Organic analysis

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Question 2
Medium
a.

Describe the process of electron impact ionisation of a sample in a time-of-flight (TOF) mass spectrometer.

Give an equation to represent the ionisation of a general molecule, symbolised as MMM, in this process.

[3]
b.

A molecule QQQ is ionised by electron impact in a TOF mass spectrometer.

  • The Q+Q^+Q+ ion has a kinetic energy of 1.95×10−15 J1.95 \times 10^{-15}\text{ J}1.95×10−15 J.
  • This ion takes 1.20×10−5 s1.20 \times 10^{-5}\text{ s}1.20×10−5 s to reach the detector.
  • The length of the flight tube is 1.50 m1.50\text{ m}1.50 m.

Calculate the relative molecular mass of QQQ.

Use the equations: KE=12mv2KE = \frac{1}{2}mv^2KE=21​mv2 where m=mass (kg)m = \text{mass (kg)}m=mass (kg) and v=speed (m s−1)v = \text{speed (m s}^{-1}\text{)}v=speed (m s−1).

The Avogadro constant, L=6.022×1023 mol−1L = 6.022 \times 10^{23}\text{ mol}^{-1}L=6.022×1023 mol−1.

[5]

Organic analysis Questions

  1. A Level
  2. /Chemistry
  3. /Organic analysis