Topic 11 covers analytical techniques used to identify unknown substances and proper data handling. SL focuses on uncertainties and basic spectroscopy. HL adds ¹H NMR and combined spectroscopic analysis.
Systematic vs random errors. Precision (reproducibility) vs accuracy (closeness to true value). Propagation of uncertainties through calculations. Graphical analysis: best-fit lines, gradient and intercept with uncertainties. Linearising non-linear relationships (e.g., plotting ln[A] vs time for first-order kinetics).
Sample ionised → accelerated → deflected by magnetic field → detected. m/z ratio identifies ions. Molecular ion peak (M⁺) gives molecular mass. Fragmentation pattern identifies structural features. Isotope patterns: Cl (3:1 for ³⁵Cl:³⁷Cl), Br (1:1). Used to determine relative atomic mass from isotope abundances.
Bonds absorb IR radiation at characteristic frequencies. Key absorptions: O-H broad (2500–3300 cm⁻¹ in acids, 3200–3600 in alcohols), N-H (3300–3500), C=O sharp (1700–1750), C-O (1000–1300). Fingerprint region (below 1500 cm⁻¹) is unique to each molecule. Used to identify functional groups present.
Different H environments give different chemical shifts (δ, ppm). Number of peaks = number of distinct H environments. Integration (area ratio) = ratio of H atoms. Splitting pattern (n+1 rule): neighbouring non-equivalent H atoms split the peak. TMS reference at δ = 0. Combined with MS and IR for full structural determination.
You should know the key ranges: O-H (broad, ~3000+ for acids, ~3300+ for alcohols), C=O (sharp, ~1700), N-H (~3400). The IB data booklet provides a table of characteristic absorptions, but you need to be able to interpret a spectrum quickly. Focus on recognising patterns: broad O-H + sharp C=O = carboxylic acid; broad O-H alone = alcohol; sharp C=O alone = aldehyde/ketone/ester.
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