Mercury, Silver & Zinc Notes |NEB chemistry| - Note Library


Mercury, Silver & Zinc Notes |NEB chemistry|


   The symbol of mercury, Hg, has been derived from hydrargyrum which is a latin name meaning liquid silver. It is the last element of IIB group of the modern periodic table.
1.It occurs in small quantity in free or native state.
2.In combined state, it occurs mainly as the sulphide ore called cinnabar (HgS)
Mercury can be extracted from its sulphide ore i.e. cinnabar(HgS) going through the following steps:
1.Concentration: The ore is first crushed in a jaw crusher and then powdered in ball mills to a very fine state. Since, the main ore is sulphide, the powdered ore is then subjected to froth flotation process by mixing the ore with pine or eucalyptus oil and water in a tank. The ore is then stirred by blowing current of air, froth of the sulphide ore is formed which is skimmed off as concentrated ore. The gangue particles remain at the bottom and are removed.
2.Roasting and distillation: The concentrated ore is roasted, on heating with coke,in the presence of excess air to get mercuric oxide which, in turn, decomposes into metallic mercury.
2HgS +3O2------->2HgO+ 2SO2↑    

2HgO------->2Hg + O2 ↑ 

HgO +C------>Hg + CO↑  

Roasting is carried out in a modern plant called " Shaft furnace" where the concentrated cinnabar mixed with coke is heated in a current of air ( at 5000C to 6000C). The metallic mercury distills over as vapours along with other impure gases into the condenser which contains Y-shaped water cooled pipes. Vaours of mercury get condensed and settle down at the bottom of the condenser.

          Fig: Shaft furnace for the extraction of mercury.
Advanatges of the modern process: 
⚫It is continuous.
⚫Loss of mercury vapours is very small.
⚫Cinnabar of all grades can be employed.

Mercury thus obtained is not pure and contains copper,zinc,bismuth and lead as impurities. The crude mercury is refined by following methods.
⚫Certain metals dissolved in crude mercury are partially oxidized in the air. These oxides form a very thin layer on the surface. This thin film is removed by filtering the mercury through canvas or chamois leather.
⚫The (soluble ) impurities like Zn, Cu and Fe etc are removed by running the crude mercury dropwisely through a long column of dil.HNO3 where metal impurities are dissolves in acid to give their nitrate or react with the nitrate of mercury(I) leaving pure mercury.
4Zn +10 HNO3--------->4Zn(NO3)2 + 5H2O + N2O↑
6Hg + 8HNO3------->3Hg2(NO3)2 + 4H2O + 2NO ↑
Hg2(NO3)2 + Zn------>2Hg ↓+ Zn(NO3)2

The mercury thus purified may contain non-volatile impurities like Au, Ag, Pt etc. These are removed by distillation under reduced pressure where volatile Hg distills over leaving impurities.

Fig: Extraction of mercury  
Chemical Properties: 
1.Action with air: At ordinary temperature, mercury does not react with air. On heating to 3500C, it gets oxidized to mercuric oxide.
2Hg +O2----->2HgO (red oxide)
2.Action with water:  
Mercury, being less electropositive metal, is unable to decompose water molecules in the chemical reaction. So, it does not react with water.
3.Actions of acids: 
With HCl : Mercury is not affected by dilute or concentrated hydrochloric acid.
⚫With hot and conc. H2SO4: Mercury reacts with hot and conc. H2SO4 evolving sulphurdioxide gas.
Hg + 2H2SO4------>HgSO4 +SO2 + 2H2O

With dil. HNO3: Mercury reacts with dil. HNO3 to give mercurous nitrate evolving nitric oxide gas.
6Hg + 8HNO3------>3Hg2(NO3)2 + 4H2o + 2NO↑

With conc. HNO3: Mercury reacts with conc. HNO3 to give mercuric nitrate evolving nitrogen dioxide gas.
Hg + 4HNO3----->Hg(NO3)2 + 2H2O + 2NO2↑

4.Action with halogen: Mercury combines readily with halogens forming halides.
 Hg+Cl2------>HgCl2 ( mercuric chloride) / corrosive sublimate
2Hg + Cl2 Hg2Cl2 ( mercurous chloride) /                                                        Calomel

5.Action with sulphur: When heated with sulphur produces mercuric sulphide.
                  Hg + S----> HgS
6.Action with aqua-regia:
 Aqua-regia is the mixture of conc.HNO3 and conc.HCl in the ratio of 1:3. Mercury quickly reacts with aqua-regia to form mercuric chloride.
HNO3 + 3HCl------>NOCl + 2H2O + 2[Cl]
HNO3+3HCl+Hg   NOCl+Hgcl2+2H2O

7.Action of O3 : 
When mercury comes in contact with O3, mercurous oxide is formed. So, the meniscus of mercury gets lowered and it leaves a tail when allowed to run through an inclined surface. This is called tailing of mercury.
    O3-------->O2 + O
    2 Hg + [O]------>Hg2O 

⚫It is used in thermometers, barometers etc.
⚫It is used for making amalgams as Na-Hg, Cu-Hg etc to use them as reducing agent while carrying out organic reactions.
⚫It is used in mercury vapour lamp.
⚫It is used in preparing its compounds.
Compounds of Hg 
A. Hg2Cl2 ( Mercurous chloride or Mercury(I) chloride or Calomel) 
Calomel is a non-poisonous mercurous compound. It contains Hg in dimer form as [Hg+-Hg+] ion. There is a covalent bond between two atoms of Hg. So, its molecular formula is Hg2Cl2 rather than HgCl.
1.From Hg2(NO3)2:  
It can be prepared by treating solutions of mercurous nitrate and sodium chloride.
Hg2(NO3)2 +2NaCl---->Hg2Cl2↓ + 2NaNO3
                                                               (white                                                                                                                                                               ppt)
2.From HgCl2 (ic chloride): 
It can be prepared by heating HgCl2 with mercury in iron vessel.
 HgCl2 + Hg---->Hg2Cl2↓
     (ic).                  (ous)

3.From mercuric sulphate: 
When mercuric sulphate is treated with sodium chloride in presence of mercury then Hg2Cl2 is obtained.
HgSO4 + Hg+ NaCl----->Hg2Cl2 + Na2SO4    Properties: 
1.It is white powder.
2.It is tasteless and odorless.
3.It is insoluble in water and acids.
4.It dissolves in aqua-regia by forming HgCl2.
HNO3 + 3HCl NOCl +H2O + 2[Cl]
Hg2Cl2 + 2[Cl] 2HgCl2 
HNO3 + 3HCl+ Hg2Cl2-------->NOCl + 2HgCl2+ 2H2O
                                      (Nitrosyl chloride)
5.Action with ammonia:
Calomel reacts with ammonia to form grey black product due to the formation of mixture of finely divided Hg(black) and amido-mercuric chloride (white).
 Hg2Cl2+2NH3------>Hg + Hg(NH2)Cl + NH4Cl
                                      Grey-black colour
6.Action with stannous chloride: 
Mercurous chloride gets reduced to metallic mercury on reacting with SnCl2.
Hg2Cl2 + SnCl2 2Hg + SnCl4
⚫It is used in medicine as purgative.
⚫It is used as an antiseptic drug also.
⚫It is used as electrode
⚫It is used in preparing other compounds of mercury. 

B. HgCl2 ( Corrosive sublimate or Mercuric chloride or Mercury(II) chloride):
Mercuric chloride is called corrosive sublimate. Corrosive sublimate is poisonous compound of mercury(II) state.
 1. From mercury: 
It can be prepared by passing excess chlorine gas over heated Hg. 
    Hg + Cl2------>HgCl2 ↑ 
During this, HgCl2 get sublimed off.

2.From mercuric sulphate: 
It can be prepared by heating mercuric sulphate with sodium chloride in the presence of manganese dioxide.
HgSO4 + 2NaCl------->HgCl2↑ + Na2SO4     
(ic).                                (ic)                          
During this, HgCl2 get sublimed off.
3. From mercuric oxide: 
Corrosive sublimate can be obtained by dissolving mercuric oxide with dil. HCl. Mercuric oxide is obtained by the reaction of Hg2+compound with NaOH.
 HgO +2HCl-------->HgCl2 + H2O        

Chemical Properties : 
Action with SnCl2: 
On reacting with stannous chloride, mercuric chloride first gets reduced to mercurous chloride and then to metallic Hg.
   2HgCl2+SnCl2--->Hg2Cl2↓ + SnCl4 ( stannic chloride)
    (ic)                         (ous)
  Hg2Cl2+SnCl2--->2Hg + SnCl4
   (ous)                  (silvery)
Action with KI: 
On reacting with potassium iodide solution, HgCl2 solution gives scarlet precipitate of mercuric iodide which gets dissolved on adding excess pot.iodide solution by forming potassium mercuric iodide complex called Nessler's reagent and used to detect ammonia.
      HgCl2 + 2KI----->HgI2↓ + 2KCl 
                   (less)      (scarlet ppt)
     HgI2 +2KI-----> K2HgI4
        (excess)       (Pot. Mercuric iodide)
Action with ammonia:
 HgCl2 reacts with ammonia to form white ppt of mercuric amino chloride.
     HgCl2 +2NH3----->Hg(NH2)Cl↓ + NH4Cl
Action with SO2: 
Aq. Solution of mercuric chloride gets reduced to mercurous chloride on passing SO2 gas.
 2HgCl2+2H2O+SO2-->Hg2Cl2 + H2SO4 + 2HCl
 (ic)                                    (ous)
⚫It is used as antiseptic in sterilizing surgical instruments.
⚫It is used in preserving skin, wood, fur etc.
⚫It is used as electrode.
⚫It is used in preparing other compounds of mercury.


Symbol: Ag
Atomic weight: 107.9
Atomic number: 47
Silver occurs in free state as well as combined state. The important ores of silver in combined state are:
1.Argentite or silver glance, Ag2S
2.Horn silver, AgCl
3.Ruby silver, Ag2SbS3
Extraction of silver: The silver can be extracted by Cyanide process.
Cyanide process: (Macarthur-Forrest process)
This process is modern and involves the following process:
The sulphide ore is concentrated by froth-floatation process.
2.Treatment with sodium cyanide:
 The concentrated ore is treated with 0.4 to 0.7% aqueous solution of sodium cyanide and a current of air is passed through it. The reaction involved is,
Since, the nature of reaction is reversible, the air is passed through the solution to oxidise Na2S so that the equilibrium shifts towards forward direction. The involved reaction is 
 Na2S+ 2O2---->Na2SO4
3.Precipitation of silver:
The solution obtained above is filtered and silver is precipitated by treating scrap zinc to the solution.
Zn +2Na[Ag(CN)2]--->Na2[Zn(CN)4] +.2Ag↓
                                              (sodium         zincocyanide)
Thus, obtained precipitated silver is filtered, washed and fused with borax to get compact mass of silver. 
4.Refining: ( Electrorefining)
The pure silver is obtained by refining process(electrolytic). In this process, impure silver block is made as anode and pure thin silver foil as cathode. Both anode and cathode are suspended in aqueous solution of AgNO3(6%) and nitric acid (1%) as the bath electrolyte. When the current is passed, anode dissolves out, and equivalent amount of pure silver is deposited at the cathode leaving behind the impurities (Zn.Cu or Au if present) as anode mud.
 The impure silver (containing lead as impurity) is fused in a cupel in reverberatory furnace with hot blast air, lead gets oxidised to oxide, which surface of silver becomes visible . This whole process is known as cupellation.
⚫Melting point of silver is 9560C and boiling point is 19550C.
⚫Silver is malleable and ductile.
1.Action with air
Silver is not chemically active metal. Therefore, under ordinary condition, it does not react with air. However, it is tarnished by air containing even traces quantity of hydrogen sulphide.
      2Ag + H2S---> Ag2S ↓+ H2
                           (black ppt)
Due to hydrogen sulphide pollution , silver monuments are being tarnished. This demands regular cleaning of silver wares.
2.Action with acids: 
Silver lies below hydrogen in electrochemical series. So, it cannot displace hydrogen gas from dilute, mineral and non-oxidizing acids such as HCl, H2SO4. However, silver reacts with concentrated nitric acid and concentrated sulphuric acid as follows:
  2Ag + 2H2SO4---->AgSO4↓ + SO2↑+ H2O
 3Ag+4HNO3(conc.)--->3AgNO3+2H2O + NO↑
3.Action with non-metals:
Some non-metals such as sulphur, chlorine etc react with silver on heating to form corresponding compounds.
      2Ag +S-----> Ag2S

      2Ag + Cl2----->AgCl 
Uses of Silver:
⚫Silver were used to prepare coins in the early days, so they are regarded as coinage metals.
⚫It is used to prepare jewellery.
⚫It is used to prepare electrodes.
⚫It is used in photography.

   Compounds of Silver:
1.Silver nitrate: It is the most well-known compound of silver. It is also called lunar caustic.
Silver nitrate is prepared by dissolving silver in hot and dilute nitric acid and the resulting solution is evaporated upto crystallization point.
    3Ag + 4HNO3---->3AgNO3 + NO +2H2O
                         Crystallization point
Physical properties
⚫It is colourless crystal with rhombic structure.
⚫It has melting point 2120 C and density 4.35.
⚫It is highly soluble in water.
⚫It forms stain on the skin due to deposition of silver and used for making tatoos. 
Decomposition by organic matter:
Some organic compounds such as skin, paper, cloth etc. decomposes silver nitrate into finely divided metallic silver(black) in presence of light.
   2AgNO3---------->2Ag+2NO2 + O2

 This property of silver nitrate is used to prepare indelible ink which is used to mark. This indelible ink is used in nail and skin after casting vote.
       Chemical properties:
Effect of heat: It decomposes on heating to give silver nitrite first and then to metallic silver at high temperature.
    2AgNO3------> 2AgNO2 + O2  
                   above 4500°C
   2AgNO2 -------------> 2Ag + 2NO2
Action of ammonium hydroxide: 
When ammonium hydroxide is added to an aqueous solution of silver nitrate, brown precipitate of silver oxide is formed which dissolves excesss of ammonia solution to form complex (diamine silver (I) nitrate).

 2AgNO3 + 2NH4OH----->Ag2O + 2NH4NO3 + H2O
                                                 Silver oxide( brown ppt)

Ag2O + 2NH4OH + 2NH4NO3----->                2[Ag(NH3)2]NO3 +3H2O
                                                                Diammine silver(I) nitrate (soluble)   

Reactions with soluble halides and sulphides: 
Silver nitrate solution reacts with chloride, bromide, iodide and sulphide give insoluble salt of silver with different colour.
   AgNO3 + Cl- ---->AgCl + NO3-
                                      (white ppt)
   AgNO3 + Br- ------->AgBr + NO3-
                                      (pale yellow ppt)
   AgNO3 + I- ------>AgI + NO3-
                                      (yellow ppt)
   AgNO3 + S-- ------>Ag2S + 2NO3-
                                     (black ppt)
The above reaction is used in qualitative analysis for the detection of Cl-, Br- and I-.
⚫It is used as a laboratory reagent.
⚫It is used for silvering mirror.
⚫It is used for indelible ink for markings.
⚫It is used for making eye drops.
⚫It is used to prepare silver halides for photography. 
Silver chloride (Horn Silver), AgCl:
When aqueous solution of soluble halides (KCl) is added to the aqueous solution of AgNO3, silver chloride is obtained .
     AgNO3 + KCl----> AgCl↓ + KNO3 
                               (white ppt)
Thus formed precipitate is filtered washed and dried at about 700C.
1.It is colorless solid ( white ) and turns violet in the exposure to light.
 2.It is insoluble in water but dissolves in ammonia solution, potassium cyanide and sodium thiosulphate form complex.
AgCl +2NH4OH----->[Ag(NH3)2]Cl + 2H2O
                                                               [Diamine silver(I)chloride]

3. AgCl fused with sodium carbonate gives metallic silver.
  4AgCl +2 Na2CO3--->4NaCl + 4Ag + 2CO2 + O2
4.Action with potassium cyanide solution (KCN) :
With excess of KCN solution , it forms colourless complex due to the formation of potassium argentocyanide.

  AgCl + 2KCN----->K[Ag(CN)2] + KCl
                                      (Potassium argentocyanide)

5. Action of light :
It is light sensitive so it is converted to metallic silver.
     2AgCl--------------> 2Ag + Cl2           
⚫Silver chloride is used to prepare photographic film and paper.


Zinc is non typical transition element :
To be true transition element, the element should be d-block element and there should be incompletely filled d-orbitals in metallic state or in its important compounds.
Zn(30) = 1s2 2s22p63s2 3p64s2 3d10 is the d-block element but it has completed d-orbital in its all states . Hence, Zn is non typical transition element.
(Transition elements may be defined as those elements that have partially filled d-orbitals either in metallic form or in their important compounds.)    
Occurence of Zn :
Being reactive metal, Zinc is not found in free or native state.
In combined state, it is found as the following ores.
a. Zinc blende ( ZnS)
b. Calamine or Zinc spar ( ZnCO3)
c. Zincite or Red Zinc ore (ZnO)
d. Franklinite (ZnO.Fe2O3)
e. Willimite (ZnO.SiO2)
Extraction of Zinc:
Zinc can be extracted from carbon reduction process ( vertical retort process)
In carbon reduction process, Zn is extracted from zinc blende as well as calamine going through the following steps:
1. Concentration: 
The ore is first crushed by jaw crusher and ground into fine powder in the ball mill. The powdered ore is then subjected to froth flotation process.
2.Roasting or Calcination: Zinc blende is roasted or calamine is calcined into the oxide of zinc at high temperature ( 9000C or above) in reverberatory furnace.
      2ZnS + 3O2----->2ZnO + 2SO2 ↑
       ZnCO3----->ZnO + CO2 ↑     
During this, 
a. Moisture is removed off 
b.Impurities like sulphur, phosphorus, arsenic etc are removed off as their volatile oxides 
S + O2 -->SO2 ↑
4P + 5O2--->2P2O5 ↑
3.Vertical Retort process ( Smelting): 

   Fig: Vertical retort process
Zinc oxide obtained from roasting or calcination is mixed with carbon ( anthracite or coke dust) roasted zinc oxide and carbon in the ratio of 2:1 and small briquettes which are fed into vertical retort furnace from the charging door. It is heated to redness where zinc oxide is ( made up of silicon carbide brick) reduced to metallic zinc.
             When the furnace is heated externally by burning producer gas (CO+N2) to about 14000C, the oxide ore in briquetts gets reduced and the vapours of zinc and CO formed are carried out into condenser by the current of producer gas entering from the bottom of the furnace . The zinc vapour condenses in the condenser in the molten form called zinc spelter.

Thus obtained zinc spelter ( may contain Pb, Fe, Cd, As, Sb etc ) is purified by electrolysis. 
Impure zinc is made anode and cathode consist of a pure aluminium sheet . Solution of zinc sulphate containing sulphuric acid acts as an electrolyte. When electricity is passed , impure zinc from the anode dissolves out and equivalent amount of pure zinc is deposited on cathode. The pure zinc is scrapped off.

 At cathode:
 Zn++ + 2e- ---->Zn
  At anode:  
  Zn----->Zn++ + 2e-

Physical Properties:
1.Zinc is bluish white shining metal.
2.Its m.p. is 420oC and b.p. is 907oC. 

3.Action with air:
It does not react with dry air but when it is exposed in moist, it gets covered with basic zinc carbonate coating.
  2Zn + H2O + O2 + CO2 Zn(OH)2.ZnCO3
                                                          ( Basic zinc carbonate)
4.Action of heat:
On heating strongly in air, zinc burns with a greenish blue flame giving white fumes of light and soft zinc oxide called philosopher's wool.
  2 Zn +O2---->2 ZnO

5.Action of water:
Pure zinc is not affected by water but impure zinc displaces hydrogen gas from steam.
  Zn + H2O----> ZnO + H2↑

6.Action with acids:
Pure zinc reacts very slowly with acids. When impure, it reacts vigorously with acids.
a.With HCl: 
Zinc evolves H2 gas with HCl. But the reaction is fast with conc. HCl.
 Zn + 2HCl--->ZnCl2 + H2↑ 

b.With H2SO4: 
Zinc evolves H2 gas with dil. H2SO4 but SO2 gas with conc. H2SO4.
Zn +H2SO4---> ZnSO4 + H2↑
Zn +2H2SO4---->ZnSO4 + 2H2O + SO2 ↑

c.With HNO3:
i)When zinc is treated with very dilute HNO3 , no any gas is evolved.
4Zn +10 HNO3--->4Zn (NO3)2+ NH4NO3 + 3H2O
ii)When zinc is treated with dilute HNO3, N2O gas is evolved.
4 Zn + 10HNO3--->4 Zn (NO3)2 + N2O↑+ 5H2O
iii)When Zn is treated with moderately conc. HNO3 (1:1), NO (nitric oxide) gas is evolved. 
3Zn +8HNO3--->3Zn (NO3)2 + 2NO↑ + 4H2O
iv)When Zn is treated with conc. HNO3, NO2 gas is evolved.
Zn+ 4HNO3--->Zn (NO3)2 + 2 NO2↑+ 2H2O 

7.Action with alkali :
On boiling with caustic alkali, zinc evolves H2 gas.
      Zn + 2NaOH----->Na2ZnO2 + H2↑
                                          (Sodium zincate)

8.Displacement Reaction:
Being highly electropositive, zinc displaces copper , mercury etc from the solution of their salt.
      Zn + CuSO4--->Cu + ZnSO4
      Zn + HgCl2----->Hg + ZnCl2

1.Zinc is used for galvanising iron.
2.It is used as electrode in electrochemical cell.
3.It is used in preparing alloys like Brass (Zn+ cu), Bronze ( Cu+Sn) , German silver ( Zn+ Cu+ Ni) etc.
4.It is used in lab for preparing hydrogen gas.
5.For making smoke screen in battle fields.
6.In making printing blocks .

It is defined as the process in which a thin layer of zinc is coated or deposited over the iron sheets or articles to increase their lives by protecting them from rusting.
The galvanization is done in following steps.

1.Cleaning and pickling:
 The iron article to be galvanized is first cleaned and then washed with dilute HCl to remove oxide film, if present on the surface. This is known as pickling.

2.By electroplating:
Zinc can be electroplated on iron by keeping iron article as cathode, zinc as anode and ZnSO4 solution as electrolyte. On passing electric current a layer of zinc is coated on iron article.

3.By sherardising:
The iron article, if small in size, is mixed with zinc dust at 8000C in a rotating drum for about several hours. Bolts, screw, knots etc can be sherardised by zinc.
4.By metallizing:
The iron article , if very large in size for which hot dip galvanising and sherardising are impossible, is coated by spraying molten zinc. Bridges, ships, tanks etc can be metallised by zinc.

              Compounds of Zinc
1.White vitriol (zinc sulphate, ZnSO4.7H2O)
Zinc sulphate heptahydrate is commonly called white vitriol.

    Zinc sulphate can be prepared by the action of dilute H2SO4 on zinc, zinc oxide, zinc hydroxide and zinc. Carbonate.

 Zn + H2SO4--->ZnSO4 + H2↑
 ZnO + H2SO4----> ZnSO4 + H2O
Zn(OH)2 + H2SO4-----> ZnSO4 + 2H2O
ZnCO3 + H2SO4---->ZnSO4 +H2O + CO2 ↑

On crystallization, crystals of zinc sulphate can be obtained as ZnSO4. 7H2O.
         ZnSO4 + 7H2O crystallization point ZnSO4.7H2O

2.Zinc sulphate can be manufactured by roasting zinc blende ( zinc sulphide) with excess air at moderate temperature.
   ZnS + 2O2------>ZnSO4

      When ZnSO4 solution so obtained above is heated upto crystallization point ( about 390C) and after cooling ZnSO4.7H2O is obtained.

       ZnSO4 solution crystallizationpoint ZnSO4.7H2O 

1.White vitriol is colourless crystalline solid where as the anhydrous one is white powder.
2.It is soluble in water.

3.Action of heat: 
On heating at different levels of temperature , white vitriol loses successive number of water molecules and finally gets decomposed.

4.Action with Bas ( formation of double salt): 
When Zinc sulphate solution is treated with Barium sulphide, the double salt called lithopone is formed. 
Lithopone is a white pigment used in paints, inks, leather, paper etc.
              ZnSO4 + BaS---->ZnS + BaSO4 (or ZnSO4. BaS)   

5.Formation of double salt:
With potassium sulphate, ZnSO4 reacts to produce double salt (K2SO4. ZnSO4.6H2O).
                                                            ------->K2SO4 (aq) + ZnSO4 (aq) + 6H2O C.P. K2SO4. ZnSO4. 6H2O
                                    (potassium zinc sulphate,double salt)

6.Action with ammonia : 
When ZnSO4 reacts with ammonia solution, it gives white precipitate of Zn(OH)2 at first and then complex salt with excess of ammonia solution.
       ZnSO4 + 2NH4OH----->Zn (OH)2↓ + (NH4)2SO4 

       Zn(OH)2 + (NH4)2SO4 + 2NH4OH------>                     [Zn(NH3)4].SO4 + 4H2O
                                                                       (Tetra-ammine zinc sulphate)

7.Action with NaOH: 
When a little NaOH solution is added to Zinc sulphate solution, then white ppt of zinc hydroxide is obtained.
           ZnSO4 + 2 NaOH---->Zn( OH)2↓ + Na2SO4
                            (less)        (white ppt) 
If excess NaOH is added, then ppt dissolves due to the formation of sodium zincate.
        Zn(OH)2 + 2NaOH-->Na2ZnO2
                          (Excess) (Sodium zincate)

8.Formation of isomorphous : 
Crystalline ZnSO4 is isomorphous with MgSO4. 7H2O (Epsom salt), FeSO4.7H2O (green vitriol), NiSO4. 7H2O [ nickel(II) sulfate heptahydrate] and Cr2(SO4)3.7H2O ( chromium sulphate, heptahydrate)

1.It is used in medicine as an eye lotion.
2.It is used in the manufacture of lithopone [ an important paint base].
3.It is used in preserving hides.
4.It is used in preparing other compounds of zinc.

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