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IB Chemistry > Measurement and Data Processing > Flashcards

Measurement and Data Processing Flashcards

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1
Q

How do you measure the uncertainty in analogue instruments?

A

+/- half the smallest division

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2
Q

how do you measure the uncertainty in digital instruments?

A

+/- half the smallest division

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3
Q

What are other sources of uncertainty?

A

reaction time

judging what is the

  • equivalence point
  • temperature at a particular time
  • voltage of a cell
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4
Q

significant figures

A

digits in the measurement up to and including the first uncertain digit

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5
Q

experimental error

A

difference between the recorded value and the generally excepted value

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6
Q

what are the two categories of error?

A

random or systematic

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7
Q

random error

A

equal probability of result being too high or too low

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8
Q

what causes random error?

A
  • readability of measuring instrument
  • effects of changes in surroundings (temperature variations, air currents)
  • insufficient data
  • misinterpretation of data
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9
Q

how can random error be reduced?

A

repeated measurements

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10
Q

repeatable

A

the same person duplicates the experiment with the same results

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11
Q

reproducible

A

several experimenters duplicate the results

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12
Q

systematic error

A
  • poor experimental design or procedure
  • cannot be reduced by repeating the experiment
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13
Q

what causes systematic error?

A
  • measuring volume from top of the meniscus
  • overshooting volume in titration
  • heat losses in exothermic reaction
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14
Q

uncertainty when add or subtract measurements?

A

sum of absolute uncertainties

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15
Q

uncertainty when multiply or divide measurements

A

sum of individual percentage uncertainties

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16
Q

precision of data when multiply or divide data

A

same number of significant figures at the least precise datum

17
Q

precision of data when add or subtract data

A

same number of decimal places as the least precise value

18
Q

qualitative analysis

A

detects presence but not quantity of substance in a mixture e.g. chromatography

19
Q

quantitative analysis

A

measurement of the quantity of a particular substance in a mixture

20
Q

structural analysis

A
  • description of how the atoms are arranged in molecular structures
  • e.g. spectroscopy
21
Q

infrared spectroscopy

A

identify bonds in a molecule

22
Q

mass spectrometry

A

determines relative atomic and molecular masses

23
Q

nuclear magnetic resonance spectroscopy

A

shows chemical environment of certain isotopes

24
Q

IHD

A
  • index of hydrogen deficiency
  • measure of how many molecules of H2 would be needed in theory to convert the molecule to the corresponding saturated, non-cyclic molecule
25
Q

equation for IHD

A

(2C + 2 - H)/2

26
Q

double bond IHD

A

1 IHD

27
Q

ring IHD

A

1 IHD

28
Q

triple bond IHD

A

2 IHD

29
Q

do O or S affect IHD?

A

no

30
Q

what are halogens counted as in IHD?

A

like H atoms

31
Q

N IHD

A

add one to the number of C and one to the number of H

32
Q

what happens in the mass spectrometer?

A
  • vaporized sample becomes ionized to form cation
  • some of molecular ions break down to give fragments - also deflected by the external magnetic field
  • show up as peaks on detector
  • identify particular fragments by looking at difference in mass between the parent peak and fragments
33
Q

what happens in the infrared spectroscope?

A
  • when molecules absorb energy in the infrared region they vibrate (bonds stretch and bend)
  • energy absorbed depends on particular bond and other groups attached to the two atoms forming the bond
  • possesses a ‘fingerprint’ region: characteristic pattern between about 1400-400cm-1 which is specific to a particular compound
  • possible to identify an unknown sample by comparing fingerprint region to library of known compounds
34
Q

what happens in a proton nuclear magnetic resonance spectroscope?

A
  • 1H NMR provides information on chemical environment of all hydrogen atoms in the molecule
  • nuclei of hydrogen atoms possess spin (can exist in two possible states of energy)
  • if strong magnetic field applied spin either align themselves with or against magnetic field
  • small energy difference between these states - nuclei can absorb a photon of energy when going from higher to lower spin state
  • photon energy small and in radio region
  • chemical shift: position in 1H NMR spectrum where absorption occurs for each hydrogen atom
  • height of each section is proportional to number of hydrogen atoms in each chemical environment

IB Chemistry (25 decks)

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