Measurement and Data Processing (topic 11/21)

Question 1

Qualitative data

Answer 1

Includes all non-numerical information obtained from observations not from measurements.

Question 2

Quantitative data

Answer 2

Are obtained from measurements, are associated with random errors/uncertainties determined by the apparatus, and by human limitations such as reaction times.

Question 3

Precise

Answer 3

When data points are close to each other

Question 4

Accurate

Answer 4

Close to the expected value

Question 5

Uncertainties

Answer 5

Digital instruments: ± smallest division on the apparatus

Analog instruments: ± smallest division / 2

Question 6

Rules for uncertainties

Answer 6

• Only one s.f.
• When adding or subtracting, add uncertainties.
• When multiplying and dividing, add percentage uncertainties and also give the absolute value in the end given the total percentage uncertainty
• When getting the average, add up uncertainties and divide by the amount of uncertainties.
• Add decimal after 0.1 uncertainties
• When adding or subtracting uncertainties to their respective value: Answer must have same number of decimal places as that with the least in question.
• When multiplying or dividing uncertainties to their respective value: Answer must have same number of sf as that with the least in question. If needed, use scientific notation

Question 7

Sketching a graph

Answer 7

Graph, line, labels

Question 8

Index of hydrogen deficiency (IHD)

Answer 8

Also known as degree of unsaturation. How many more H2 can fit onto the molecule. Gives information about the molecule and its potential isomers. IHD = 1 with how many H2 can fit more.

Count double bonds, also rings.

Question 9

Electromagnetic spectrum

Answer 9

High energy to low

-X-ray (inner electron excitation)
-UV - visible (valence electron excitation)
-Infrared (I.R. Spectroscopy)(bond vibrating)
-Microwaves (molecular rotations)
-Radio waves (1H NMR)(nuclear spin transitions)
-Mass spectroscopy

Question 10

X-ray (inner electron excitation)

Answer 10

They have so much energy, they excite the inner electrons of atoms to a high energy level. And from there the electrons will jump back down again releasing the x-rays giving information about the inner electron levels.

Question 11

UV - visible (valence electron excitation)

Answer 11

Excited valence electrons to high energy levels and when they come back down again, they release photon giving information about the valence energy level.

Question 12

Infrared (I.R. Spectroscopy)(bond vibrating)

Answer 12

Causes some molecules’ bonds to vibrate. If you sweep the molecules with different frequencies of infrared, find out which are absorbed then you’ll get a spectrum. The troughs in the spectrum can correlate in the data booklet to identify the bonds in the molecule.

Question 13

Microwaves (molecular rotations)

Answer 13

Causes gas molecules to rotate. Can be used to find information about molecular geometry.

Question 14

Radio waves (1H NMR)(nuclear spin transitions)

Answer 14

The interaction of radio waves and a magnetic field will flip the proton in the hydrogen nucleus. Information gained will tell you about hydrogens in molecules. Spectra in the data booklet

Question 15

Mass spectroscopy

Answer 15

Molecules are ionised and flung through a bent tube, different masses and charges on the fragments creates a spectrum. Using math, you can work out what the fragments are.

Question 16

Nuclear magnetic resonance

Answer 16

H1 NMR (MRI)

Measures the number of different H1 environments in your molecule. Also measures the ratio of 1H in each of these environments

Question 17

How does ‘mass spec’ identify molecules?

Answer 17

• 15 loss of CH3 (methyl)
• 17 loss of OH (alcohol or carboxylic acid)
• 29 loss of C2H5 or CHO (ethyl or aldehyde)
• 31 loss of CH3O
• 45 loss of COOH (carboxylic acid group)