All AO1 Flashcards
Why is it necessary to ionise the isotopes of an atom before they can be analysed in a TOF mass spectometer
(Ions will interact with and) be accelerated (by an electric
field)
Ions create a current when hitting the detector OR
ions create a current in the detector/electron multiplier.
Isotope
Have same number of electron and proton but different number of neutrons.
Why isotopes of an atom have same chemical properties
Have same electronic configuration and chemical properties depend on the number of electrons in an atom
Relative atomic mass
Average mass of an atom of an element compared to 1/12 of mass of one atom in C12 isotope
Find the mass of ^53Cr
(53x10^-3)/6.02 x10^23
Why TMS is used as standard NMR
It generates on shears peak
Peak is always found in far right of spectrum
It is highly volatile this means can be removed from sample being tested after analysis fairly easily
Non reactive so won’t affect the sample being analysed
Resonance
The nuclei in lower energy state can absorb energy in form of radio waves and flip between the lower and higher levels
This is called resonance
C spectrum
No of peaks is same as no of carbon environment
Location of peaks tell u about the location of carbon environment
TMS
Reference of NMR spectrum
Tetra methylsilane
Why solutions with Fe3+ ions have lower pH than Fe2+ ions
Fe3+ ions have smaller atomic radius and a greater charge
Fe3+ ions can polarise water molecules easily
More O-H bonds can be broken so more H+ ions
More H+ ions more acidic the solution is and lower the pH is ,
Trend of atomic radius across period 3
Decreases because of increase in nuclear charge however sheilding remains same
Trend of electronegativity across P3
Inceases
Trend of 1st ionisation energy
increases along the period
same shielding effect and increase in nuclear charge
Why Al has lower IE than Mg
Mg has a 3s electron removed
Al has 3p electron removed
3p is higher energy than 3s
Why S has lower IE than P
P has a 3p electron removed which is unpaired
S has a 3p electron removed which is paired
S has a lower ionisation energy than P becuse of electron pair repulsion
Cl recation with water
Cl2 + H2O = HClO + HCl
this reaction is reversible
Cl + H2O =
HCl + O2
2Na + 1/2O2 =
Na2O
observation when Na reacts with oxygen
orange flame and white solid ppt
2Mg + O2 =
and observation?
2MgO
White flame
white solid ppt
4Al + 3O2 =
observation
2Al2O3
if you sprinkle aluminium powder you get bright white flames/ sparks
white solid
Si + O2
Observation
SiO2
Orange flame
white solid ppt
P4 + 5O2 =
Observation
P4O10
white flame
white fumes poduce (no ppt)
S + O2 =
observation
SO2
pale blue flame
no ppt ( colourless gas)
Trend of bonding across P3
ionic to basic
Why does Al2O3 have more covalent character than MgO
Al3+ ions are smaller in than Mg2+
This means the Al3+ ions is more polarising than Mg2+ ions
This distorts the electron cloud around the O2- ion more so that there is more electron density shared between two ions
Why sodium oxide form alkaline solution when reacts with water
Sodium oxide contains O2- ions
These O2- ions react with water to form OH- ions
Name insoluble oxides
Aluminium oxide and silicon dioxide
Relationship between bonding and acid/basic properties of P3 oxides
The oxides that are ionically bonded are alkaline
The oxides that are covalentalt bonded tend to be acidic
Amphoteric oxides
Al2O3
Can act as acid and a base
write an ionic equation for the reaction of phosphorus oxide with an excess of NaOH solution
P4O10 + 12OH- = 4PO4^3- + 6H2O
Explain using the equation why SiO2 is classified as an acidic oxide
SiO2 neuttralises bases
SiO2 + 2NaOH = Na2SiO3 + H2O
Dynamic equilibrium
The rate of forward reaction is same a rate of backward reaction
the amount of reactants and products is constant
Le chatalier principle
The equilibrium shift to oppose change
condition for equilibrium
closed system
Why does a catalyst not affect the position of equilibrium?
Catalysts increase the rate of the forward and backward reactions equally.
Why are catalysts added to the Haber process, which is a reversible reaction that produces ammonia?
To reduce the time taken to reach dynamic equilibrium
This question is about the equilibrium which occurs at temperature T1 between compounds as shown in the equation.
A(g)2B(g) ΔH = –50 kJ mol–1
The mixture was allowed to reach equilibrium at a different temperature T2, and the position of equilibrium had shifted to the right.
State and explain which of T1 or T2 is the lower temperature.
Forward reaction is exothermic
Equilibrium has shifted right to oppose the decrease in temperature
T2 is lower
Why are compromising conditions important in equilibrium
higher pressures would be too expensive
450oC gives a good yield in a fast time
Why is Kc used for?
Kc is a measure of how much the equilibrium has shifted to the right or left.
How does an increase in pressure alter Kc? (1 Mark)
It remains unchanged
State the features of homologous series.
Have same chemical properties
Have same functional group
Same general formula
Members show change in physical properties like boiling point increases as C chain gets longer
Functional group isomers
Functional group changes but molecular formula is same
To have E/Z isomerism a molecule must have
A double bond that restrict rotation
Each carbon has 2 different groups attached to it
Alkane
alkanes are saturated hydrocarbons that contain Carbon-carbon and carbon-hydrogen single bonds only
Why boiling point of alkanes increases as carbon chain length increases
More electrons so stronger vander waals
Why increase in number of branches decreases boiling point
Less surface contact so weaker vander waals between chains
what is fraction
Mixture of hydrocarbon with similar boiling points
Explain why oil companies need to crack heavy fractions
Higher demand for more useful shorter chains (alkane and alkene)
Thermal cracking gives
2 alkenes and 1 alkane
Condition for thermal cracking
High temperature ( 700-1200 K)
High pressure (7000kPa)
Catalytic cracking gives
High % of branched alakane and cycloalkane
Condition for catalytic cracking
High temperature (700K)
catalyst = zeolite
mild pressure = 100kPa
CO2, H2O are greenhouse gases and cause
Ozone depletion global warming
why is incomplete combustion not desirable
produces
1 CO which is toxic ..binds to heamoglobin and reduces its oxygen carrying capacity
C particulate which can damage lungs and can make it difficult for asthma sufferers to breath
SO2
Can cause acid rain
SO2 +1/2O2 +H2O = H2SO4
causes erosion of building , kill plants and aquatic animals
Oxides of nitrogen
Nitrogen only reacts under high temperature
forms NO, NO2 and N2O4
N2 + O2 =2NO
NO + O2 = NO2
4NO2 + H2O + 1/2 O2 = 4HNO3
Nitogen oxides can bind with hydrocarbons and form photochemical fog
Unburnt hydrocarbons can cause
cancer because they are toxic
catalysts used in catalytic convertors
Pt and rhodium metal
How can the amount of further substitution be reduced.
Add alkane in excess so halogen radical get used up by attacking alkane
Why alkenes are ore reactive than alkanes
They are unsaturated so there is a scope to add atoms onto the molecule on either end of double bond to make it saturated
Conditions for electrophillic addition with sulphuric acid
H2SO4 catalyst
70 atm pressure
high temperature (300-600 C)
addition polymer
monomer = alkene
repeating unit = alkane
plasticers
They are used to make polymers more flexible or less rigid
Mechanical recycling for plastics
Plastics are sorted into different types
They are ground into pallet
Pallets are melted down and remould into new objects
Feedstock recycling of plastics
Plastics are sorted into different types
They are then heated to break the polymer bonds
They are then repolymerised to make new plastics
Why is reflux used to oxidise alchohol into carboxylic acid
It does not allow the reactants vapours to escape
Test for H2 gas
Add a lit splint
A squeaky pop occurs
Test for CO2
Bubble through lime water
Solution turns cloudy
Test for O2
Add a glowy splint
The splint will re light
What is low resolution mass spectrometery
Measure the Mr to 1 dp
Mr is same as m/z value
Why high resolution spectrometry cannot measure the mr of propan-1-ol and propan-2-ol
Because they have same mr because they have same molecular formula
Why does C has a relative molecular mass of 12
12C is standard reference
Why can nucleophillic addition of aldehyde and ketones can form receamic mixture
The bonding about C double bond O is planer
This means 50 50 chance of nucleophile attacking on either side of molecule or other
This results in equal proportion of both optical isomer being made and so receamic mixture is formed
Receamic mixture is not optically active. The rotation of polarised light cancel out.
Uses of quaternary ammonium salt
Hair conditioner and fabric softener
Also called catoinic sufacant
How to ensure the higher yield of primary amine
Use large excess of ammonia
What is the condition for further substitution in amines
Require excess haloalkane
How is nitrile converted into amine
Reduction reaction
Requires H2 and nickle catalyst
CH3 CN + 2H2 = CH3CH2NH2
Aycle chloride + water
Carboxylic acid
Acyl chloride + alchohol
Ester
Acyl chloride + ammonia
Amide
Acyl chloride + amine
N substituted amide
Why acid anhydrides are used more than Acyl chloride
Cheaper
Less corrosive
Don’t react with water
Less voilent so less exothermic
What is the stationary phase in TLC
Silica gel
how is a mixture seperated in chromatography?
Mixture is seperated either due to the difference in solubility in mobile phase or due to different affinities to stationary phase.
Rf value
Distance moved by the component/ distance moved by solvent front
Advantages of TLC
faster than paper chromatography
Will work on very small samples
Can be used to determine when a chemical reaction is complete
Limitation of TLC
similar compounds may have similar Rf values
Condition must be kept same to fairly compare the Rf value
It can be difficult to find the solvent which separates all components of mixture
Cannot be used to separate large quantities
Advantage of column chromatography
larger quantities can be separated
What happens to the solubility of a polar compound if polar solvent is used in TLC?
solubility of compound increases and it travels further up the TLC plate
What happens to the affinity of a polar compound if polar stationary phase is used in TLC?
Affinity increases and compound will not move very far
column chromatography and polarity
If polar solvent is used,the polar molecule will dissolve well and will be collected at the bottom first and if a polar stationary phase is being used, the polar molecule will have a higher affinity and it will take longer for the polar compound to be collected at the bottom.
Limitation of GC
Not all substances in the sample may ne separated and detected/peaks may be hidden behind others
Unknown compounds have no reference retention time
GC-MS
GC can separate the components of the mixture but cannot identify them conclusively
MS cannot seperate the components in mixture but can identify them.
USES of GC-MS
Forensics- minute particles at the scene of crime
can be identified, often providing evidence in court trial
Environmental analysis- Used to identify organic pollutants
Airport security- used to detect traces of explosive in luggage and on human
Space probes - spectometers have been sent to the Mars and Venus to collect and analyse materials and their environments
Why data book do not usuall contain values of Ka for a strong acid
Strong acid dissociates completely
Ka value for strong acids tend to infinity/ very large/ cannot be divided by zero
Explain how vander waals arise between between molecules
Electrons movement in first molecule forms a temporary dipole
This induces dipole in the other molecule
Attraction between opposite charges in adjacent molecules
Identify the reagent or test that could distinguish between aqeous solution of SO2 or SO3 with same concentration
Reagent: pH meter
SO2 2-3
SO3 0-1
ORRR
Universal indicator
SO2 orange red
SO3 red
