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HL Chem > 11 measurement and data processes > Flashcards

11 measurement and data processes Flashcards

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1
Q

what does qualitative data include?

A

all non numerical info obtained from observations NOT measurement
- detection of the presence but not quantity

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2
Q

what kind of error will repeat trials reduce?

A

random error
(will not reduce systematic)

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3
Q

where do you take the volume reading in a measuring cylinder

A

the bottom of the meniscus!

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4
Q

what is the uncertainty of an instrument?

A

+/- half the smallest division

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5
Q

uncertainty pertaining to the experimenter 2

A
  1. reaction time (time measurements)
  2. judgement of when an indicator changes colour
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6
Q

when is scientific notation used?

A

when the number of sf is uncertain
(hence making it like 1 x 10^3)

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7
Q

what are random errors caused by 4

A
  • readability of measuring instrument
  • effect of changes in surroundings eg temp var.
  • insufficient data
  • observer misinterpretation
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8
Q

in terms of experimental results whats repeatable vs reproducable

A

repeatable: same experimenter gets same results
reproducable: many experimenters get same results

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9
Q

what are systematic errors a result of

A

poor experimental design / procedure
eg electronic mass balance incorrectly zeroed

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10
Q

examples of systematic sampling 4

A
  1. measuring water volume from meniscus top not bottom
  2. overshooting volume of liquid added in titration = vols too high
  3. use of acid-base indicator whose end point doesn’t correspond to equivalence pt
  4. heat losses in exothermic reaction = smaller temp changes)
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11
Q

the smaller the systematic error, the greater the ______

the smaller the random error, the greater the ______

A

accuracy

precision

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12
Q

the smaller the value, the ______ the uncertainty

A

more significant

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13
Q

what happens to uncertainty when you add or subtract

A

uncertainty is the SUM of the absolute uncertainties

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14
Q

how to find absolute uncertainty of a multiplied/divided value

A

find maximum value and minus the middle value = +/- absolute uncertainty

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15
Q

how to find percentage uncertainty after multiplication and division?

A

find the absolute uncertainty as a percentage of the value

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16
Q

significant figures when multiplying or dividing data

A

same sf as least precise data

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17
Q

significant figures when adding or subtracting

A

NOT sf but dp. same dp as the one with the most dp

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18
Q

things to remember when plotting a graph

A
  • title
  • label axes: quantities and units
  • line of best fit should show overall trend
  • identify anomalies
  • carefully consider inclusion of origin
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19
Q

how to find gradient

A

draw that tangent and triangle girl

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20
Q

systematic error best fit graph vs random error best fit graph

A

systematic: higher/lower than perfect, but same trend
random: slightly scattered points around the perfect line

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21
Q

what does the presence of an outlier suggest

A

some of the data may be unreliable

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22
Q

given ideal gas equation PV = nRT, what can be said about the pressure and volume relationship? + how would the graph look like

A

pressure is inversely proportional to volume

vol against pressure:
decreasing slope (steep then more gradual)

pressure against 1/volume
straight increasing line

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23
Q

what does the use of log scales allow for

A

the rearrangement of some relationships into a straight line

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24
Q

what is quantitative analysis?

A

the measurement of the QUANTITY of a substance in a mixture

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25
Q

what is structural analysis

A

description of how atoms are arranged in molecular structures

26
Q

what is Infrared spectroscopy for

A

to identify BONDS in a molecule

27
Q

what is mass spectrometry for

A

determine RELATIVE ATOMIC AMASS and molecular mass

28
Q

how are fragmentation patterns formed in mass spectometry

A

ionisation process! electron from electron gun hits species and removes an electron
- energetic collision = molecule breaks up

29
Q

what are fragmentation patterns for in mass spectrometry

A

provide evidence for structure of the compound

  • the lines are possible breakdowns of the compound eg losing certain elements = certain mass lost
30
Q

highest mass line in mass spectrum represents?

A

the Mr of the PARENT MOLECULE

  • subtract other lines to find loss in mass = find out what part was lost
31
Q

what is the degree of unsaturation / IHD (index of hydrogen deficiency)

A

in theory, how many H2 would be needed to convert the molecule (formula determined with mass spectrometry) into the corresponding saturated, non cyclic molecule

32
Q

what is the frequency of radiation measured as

A

number of waves per centimeter / wavenumber

33
Q

what waves are used in NMR

A

radio waves
give info abt environment of certain atoms

34
Q

what effect do microwaves have on molecules

A

increaed rotational energy = info about bond lengths

35
Q

what effect does infrared radiation have on molecules

A

absorbed by certain bonds = stretch / bend

36
Q

what effect does visible and ultraviolet light have on molecules

A

can produce electronic transitions and give info about electronic energy levels

37
Q

x rays are produced from electrons when…

A

electrons make transitions between inner energy levels

38
Q

a bond will only interact with Infrared radiation IF it is ____

A

polar

39
Q

how does a bond being polar allow it to interact with infrared radiation in IR spectroscopy

A

seperate areas of partial pos and neg charge = electric field of electromagnetic wave to excite vibrational energy of the molc

change in vibrational energy = change in dipole moment

intensity of absorption depends on bond polarity

40
Q

what shape does O-H give in IR spec

A

broad trough

41
Q

what shape does C=O give in IR spec

A

sharp spike

42
Q

how can hydrogen bonding be detected in IR spec

A

hydrogen bonds = absorption BROADENS and shifts to lower freq

43
Q

what is NMR (nuclear magnetic resonance) spectroscopy for

A

finding structure and shape of molecules

44
Q

what is resonance and how is it formed in NMR

A

sample placed in electromagnet

field strength varied until radio waves have EXACT frequency needed to make the nuclei FLIP over and SPIN in OPPOSITE DIRECTION

45
Q

nuclei in different ________________ produce different signals on an NMR spectrum

A

hydrogen environments

46
Q

the signals of a H NMR are measured against the standard signal produced by?

A

the 12 hydrogen nuclei in tetramethylsilane (TMS)

Si in middle, 4 sides having CH3 (methyl grp)
= total 12 hydrogens

has a chemical shift of ZERO

47
Q

position of NMR signal relative to the standard signal is called the ________ of the proton

A

chemical shift

48
Q

what does the heights of H NMR spectra indicate

A

the relative number of protons in each environment

eg 3x as tall = 3x as many protons

49
Q

why is TMR used as a standard in NMR spec?

A

tetramethylsilane

has 12 hydrogen nuclei all in the same environment = ONE signal

silicon has lower electronegativity = wont overlap with possible tested (like if they used C)

50
Q

what does a split peak in NMR mean

A

the effective magnetic field is modified by the mag field of neighbouring protons (aka SPIN-SPIN coupling)

51
Q

one signal in a low res NMR spec = 2 signals in a high res (doublet), explain????

A

each line correspodns to diff spin of neighbouring proton

51
Q

what is spin-spin coupling

A

effective magnetic field of a particular nuclei is modified by the magnetic fields of neighbouring proton

looks like a SPLIT PEAK in a NMR spectrum

52
Q

how does electronegativity affect NMR

A

electroneg = pulls valence electrons away from atoms = decr electron density = lower energy needed to reach resonance frequency

53
Q

predict the splitting pattern produced by a neighbouring –CH2– group in a H NMR spectrum

A

2^2 different combinations (3 different local magnetic fields)

  1. both protons aligned WITH ext mag field
  2. one proton alighed AGAINST and one WITH (either direction = 2)
  3. both protons aligned AGAINST

total 4 combinations, lines with intensities 1,21

54
Q

do protons bonded to same group interact with each other? NMR

A

NO. they are equivalent and behave as a group

55
Q

do protons on non-adjacent carbons interact with e/o? NMR

A

NO

56
Q

the O-H peak in ethanol does not split in HNMR unless?

A

unless the sample is PURE.

rapid exchange of protons between ethanol molc averages out possible spins

57
Q

the number of lines in a HNMR spectrum = to?

A

total number of hydrogens

58
Q

x ray diffraction constructive vs destructive interferance

A

constructive: waves in phase = reinforce e/o = resultant wave larger amplitude

destructive: waves out of phase by 180deg = peak aligned with another trough = cancel e/o out

59
Q

what can be obtained from X ray diffraction of a solid

A

map of electron density

60
Q

are H atoms visible on X ray diffraction electron density map?

A

nope! electron densities are too low

HL Chem (28 decks)

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