Relative Mass and the Mass Spectrometer
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1
Relative masses compare the mass of atoms to which element?
Carbon-12
2
Why is the actual mass of an atom not measured directly?
It is too small to weigh directly, so relative mass is used instead.
3
What is the relative atomic mass (Ar)?
The average mass of an atom of an element on a scale where carbon-12 is 12.
4
What is relative isotopic mass?
The mass of an atom of a specific isotope of an element on a scale where carbon-12 is 12.
5
What is the relative molecular mass (Mr)?
The average mass of a molecule on a scale where carbon-12 is 12.
6
Is relative atomic mass usually a whole number?
No, because it is an average.
7
Is relative isotopic mass usually a whole number?
Yes, relative isotopic mass is usually a whole number.
8
How do you find the relative molecular mass of a molecule?
Add up the relative atomic masses of all atoms in the molecule.
9
What is relative formula mass used for?
For ionic or giant covalent compounds.
10
How does a mass spectrometer help in measuring relative masses?
It measures relative atomic mass, relative molecular mass, and relative isotopic abundance.
11
What are the two methods of ionization in a mass spectrometer?
Electrospray ionization and electron impact ionization.
12
What happens during electrospray ionization?
The sample is dissolved, pushed through a nozzle at high pressure, and gains H+ ions to form positive ions.
13
What happens during electron impact ionization?
The sample is vaporized, and high-energy electrons knock off one electron, forming +1 ions.
14
How are ions accelerated in a mass spectrometer?
An electric field accelerates the positive ions, giving them the same kinetic energy.
15
What happens in the ion drift stage of mass spectrometry?
Ions drift through a region without an electric field, with lighter ions moving faster.
16
Why do lighter ions reach the detector faster?
They travel at higher speeds in the drift region due to their lower mass.
17
What does the detector in a mass spectrometer do?
It detects charged particles and produces a mass spectrum.
18
How can the relative atomic mass of an element be calculated from a mass spectrum?
Multiply each isotopic mass by its relative abundance, sum the results, and divide by the total abundance.
19
Why do elements with different isotopes produce multiple lines in a mass spectrum?
Isotopes have different masses, creating distinct lines.
20
What is the molecular ion (M+) in mass spectrometry?
A positively charged molecule formed by removing one electron from the molecule.
21
How does the M+ peak help identify a molecule?
Its mass/charge ratio matches the molecule's relative molecular mass, aiding identification.
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