Topic 11: Measurement and Data Processing

Question 1

Qualitative analysis

Answer 1

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

Question 2

Quantitative analysis

Answer 2

The amount or concentration of an analyte may be determined (estimated) and expressed as a numerical value in appropriate units.

Question 3

Neutrinos

Answer 3

extremely small, electrically neutral particles produced i nuclear reactions

Question 4

Precision

Answer 4

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.

Question 5

Accuracy

Answer 5

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) .

Question 6

Name two types of experimental error and explain what they are.

Answer 6

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

Question 7

Absolute uncertainty

Answer 7

the margin of uncertainty associated with the result from a given measurement. Its symbol is ∆A

Question 8

Relative uncertainty

Answer 8

the ratio comparing the size of the absolute uncertainty, ∆A, to the size of the measured experimental result, A.

relative uncertainty = ∆A/A

Question 9

Formula for percentage of relative uncertainty

Answer 9

% of relative uncertainty = (∆A/A) x 100%

Question 10

Formula for percentage error

Answer 10

Percentage error = ((literature value - experimental value)/literature value) x 100%

Question 11

Formula to calculate density.

Answer 11

d = m/V

d - density
m - mass
V - volume

Question 12

Correlation coefficient, r.

Answer 12

A measure of the strength of the relationship between two variables.

Values range from -1 to +1

Question 13

IHD

Answer 13

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.

Question 14

1 degree of unsaturation

Answer 14

double bond or a ring

Question 15

2 degrees of unsaturation

Answer 15

triple bond

Question 16

4 degrees of unsaturation

Answer 16

aromatic ring

Question 17

Calculating IHD using molecular formula

Answer 17

for the generic molecular formula CcHhNnOoXx, where X is a halogen atom

IHD = (0.5) (2c + 2 - h - x + n)

Question 18

X-ray crystallography

Answer 18

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

Question 19

UV-vis spectroscopy

Answer 19

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

Question 20

IR spectroscopy

Answer 20

IR causes certain bonds in a molecule to vibrate (for example, stretch and bend) and as such provides information on the functional groups present

Question 21

Microwaves

Answer 21

cause molecular rotations and can give information on bond lengths.

Question 22

Nuclear magnetic resonance (NMR) spectroscopy

Answer 22

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.

Question 23

List 3 types of spectroscopy that identify organic compounds.

Answer 23

1) IR spectroscopy
2) proton NMR (1H NMR) spectroscopy
3) mass spectrometry

Question 24

What is a spring model?

Answer 24

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.

Question 25

Wavenumber

Answer 25

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.

Question 26

List three modes of vibration.

Answer 26

1) symmetric stretch
2) asymmetric stretch
3) symmetric bend

Question 27

Fingerprint regions of an IR spectrum

Answer 27

region of more complex vibrations between 300-1400 cm^(-1)

Question 28

1H NMR spectroscopy

Answer 28

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.

Question 29

Chemical shift

Answer 29

In 1H NMR spectrum, the position of the NMR signal relative to a standard.

Expressed in ppm of the proton.