I85PREP
⌘ K
European Baccalaureate Chemistry study materials
European Baccalaureate Chemistry study resources

European Baccalaureate Chemistry: Analytical and instrumental techniques

European Baccalaureate Chemistry · Work through your exam, one topic at a time.

All guide sections

Analytical and instrumental techniques

Analytical and instrumental techniques covers qualitative identification and quantitative determination. The exam tests tests for ions and gases, IR, mass spectrometry, NMR, chromatography and calibration, and expects you to combine evidence.

Core rules

  • Qualitative tests: flame tests identify metal cations (Li crimson, Na yellow, K lilac, Ca brick-red, Cu blue-green); precipitation with NaOH or NH3 identifies metal ions; dilute acid and barium chloride test sulfate; silver nitrate test halide; limewater test CO2.
  • Infrared spectroscopy identifies functional groups by absorption: O-H broad 2500-3300 cm−1, C=O 1650-1750, C-H 2850-3300, N-H 3300-3500.
  • Mass spectrometry gives the molecular ion M+ and fragmentation; the M+ peak gives relative molecular mass, and M+1 indicates carbon-13.
  • 1H NMR: number of environments = number of peaks; integration = relative number of H; splitting = n+1 from neighbouring equivalent H; chemical shift indicates environment. TMS is the 0 ppm reference.
  • Chromatography separates by differential affinity between mobile and stationary phases. Rf = distance travelled by spot/distance travelled by solvent; in GC and HPLC, retention time identifies components.
  • UV-visible absorption follows Beer-Lambert: A = εcl; a calibration curve converts absorbance to concentration.

Worked example

A compound has M+ = 58, a strong IR absorption at 1715 cm−1 and a single 1H NMR peak at δ 2.1 integrating to six hydrogens. Identify it. M = 58 is consistent with C3H6O (3 × 12 + 6 + 16 = 58). The IR peak near 1715 cm−1 indicates a ketone C=O. A single NMR environment for six equivalent hydrogens indicates two identical CH3 groups attached to a carbonyl carbon, with no other hydrogens. The compound is propanone, CH3COCH3.

Traps that cost marks

  • Reporting splitting without counting only equivalent neighbouring hydrogens.
  • Forgetting that OH and NH protons may exchange with D2O and disappear.
  • Confusing the molecular ion with the base peak (the most intense fragment).
  • Using Rf as a fixed identifier without specifying the solvent and stationary phase.
  • Reading concentration from a calibration curve without subtracting a blank.