further chemistry Flashcards
what are bulk chemicals?
made on large scale eg:
- ammonia
- sulphuric acid
- phosphoric acid
what are fine chemicals?
made on small scale eg:
- drugs
- fragrances
- food additives
why does the government issue strict regulations?
control:
- storage of chemicals
- chemical processes
- transportation of chemicals
explain the government law?
HSE responsible for regulating risks to health and safety eg hazard symbols
law passed to companies to encourage to reduce amount of pollution
what are chemists required to do?
- follow standard precautions
- carry out titration
- scale up production
- interpret results
- carry out quality assurance
what does the production of useful chemicals have?
- synthesis
- monitoring purity
- handling of by products and waste
- preparation of feedstocks (starting materials)
- separation of products
what is green chemistry?
based on # of principles that lead to more sustainable process
what does the sustainability of a chemical process depend on?
- atom economy
- use of renewable feedstock
- energy inputs and outputs
- health and safety risks
- waste prevention
- environmental impact
- social and economic benefits
what is the atom economy?
measure of amount of reactants that end up as useful products
mass/total mass x 100
final product should:
- contain all atoms used
- reduce waste products + increase yield
how do you calculate percentage yield?
actual yield/theoretical yield x 100
explain renewable raw materials?
should be used whenever possible
developing new materials from plants but plants take up land, fertilisers used to increase productivity but use a lot of energy
explain the energy needed to carry out a reaction?
should be minimised to reduce environment + economic impact, process should be carried out at ambient temp + pressure
what do catalysts do?
- reduce activation energy needed for reaction so process is faster + can take place at lower temp
- remain unchanged + can be used again so process is sustainable
explain risks in green chemistry?
substances should be chosen to minimise risks of chemical accidents
methods developed to detect harmful products before made
environmental impact reduced by using alternatives to harzardous chemicals
what can methanol be used as?
- chemical feedstock
- manufacture of cosmetics
what can ethanol be used as?
- solvent
- fuel
what can ethanol be produced by?
- fermentation
- biotechnology
- synthesis
what are the physical properties of alcohols?
- short alcohols have low boiling point bc intermolecular forces weak + don’t need energy to over come
- long hydrocarbons less soluble in water bc behave more like an alkane o tend to float on top of water due to low density
how do alcohols, alkanes and water react with sodium?
alcohol - sodium sinks in it, doesn’t melt, steadily gives off hydrogen
alkane - no reaction
water - sodium floats on it, melts, rushes around on surface + rapidly gives off hydrogen
how do alcohols react with sodium?
to produce salt + hydrogen gas
eg:
ethanol + sodium —> sodium ethoxide + hydrogen
why do alcohols burn in the air?
because of the presence of a hydrocarbon chain
what is equation that shows what happens when ethanol burns in the air?
C2H5OH + 3O2 —> 3H2O + 2CO2
what are the steps to the production of ethene which can be used to produce ethanol?
1) crude oil undergoes fd
2) long chain hydrocarbons are vaporised + cracked using catalyst + heat
3) molecules purified using fd
4) ethene produced used for feedstock + remaining water removed
ethane then reacted with steam at high temp in presence of catalyst to produce ethanol:
- ethene + steam —> ethanol
how is ethanol for used in alcoholic drinks produced?
1) water + yeast mixed with natural sugars at room temp
2) enzymes found in yeast catalyse formation of ethanol and carbon dioxide
3) carbon dioxide allowed to escape from reaction vessel but air is prevented from entering
glucose —> ethanol + carbon dioxide
what are social benefits of green chemistry?
- cleaner air quality
- cleaner buildings
- improve water quality in rivers + lakes
what are economic benefits of green chemistry?
- reduced energy costs
efficient chemical products could be designed to do what?
- minimal harm to people or environment
- able to be broken down into non toxic substances that don’t stay in the environment
what are alkanes?
group of hydrocarbons
carbon atoms join together by single carbon - carbon bonds
contain only single bonds so they are saturated hydrocarbons
why don’t alkanes react with aqueous reagents?
because C-C and C-H bonds are strong + unreactive but they burn in air to produce:
- carbon dioxide
- water
what are alkenes?
group of hydrocarbons
have reactive C=C double bonds, described as unsaturated
formula - CnH2n
what is the equation for the combustion of alkanes?
CH4 + 2O2 —> CO2 + 2H2O
what are alcohols?
characters due to presence of functional group -OH
formula - CnH2n+1OH
what are the 2 simplest alcohols?
- alcohol
- methanol
when ethanol solution is manufactured by fermentation, what is the concentration limited by?
- amount of sugar in mixture
- fact that above a certain conc, ethanol kills the yeast
when fermentation reaction over, conc of ethanol increased by distilling mixture
what are 2 examples when the distillation process is used to produce spirits?
- whisky
- brandy
how are optimum conditions needed for the fermentation process?
- if temp too high, enzyme denatured + reactant no longer fits
- if pH changes, enzyme denatured
- if oxygen present, ethanol oxidised to from ethanoic acid
what does the biotechnology method use to produce ethanol?
- waste biomass
- genetically modified E. coli bacteria
explain E.coli + biomass?
E.coli bacteria have had new genes introduced which allow bacteria to digest sugars in biomass + convert to ethanol
meaning wider range of biomass eg wood waste, can be converted to ethanol rather than remaining as waste
what are the optimum conditions for the process of biotechnology?
- temp should be 25-37
- optimum pH level needs to remain constant otherwise enzyme denatured
what are carboxylic acids?
characteristic properties are due to presence of functional group - -COOH
what are the 2 simplest carboxylic acids?
- methanoic acid
- ethanoic acid
what are examples of the unpleasant smells of carboxylic acids?
- taste of vinegar
- smell of sweaty socks
- taste of rancid butter
what are the chemical reactions of carboxylic acids?
weak acids meaning less reactive and their pH values aren’t as low as than strong acids like nitric + sulphuric
react with metals, carbonates + alkalis to produce salts
what do carboxylic acids react with?
- metals to form salt + hydrogen
- carbonates to form salt, water and carbon dioxide
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what do carboxylic acids react with alcohols to form?
esters
this reaction carried out in presence of a strong acid catalyst
carboxylic acid + alcohol —> ester + water
what are esters?
- have distinctive smells responsible for smells and flavour of fruits
- used in manufacture of perfumes + food products
- found in solvents + plasticizers
what are fats?
naturally occurring esters, living organisms make them to use as an energy store
esters of:
- fatty acids
- glycerol
what are animal fats?
mostly saturated molecules:
- have single C-C bonds
- molecules are unreactive
what are vegetable oils?
mostly unsaturated molecules:
- have double C=C bonds
- molecules are more reactive
what is the method preparing for esters?
1) ethanol heated under reflux in presence of sulfuric acid, reflux is a process of continual evap+cond
2) ester removed by distillation
3) distillate transferred to a separating funnel where purified
4) product transferred to flask + calcium chloride added to remove remaining water molecules, calcium chloride then removed by filtration
what are exothermic changes? (combustion)
- release energy as heat, detect bc a temp rise
- release energy bc products have less energy than reactants
what are endothermic changes?
- less common
- take in energy so feel cold to the touch, detect energy change bc temp falls
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what is qualitative analysis?
method used to identify chemicals in a substance
what is quantitative analysis?
method used to determine amount of chemical in a substance
what should you do when collecting data?
important that samples are representative of the bulk of the material under test, achieved by collecting samples at random
what should the container be after a sample has been taken?
stored in sterile container to prevent contamination
- sealed
- labelled
- stored in safe place
using system of common practices increases reliability as theres less room for human error
what is chromatography?
used to find out what unknown mixtures are made of
substances separated as they move through stationary phase at diff speeds while dissolve in the mobile phase
what is the mobile phase?
solvent used to move solution is called mobile phase
solvents can be:
- aqueous = water based
- non aqueous = made from organic liquid eg alkanes
what is the stationary phase?
medium that the solvent moves through eg paper
explain the mobile and stationary phase?
each component of the sample, dynamic equilibrium is set up between stationary and mobile phase
overall separation depends on distribution of compounds in the sample between mobile and stationary phases
what are the 5 stages of paper chromatography?
1) if substance analysed is solid, dissolve in a suitable solvent
2) place a spot of resulting solution on a sheet of paper on the pencil line and allow to dry
3) place bottom edge of paper into a suitable solvent
4) as solvent rises up paper, dissolves the ‘spot’ + carries it up the paper
5) diff chemicals in the mixture separate bc molecules have diff sizes + properties
what is thin layer chromatography?
stationary phase is thin layer of absorbent material supported on a flat unreactive surface
what are the advantages of thin layer chromatography?
- faster runs
- more even movement of mp through sp
- choice of diff absorbencies for sp
tlc usually produces better separations for wide range of substances
what is chromatogram?
formed when chemicals come out of solution + bind to sp. the chromatogram can then be compared to standard chromatograms of known substances to identify the diff chemicals
what are examples of when chromatograms are developed using locating agents to show the presence of colourless substances?
- colourless spots sometimes be viewed under UV light + marked on the place
- chromatogram can be viewed by being sprayed with a chemical that reacts with spots to cause coloration
what is Rf value?
movement of a substance relative to the movement of the solvent front
how can you calculate the Rf value?
distance travelled by substance/distance travelled by solvent
calculating it can help identify unknown substances + can be compared to known values for diff substances
what happens in gas chromatography?
- mp is a carrier gas
- sp is a microscopic layer of liquid on an unreactive solid support
- liquid is inside glass or metal tubing called a column
what can gas chromatography do?
sample of substance to be analysed is injected into 1 end of heated column where it vaporises. carrier gas then carries through column where separation takes place
gc able to separate components in a mixture bc of their different solubilities
what are the advantages of gas chromatography?
- greater separating power
- ability to separate complex mixtures
- ability to produce quantitative data from small samples of liquids, gases and solids
what are the uses of gas chromatography?
- detecting banned substances in blood samples
- analysing oil spills to identify sources of pollution
how can you analyse gas chromatography?
size of each peak shows relative amount of each chemical in the sample
what is the retention time?
time taken for each substance to pass through chromatographic system
in gc, retention time is time taken from substance being injected into system to when detected
tables show retention times of diff chemicals relative to the retention time of a specific compound
what are the 6 main stages of quantitative analysis?
1) choose an analytical method + take sample that represents bulk material
2) measure
3) dissolve, taking care not to lose any sample
4) measure property of solution that’s proportional to amount of chemical in the sample
5) calculate a value
6) estimate uncertainty of results
- work out average value
- state how confident you are
- find range
what are reversible reactions?
products can react together to produce original reactants - ⇌
eg decomposition of ammonium chloride is reversible:
ammonia chloride ⇌ ammonia + hydrogen chloride
what is the haber process?
converts atmospheric nitrogen to ammonia by reacting with hydrogen from natural gas
N2 + 3H2 ⇌ 2NH2
as reversible, small amount of gas leaving reactor is ammonia. unreactive nitrogen and hydrogen recycle to improve yield, most cost effective leaving reaction long enough to reach dynamic equilibrium
what is ammonia used for?
- fertilisers
- explosives
- dyes
- medicines
how do you calculate the concentration of a solution?
concentration = mass/volume
what are standard concentrations?
conc of standard solutions known accurately so can be used to measure conc of other solutions
what is the procedure used to make up a standard solution?
1) weight 5g of solid in beaker
2) transfer solid into flask. pour washings into flask to make sure all solid is transferred
3) add distilled water to flask until 3 quarters full. place stopper in top. place stopper in top + gently shake until all solid dissolved
4) place flask on level surface + fill water until level of solution reaches 100cm3 mark
5) invert flask to mix content + ensure evel conc
what is the method for titration?
1) fill burette with alkali + take reading
2) weight 4g + dissolve
3) use pipette to measure 25cm3 of aqueous acid + put in flask. add drops of indicator to flask, place flask on white tile under burette
4) add alkali from burette to acid in flask. swirl. near end, indicator will show alkali colour. when colour changes, acid neutralised.
5) record vol of alkali added by subtracting amount in burette at end of reaction from starting
6) repeat
what is titration?
acid alkali titration important method of quantitative analysis
how can you measure pH?
pH probe used to measure change in pH, pH vol graph used to show how much alkali has been added to neutralise acid
what can you find from a pH/volume graph?
- volume of alkali added
- end point of reaction where rapid change occurs
what are the 2 general sources of measured uncertainty?
- systematic error
- random error
what are systematic errors?
repeat measurements too high or low, results from incorrectly zeroed balance eg scales showing 0.06 than 0.00
all repeats would be incorrect by same amount
what are random errors?
- mean repeat measurements give diff values
- introduced when meniscus isn’t on calibration line
- 1 off errors + wouldn’t be same for all repeats
what does validity depend on?
accuracy of results, inaccurate results can be result of errors of measurement or mistakes
what can mistakes include?
- misreading scale
- forgetting to fill burette to correct level
- taking thermometer out to read sale
what is accuracy, precision and uncertainty?
accuracy - how lose result is to actual value
precision - measure of spread of measured values. big spread leads to greater uncertainty
degree of uncertainty assessed by working out average and stating range
explain the making and breaking of bonds?
in reaction, bonds in reactants must be broken + new bonds made to form the products
activation energy is energy needed to break bonds to start reaction
- breaking bonds - endo
- making bonds - exo
