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testing for C=C bonds
bromine water test
iodine number
bromine water test
unsaturated compound + Br2 → brominated product (addition reaction)
orange/brown → colourless
saturated compound + Br2 → no reaction
orange/brown colour persists
iodine number
m (I2) reacts with 100g chemical substance
1 mol of I2 = 1 mol of C=C
testing for hydroxyl groups
sodium metal test
oxidation test
esterification test
sodium metal test
if sample is alcohol, mixing it with Na (s) will create H2 (g)
pop test to confirm
oxidation test
primary alcohol → oxidising agent (Cr2O72-/H+) (low temp) aldehyde → oxiding agent (Cr2O72-/H+) (high temp) carboxylic acid
orange → green
secondary alcohol → oxidising agent (Cr2O72-/H+) ketone
orange → green
tertiary alcohol → no reaction
orange persists
esterification test
if fruity smell detected, ester is produced
testing for carboxyl group
pH test
metal hydrogen carbonate test
esterification test
pH test
acid-base indicators
carboxylic acids are weak and only partially ionise
↑ [H+]/[H3O+], ↑ acidity, ↓ pH
metal hydrogen carbonate test
if sample is a carboxylic acid, mixing it with HCO3- will produce CO2 (g)
can confirm it is CO2 (g) if it turns limewater cloudy
melting point determination
allows for identification of compound by comparing with literature value
purity of compounds can be determined
simple distillation
mixture heated to target temp to vaporise component to be seperated
vapour passes through condenser
distillate obtained
cannot seperate compounds with similar BP
fractional distillation
mixture heated to target temp to vaporise component to be seperated
vapour moves up the fractionating column, some condenses & flows down until hot enough to vaporise again
after each boil-condense cycle, the more volatile substance will be at the top
vapour passes through condenser
distillate obtained
features of the fractionating column
colder at the top
glass beads to increase surface area
standard solution
solution with accurately known concentration by dissolving water & a primary standard
primary standard
substance with high purity & stability
what is the volumetric glass rinsed with?
distilled water
what is the conical flask rinsed with?
distilled water
what is the volumetric pipette rinsed with?
substance it will deliver
what is the burette rinsed with?
substance it will deliver
what is the volumetric flask used for?
prepare standard solution
what is the conical flask used for?
hold the aliquot of solution that will be titrated
what is the volumetric pipette used for?
deliver an aliquot of a solution
what is the burette used for?
deliver the solution
equivalence point
two reactants have reached correct mole proportions
estimated by the end point
end point
permanent colour change
mass spectrometry
investigation and measurement of masses of isotopes, molecules and molecular fragments by ionising samples & seperating fragments produced using electric and magnetic fields
only positively charged ions detected
measures the mass-to-charge ratio (m/z) of particles
ionisation
generates molecular ion by bombarding sample with high energy e-
M (g) + e- → M+ (g) + 2e-
fragmentation
unstable molecular ions produce a variety of smaller ions as bonds are broken
fragmentation pattern can help determine structure of original molecule
molecular ion
positive ion produced by ionisation of a whole molecule
the isotope effect
generation of multiple peaks for fragments with the same formula due to presence of isotopes of constituent elements
infrared (IR) spectroscopy
measures vibration of atoms in a molecule and gives information on functional groups present
infrared radiation change vibrational energy in covalent bonds
each type of covalent bond absorbs different wavelengths of infrared radiation
vibration of covalent bonds
‘ground state’
‘excited-state’
fingerprint region
region below 1500cm-1 containing a pattern of peaks specific for an individual molecule
factors affecting bond vibration energy
strength of bonds
mass of atom
strengths of bonds
stronger bonds require more energy to change their vibration
→ higher frequency, higher wave number
mass of atom
bonds between lighter atoms require more energy to change their vibration
→ higher frequency, higher wave length
fundamentals of NMR spectroscopy
measures change in spin state of nuclei, which gives information on number of chemical environments
involves absorption of radio waves, chemical shift alters with neighbouring environments
shielding & chemical environments
e- surrounding the nucleus will shield it from magnetic field
nuclei connected to the same atoms are in the same chemical environment
→ produce one NMR signal
chemical shift
horizontal scale on an NMR spectrum
represents difference in energy required to flip a nucleus in a sample compared to TMS
TMS
all NMR produced are compared to a sample (TMS)
added to samples prior to analysis, producing single peak for 1H- & 13C-NMR
value for TMS set to 0 & position of signal generated is known as chemical shift
advantages of TMS
signal peak away from other peaks
volatile, easily recovered
allows data from different NMR spectrometers to be compared
low-resolution proton NMR
includes:
number of peaks indicate the number of unique hydrogen environments
chemical shift provides information about specific environments
high-resolution proton NMR
number of peaks indicate the number of unique hydrogen environments
chemical shift provides information about specific environments
ratio of areas under peaks shows ratio of hydrogen atoms in that environment
n+1 rule
n+1 rule
peak splitting pattern is one more than number of hydrogen atoms on neighbouring carbons
low-resolution carbon NMR
includes:
number of peaks indicate the number of unique carbon environments
chemical shift provides information about specific environments
stationary phase
solid onto which the components of a sample adsorb
mobile phase
liquid/gas that flows through a chromatography system, moving the materials to be seperated at different rates over the stationary phase
chromatography
components go through adsorption to stationary phase & desorption back to mobile phase
mobile & stationary phase must be two different polarites
adsorption
sticking/adhering to the surface
desorption
removal of a substance from a surface
affinity
attraction of a component to the mobile/stationary phase
retention time (Rt)
time taken for component in a sample to travel from the injection port to end of the column
factors affecting retention time
polarity of mobile/stationary phases
temperature
viscosity of mobile phase
pressure applied
length of column
polarity of mobile/stationary phase
changing will affect relative affinity of a component
temperature
higher temperature increases time component spends in mobile phase, reducing Rt
reduce viscosity of mobile phase
viscosity of mobile phase
lower viscosity will increase rate mobile phase flows through, reducing Rt
pressure applied
higher pressure will increase rate of mobile phase flow, reducing Rt
length of column
shorter column will reduce time required for component to exit, reducing Rt