Mass number and isotopes (TOF)

Question 1

mass number definition

Answer 1

the number of protons + neutrons

Question 2

Relative Atomic Mass definition

Answer 2

The mean mass of an atom of an element, compared to 1/12th of the mean mass of an atom of carbon-12 atom.

Question 3

What are isotopes?

Answer 3

Isotopes are the same element with the same atomic number, but with a different number of neutrons, and therefore a different mass number.

Different mass number means different physical properties

Question 4

Mass Spectrometry

Answer 4

An analytical technique to identify isotopes and find overall relative mass of an element

Question 5

1st step of TOF: electron impact

Answer 5

Ionisation: used for lower molecular masses

Electron Impact:
1. the sample is vaporised
2. then fired with high energy electrons from an electron gun.
3. This knocks an electron out of the shell which creates a positive ion.

Question 6

1st step of TOF: electrospray ionisation

Answer 6

Ionisation: used for higher molecular masses

Electrospray Ionisation:
1. the sample is dissolved in a volatile solvent
2. injected by a hypodermic needle which is attached to a high voltage power supply.
3. Samples gain a proton

Question 7

2nd step of TOF

Answer 7

Acceleration:
the molecules are accelerated using an electric field so that they all have the same kinetic energy

Question 8

3rd step of TOF

Answer 8

Ion Drift:
ions will move into the “flight” tube.
the larger the mass, the lower the velocity/speed

Question 9

4th step of TOF

Answer 9

Detection:
When the positive ions hit the negatively charged detection plate, they gain an electron which produces a flow of charge.

The greater the abundance, the greater the current produced

Question 10

5th step of TOF

Answer 10

Data Analysis:
able to produce a spectra-print out graph of abundance vs mass to charge ratio.

Question 11

Equation to calculate atomic mass

Answer 11

m/z x abundance / total abundance

Question 12

Answer 12

Answer: D

Question 13

Answer 13

Answer: A

Question 14

Give the TOF equation + Avagadros Constant + speed equation

Answer 14

speed = distance(m)/time(s)
avagadros constant = 6.022 x10(23)

Question 15

EQ: Why is it important to ionise the isotopes in a TOF mass spec?

Answer 15

1. Ions will interact with and be accelerated by an electric field.
2. Ions create a current when hitting the detector.

Question 16

Give an equation, including state symbols, for the process that occurs during the ionisation of a germanium atom using electron impact.

Answer 16

Ge(g) + e– → Ge+(g) + 2 e–

Question 17

Give the formula of C3H5O2N ion when electrospray ionisation is used in TOF.

Answer 17

C3H6O2N+ or C3H6O2NH+

Question 18

Answer 18

Answer: B

Question 19

Answer 19