanol
fermentation- using yeast to turn carbohydrates into alcohol
sugar cane and sugar beet often used as carbohydrates
yeast contains an enzyme naturally occurring catalyst speeds up reactions
- mix yeast and a solution of carbohydrate in clean container seal and leave in warm place
- keep between 30oC and 40oC as optimum temp ( low temp slow reaction high temp enzyme dnatures)
- anaerobic conditions no oxygen as it converts ethanol to ethanoic acid vinegar
- concentration of alcohol at 10-20% reaction stops
brandy distilled from wiine whisky srom fermented grain and vodka fom \fermented grain or potatoes
different drinks have different concentrations of ethanol beer 4% some spirits 40%
fractional distillation concentrates ethanol: to make it above 20% fd to separate mixture by heating them as ethanol has lower boiling point than water. liebig condenser condenses ethanol vapour by cooling it. concentrated ethanol can be seaparated
fermentation uses renewable resource so wont run oout
quality isnt great. expensive to concentrate and purify ethanol
industrially: ethene reacted with steam to make ethanol
ethene made by cracking crude oil which reacts with steam. quite cheap process not much wasted. made in large chemical plant so continuously and quickly. high quality doesnt need further processing. made from crude oil non renewable start running out. so will make alcohol very expensive
issues with alcohol
BODY: less inhibited, reduces reactiions, activity of nervous system, poor balance, coordination, unconsciousness even coma, excess causes dehydration, damage brain cells drop in brain function, long term memory loss, severe liver damage leading to liver disease. rise in binge drinking
SOCIETY: loutish lairy fights, sti's sex, violence, crime, expensive as take up hospitals a and e, drink driving deaths etc. addicts lose home jobs family
ethene and ethanoic acid
plastics and plymers use lots of ethene. dehydrate alcohol. ethanol vapour passed over hot aluminium oxide catalyst reverse the reaction.
wine or beer left to open air ethanol oxidised to become ethanoic acid. acid in vinegar. commercial production of vinegar. used in flavouring and preserving food.
ethanoic acid is a type of carboxylic acid reacts like other acids with metals bases and carbonates
salts formed are ethanoates
turns universal indicator orange,red
blue litmus paper red
alcohol reacts with carboxylic acid. acid catalyst usually used eg concentrated sulfuric acid. release ester and water.
used in flavourings, aromas and perfumes as have smells or tastes
polyetsers used in fabrics and plastics
polyetsers are polymers that contain ester functional group.
plastic bottles made frorm polyester
fibres made into fabriccs for clothing as lighter than traditional materials.
recycled and turned into fleece thats used to make clothing
soaps are ester react with alkali. fats or oils type of ester boiled with concentrated alkali solyution to make soap. oil or fat breaks down in glycerol amd lomgchain carboxylix acod which carboxylic acid then react with alkaili to form salt and water
in water soap molecules from aniojns (negative ions) have hydrophobic part and hydrophilic part. hydrophobic doesnt like water but is attracted to grease usually long hydrocarbon chain
hydrophilic dissolves in water normally amall and ionic.
soap anions let water and oil mix as surround oil to form droplets.
vegetable oild hydrogentated for food industry
unsaturated oils with C=C double bond are less viscoius runnier than staurated oils. liquid unsaturated oils can be changed into saturated oils by breaking the doouble bond and adding hydrogen,. nickel catalyst used to speed up reaction called catalytic hydrogenation
nickel is solid so filtered out and used again. as oil cools to room temp turns into solid fat
polyunstaurated oils are hydrogenated to make margarine but not all double bonds broke so some is unsaturated so firm enough to spread on toast but low in saturates.