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chemistry > EL 1&2: Mass spectrometry; fusion; emission/absorption spectra > Flashcards

EL 1&2: Mass spectrometry; fusion; emission/absorption spectra Flashcards

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1
Q

What are the symbols for mass and atomic number?

A

Mass number = A

Atomic number = Z

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2
Q

What are isotopes?

A

Atoms of the same element with different mass numbers.

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3
Q

Explain how mass spectrometry works.

A
  • Sample atoms/molecules are ionised to cations, then accelerated by a charged region
  • They pass through a drift region (vacuum) then hit a detector
  • Ek = 1/2mv2 so isotopes with a higher m/z (mass to charge) ratio have a greater time of flight
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4
Q

How do you work out relative mass when looking at a mass spectrum?

A

Relative isotopic abundance =

peak height of isotope or relative intensity

total peak height or total intensity

Relative mass =

sum of (relative abundance x mass number)

100

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5
Q

Calculate the relative atomic mass of iron.

A
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6
Q

The relative atomic mass of iridium is 192.2. It occurs naturally as both iridium-191 and iridium-193. Calculate the % abundance of each isotope.

A

Let x + y = 100% then y = 100 - x

191x + 193y = 100(192.2)

191x + 193(100 - x) = 19,200

-2x = -80 so x = 40%

y = 100 - 40 = 60%

40% iridium-191; 60% iridium-193

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7
Q
A

40% antimony-123

60% antimony-121

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8
Q
A

C

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9
Q

Define nuclear fusion.

A

The process by which, under high temperature and pressure, lighter nuclei fuse, forming a heavier nucleus of a new element.

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10
Q

Write a nuclear equation for the formation of 3He from hydrogen.

A
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11
Q
A
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12
Q

In stars, a reaction called the ‘triple alpha process’ occurs where three helium nuclei fuse together. Write a nuclear equation for this process.

A
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13
Q

What is spectroscopy?

A

The study of how light and matter interact.

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14
Q

What equation links the wave and particle theories of light?

A

E = hν

E = hf

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15
Q

Compare the wavelength and frequency of red and blue visible light.

A
  • Red: lower frequency, longer wavelength
  • Blue: higher frequency, shorter wavelength
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16
Q

Give Bohr’s explanation for why an atom only emits or absorbs certain frequencies of light.

A
  • Electrons in atoms exist only in certain energy levels since energy is quantised
  • A photon of light is emitted/absorbed when an electron decreases/increases energy level
  • Energy of photon = ΔE, difference between energy levels
  • Since E = hν, frequency of emitted/absorbed light is related to ΔE by ΔE = hν
17
Q
A
  • Both arrows point down
  • Shorter arrow = red line
18
Q

Describe the similarities and differences between an emission and absorption spectrum for the same element.

A

Similarities

  • Line spectrums
  • Lines in same place; same frequency
  • Lines become closer together with higher frequency

Differences

  • Absorption: black lines on a rainbow background
  • Emission: coloured lines on a black background
19
Q

How may an atomic spectrum provide information about the abundance of an element?

A

The intensity of lines provides a measure.

20
Q

Describe how an atomic emission spectrum is produced.

A
  • Energy transferred to atoms
  • Electrons excited from ground state to higher energy level
  • They fall back to a lower energy level since energy is quantised
  • Photon of light emitted; energy = ΔE, difference between energy levels
  • As E = hν, frequency of emitted light is related to ΔE by ΔE = hν
  • Radiation detected, producing coloured vertical lines on a black background
21
Q

The first ionisation enthalpy of sodium is 496 kJ mol-1. Calculate the frequency that corresponds to this energy.

A

Enthalpy for one atom = 496,000 / (6.02 x 1023) = 8.239 x 10-19 J

ν = e/h = 8.239 x 10-19 / (6.63 x 10-34) = 1.24 x 1015 Hz (3 s.f.)

22
Q

Explain why an atomic emission spectrum is unique to a particular element.

A
  • Energy transferred to atoms; electrons excited to higher energy levels then fall back to lower ones
  • Photons of light emitted; energy = ΔE, difference between energy levels
  • Since E = hν, ΔE = hν
  • Energy levels are quantised + unique to each element
  • So frequency of light emitted is also unique
  • Produces unique colours on spectrum
23
Q

Explain how the atomic emission spectra of elements show that electrons exist in energy levels.

A
  • They show lines of specific frequencies, rather than a continuous spectrum
    • Shows energy is quantised; E = hν
  • From violet to red (left to right), frequency of lines decreases
    • Shows e- drop down energy levels
24
Q
A

D

2 wrong since lower energy levels

3 wrong since higher frequency not wavelength

25
Q

Draw a diagram of the energy levels in a hydrogen atom. Draw arrows to show the origin of 2 lines on its absorption spectrum.

A
  • At least three horizontal lines with upper gaps smaller than lower ones
  • 2 upward arrows connecting energy levels (different combinations)
  • Y-axis labelled “energy”
26
Q

Describe generally how to carry out a flame test.

A
  • Dip wire loop into HCl (cleaning + adhesion)
  • Dip into solid sample
  • Hold in blue Bunsen flame
  • Record flame colour observed
27
Q

What flame colour is produced by burning a splint soaked in a solution of lithium chloride?

A

Bright red

28
Q

What flame colour is produced by burning a splint soaked in a solution of sodium chloride?

A

Yellow

29
Q

What flame colour is produced by burning a splint soaked in a solution of potassium chloride?

A

Lilac

30
Q

What flame colour is produced by burning a splint soaked in a solution of calcium chloride?

A

Brick red

31
Q

What flame colour is produced by burning a splint soaked in a solution of barium chloride?

A

Green

32
Q

What flame colour is produced by burning a splint soaked in a solution of copper chloride?

A

Blue-green

33
Q
A

A

  • IR > visible > UV
  • Reciprocal relationship between frequency + wavelength

chemistry (50 decks)

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