AQA A-Level Chemistry AS Paper 1, November 2021: Question 11

1 mark · Easy difficulty · Multiple Choice

Identify the correct equation for the electrospray ionisation of molecule X in a time of flight mass spectrometer.

Practise this question

Question

Multiple-choice question asking for the equation representing electrospray ionisation of molecule X in a mass spectrometer. Four options are provided: A) X(l) + e- -> X+(g) + 2 e-, B) X(g) + e- -> X+(g) + 2 e-, C) X(l) + H+ -> XH+(g), D) X(g) + H+ -> XH+(g).
Question text

11 In a time of flight mass spectrometer, molecule X is ionised using

electrospray ionisation.

What is the equation for this ionisation?

[1 mark]

A X(l) + e– → X+(g) + 2 e–

B X(g) + e– → X+(g) + 2 e–

C X(l) + H+ → XH+(g)

D X(g) + H+ → XH+(g)

Mark scheme

Show the mark scheme A table showing the correct answer for question 11 is D, awarding 1 mark with the equation X(g) + H+ -> XH+(g).

Question Marking Guidance Mark Comments

11 D 1 X(g) + H+ → XH+(g)

How to answer it

Electrospray Ionisation Equation

What this question tests: Knowledge and recall of the two ionisation methods used in time of flight (TOF) mass spectrometry—specifically electrospray ionisation (soft ionisation via proton transfer)—along with correct state symbols and equation balancing.
Question 1.1

Identifying the Ionisation Equation

Multiple Choice Question (1 Mark)

✅ Correct Answer

D: X(g) + H⁺(g) → XH⁺(g) (Note: state symbols for protons can also be omitted or represented in solution, but key is X(g) and proton addition giving XH⁺(g) ).

Awarded 1 mark for selecting option D.

💡 Key Knowledge

  • Electrospray Ionisation: A "soft" ionisation technique where sample molecules are dissolved in a volatile solvent and injected through a high-voltage needle.
  • The Process: Molecules gain a proton ( H⁺ ) from the solvent/environment, forming XH⁺ ions.
  • State Symbols: The sample is vaporised into a fine mist, meaning equations feature gaseous state symbols ( g ) for the resulting ions.

🧠 Exam Technique

Break down the options using a checklist:

  1. Does it gain a proton? Look for + H⁺ forming XH⁺ (rules out A and B, which show electron impact / electron loss).
  2. Are state symbols correct? Electrospray involves vaporised particles entering the vacuum chamber, hence (g) .

❌ Common Errors

  • Confusing methods: Selecting options A or B, which describe Electron Impact ionisation ( X(g) + e⁻ → X⁺(g) + 2e⁻ ).
  • State symbol mistakes: Choosing option C ( X(l) ) instead of the vaporised form X(g) .

Topics

Physical Chemistry · Organic Chemistry · 3.1.1 Atomic Structure · 3.3.6 Organic Analysis

Question and mark scheme from the AQA A-Level Chemistry examination, AS Paper 1, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.