Characteristic reactions of Silver cations Ag+ Characteristic reactions of Lead cations Pb2+
Characteristic reactions of Mercury cations Hg2+
2. qualitative reactions of cations of analytical group 3:
Charateristic reactions of сations Ba2+
Characteristic reactions of strontium сations Sr2+
Characteristic reactions of strontium сations Ca2+
Characteristic reactions of Silver cations Ag+
Water ammonia NH4OH, reacting with Ag+, precipitates silver in form of Ag2O, which dissolves in excess of reactant:
Ag+ + NH4OH = AgOH↓ + NH4+
2AgOH↓ = Ag2O↓ + H2O
Ag2O↓ + 4 NH4OH = 2[Ag(NH3)2]+ + 2OH- + 3H2O or
AgNO3 + NH4OH = AgOH↓ + NH4NO3
Ag2O↓ + 4 NH4OH = 2[Ag(NH3)2]OH + 3H2O
Test carrying out
Add by drops ammonia solution to 1-2 drops of silver nitrate solution till precipitation formation. Observe dissolving of turbidity at adding of excess of ammonia.
Characteristic reactions of Lead cations Pb2+
Potassium Chromate (Dichromate) K2CrO4 (K2Cr2O7) forms yellow precipitation PbCrO4 with ions Pb2+. This sediment doesn’t dissolve in acetic and hydrochloric acids, but solutes in alkalis and nitrate acid. Conditions: pH less then 7 (in presence of acetic acid), absence of reducing agents, reduced Cr6+ till Cr3+ (for example, Fe2+), absence of cations, formed with CrO42- sediments:
Pb2+ + CrO42- = PbCrO4↓
or 2Pb2+ + Cr2O72- +H2O = 2PbCrO4↓ +2H+
For example:
Pb(NO3)2 + K2CrO4 = PbCrO4↓ +2KNO3
or
2Pb(CH3COO)2 + K2Cr2O7 + H2O = 2PbCrO4↓ + 2KCH3COO + 2CH3COOH
Test carrying out
Add 1-2 drops of potassium chromate or dichromate solution to 1-2 drops of lead salt solution. Yellow precipitate formed.
Characteristic reactions of Mercury cations Hg2+
Iodide of potassium with a cation Hg2+ gives red precipitate of mercury iodide (II):
Test-carrying out
Pour into a test tube of 1 to 2 cm3 solution of nitrate of mercury (II) and add a few drops of potassium iodide. Thus fall red precipitate of mercury iodide (II), soluble in excess of reagent. Write molecular and ion-molecular reactions.
Characteristic reactions of сations Ba2+
1. Potassium chromate gives with the cation of barium, a yellow precipitate of barium chromate.
Test carrying out
In a test tube with solution of salt of barium add 2 - 3 см3 solution of dichromate of potassium.
2.The flame coloration. Volatile barium salts color a flame colorless to yellow-green.
Characteristic reactions of strontium сations Sr2+
The flame coloration Strontium salts color a flame colorless to carmine-red.
Characteristic reactions of strontium сations Ca2+
1.Ammonium oxalate (NH4)2C2O4. Ammonium oxalate forms white crystalline precipitation with Calcium ions:
Ca2+ + C2O42- = CaC2O4↓
For example,
CaCl2 + (NH4)2C2O4 = CaC2O4↓ + 2NH4Cl
The precipitation is soluble in mineral acids but is insoluble in acetic acid:
CaC2O4↓ + 2H+ = Ca2+ + H2C2O4
CaC2O4 ↓ + 2HCl = CaCl2 + H2C2O4
Test carrying out
Add 2-3 drops of Ammonium oxalate to 3-4 drops of Calcium salt solution.
2. Salts of calcium paint colourless flame of gas-ring in a brick-red color.
3-LW Qualitative reactions for cations of analytical group 4-5.
Task:
In notebook to prepare the report on laboratory work that includes the General characteristics of this group of ions, reaction with group reagent and private reactions of ions. To perform laboratory work (experiments, see below), to complete the report observations.
Еxperiments:
1.qualitative reactions of cations of analytical group 4:
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