Home Random Page


CATEGORIES:

BiologyChemistryConstructionCultureEcologyEconomyElectronicsFinanceGeographyHistoryInformaticsLawMathematicsMechanicsMedicineOtherPedagogyPhilosophyPhysicsPolicyPsychologySociologySportTourism






Germanium, tin, and lead

Ge, Sn and Pb do not react with H2 directly. The common method of obtaining hydrides:

decomposition of their compounds by diluted acids:

Mg2Å + 4HCl = ÅH4 + 2MgCl2

Hydrides in the series Ge—Sn—Pb elements are low stable. In the series SiH4 (silane) - GeH4 (germane) - SnH4 (stannane) - PbH4 (plumbane) stability decreases so that the existence of PbH4 has been confirmed indirectly (increase of fugitivity of Pb in the stream of hydrogen):

GeH4 = Ge + H2 (rapidly at 300 oC)

SnH4 = Sn + H2 (rapidly at 150 ° C)

PbH4 = Pb + H2 (immediately at STP)

Ge has the maximal number of compounds with hydrogen, with the homologous series of germanes from GeH4 to Ge9H20. All of them have chemical properties that are similar to GeH4 (gas b.p. = -90 oC).

Preparation:

GeO2 + Na[BH4] + HCl + H2O = GeH4­ + H3BO3 + NaCl

Germanes are rapidly oxidised:

GeH4 + O2 = GeO2 + 2H2O

Degree of hydrolysis of germanes is lower compared with silanes. GeH4 is stable even in 30% solution of alkali, while SiH4 is easily decomposed even by water.

SnH4 and Sn2H6 are only known in case of tin. SnH4 is a strong reducing agent that in 15% NaOH and dilute acids reduces HgCl2 easily:

SnH4 + 3HgCl2 = 3Hg + SnCl2 + 4HCl

There are many derivatives of hydrogen compounds, including relatively stable tetraethyllead, Pb(C2H5)4, used as antidetonator of fuel for internal combustion engines.


OXYGEN CONTAINING COMPOUNDS

Carbon

Carbon forms compounds ÑÎ, ÑÎ2, Ñ3Î2, Ñ5Î2, Ñ6Î9 and cyclic Ñ12Î12 and (C4O3)n.. To inorganic belong mono- and dioxide of carbon. others are derivative of organic substances.

carbon Dioxide (carbon dioxide) CO2.

It forms at burning of coal and all organic substances.

Preparation.In industry: roasting of limestone:

ÑàÑÎ3 = ÑàÎ + ÑÎ2­ DÍ = 180 kJ/mol

In a laboratory:

ÑàÑÎ3 + 2HCl = CaCl2 + CO2­ + H2O (Kipp apparatus)

Structure.CO2 consists of symmetric linear unpolar molecules (distance of C—O is 0,113 nm): It has sp-hybridization: two s-bonds are formed at overlapping of 2 sp-hybride orbitals of C and two 2px-orbitals of O.Two other localized p-bonds are formed at overlapping of 2py and 2pz-orbitals of C with 2py and 2pz-orbitals of O.

Properties.At ordinary conditions, CO2 is colourless, uncombustible gas with a weak sourish smell and taste. It is heavier then air - specific density in respect to air makes up 1,529.

Therefore, in the absence of air motion CO2 is going on the bottom of hollows, where it forms (caves, wells, mines and others. As a result, there is known Dog’s cave near Naples - a man is not hurt, dogs perish. It follows to be very careful at the entrance in such premises, because CO2 does not support breathing, at concentrations higher then 3% it causes heavy disorder of organism functioning.At concentration 10%, the loss of consciousness and death through the stop of breathing comes quickly.

CO2 is easily liquefied at 20° and pressure 57 atm. into a colourless mobile liquid with density 0,766 g/cm3. In the liquid state, it is stored in the balloons painted in a black with yellow inscription carbonic acid.



At rapid evaporation “dry ice” is created, which in the preliminary compressed state slowly evaporates and is used therefore as an effective cooling medium. Sublimation of “dry ice” at ordinary conditions occurs at –78,48 °C.

Chemically, CO2 is rather inert. It does not support burning, because it is the final product of combustion (it is used as a fire-extinguisher media). In its atmosphere burn only the substances, affinity to oxygen at which are greater than at carbon, for example, magnesium:

CO2 + Mg = MgO + C DH°298 = –811,7 kJ/mol

At ordinary conditions, CO2 is well dissolved in water (» 1:1 on a volume). Its saturated water solution has concentration » 0,04 M CO2, pH of solution = 3,7.

At CO2 dissolution is formed partly H2CO3, anhydride of which it is:

CO2 + Í2Î Û Í2ÑÎ3

This reaction equilibrium is very strongly displaced to the left, therefore greater part of CO2 is found simply in the dissolved state, and not as H2CO3. Taste of this solution is slightly sour.

Carbonic acid

H2CO3 is weak dibasic acid:

Í2ÑÎ3 Û Í+ + ÍÑÎ3- Ê1 = 4,2•10-7

ÍÑÎ3- Û Í+ + ÑÎ32-­ Ê2 = 4,8•10-11

At higher temperatures an equilibrium is displaced toward the practically complete removal of CO2 from the solution (to the left), and in an alkaline medium as a result of binding of ions H+ - to the right.

 
 

In the anion ÑÎ32- atom of carbon is found in the state of sp2-hybridization:

 

p-Electrons, which remains by one at every atom, form delocalized pp-p bonds which substantially increase the strength of the structure. This ion is flat in accordance with sp2-hybridization.

To H2CO3 correspond two types of salts - neutral, carbonates with an ion ÑÎ32- and acidic – hydrogen carbonates which contain an ion HCO3-. Most salts of carbonic acid are colourless.

Carbonates.Among them, the water-soluble are only salts of alkali metals (excepting Li2CO3) and ammonium. In solution carbonates hydrolyze strongly:

ÑÎ32- + Í2Î Û ÍÑÎ3- + ÎÍ- ðÍ > 7

Often this reaction is complicated by the reactions of double exchange between two-charged cations of weak bases and soluble carbonates:

2CuCl2 + 2Na2CO3 + H2O = (CuOH)2CO3¯ + CO2­ + 4NaCl

In the case of multicharge cations (Fe3+, Cr3+, Al3+, Ti4+, Zr4+) hydroxide carbonates are not form even, but as a result of complete hydrolysis are precipitated hydroxides:

2AlCl3 + 3Na2CO3 + 3H2O = 2Al(OH)3¯ + 3CO2­ + 6NaCl

2Al3+ + 3CO32- + 3H2O = 2Al(OH)3¯ + 3CO2­

Thermally, the more stable are carbonates, the more active are metals, from which they are formed. So, Na2CO3 is melted without decomposition, CoCO3 decomposes on CoO and CO2 at 825°, and Ag2CO3 - at 100°. (Analogy with nitrates).

At action of strong acids all carbonates are decomposed with the elimination of CO2.

Hydrogen carbonates.All known hydrogen carbonates are soluble. In nature, they are slowly formed at interaction of insoluble carbonates with carbonic acid:

ÑàÑÎ3 + ÑÎ2 + Í2Î = Ñà(ÍÑÎ3)2,

therefore, they are always present in natural water. The most used among them is NaHCO3 - washing soda. Its hydrolysis occurs so:

ÍÑÎ32- + Í2Î Û Í2ÑÎ3 + ÎÍ-h)

ÍÑÎ32- Û Í+ + ÑÎ32- d)

it is needed to confront them, in this case Kh >> Kd, therefore pH ~ 8.

Like carbonates hydrogen carbonates are decomposed by strong acids. At heating higher then 60° they begin to decompose with evolving carbon dioxide:

NaHCO3 Na2CO3 + CO2 + H2O

On that thermal decomposition is based one of methods of removal of hardness of water.


Date: 2016-01-03; view: 793


<== previous page | next page ==>
Germanium, tin, and lead | Carbon Monooxide (charcoal gas).
doclecture.net - lectures - 2014-2024 year. Copyright infringement or personal data (0.009 sec.)