Mass Spectrometry

• What is the relative atomic mass (A_r) of an element?

  It measures the atomic weight of an element.
• How is the relative atomic mass (A_r) defined?

  As the average mass compared to carbon-12.
• What does the A_r of an element combine?

  It combines the masses of different isotopes.
• What are the two major isotopes of chlorine (Cl)?

  35Cl and 37Cl
• What percentage of chlorine is 35Cl?

  75% of all chlorine.
• What is the relative atomic mass of chlorine considering its isotopes?

  35.5Cl
• What is the relative molecular mass (M_r) of a molecule?

  It measures the molecular weight of a molecule.
• How is the M_r of a molecule defined?

  As the average mass compared to carbon-12.
• How do you calculate the M_r of calcium hydroxide, Ca(OH)₂?

  Combine A_r values: 40 + (2 × 16) + (2 × 1) = 74.
• What is the M_r of calcium hydroxide?

  74
• What is the molecular formula of penicillin?

  C₁₆H₁₈N₂O₄S
• How do you calculate the M_r of penicillin?

  192 + 18 + 28 + 64 + 32 = 334.
• What is the M_r of penicillin?

  334
• What is the relative formula mass of giant lattices like NaCl calculated from?

  It is calculated in the same way as M_r.
• What is mass spectrometry used for?

  To analyze elements or compounds.
• What can mass spectrometry determine about an element?

  It can determine the A_r of an element.
• What does a time of flight (ToF) mass spectrometer do?

  It identifies relative atomic and molecular masses.
• What are the four key stages of ToF mass spectrometry?

  1. Ionisation
  2. Acceleration
  3. Ion drift
  4. Detection
• When did ToF mass spectrometers become key analytic instruments?

  Since the 1960s.
• What must happen to a sample before entering the mass spectrometer?

  The sample must be ionised.
• What are the two main ways to ionise samples?

  Electrospray ionisation and electron impact ionisation.
• How does electrospray ionisation work?

  Sample is dissolved and pushed through a nozzle.
• What happens during electrospray ionisation?

  High voltage causes particles to gain H⁺ ions.
• What is the result of electron impact ionisation?

  Particles lose electrons, forming positively charged ions.
• How are ions accelerated in a mass spectrometer?

  Using an electric field with a negatively charged plate.
• What happens to lighter ions in the drift region?

  Lighter ions drift at higher speeds.
• What occurs when ions hit the detector plate?

  They gain an electron, producing a current.
• What does the mass spectrum display?

  Information about the sample that passed through.
• What does the y-axis of a mass spectrum show for an element?

  The abundance of the ions, often as a percentage.
• What does the x-axis of a mass spectrum represent?

  The mass/charge ratio of the ions.
• How is the mass/charge ratio related to A_r or M_r?

  It is related to the A_r of an element or M_r of a compound.
• If an ion has a mass of 28 and a charge of 1+, what is its mass/charge ratio?

  28
• What can mass spectra be used to calculate?

  The relative atomic mass of elements.
• How do you calculate the relative atomic mass of zirconium with its isotopes?

  Sum the products of mass and abundance, then divide by 100.
• What is the formula for kinetic energy (KE) of ions in a TOF mass spectrometer?

  KE = $\frac{1}{2}mv^2$
• How do you calculate the time of flight (t) for ions?

  t = $\frac{d}{v}$
• If a sample of zinc contains the isotope 68Zn, what is its time of flight if it travels 1.2 m at 5.15 × 10⁴ m/s?

  Approximately 2.33 × 10⁻⁵ seconds.
• What are the steps to calculate the time of flight for ions in a TOF mass spectrometer?

  1. Determine the kinetic energy (KE).
  2. Calculate the velocity (v).
  3. Use the formula t = d/v.