{"id":582,"date":"2025-08-12T15:01:28","date_gmt":"2025-08-12T15:01:28","guid":{"rendered":"https:\/\/pressbooks.hccfl.edu\/introchemlabmanual\/?post_type=chapter&p=582"},"modified":"2026-02-24T14:27:39","modified_gmt":"2026-02-24T14:27:39","slug":"introduction-to-qualitative","status":"web-only","type":"chapter","link":"https:\/\/pressbooks.hccfl.edu\/introchemlabmanual\/chapter\/introduction-to-qualitative\/","title":{"raw":"Introduction to Qualitative Analysis","rendered":"Introduction to Qualitative Analysis"},"content":{"raw":"https:\/\/youtu.be\/AZIDe-f8KoY\r\n
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Learning Outcomes<\/p>\r\n\r\n<\/header>\r\n

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    \r\n \t
  • Apply the safety rules in the chemistry laboratory through proper and safe handling of chemicals and chemical equipment.<\/li>\r\n \t
  • Identify and use common equipment and measuring devices in the chemistry laboratory.<\/li>\r\n \t
  • Properly perform the technique of filtration, quantitative transfer of materials, pipetting and use of the Bunsen burner.<\/li>\r\n \t
  • Identify chemical and physical properties and changes.<\/li>\r\n \t
  • Identify unknown substances through qualitative analysis.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n

    One of the most useful indicators in qualitative analysis is the formation of a precipitate \u2014 an insoluble solid that forms when two aqueous solutions react. When a precipitate appears, it signals that a chemical reaction has occurred, specifically a double displacement reaction (also called a double replacement or metathesis reaction). The general form of a double displacement reaction is:<\/p>\r\nA<\/mi>B<\/mi>(<\/mo>a<\/mi>q<\/mi>)<\/mo><\/mrow><\/msub>+<\/mo>C<\/mi>D<\/mi>(<\/mo>a<\/mi>q<\/mi>)<\/mo><\/mrow><\/msub>\u2192<\/mo>A<\/mi>D<\/mi>(<\/mo>s<\/mi>)<\/mo><\/mrow><\/msub>+<\/mo>C<\/mi>B<\/mi>(<\/mo>a<\/mi>q<\/mi>)\u200b<\/span><\/mo><\/mrow><\/msub><\/mrow><\/semantics><\/math>\r\n\r\nHere, the cations and anions exchange partners. If one of the new combinations forms an insoluble compound, it appears as a solid precipitate, which may have a characteristic color or texture.\r\n

    Predicting whether a precipitate will form depends on solubility rules, which summarize the tendency of ionic compounds to dissolve in water:<\/p>\r\n\r\n

      \r\n \t
    1. \r\n

      Always soluble: All salts of Group 1 metals (Li\u207a, Na\u207a, K\u207a, etc.) and ammonium (NH\u2084\u207a) are soluble.<\/p>\r\n<\/li>\r\n \t

    2. \r\n

      Always soluble: All nitrates (NO\u2083\u207b), acetates (C\u2082H\u2083O\u2082\u207b), and most perchlorates (ClO\u2084\u207b) are soluble.<\/p>\r\n<\/li>\r\n \t

    3. \r\n

      Chlorides, bromides, iodides: Soluble except those containing Ag\u207a, Pb\u00b2\u207a, or Hg\u2082\u00b2\u207a.<\/p>\r\n<\/li>\r\n \t

    4. \r\n

      Sulfates (SO\u2084\u00b2\u207b): Soluble except those of Pb\u00b2\u207a, Ba\u00b2\u207a, Sr\u00b2\u207a, and Ca\u00b2\u207a.<\/p>\r\n<\/li>\r\n \t

    5. \r\n

      Carbonates (CO\u2083\u00b2\u207b), phosphates (PO\u2084\u00b3\u207b), chromates (CrO\u2084\u00b2\u207b): Insoluble except when paired with Group 1 metals or NH\u2084\u207a.<\/p>\r\n<\/li>\r\n \t

    6. \r\n

      Hydroxides (OH\u207b): Insoluble except for Group 1 metals, NH\u2084\u207a, and slightly soluble for Ca\u00b2\u207a, Sr\u00b2\u207a, and Ba\u00b2\u207a.<\/p>\r\n<\/li>\r\n<\/ol>\r\n

      By applying these rules, you can predict which combinations of ions will produce a precipitate.<\/p>\r\n

      Suppose you mix aqueous solutions of silver nitrate (AgNO\u2083) and sodium chloride (NaCl). The cations (Ag\u207a and Na\u207a) will exchange partners with the anions (NO\u2083\u207b and Cl\u207b):<\/p>\r\n \r\n\r\nAgNO<\/mtext>3<\/mn><\/msub>(<\/mo>a<\/mi>q<\/mi>)<\/mo>+<\/mo>NaCl<\/mtext>(<\/mo>a<\/mi>q<\/mi>)<\/mo>\u2192<\/mo>AgCl<\/mtext>(<\/mo>s<\/mi>)<\/mo>+<\/mo>NaNO<\/mtext>3<\/mn><\/msub>(<\/mo>a<\/mi>q<\/mi>)<\/mo><\/mrow><\/semantics><\/math>\r\n\r\n \r\n

      From the solubility rules, most chlorides are soluble, but AgCl is an exception \u2014 it is insoluble in water and appears as a white precipitate. Sodium nitrate, on the other hand, is soluble and stays dissolved in the solution. This white precipitate of AgCl provides clear visual evidence that a reaction has occurred and that silver ions were present in the original solution.<\/p>\r\n

      In your experiment, you will systematically mix known cation solutions with various anions and look for precipitates, noting their color and texture. Each cation produces a distinct pattern of reactions \u2014 a kind of chemical \u201cfingerprint.\u201d By comparing the reaction pattern of your unknown sample to those of the known cations, you will be able to identify the unknown. Careful observation and accurate recording of results are critical for making a correct identification.<\/p>\r\n\r\n

      Solubility Rules Quick Reference Chart<\/strong><\/h2>\r\n
      \r\n
      \r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
      Ion or Compound Type<\/strong><\/th>\r\nSoluble Compounds<\/strong> (No Precipitate)<\/em><\/th>\r\nInsoluble Compounds<\/strong> (Precipitate Likely)<\/em><\/th>\r\n<\/tr>\r\n<\/thead>\r\n
      Group 1 Cations (Li\u207a, Na\u207a, K\u207a, Rb\u207a, Cs\u207a)<\/td>\r\nAll compounds soluble<\/td>\r\n\u2014<\/td>\r\n<\/tr>\r\n
      Ammonium (NH\u2084\u207a)<\/td>\r\nAll compounds soluble<\/td>\r\n\u2014<\/td>\r\n<\/tr>\r\n
      Nitrates (NO\u2083\u207b)<\/td>\r\nAll nitrates soluble<\/td>\r\n\u2014<\/td>\r\n<\/tr>\r\n
      Acetates (C\u2082H\u2083O\u2082\u207b)<\/td>\r\nAll acetates soluble<\/td>\r\n\u2014<\/td>\r\n<\/tr>\r\n
      Chlorides (Cl\u207b), Bromides (Br\u207b), Iodides (I\u207b)<\/td>\r\nSoluble except with Ag\u207a, Pb\u00b2\u207a, Hg\u2082\u00b2\u207a<\/td>\r\nAgCl, PbCl\u2082, Hg\u2082Cl\u2082 (and similar Br\u207b, I\u207b salts)<\/td>\r\n<\/tr>\r\n
      Sulfates (SO\u2084\u00b2\u207b)<\/td>\r\nSoluble except with Pb\u00b2\u207a, Ba\u00b2\u207a, Sr\u00b2\u207a, Ca\u00b2\u207a<\/td>\r\nPbSO\u2084, BaSO\u2084, SrSO\u2084, CaSO\u2084<\/td>\r\n<\/tr>\r\n
      Carbonates (CO\u2083\u00b2\u207b), Phosphates (PO\u2084\u00b3\u207b), Chromates (CrO\u2084\u00b2\u207b)<\/td>\r\nSoluble only with Group 1 or NH\u2084\u207a<\/td>\r\nMost others are insoluble<\/td>\r\n<\/tr>\r\n
      Hydroxides (OH\u207b)<\/td>\r\nSoluble with Group 1, NH\u2084\u207a, and slightly soluble with Ca\u00b2\u207a, Sr\u00b2\u207a, Ba\u00b2\u207a<\/td>\r\nMost others insoluble<\/td>\r\n<\/tr>\r\n
      Sulfides (S\u00b2\u207b)<\/td>\r\nSoluble with Group 1, Group 2, and NH\u2084\u207a<\/td>\r\nMost others insoluble<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<\/div>\r\n<\/div>","rendered":"