Topic 11: Measurement and Data Processing Flashcards
Qualitative analysis
Substances are identified or classified on the basis of their chemical or physical properties, such as chemical reactivity, solubility, molar mass, melting point, radiative properties (emission, absorption) , mass spectra, nuclear half-life, etc
Quantitative analysis
The amount or concentration of an analyte may be determined (estimated) and expressed as a numerical value in appropriate units.
Neutrinos
extremely small, electrically neutral particles produced i nuclear reactions
Precision
Closeness of agreement between independent test results obtained by applying the experimental procedure under stipulated conditions.
The smaller the random part of the experiment error the more precise the procedure.
Accuracy
Closeness of the agreement between the result of a measurement and a true value of the measurand (which is the particular quantity to be measured) .
Name two types of experimental error and explain what they are.
1) systematic error - associated with a flaw in the actual experimental design or with the instrumentation used.
Affect the accuracy of the results
2) random error - occurs because of uncontrolled variables in an experiment and hence cannot be eliminated.
Affect the precision of the results
Absolute uncertainty
the margin of uncertainty associated with the result from a given measurement. Its symbol is ∆A
Relative uncertainty
the ratio comparing the size of the absolute uncertainty, ∆A, to the size of the measured experimental result, A.
relative uncertainty = ∆A/A
Formula for percentage of relative uncertainty
% of relative uncertainty = (∆A/A) x 100%
Formula for percentage error
Percentage error = ((literature value - experimental value)/literature value) x 100%
Formula to calculate density.
d = m/V
d - density
m - mass
V - volume
Correlation coefficient, r.
A measure of the strength of the relationship between two variables.
Values range from -1 to +1
IHD
Index of hydrogen deficiency, or degree of unsaturation
Used to determine from a molecular formula the number of rings or multiple bonds in a molecule.
1 degree of unsaturation
double bond or a ring
2 degrees of unsaturation
triple bond
4 degrees of unsaturation
aromatic ring
Calculating IHD using molecular formula
for the generic molecular formula CcHhNnOoXx, where X is a halogen atom
IHD = (0.5) (2c + 2 - h - x + n)
X-ray crystallography
as their energy is high, these cause electrons to be removed from the inner energy levels of atoms. Diffraction patterns can lead to information such as the bond distances and bond angles in a structure
UV-vis spectroscopy
Visible and UV light give rise to electronic transitions and hence this type of spectroscopy gives information about the electronic energy levels in an atom or molecule
IR spectroscopy
IR causes certain bonds in a molecule to vibrate (for example, stretch and bend) and as such provides information on the functional groups present
Microwaves
cause molecular rotations and can give information on bond lengths.
Nuclear magnetic resonance (NMR) spectroscopy
Radiowaves can cause nuclear transitions in a strong magnetic field because radiowaves can be absorbed by certain nuclei, which causes their spin states to change.
List 3 types of spectroscopy that identify organic compounds.
1) IR spectroscopy
2) proton NMR (1H NMR) spectroscopy
3) mass spectrometry
What is a spring model?
In a spring model, every covalent bond is considered as a spring, which can be stretched, bent, or twisted, giving rise to distortion.
Based on Hooke’s Law:
F = -kx
F - force caused by the load applied to the spring
x - the length of expansion of the string from its equilibrium
k - spring constant
The stronger the bond connecting the two atoms the tighter the string will be and therefore more energy is required to stretch it.
Wavenumber
IR absorptions cited as the reciprocal of the wavelength (1/λ).
Different molecules absorb at different frequencies because the energy required to execute a vibration will depend on the bond enthalpy.
List three modes of vibration.
1) symmetric stretch
2) asymmetric stretch
3) symmetric bend
Fingerprint regions of an IR spectrum
region of more complex vibrations between 300-1400 cm^(-1)
1H NMR spectroscopy
Gives information on the different chemical environments of hydrogen atoms in a molecule.
The nuclei of hydrogen atoms can exist in two possible spin states, so they can as tiny magnets. In a magnetic field, the spins may align with or against the magnetic field resulting in two nuclear energy levels.
Chemical shift
In 1H NMR spectrum, the position of the NMR signal relative to a standard.
Expressed in ppm of the proton.
