IB Chemistry: Option A

Fragment of molecule/ ion with mass of 15
Fragment of molecule/ ion with mass of 17
Fragment of molecule/ ion with mass of 29
Fragment of molecule/ ion with mass of 29
Fragment of molecule/ ion with mass of 31
Fragment of molecule/ ion with mass of 45
Factors that affect the colour of transition metal complexes
Identity of central ion
Oxidation no of central ion
Charge density of ligand
Geometry of complex ion
State the reasons for using analytical techniques
Determine the structure, analysing different compositions of substances, and determining purity of substance
Is info from one technique Sufficient to determine things?
No usually require multiple techniques.
Describe atomic and molecular processes that occur in which absorption of energy occurs.
1. Em radiation is absorbed = used to move electrons from lower to higher energy level.
2. Vibrational energy of molecules are increased when infrared rad is absorbed as they move to a higher vibrational energy level.
Describe how information from IR spectrum can be used to identify bonds?
Chemical bond has a natural frequency of vibration at which it vibrates.
Infrared red energy provides the correct amount of energy for only POLAR bonds to vibrate with greater amplitude.
Therefore polar bonds absorbs infrared radiation – and they are of specific frequencies.
By looking at a IR spectrum, which plots the transmittance (y) by the wavenumber (x) you can see which wavenumbers had the lowest transmittance and compare to bonds of a know wavenumber.
What happens at a MOLECULAR level during absorption of IR?
ONLY POLAR BONDS WILL ABSORB IR RADIATION. vibrational energy of bonds = change in dipole moment = change in BOND polarity THEREFORE ABSORBANCE.
Symmetrical stretch
Change in bond length
Asymmetric stretch
Change in bond angle
Change in bond angle
IR spectroscopy: does it give an idea about functional groups?
No tells you bond ie O-H but does not inform whether that is from an alcohol or a carboxylic acid.
Operating principles of double beam IR spectrometer?
Split a beam of monochromatic light into two beams of equal wavelength.
Pass one beam through a sample and the other through the reference.
Photomultiplier is used as the detector.
The TRANSMITTANCE is compared to the reference.
Reference takes into account absorption due to co2 and water vapour.
Then repeat with infrared radiation of a different wavelength.
What is the integrated trace?
It indicates the relative no of hydrogen atoms in the environment.
Effect of NMR spectroscopy due to environment surrounding hydrogen
If electrons surrounding = cut size of external mag field felt by hydrogen therefore need to increase external mag field.
If more electronegative atom attached then more exposed to magnetic field as electrons are further away and therefore need a lower magnetic field.
Neighbouring carbon atoms on split
0 H = no split
1 H = doublet
2 H = triplet
3 H = quartet
In fragmentation pattern are you measuring the mass:charge of individual atoms?
No one line will correspond to whole molecule.
Due to energetic collision between electron and molecule it can break up which would causes different fragments (obv with smaller mass).
State the uses of atomic absorption spectroscopy.
Identification of metals in water, blood, soil and foods.
Describe the principles of atomic absorption.
Obtain light made from element under investigation and pass through sample.
If element is present will absorb the light.
Degree of absorption relates to concentration of atoms present in sample irrespective of how they are bonded
Determine use of fuel in AA spectrophotometer
Fuel forms a combustion mixture to produce heat
To turn ions in the sample to atoms. To dehydrate sample
Monochromatic light source
Used to produce light of specific frequency made from element under investigation. Wavelength of maximum absorbance is used generally
Monochromatic detector in AA
Converts reference beam and beam that passes through sample into electrical signal by a photomultiplier.
Effect of different ligands on the splitting of the d orbitals in transition ion complexes.
Compare NH3, H2O, Cl-
Cl- has lowest charge density
Water – higher charge density
Ammonia – highest charge density
Increased charge density means increased split in d orbitals therefore absorbs shorter wavelengths
Factors that affect colour of transition metal ion complexes
Identity of metal ion
Oxidation number of metal ion
Identity of ligand.
Increase charge on metal ion =
Organic molecules that contain a double bond absorb…why? And list 3 examples
UV radiation.
Arenes, alkenes and chlorophyll
Conjugate systems means
Compound containing alternate double and single carbon bonds. System of connected p orbitals with delocalised electrons that increases stability therefore longer wavelength absorbed.
A compound with conjugate bonds is more likely to absorb…
Visible light
Beer lambert law – when is it used and what is the law ?
Used in uv-vis spectroscopy. Absorbance = data booklet
State reasons for using chromatography
To separate and identify components in a mixture
Explain that all chromatographic techniques involve adsorption on a stationary phase and partition between a stationary phase and a mobile phase.
Components in a mixture have different tendencies to adsorb on a stationary phase or dissolve in a solvent – this provides a means of separating the components of a mixture
Outline use of paper chromatography
Stationary phase = non volatile liquid – in paper 10% water
Mobile phase = liquid solvent
Water adsorbed by forming hydrogen bonds with OH groups in cellulose.
Moves up paper by capillary action
Spot of sample placed on paper at pencil mark
Lower part of paper below pencil line dipped into solvent.
Paper removed and dried.
Rf values calculated = distance moved by component / distance moved by solvent front.
Compared to known rf values.
Outline use of thin paper later chromatography
Adsorption chromatography
Small spots of test solutions placed on baseline.
Stationary phase: thin layer of adsorbent particles of alumina or silica supported on a glass plate.
Mobile phase = liquid solvent
Outline use of column chromatography
TLC on large scale
Column filled with adsorbent material (silica or alumina).
Tap is closed and column saturated with solvent.
Sample to be sep dissolve in min volume of solvent and added to top. Fresh solvent added to wash sample down – doesn’t stagnate at top.
Different components separate as they pass through column at different rates- collected as sifferent fractions.
Describe technique of gas-liquid chromatography
Used to separate and identify small samples of gases and volatile liquids.
Sample injected through self sealing cap into oven – gets vaporised. Vapour is carried through unreactive gas (mobile phase
Describe technique for high performance liquid chromatography
For non volatile substances OR substance which decompose at temps near boiling points.
Column tightly packed with fine solid particles. High pressure forces mixture to separate components. Ultraviolet light used to detect different components.
When to use GLC v. HPLC?
HPLC: identify temp sensitive compounds, analysis of oil, alcoholic bev, antioxidant, sugars and vits in foods, pharmaceuticals, polymers, biotech and biochemical research, quality control of insecticides and herbisicdes.

GLC: compounds that vaporise without decomp, analysis of urine samples from athletes for drugs, underground mine gases and blood alcohol levels

When is column chromatography proffered
Using large amounts of sample.
Discuss calibration of GLC
Sub of known concentration (that you are testing lets say ethanol in blood) passed through column. Ratios directly proportional to relative concentration – predict concentration by comparing to known.
Detection of components in GLC and HPLC
GLC: Detected using flame ionisation. Gas is ionised as it passes through hydrogen flame. Resulting current = measure of component present.
Or using mass spectrometer.
HPLC: same but with uv light.
Possible stationary and mobile phase for HPLC
Stat: silica / silicon dioxide/ long chain hydrocarbon.
Mobile: hexane, water, alcohol, solvent.
Possible mob and stat phase for GLC
Stat: long chain hydrocarbon/ alkanes.
Mob: nitrogen gas/ helium gas/ argon gas
Greenhouse gases name five
Co2, ch4, h20, o3, N20,
Describe how Greenhouse gases cause greenhouse effect
1. Greenhouse gases do not absorb uv light therefore uv light from sun is allowed heats up planet surface.
2. When radiation is re radiated from earth = infrared radiation.
3. Greenhouse gases absorb IR radiation.
4. Part of absorbed radiation reemitted to earth = increase temp
Region of em
Spectrum used in HNMR
Radio waves
Why is TMS used as reference standard. Tetremethylsilane.
Si surrounded by four methyl groups.
Strong single peak – 12
Protons in identical chemical environment.
Low boiling point.
Non toxic.
Does not interfere with sample.
Which nuclei can be used in NMR and why?
Odd number of proton in nucleus. Odd no of proton therefore Proton behaves as tiny bar magnet. ( higher understanding – do not need to know).
Why do molecules absorb IR radiation ?
Vibration / stretching of molecules produces change in dipole moment – allows absorption of IR.
Source of SO3/SO2 in atmosphere
Combustion of COAL containing sulphur – fossil fuels will not be accepted
Aerobic decay of C, N, S, P
CO2, SO42-, NO3-, PO43-
Anaerobic decay of C, N, S, P
CH4, NH3, H2S, PH3
Methods for reducing CO : name 3
1. Thermal exhaust reactor
2. Lean burn engines
3. Catalytic convertor