OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2018: Question 1

1 mark · Easy difficulty · Multiple Choice

Identify the standard compound used for NMR chemical shift measurements from the given multiple-choice options.

Practise this question

Question

Multiple choice question 1 asking which compound is used as a standard for NMR chemical shift measurements, with options A: Si(CH3)4, B: CDCl3, C: D2O, and D: CCl4, followed by an answer box and 1 mark allocation.
Question text

1 Which compound is used as a standard for NMR chemical shift measurements?

A Si(CH3)4

B CDCl3

C D2O

D CCl4

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme shows the correct answer for question 1 is A, worth 1 mark.

1 A 1

How to answer it

NMR Chemical Shift Reference Standards

What this question tests: Recall and understanding of practical analytical chemistry techniques, specifically identifying the standard reference compound used in both 1H and 13C nuclear magnetic resonance (NMR) spectroscopy to calibrate chemical shift values (delta = 0 ppm).
Question Part 1

Identifying the NMR Standard Compound

✅ Correct Answer

A — Si(CH₃)₄ (Tetramethylsilane, commonly abbreviated as TMS)

Mark Awarded: 1 / 1 mark for selecting option A.

💡 Key Knowledge

  • Name: Tetramethylsilane (TMS).
  • Formula: Si(CH₃)₄ .
  • Why it is used: It gives a single, intense, sharp peak well away from most organic proton/carbon signals (at exactly 0 ppm). It is also non-toxic, inert, volatile (easy to remove from the sample after analysis), and soluble in common organic solvents.

🧠 Exam Technique

Direct recall multiple-choice question. Do not waste time calculating or over-analyzing. Memorise the specific roles of NMR solvents/standards ( TMS for calibration, CDCl₃ or D₂O as deuterated solvents).

❌ Common Errors

  • Confusing TMS with deuterated solvents like CDCl₃ (Option B) or D₂O (Option C), which are used to dissolve samples without interfering with proton signals, not to calibrate the 0 ppm chemical shift scale.
  • Guessing CCl₄ (Option D), which is sometimes used as a non-polar solvent because it contains no hydrogen atoms, but is not the chemical shift reference standard.

Topics

Module 6: Organic chemistry and analysis · 6.3 Analysis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.