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FY13CE Chemistry study materials
FY13CE Chemistry study resources

FY13CE Chemistry: Analytical Chemistry and Laboratory Techniques

FY13CE Chemistry · Work through your exam, one topic at a time.

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Analytical Chemistry and Laboratory Techniques

This domain tests identification tests, instrumental analysis, separation methods, accurate titration technique and the treatment of measurement results - the practical skills that decide marks in the written and assessed practical components.

Qualitative tests

  • Flame tests: Li crimson, Na yellow, K lilac, Ca brick-red, Cu blue-green. Clean the nichrome wire between samples.
  • Adding NaOH then excess NH3: Cu2+ gives a blue precipitate soluble in excess NH3; Fe2+ green; Fe3+ brown; Al3+ and Pb2+ white, soluble in excess NaOH.
  • Halides: acidify with dilute HNO3, then add AgNO3. AgCl is white and soluble in dilute NH3, AgBr cream and sparingly soluble, AgI yellow and insoluble.
  • Carbonates fizz with acid and turn limewater milky; sulfates give a white precipitate with BaCl2 after acidification, which excludes carbonate and sulfite interference.

Instrumental methods

  • Infrared: broad O–H around 2500–3300 cm−1, C=O about 1680–1750 cm−1, C–O about 1000–1300 cm−1.
  • Mass spectrometry: the molecular ion peak gives Mr; fragmentation patterns support structure.
  • NMR: number of environments, integration ratios and splitting pattern.
  • Chromatography: Rf = distance moved by spot ÷ distance moved by solvent front; retention time identifies components in GC and HPLC.

Quantitative technique

  • Read the burette to the nearest 0.05 cm3 at the bottom of the meniscus; use the average of concordant titres and discard the rough one.

Worked example

25.0 cm3 of hydrochloric acid requires 23.40 cm3 of 0.1000 M NaOH. n(NaOH) = 0.1000 × 0.02340 = 2.340 × 10−3 mol. The equation is 1:1, so n(HCl) = 2.340 × 10−3 mol and c = 2.340 × 10−3/0.0250 = 0.0936 mol dm−3.

Traps that cost marks

  • Failing to acidify before the silver nitrate test, so carbonate gives a false precipitate.
  • Quoting flame colours without the correct metal, or contaminating the wire between tests.
  • Including the rough titre in the average.
  • Quoting Rf greater than 1 or measuring the solvent front incorrectly.
  • Reporting more significant figures than the burette reading supports.