Практикум (русский язык). 6 Лабораторная работа 1

Characteristic reactions of Sodium cations Na+

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Characteristic reactions of Sodium cations Na +
Characteristic reactions of ammonia cations NH 4 +

Characteristic reactions of Sodium cations Na⁺

Characteristic reactions of ammonia cations NH₄⁺

Characteristic reactions of Potassium cations K⁺

Potassium hexanitritocobaltate (III) Na₃[Co(NO₂)₆] isolates yellow crystalline precipitation of double salt of potassium and sodium from K⁺ salt solution:
2 K⁺ + Na⁺ +[Co(NO₂)₆]^3- = K₂Na[Co(NO₂)₆]↓

2 KCl + Na₃[Co(NO₂)₆] = K₂Na[Co(NO₂)₆] ↓+ 2NaCl

Test carrying out

Add 3-4 drops of reagent to 2-3 drops of potassium salt solution.

Analyzed solution should have pH not more than 7 because reagent is easily destroyed in alkali medium:
Na₃[Co(NO₂)₆] + 3NaOH = Co(OH)₃↓+ 6NaNO₂
At pH less than 7 unstable acid is formed:
K₂Na[Co(NO₂)₆]↓+3HCl=H₃[Co(NO₂)₆] (solution) + NaCl + 2KCl

2H₃[Co(NO₂)₆]+ 4HCl = 5NO + 2CoCl₂ +7NO₂ + 5H₂O

Reagent and precipitation are not destroyed in acetic acid.

The ions of ammonia prevent the determination of Potassium ions, because ammonia forms the same yellow precipitation like potassium ions:

2 NH₄Cl + Na₃[Co(NO₂)₆] = (NH₄)₂Na[Co(NO₂)₆] ↓+ 2NaCl

Concentration limit с = 1:13000.

Characteristic reactions of Sodium cations Na⁺

Flame test Sodium (pharmacopeia’s reaction). Salts of Sodium paint flame in a persistent yellow color.

Implementation of reaction. A platinum wire moistens with solution HCl and heat in a flame. A clean platinum wire moistens with solution of salt Sodiumand heat in a flame. If there are ions to Sodium, flame paints in a persistent yellow color.

Characteristic reactions of ammonia cations NH₄⁺

1. Alkalis (NaOH, KOH). Alkalis isolate ammonia from ammonia salts at heating:

NH₄⁺ + OH^-= NH₃ +H₂O

NH₄Cl + NaOH

NH₃↑ + NaCl + H₂O

Reaction is highly sensitive, specific; concentration limit с=1:5000000.

Test carrying out

Add 4-5 drops of NaOH or KOH solution to 3-4 drops of ammonia salt and heat at water bath. Isolated ammonia is detected on odor or red litmus paper wetted by DW, which becomes blue in ammonia vapor.

2. Nessler’s reagent K₂[HgI₄]+KOH forms red-brown precipitation with ammonia ions:

NH₄⁺ + 2[HgI₄]^2- + 4KOH = + 7 I^- + 3H₂O

NH₄Cl+2K₂[HgI₄]+4KOH = + 7KI + KCl+3H₂O

Test carrying out

Add 2-3 drops of Nessler’s reagent to 1-2 drops of diluted ammonia salt. In presence of ammonia ion trace the solution becomes orange.

Reaction is highly sensitive, concentration limit с = 1:10000000.

Qualitative reactions for cations of analytical group 2-3.

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 2:

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Практикум (русский язык). 6 Лабораторная работа 1

Characteristic reactions of Sodium cations Na+

Characteristic reactions of Sodium cations Na+

Characteristic reactions of ammonia cations NH4+

Characteristic reactions of Sodium cations Na+

Characteristic reactions of ammonia cations NH4+

Characteristic reactions of Sodium cations Na⁺

Characteristic reactions of ammonia cations NH₄⁺

Characteristic reactions of Sodium cations Na⁺

Characteristic reactions of ammonia cations NH₄⁺