Analytical Chemistry Reviewer (Finals)

CHEMISTRY FINALS Sources & Nature of Errors o Accuracy – closeness of a result to its true or accepted value o Precision – closeness of data to other data obtained the same way o Replicates – samples of about the same size that are carried through an analysis in exactly the same way o Absolute error – difference between the measured value and the true value o Relative error – absolute error divided by the true value Types of Errors: o Random or indeterminate error – errors that affect the precision of measurement o Systematic or determinate error – errors that affect the accuracy of the result Sources of Systematic Errors: o Instrument errors – calibration eliminates most instrument errors o Method errors – most difficult to identify and correct o Personal errors – based on personal judgment Classification of Method Analysis Acc. to Final Measurement o Gravimetric – how much of analyte is present in a sample o Volumetric – volume o Instrumental – could vary Ex. a. Electroanalytical (potential difference, voltage, multimeter) b. Chromatography c. Spectroscopic (electromagnetic radiation) Classification of Quantitative Analysis Acc. to Number of Analyte or Extent of Analysis o Complete/ ultimate o Partial o Constituent Acc. to Nature of Analyte o Elemental o Molecular Acc. to Concentration of Analyte o Macro – major constituent (mostly present) o Trace – small amount present Acc. to Sample Size Mass Volume Macro >100 mg >100 mL Semi micro 10 – 100 mg 50 – 100 mL Micro 1 – 10 mg