Characteristic reactions of Copper cations Cu2+

Characteristic reactions of Copper cations Cu²⁺

the 1^st: 2Cu²⁺ + SO₄^2- + 2NH₄OH = (CuOH)₂SO₄ + 2NH₄⁺;

the 2^d: (CuOH)₂SO₄ + 2NH₄⁺ + 6NH₄OH = 2[Cu(NH₃)₄]²⁺ + 8H₂O

For example,

2CuSO₄ + 2NH₄OH = (CuOH)₂SO₄↓ + (NH₄)₂SO₄;

(CuOH)₂SO₄↓+(NH₄)₂SO₄ + 6NH₄OH = 2[Cu(NH₃)₄]SO₄ + 8H₂O.

Add little by little NH₄OH solution to 3-4 drops of copper salt solution up to basic salt formation (precipitation) and then the excess of NH₄OH up to the dilution of precipitation and formation of complex compound which has dark blue color. This reaction is highly sensitive (c=1:500000).

Co²⁺ + 4SCN^- = [Co(SCN)₄]^2-.

For example,

CoCl₂ + 4NH₄SCN = (NH₄)₂[Co(SCN)₄] + 2NH₄Cl.

Reaction is very sensitive. Complex compound solves better in the layer of organic solvent, that in water solution.

Test carrying out

Add 4-5 drops of saturated solution of ammonium or potassium thiocyanide in organic solvent to 3-4 drops of Cobalt (II) salt. Shake up content of tube and wait a few seconds. The upper layer is colored in dark-blue color.

Presence of Fe³⁺-ions in analyzing mixture prevents to determination of cobalt(II), because complex ion [Fe(SCN)₆]^3- is more stable that Co(SCN)₄]^2-. In such case it is necessary to mask Fe³⁺-ion added solid NaF, where F^- ions form with Iron (III) ions stable colorless complex ion [FeF₆]^3-, when cobalt (II) ions don’t compexing with this masking agent. As masking agent orthophosphoric acid and wine acid H₂C₄H₄O₆ might be used.
Characteristic reactions of Nickel cations Ni²⁺
Dimethylglioxime (Chugaev’s reagent) C₄H₈N₂O₂ in ammonia medium (pH=9) forms bright pink precipitation of intra-complex salt with Ni²⁺ ions [Ni(C₄H₇N₂O₂)₂]↓. Precipitation solves in acids, alkalis, but doesn’t dissolve in diluted ammonia solution.

Reaction is very sensitive, concentration limit с=1:300000:

Ni²⁺+2C₄H₈N₂O₂+2NH₃=[Ni(C₄H₇N₂O₂)₂]+2NH₄⁺.

For example:

NiSO₄ +2C₄H₈N₂O₂+2NH₃=[Ni(C₄H₇N₂O₂)₂]+(NH₄)₂SO₄.

Test carrying out

Add 12-16 drops of ammonia solution and 8-10 alcohol solution of Chugaev’s reagent to 4-5 drops of nickel salt solution. Study solubility of prepared precipitation in mineral acids, alkalis and ammonia solution. For this to divide prepared precipitation into 4 tubes and add corresponding reactant in every doze of precipitation.

Ions of Fe²⁺, Fe³⁺, Cu²⁺ prevent to determination of nickel(II) ions with Chugaev’s reagent.
Characteristic reactions of mercury Hg²⁺
Reagent for Hg²⁺is KI, which forms a bright red precipitate HgI₂ soluble in excess of reagent:

Hg(NO₃)₂+ 2 KI → HgI₂↓ + 2 KNO₃

Hg²⁺+ 2 I‾ → HgI₂

HgI₂+ 2 KI → K₂[HgI₄]

HgI₂+ 2 I‾→ [HgI₄]²‾

colorless solution

1. Various system of classification of cations: hydrogen sulfide, ammonium phosphate, acid-base.

2. The principles underlying the classification of cations on each of these systems.

3. The number of analytical groups in each system, group reagents.

4. Advantages and disadvantages of each system of classification of cations.

5. Characterization of acid-base classification system:

• The relationship of this classification system with the arrangement of the elements in the Periodic system of chemical elements D. I. Mendeleev;

• Detailed description of each of the groups of the cations • Qualitative reactions of individual cations.

6. Mapping analysis of mixture of cations (a thought experiment):

• Cations are treated as one analytical unit;

• Cations belong to two different analytical groups

6-LW Analysis of mixture of cations 1-3 analytical groups (control task).

Each student is issued with a bottle of the mixtures containing 3 cation of these groups.

Determine which of the cations contained in the mixture (p99-101, application5, circuit5). The result of the issue the report, which should reflect the procedure for opening the ion reaction equations the opening, the observed effects, the circuit opening.