TIPS TO IDENTIFY INORGANIC COMPOUNDS IN 70 (b) PROBLEMS

FROM d – BLOCK ELEMENTS

1. Chromium                                                                         Cr

Position in the periodic table: Period Number – 4, Group Number – 6

Chief ore: Chromite ore / Chrome ore, FeO.Cr₂O₃

Colour: Silvery white metal

Extraction:

     Chromite ore is roasted with molten Na₂CO₃ gives Sodium chromate.

     Na₂CrO₄.on acidification with conc. H₂SO₄ gives Sodium dichromate.

     Na₂Cr₂O₇ is heated with Carbon to give Sodium chromite.

     Na₂Cr₂O₄ on treatment with H₂O gives Chromic oxide precipitate.

    Cr₂O₃ is reduced by Aluminium to Chromium (Aluminothermic process).

with air:

unaffected at ordinary temperatures

at about 2000°C gives Chromic oxide

with water /steam: Red hot, decomposes steam forming Chromic oxide and Hydrogen

with dil. HCl: gives Chromous chloride and Hydrogen

with dil. H₂SO₄:  gives Chromous sulphate and Hydrogen

with dil. HNO₃: No reaction

with Conc. H₂SO₄: gives Chromic sulphate along with Sulphur dioxide, SO₂ and Water

with Conc. HNO₃: renders inactive or passive

with Halogens: give Chromium (III) halides

2. Potassium dichromate                                                       K₂Cr₂O₇

Chromium exists in + 6 Oxidation State 
Colour: Red orange

Preparation:

      Chief ore of chromium Chromite ore on roasting with molten Na₂CO₃ gives Sodium chromate.
     Na₂CrO₄ on acidification with conc. H₂SO₄ gives Sodium dichromate.
     Na₂Cr₂O₇ on treatment with KCl gives Potassium dichromate.

action of  heat: gives Potassium chromate, Chromic oxide and Oxygen

with NaOH:  gives Potassium chromate

Powerful oxidising agent-
             liberates I₂ from KI and dil. H₂SO₄,

oxidises Ferrous salt in presence of dil. H₂SO₄ to Ferric salt,

            oxidises H₂S in presence of dil. H₂SO₄ to Sulphur

with chloride salt and conc. H₂SO₄: gives reddish brown Chromyl chloride, CrO₂Cl₂ (Chromyl chloride Test)

use: in the detection of chloride ions in qualitative analysis , in leather industry,

3. Copper                                                                               Cu

Position in the periodic table: Period Number – 4, Group Number – 11

Chief Ore: Copper pyrite (Mixed Sulphide ore)

Colour: Reddish brown metal

action of heat: in the presence of air / oxygen

below 1370 K gives Cupric oxide (Black) &

above 1370 K gives Cuprous oxide (Red)

with air and moisture / water: gives basic Copper carbonate, Cu(OH)₂ . CuCO₃

with dil. HCl: in the presence of air gives Copper chloride and Water

with dil. H₂SO₄: in presence of air gives Copper sulphate and Water

with dil. HNO₃: gives Copper nitrate along with Nitric oxide, NO and Water

with Conc. H₂SO₄: gives Copper sulphate along with SO₂ and Water

with Conc. HNO₃: gives Copper nitrate along with NO₂ and Water

with NaOH: No reaction

use: for making utensils, containers, calorimeters, coins, etc, alloyed with gold and silver for making coins and jewellery

4. Copper sulphate Pentahydrate / Blue vitriol        CuSO₄ . 5H₂O

Colour: 
           Blue (Hydrated Salt)
           Colourless (Anhydrous Salt)

action of heat: Decomposes at various temperatures.

gives Copper sulphate Monohydrate at 373K / 100^oC,

Copper sulphate at 503K /230^oC,

Cupric oxide + SO₃ at 993K /720^oC

with ammonia: gives Deep blue coloured Complex compound - [Cu(NH₃)₄]SO₄

with KI: gives Cuprous iodide (White)

with KCN: first gives Yellow precipitate of Cupric cyanide and it decomposes to give Cyanogen gas

with NaOH: gives Pale blue precipitate of Copper hydroxide

with H₂S: gives a Black precipitate of Copper sulphide

use: germicide and insecticide in agriculture, Bordeaux mixture (mixture of Copper sulphate and Lime) is used as fungicide

5. Zinc                                                                                     Zn

Position in the periodic table: Period Number – 4, Group Number – 12,

Chief ore: Zinc blende

Colour: Bluish white metal,

with air: gives white cloud of Zinc oxide / Philosopher's wool which on reduction with Carbon gives Zn

with dil. HCl: gives Zinc chloride and Hydrogen

with dil. H₂SO₄: gives Zinc sulphate and Hydrogen

with dil. HNO₃: gives Zinc nitrate along with Nitrous oxide, N₂O and Water

With very dil. HNO₃: gives Zinc nitrate along with Ammonium nitrate and Water

with hot Conc. H₂SO₄: gives Zinc sulphate along with SO₂ and Water

with Conc. HNO₃: gives Zinc nitrate along with NO₂ and Water

with NaOH: gives Sodium zincate, Na₂ZnO₂

use: for galvanizing iron sheets, extraction of gold and silver, in batteries and dry cells

6. Zinc carbonate                                                                   ZnCO₃

Occurs in nature as Calamine

Preparation: NaHCO₃ is added to Zinc sulphate solution

action of heat: at 300°C gives Zinc oxide and Carbon dioxide

use: in making ointment for curing skin diseases, pigment for rubber

7. Silver                                                                                  Ag

Position in the periodic table: Period Number – 5, Group Number – 11

Chief ore: Silver glance / Argentite

Extraction: By the Mac-Arthur and Forrest’s cyanide process

Colour: White lustrous metal

with dil. HNO₃: gives Silver nitrate along with Nitric oxide, NO and Water

with Conc. H₂SO₄: Silver sulphate along with SO₂ and Water

with Conc. HNO₃: gives Silver nitrate along with NO₂ and Water

with Cl₂: gives Silver chloride

with Alkalies: No reaction

8. Silver nitrate / Lunar caustic                                            AgNO₃

Action of heat: 
     at 723K gives Silver nitrite, AgNO₂
     at 980 K gives Silver and NO₂

with KBr: gives Silver bromide, a Yellow precipitate, which is highly useful in Photography

with KI: gives Silver iodide, a Yellow precipitate

with organic compounds like Formic acid, Formaldehyde or Glucose: Ammoniacal Silver nitrate (Tollen’s reagent) is reduced to Silver mirror

use: in marking inks and hair dyes

9. Gold                                                                                    Au

Position in the periodic table: Period Number – 6, Group Number – 11

Extraction: By the Mac-Arthur and Forrest’s cyanide process

Colour: Lustrous Yellow metal

the most malleable and ductile of all metals

with air: Unaffected by dry or moist air or oxygen

with Alkalies: No reaction

with Cl₂: gives Auric chloride

with Aquaregia (3 parts of Conc. HCl + 1 part of Conc. HNO₃): gives Auric chloride 

  Inorganic Problem from d-Block elements.