2.2 Relative mass

Question 1

Why is carbon-12 so important?

Answer 1

Because it is the standard isotope which we base all atomic masses to

Question 2

What is the relative isotopic mass = to?

Answer 2

The mass number (which is not given on the periodic table)

Question 3

What does the weighted mean take into account?

Answer 3

The percentage abundance of each isotope

The relative isotopic mass of each isotope

Question 4

What is a simple way of explaining the relative atomic number?

Answer 4

It is an average of all the isotopes of an element

Question 5

What can a mass spectrometer be used for?

Answer 5

The percentage abundance of the isotopes in a sample of an element
or
To record the accurate m/z ratio for each isotope so that accurate values of relative isotopic mass can be measured

Question 6

How does a spectrometer work?

Answer 6

1) A sample is placed in the mass spectrum
2) The sample is vaporised and then ionised to form positive ions
3) The ions are accelerated (the heavier ions move more slowly and are more difficult to deflect than lighter ions, so the ions of each istope are sperated
4) The ions are detected on a mass spectrum as a mass-to-charge ratio m/z. Each ion reaching the detector adds to the signal, so the greater the abundance, the larger the signal

Question 7

What does the mass-to-charge ratio = to?

Answer 7

Relative mass of ion/relative charge of an ion

Question 8

12g Carbon =

Answer 8

1 mol = 24dm3

Question 9

How many mols does 2H2O have?

Answer 9

2

Question 10

How many moles does H2 have?

Answer 10

1

Question 11

When finding the ratio what do you look at?

Answer 11

The moles

Question 12

What is the equation to work out n?

Answer 12

n = m/Mr
or
n = c x v/1000