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chemistry a level > mass spectrometry > Flashcards

mass spectrometry Flashcards

1
Q

what is mass spectrometry?

A

a form of molecular chemical analysis. There are many different types of mass spectrometer. They all work on the same principle of:

  • forming ions from a sample
  • ions separated (according to mass charge ratio) m/Z
  • ions detected
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2
Q

what can mass spectrometry be used for?

A
  • provide structural information
  • identify an unknown compound
  • determine the relative abundance of each isotope of an element
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3
Q

what is the time of flight mass spectrometry?

A

it consists of the apparatus held under a vacuum that excludes air to prevent the ions from colliding with those in the air

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4
Q

what is step 1 of the practical for time of flight mass spectrometry?

A

step 1: the sample is dissolved in a volatile solvent.
The vaporised solvent is forced through a hollow needle which is connected to the +ve terminal of a high voltage supply. Producing tiny positively charged droplets (they have lost electrons). The solvent evaporates. As a result of this the droplets reduce in size and are reduced to a single positively charged ion.
-vaporisation-

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5
Q

what is step 2 of the practical for time of flight mass spectrometry?

A

step 2: the positive ions are attracted towards an electric plate the plate is negatively charged and causes the ions to accelerate. The ions accelerate towards the plate so that all ions have the same KE. Thus larger and heavier ions travel at a lower speed .
-ionisation-

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6
Q

what is step 3 of the practical for time of flight mass spectrometry?

A

the ions pass through a hole in the negatively charged plate which then forms a beam.The beam of ions travel along a tube (this is the flight tube)
-acceleration-

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7
Q

what is step 4 of the practical for time of flight mass spectrometry?

A

when the ions arrive at the detector, their flight times are recorded.At the detector, positively charged ions will pick up an electron which causes a current to flow
-deflection-

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8
Q

what is step 5 of the practical for time of flight mass spectrometry?

A

the data passes a signal to a computer which generates a mass spectrum
-detection-

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9
Q

what are isotopes?

A

atoms that have the same number of protons but different numbers of neutrons

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10
Q

what is low resolution mass spectrometry? e.g. Cl

A

Cl=2 isotopes
Cl^35,Cl^35
both isotopes have different masses i.e
Cl^35: n=18, p=17
Cl^35: n=20, p=17
so the isotopes will have a different m/z ratio thus are done separately .
the process of mass spectrometry can be carried out to a high level of precision ( 5 decimal places) when it is calculated to 1 d.p. it can be called low resolution mass spectrometry

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11
Q

how is mass spectrum calculated ?

A

relative abundance / mass:charge

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12
Q

what is the mass:charge for Cl?

A

35,37 respectively for its isotopes.

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13
Q

what’s the RAM of Cl?

A

35.5

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14
Q

what is the RAM of element x when the mass spectrum shows : RA 78.7,M:C 24 RA 10.13,M:C25 RA 11.17 M:C 26?

and thus suggest an identity of element x

A 
(24 x0.787) + (25x0.1013) + (26 x0.117)
=24.4625
2d.p
-> 24.46
Magnesium
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15
Q

what happens to the particles in a mass spectrometer following vaporisation, before they re detected . which of these steps separates the isotopes?

A

ionisation, acceleration and deflection. Deflection separates the isotopes based on their mass to charge ratio.

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16
Q

In acceleration, what is the equation?

A

V= root (2KE/m)

17
Q

What is the time of flight equation ?

A

Time= d root(m/2KE)

D being distance / length of tube

18
Q

What are the main rearrangements of the formula for TOF

A

Mm/t =mm/t

19
Q

Explain why the 3 stable isotopes of oxygen , o 16, o 17 and o 18, travel at different speeds in the TOFMS?

A

The 3 isotopes have different masses in a mass spectrometer they all have the same KE and so lighter isotopes will move at higher speeds

20
Q

Explain why TOF MS works and how it can be used to accurately measure the relative. Abundance’s of the different isotopes present in a sample of an element?
S1

A

Stage one: a sample is ionised to form 1+ ions , the two common methods for this is electro spray ionisation and electron impact. In electrospray ionisation the sample is dissolved in a volatile solvent and forced through a small nozzle at high pressure a high voltage is applied to cause each sample particle rot gain an H+ ion .
In electron impact ionisation, the sample is vaporized and high energy electron are fired at it this knocks one electron off each sample so they become 1+ ions. The ions are accelerated in an electric field causing all the ions have the same KE. The ions are allowed to drif t a fixed distance through a region with no electric field until they hit the detector

21
Q

Explain why TOF MS works and how it can be used to accurately measure the relative. Abundance’s of the different isotopes present in a sample of an element?
S2

A

X

22
Q

Explain why TOF MS works and how it can be used to accurately measure the relative. Abundance’s of the different isotopes present in a sample of an element?
S3

A

YOU

23
Q

What are the main difference between electrospray ionisation and electron impact?

A

Electrospray is where a proton is ripped from the solvent and attached to the atom to form 1+ ions this method prevents fragmentation

Electron impact is when electron s are fired at the sample to knock off an electron to form +1 ions

24
Q

What can mass spectrometry be used for?

A
  • accurate information about relative isotopic mass and also relative abundance of isotopes.
  • identify elements
  • determine the value of molecular mass.
25
Q

What is the electron configurations of atoms and ions up to Z=36?

A

1s2 , 2s2, 2p6, 3s2, 3p6,4s2,3d10, 4p6, 4d10, 4f14

26
Q

What is the first ionisation energy ?

A

The energy required to remove one electron from one mole of gaseous atoms.
To form +1 ions

27
Q

Successive ionisation energy definition

A

No

28
Q

Chlorine exists as two isotopes, Cl 35 and Cl 37 in the ratio 3:1
What ratio do the peaks in the mass spectrum of Cl2 is there?

A

9:6:1

29
Q 
Which of the following atoms has only two unpaired electrons in its ground energy ?/
A: helium
B: beriliym 
C: nitrogen
D: oxygen
A

A: helium 1S2 (paired )
B: beriliym 1S2,2S2 (paired)
C: nitrogen 1S2, 2S2, 2P3 (3 unpaired)
D: oxygen

So it must be oxygen
Because it’d be 1s2, 2s2, 2p4 where there will be 2 unpaired

30
Q

What is electron impact for

A

Small molecules

31
Q

What Is electrospray used for?

A

Large delicate molecules

chemistry a level (53 decks)

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