Chem 122 Lab 8 UNR

Qualitative Analysis

A process or series of processes used to determine the presence of a chemical substance based on its reactivity rather than its quantity.

Qualscheme

A systematic chemical procedure or flowchart used to separate and identify a mixture of ions.

Gas Chromatograph / Infrared Spectrometer / Mass Spectrometer

Modern analytical instruments that replace traditional qualitative analysis by identifying both the compounds present and their specific concentrations.

Speed and Mobility

A primary advantage of chemical qualitative analysis, allowing for "on-site" testing in field work or crime scene investigations (CSI).

Firm Understanding of Chemical Reactivity

A benefit of manual qualitative analysis, requiring knowledge of acid-base, solubility, and redox reactions to predict chemical behavior.

Qualitative Groups

Ion classifications based on shared chemical reactivity and precipitation behavior, not their arrangement on the periodic table.

Confirmatory Reactions

Specific chemical tests used to verify the identity of a single ion after it has been separated from a group.

Group 1 Cations

Silver (Ag+), Mercury I (Hg2 2+), and Lead II (Pb2+), characterized by their ability to form precipitates with HCl.

Group IV Cations (Experimental)

Barium (Ba2+), Strontium (Sr2+), and Calcium (Ca2+), which form insoluble carbonates in basic solutions.

Group V Cations (Experimental)

Sodium (Na+), Potassium (K+), and Ammonium (NH4+), which are generally soluble and require flame or gas tests for identification.

Ammonium Carbonate ((NH4)2CO3) at pH 10

The reagent used to precipitate Group IV cations as white carbonates (BaCO3, CaCO3, SrCO3).

Bright Yellow Precipitate (BaCrO4)

The result of adding Potassium Chromate to a Barium solution; confirms the presence of Ba2+.

White Precipitate (CaC2O4)

The result of adding Sodium Oxalate to a Calcium solution; confirms the presence of Ca2+.

Strong Yellow Flame Test

The visual confirmation for Sodium (Na+).

Weaker Violet Flame Test

The visual confirmation for Potassium (K+), often viewed through cobalt glass to filter out sodium interference.

Litmus Paper Color Change (Red to Blue)

Indicates the presence of Ammonium (NH4+) after reaction with NaOH and heating, which releases NH3 gas.

Vigorous Effervescence (Bubbling)

Indicates Carbonate (CO3 2-) due to the evolution of CO2 gas when reacting with acids like H2SO4.

White Precipitate (BaSO4)

The result of adding BaCl2 to Sulfate (SO4 2-); notably insoluble in strong acids like HCl.

White Precipitate (AgCl)

The result of adding AgNO3 to Chloride (Cl-); uniquely dissolves in ammonia (NH3).

Cream Precipitate (AgBr)

The result of adding AgNO3 to Bromide (Br-); insoluble in dilute nitric acid.

Yellow Precipitate (AgI)

The result of adding AgNO3 to Iodide (I-); insoluble in both nitric acid and ammonia.

Reddish-Brown Pungent Gas (Br2)

Produced when solid Bromide (Br-) reacts with concentrated sulfuric acid.

Violet Vapors (I2)

Produced when solid Iodide (I-) reacts with concentrated sulfuric acid.

Brown Ring Test

The positive result for Nitrate (NO3-), occurring at the junction of FeSO4 and concentrated H2SO4.

Vinegary Smell

The characteristic odor produced when Acetate (CH3COO-) reacts with acid to form acetic acid.

Deep Red Color (Fe(C2H3O2)3)

Formed when Iron(III) chloride is added to a neutral Acetate solution.

Canary-Yellow Precipitate

The result of the Ammonium Molybdate test for Phosphate (PO4 3-).

White Pearlescent Precipitate

The appearance of silver sulfate, which is distinct from the truly white AgCl.

Crimson-Red Flame Test

The visual confirmation for Strontium (Sr2+).

Safety Note for Sulfuric Acid

Concentrated H2SO4 (18 M) causes severe burns and must be handled with extreme care.

Interference in Chloride Test

Bromide and Iodide ions will interfere with the AgNO3 test for Chloride.

Interference in Nitrate Test

Bromide and Iodide ions will interfere with the Brown Ring test for Nitrate.

Nitric Acid (HNO3) Acidification

Necessary before some silver nitrate tests to eliminate interfering Carbonate or Sulfite ions.

Nichrome Wire

The tool used for flame tests; must be cleaned in 12 M HCl until no color is visible in the Bunsen burner flame.

Solubility vs. Reactivity

Qualitative analysis relies on ions having "known specific compounds" that they will predictably form precipitates with.