Zusammenfassung der Ressource
Colour by design: 6.8, 7.3. 13.6
- UV and visible spec
Anmerkungen:
- Explain why there are many shades of blue.
The shade depends on what other colours are absorbed besides red
- Describe the absorption spectrum of grey pigment.
Partially abssorbs all frequencies of light.
- Many unsaturated
molecules and those with
conjugated systems absorb
UV and visible light
- The delocalised electrons in
these systems require less
energy to become excited
compared with electrons in
single bonds
- Conjugated system has C=C
bonds, benzene rings or/and N=N
- Absorb UV, eyes do not
detect UV, appears
colourless
- Spectrometer measures the
quantity of light absorbed
by the solution at each
wavelength
- Source of radiation: UV and visible
- Causes electronic transitions
- Light split into two beams:
one through sample, one
through pure solvent
- Intensity of the spectrum depends
on concentration, and the distance
the light travels in solution
- X - axis wavelength nm
- Y- axis intensity of absorption
- Identify the colour of the solution,
find the wavelength at which
absorption is greatest.
- Absorption is most intense and the
wavelengh of lambda max increases for
molecules with large delocalised systems
- For organic molecules with delocalised
systems; the longer the conjugated chain,
the more intense the absoption, longer
the wavelength of lambda max
- Reflectance spectrum - UV and visible light
shone onto the surface of the sample and any
reflected light is collected and analysed
- Analyse pigments on old paintings
- Opposite of absorption spec
- Shape and width tells you shade
+ purity
- Gas-liquid chromatography
Anmerkungen:
- Different types of chromatography: paper, thin layer, gas-liquid, high-pressure liquid.
- Method of seperating and
identifying the components of a
mixture
- All types depend on
equilibrium set up and the
components a mixture
distribute themselves
between the stationary phase
and the mobile phase.
- Each component
has a different
affinity for
stationary phase.
- A higher temperature will tend to excite the molecules
into gas phase. Because they evaporate more readily or
because they are so energetic that the attractions of the
liquid no longer hold them
- At the beginning, compounds which spend
most of their time in the gas phase will pass
quickly through the column and be detected.
Increasing the temperature a bit will encourage
the slightly "stickier" compounds through.
Increasing the temperature still more will force
the very "sticky" molecules off the stationary
phase and through the column.
- Outlet can be directly
connected to a mass
spectrometer - this will give
the relative molecular mass
- Methyl esters of fatty acids are
used to run g.l.c traces rather than
the acid themselves.
- Because methyl esters are more volatile, than fatty
acids, have less of an affinity for the column.
Chromatograms can be produced more quickly
- Mobile phase - unreactive
carrier gas, coated on the
surface of finely divided
solid particles
- Stationary phase - small
amount of high boiling point
liquid
- 3 things can happen to the molecule;
condense at stationary phase, dissolve
in the liquid of stationary phase, remain
in gas phase
- Dissolve in the liquid, so
remains in stationary
phase for longer.
- Main parts: syringe containing
sample, inert gas carrier, column,
thermostatically controlled oven,
recorder, detector, outlet tube
- As each component emerges from the
column, a peak is recorded on a
chromatogram.
- The area under each peak is proportional to the
amount of that component in the mixture
- Use this to work out the relative amount of
each component
- The time that a component
takes to emerge is the retention
time
- Factors that affect retention
time: length and packing of
the column, nature and flow
of carrier gas, temperature
of the column.
- Need to calibrate with an instruments with
known compounds, and keep conditions
constant
- Oils and fats
Anmerkungen:
- How does the shape of a saturated trimester differ from that of an unsaturated trimester?
more linear
- Why are saturated fats solids?
Intermolecular bonds are stronger because they act over a shorter distance due to packing
- The degree of unsaturation can be determined by measuring the mass of iodine which react with 100g of oil or fat. Explain why
Each C=C reacts with an iodine molecule, more iodine used, the more unsaturated the oil or fat is.
- Naturally occurring triesters of
propane-1,2,3-triol and long chain
carboxylic acids
- Mixed triester has
different fatty acids
attached
- 3 alcohol groups in each
molecule, 3 carboxylic acid
can attach to each alcohol
group
- Natural oils and fats can be broken
down into the sodium salt of the fatty
acid and glycerol by heating with
dilute NaOH solution
- If the acid, rather than the carboxylate ion
is required, can treat the sodium salt with
dilute HCl
- Hydrogenation
- Addition of hydrogen to
unsaturated oils
- Use a Nickel catalyst, high
pressure and high temperature
- Heterogeneous
catalyst, different
physical state
- Produces a more solid fat - used in the
manufacture of margarine
- Not all C=C bonds are
hydrogenated, this gives
a more spreadable fat
- Saturated can pack closer
together. Unsaturated have Z
double bonds, causing
molecules to kink
- Attractive bonds
between molecules will
be weaker
- Oils have a higher
proportion of
unsaturated triglycerides