General description, qualitative reactions and motion of analysis of cations, V and the VI analytical groups


Химия и фармакология

The V nlyticl group of ctions include: Fe2 Fe3Mn2Mg2Bi3 nd de bene esse SbIII nd SbV. Consequently the group regent of the V group of ctions is 2N solution of hydroxide sodium. hydrolysis of slts nd use of this property is in highqulity nlysis in prticulr t determintion of ctions of the V group.



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Lecture #6

General description, qualitative reactions and motion of analysis of cations, V and the VI analytical groups


  1.  General description of the V analytical group of cations
  2.  A hydrolysis of salts and use of this property is in a high-quality analysis, in particular at determination of cations of the V group
  3.  Characteristic reactions of cations of the V group
  4.  Motion of analysis of mixture of cations of the V group
  5.  General description of analytical group of VI cations
  6.  Oxidation- redaction reactions and their applications in a high-quality analysis, in particular at opening of cations
  7.  Characteristic reactions of cations of the VI group
  8.  Motion of analysis of mixture of cations of the VI group

  1.  General description of the V analytical group of cations.

The V analytical group of cations include: Fe2+, Fe3+,Mn2+,Mg2+,Bi3+ and de bene esse Sb(III) and Sb(V). Last mostly in solution are in the state of ascido- or hydroxycoordination anions, for example: [Sb+3Cl6]-3  and [Sb+5(OH)6]-.. These ions are incorporated in the V group due to their properties to form under the action of alkali precipitations, insoluble in his surplus, unlike hydroxide of the previous IV group, which are amthoteric. Consequently the group reagent of the V group of cations is 2N solution of hydroxide sodium.

  1.  A hydrolysis of salts and use of this property is in a high-quality analysis, in particular at determination of cations of the V group.

A hydrolysis of salts is a time-table by their water (reaction with water), due to displacement of equilibrium of its dissociation to the right:

                                  H2O ↔ H+ + OH-

Due to fastening of ions of hydrogen and hydroxide ions by the proper anions and cations, three types of hydrolysis are known. It is a hydrolysis of salts formed by weak acid and strong basis (a hydrolysis is on an anion), for example, of cyanides:

                     CN- + H2OHCN + OH-    is  an alkaline environment, рН > 7.

Hydrolysis of salts, formed strong acid and weak basis (a hydrolysis is on cation), for example, of ammonium salts:

                    NH4+ + H2O NH3٠ H2O + H+    is a acid environment, рН < 7.

Hydrolysis of salts, formed weak acids and weak bases (a hydrolysis is on cation and anion), for example, of acetate to the ammonium:

                                       CH3COO- + NH4+ + H2O NH3٠ H2O + CH3COOH

Salts, which formed polybasic acids or polybasic bases has step hydrolysis. For example, first the degree of hydrolysis of FeCl2  looks so:

                                  FeCl2 + H2OFeOHCl + HCl

                        Fe2+ + H2OFeOH+ + H+

And second:

                                           FeOHCl + H2OFe(OH)2 + HCl

                          FeOH+ + H2OFe(OH)2 + H+

Degree of dissociation of every next stage on an order less than previous, that is why usually in practice consider only by the first stage of hydrolysis.

The example of the use of the phenomenon of hydrolysis in an analysis is a characteristic reaction on Bi3+. At breeding of solution of salt of Bi white sediment falls out due to motion of reaction:

                                                 Bi3+ + Cl- + H2O BiOCl↓ + 2H+

Salts of Sb3+ hydrolysis a similar rank.

Other example of the use of hydrolysis at the analysis of mixture of cations of the V group is dissolution of гідроксиду magnesium in salts to the ammonium:

                         Mg(OH)2↓ + 2NH4ClMgCl2 + 2NH3٠H2O

                         Mg(OH)2↓ + 2NH+Mg2+ + 2H2O

                                       Mg(OH)2↓ + 2NH+Mg2+ + 2NH3٠H2O

  1.  Characteristic reactions of cations of the V group.

The characteristic reactions of cations of the V group are partly described in the previous sections of lecture. Reactions are on Fe2+   from K3[Fe(CN)6], Fe3+   from K4[Fe(CN) 6] and KCS, Mn2+ from NaBiO3 (or PbO2), Mg2+ from phosphat- and ammonium- ions described in practical work from a high-quality analysis. Stopped here for difficult enough reactions with participation of tioangidrides, tioacids and their salts which relate to the analysis of stibiy, and also arsen and tin.

Tioangidrides, like ordinary anhidrides, co-operate with alkali:

               Sb2S5↓ + 2NaOH + 10H2O 2Na[Sb(OH)6] + 5H2S

                      As2S3↓ + 6NaOH Na3AsS3 + 3H2O

Except for that, they dissolve in sulfides and polysulfides of alkaline metals an ammonium, for example:

                  Sb2S3↓ + Na2S ↔ 2NaSbS2

                 Sb2S5↓ + 2Na2S ↔ 2Na3SbS4 + 3S↓

Thus salts of tioacids appear on occasion, from which it is possible to select tioacids the action of acids:

                               Na3SbS3 + 3HClH3SbS3 + 3NaCl

The last are unsteady connections in the moment of formation laid out:

                                 2H3SbS3 ↔ 3H2S↑ + Sb2S2

At co-operation of sulfide ammonium from tioangidrides, which tin is in, arsen and stibiy are in the lower degrees of oxidation, last oxide, for example:

                                    As2S3↓ + 3(NH4)2S2  2(NH4)3SbS4 + S↓

Is it explained oxidizing properties of disulfide sulfur −S-1−S-1−. Is this chainlet similar to О-1О-1.

Differences of properties of tioangidrides from the ordinary sulfides of metals enable to separate tin during an analysis, stibiy and arsen from other cations.

  1.  Motion of analysis of mixture of cations of the V group.

During the analysis of mixture of cations of the V analytical group some features of their connections are taken into account, such as:

  •  Propensity of cations of Ві3+ and  Sb3+  is to the hydrolysis;
    •  Bad solubility of MnO2 is in an nitric acid;
    •  Solubility of Mg(OH)2 in solution of NH4Cl.
  1.  General description of analytical group of VI cations.

To the VI analytical group of cations behave Cu2+, Co2+, Ni2+, Cd2+ і Hg2+. These cations are united by a that feature, that they form soluble aminocomplexes (amiakaty), and it enables by the concentrated solution of ammonia to dissociate them from cations foremost the V groups:

                                        Fe(OH)2↓ + NH3٠H2O

                  Cd(OH)2↓ + 4NH3٠H2O ↔ [Cd(NH3)4](OH)2 + 4H2O

Those ions which did not enter in the complement of the VI group, but also form aminocomplexes, become separated from for the step of analysis before, for example, Ag+ with the chlorides of the II group and Zn2+ from amphoteric hydroxides of the IV group.

  1.  Oxidation-redaction reactions and their applications in a high-quality analysis, in particular at determining of cations.

All are known types of oxidation-redaction reactions: intermolecular, internal molecular and disproportionally – use in an analysis. So Mn2+, as known, is oxidate to the ion of permanganate, which has the characteristic colouring, by bismut of sodium, persulphat of ammonium or by dioxide of lead:

                2Mn(NO3)2 + 5PbO2 + 6HNO3 ↔ 2HMnO4 + 5Pb(NO3)2 + 2H2O

                                           Mn+2 – 5e- → Mn+7        2

                                            Pb+4 – 2e- → Pb+2               5

HMnO4 – provides the violet-red color of solution

By the characteristic reactions of such there is redacting of mercury (I)  (II) to metallic tin (II), similar reaction from Bi3+, oxidation Cr3+ to CrO-24, painted in yellow by peroxide of hydrogen and a lot of other.

By the example of the use of reaction of disproportionally in an analysis the can serve reaction decomposition of chloride of mercury (I) by an ammonia during determination proper cation:

             Hg+12Cl2 + 2NH3٠H2O → [NH2Hg+2]Cl+ Hg+NH4Cl + 2H2O

                         Hg+1 – 1e- Hg2+           1

                         Hg+1 + 1e-Hg0            1

Most pirochemical methods of high-quality analysis connections with decomposition compounds, it consist oxigen, is internal molecular reactions, for example, decomposition of nitrates:

                2Pb(NO3)2  2PbO + 4NO2↑ + O2

                        2O-2 – 4e- 2O0                1

                          N+5 – 1e-  N+4                4

  1.  Characteristic reactions of cations of the VI group.

The feature of cations of the VI group is formation of the numerous painted connections. It enables to use the proper «coloured reactions» for authentication of the adopted cations.

Yes, a copper, nickel and cobalt, form at co-operating with an ammonia aminocomplexes, accordingly, intensively dark blue, blue and dirtily yellow colors. Although Co2+ determine usually by the reaction of «dark blue ring»

              Co2+ + 4SCN- → [Co(SCN)4]2-

The layer of izoamil alcohol which is added for the increase of sensitiveness of reaction extracts this complex from water solution, painted in a dark blue color.

Ions, Hg2+ reacting with iodides, form bright red sediment which afterwards can be dissolved in surplus of sediment:

                               Hg2+ + 2I-  HgI2

                 HgI2↓ + 2I-  [HgI4]2-

Dymetylglioxsim with cations of Ni2+ at certain terms forms bad disolution connection, painted in a coral-red color (the reaction of Chugaeva is known).

Finally, it is peculiar to be besieged cations of Cd2+ in a sour environment under an action the sulphuretted hydrogen, forming a яскраво-жовтий sulfide:

                        Cd2+ + H2S CdS↓ + 2H+

8. Motion of analysis of mixture of cations of the VI group.

Characteristic reactions are on Cu2+, Co2+, Ni2+ and Hg2+ , specific enough in an order to define them a detal method. However before it it is needed in a strongly sour environment to sediment CdS and select him. The sulfides of other cations do not appear at these terms. Cations of Cu2+, Co2+, Ni2+ and Hg2+ determine in the separate tests of solution by specific reactions, described in a section 6.


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