|
INORGANIC
Part 10 3d block TRANSITION METALS sub-index: 10.1-10.2
Introduction 3d-block Transition Metals * 10.3
Scandium
* 10.4 Titanium * 10.5
Vanadium * 10.6 Chromium
* 10.7 Manganese * 10.8
Iron * 10.9 Cobalt
* 10.10 Nickel
* 10.11 Copper * 10.12
Zinc
* 10.13 Other Transition Metals e.g. Ag and Pt * Appendix 1.
Hydrated salts, acidity of
hexa-aqua ions * Appendix 2. Complexes
& ligands * Appendix 3. Complexes and isomerism * Appendix 4.
Electron configuration & colour theory *
Appendix 5. Redox
equations, feasibility, Eø * Appendix 6.
Catalysis * Appendix 7.
Redox
equations
* Appendix 8. Stability Constants and entropy
changes *
Appendix 9. Colorimetric analysis
and complex ion formula * Appendix 10 3d block - extended data
* Appendix 11 Some 3d-block compounds, complexes, oxidation states
& electrode potentials * Appendix 12
Hydroxide complex precipitate 'pictures',
formulae and equations
Advanced
Level Inorganic Chemistry Periodic Table Index *
Part 1
Periodic Table history
* Part 2
Electron configurations, spectroscopy,
hydrogen spectrum,
ionisation energies *
Part 3
Period 1 survey H to He *
Part 4
Period 2 survey Li to Ne * Part
5 Period 3 survey Na to Ar *
Part 6
Period 4 survey K to Kr and important trends down a
group *
Part 7
s-block Groups 1/2 Alkali Metals/Alkaline Earth Metals *
Part 8
p-block Groups 3/13 to 0/18 *
Part 9
Group 7/17 The Halogens *
Part 10
3d block elements & Transition Metal Series
*
Part 11
Group & Series data & periodicity plots * All
11 Parts have
their own sub-indexes near the top of the pages
10.12. Chemistry
of Zinc
Zn, Z=30, 1s22s22p63s23p63d104s2

|
The Extraction and Purification of
Zinc |
- Zinc is extracted from either zinc
blende/sphalerite ore (zinc sulphide)
or sometimes calamine/Smithsonite ore (zinc
carbonate).
- (1)
The zinc sulphide ore is roasted in air to give
impure zinc oxide.
- 2ZnS(s) + 3O2(g)
==> 2ZnO(s) + 2SO2(g)
- Note: calamine ore can be used
directly in a zinc smelter because on heating it also forms zinc
oxide.
- ZnCO3(s)
==>
ZnO(s) + CO2(g) (endothermic
thermal decomposition)
- (2)
The impure zinc oxide can be treated
in two ways to extract the zinc:
- (a)
It is roasted in a
smelting furnace
with carbon (coke, reducing agent) and limestone (to remove the
acidic impurities).
- C(s) + O2(g)
==> CO2(g) (very exothermic oxidation,
raises temperature considerably)
- C(s) + CO2(g)
==> 2CO(g) (C oxidised, CO2
reduced)
- ZnO(s) + CO(g)
==> Zn(l) + CO2(g) (zinc oxide
reduced by CO, Zn undergoes O loss)
- or direct reduction
by carbon: ZnO(s) +
C(s)
==> Zn(l) + CO(g) (ZnO
reduced, C oxidised)
- The carbon monoxide
acts as the reducing agent i.e. it removes the oxygen from the
oxide.
- The impure zinc is
then fractionally
distilled from the mixture of slag and other metals like
lead and cadmium out of the top of the furnace in an
atmosphere rich in carbon monoxide which stops any zinc from
being oxidised back to zinc oxide.
- The slag and lead (with other
metals like cadmium) form two layers which can be tapped off at the base
of the furnace.
- The zinc can be further
purified by a 2nd fractional distillation or more
likely by dissolving it in dilute sulphuric acid and purified
electrolytically as described below.
- (b)Two stages
- (i)
It is dissolved and
neutralised with dilute sulphuric acid to form impure zinc
sulphate solution.
- ZnO(s) + H2SO4(aq)
==> ZnSO4(aq) + H2O(l)
- or using calamine ore/zinc
carbonate directly:
- ZnCO3(s)
+ H2SO4(aq) ==> ZnSO4(aq)
+ H2O(l)+ CO2(g)
-
(ii) Quite pure zinc is produced
from the solution by electrolysis. It can be deposited on a
pure zinc negative electrode (cathode) in the same way
copper can be purified. The other electrode,
must be inert e.g. for laboratory experiments,
carbon (graphite) can be used and oxygen is formed.
- Zn2+(aq) + 2e-
==> Zn(s)
- A reduction process, electron
gain, as zinc metal is deposited on the (-) electrode.
- You can't use solid zinc
oxide directly because its insoluble and the ions must
free to carry the current and migrate to the electrodes
in some sort of solution.
- For more details of the
type of electrolysis system used, see
purification of copper (just swap Zn for Cu in the
method/diagram).
- PLEASE note: In the
industrial production of zinc by electrolysis (called
electro-winning) the negative (-) cathode is made of
aluminium (Al, where zinc deposits) and the positive (+)
electrode is made of a lead-silver alloy (Pb-Ag, where oxygen
gas is formed). Why these particular electrode metals are used
in this 'electrowinning' process I'm not quite sure, but
aluminium is so unreactive that it is effectively inert, and
lead and silver are also of low activity, but ... ???
|

Scandium
* Titanium * Vanadium
* Chromium
* Manganese * Iron * Cobalt
* Nickel
* Copper *
Zinc
* Silver & Platinum
Website
content copyright © Dr W P Brown 2000-2010 All rights reserved
on
revision notes, puzzles, quizzes, worksheets, x-words etc. * Copying of website
material is not permitted * I do not personally endorse the adverts -
but they do pay for the site!
|