Page 202 - Chemistry ICSE Class X

188 ICSE Chemistry – 10
ƒ Cinnabar (HgS) on heating in the air gives mercury and SO .
/Ŷ ŚĞĂƚ ƌĞĚƵĐƟŽŶ ŵĞƚŚŽĚ͕ ' 2
2
2
ƌŽĂƐƟŶŐ ĂŶĚ ƌĞĚƵĐƟŽŶ ƚĂŬĞ ƉůĂĐĞ or, HgS(s) + O (g) o Hg(l) + SO (g)
ƐŝŵƵůƚĂŶĞŽƵƐůLJ͘ cinnabar oxygen (from air) mercury sulphur dioxide
ƒ Lead sulphide (galena) when heated in limited air gives lead metal
and SO .
2
'
PbS + O o Pb + SO 2
2
galena oxygen lead sulphur dioxide
ƒ Copper(I) sulphide on heating in air gives
heat
2Cu S(s) + 3O (g) o 2Cu O(s) + 2SO (g)
2
2
2
2
copper(I) sulphide oxygen (air) copper(I) oxide sulphur dioxide
heat
2Cu O(s) + Cu S(s) o 6Cu(s) + SO (g)
2
2
2
copper(I) oxide copper(II) sulphide copper sulphur dioxide
How are the metals of moderate reactivity extracted
The metals in the middle of the activity series, such as iron, zinc, lead,
copper, etc. are moderately reactive. These usually occur in nature as
sulphides or carbonates. It is easier to obtain a metal from their oxides,
than from their sulphides and carbonates. Therefore, prior to reduction,
the metal sulphides and carbonates are converted into metal oxides by
roasting or calcination.
The metal oxide in the calcined/roasted ore can be reduced to the
respective metal by using a chemical reducing agent. The choice of reducing
A copper mine agent depends upon the reactivity of the metal. Commonly used reducing
agents are carbon, aluminium and magnesium.

dŚĞ ĐĂƌďŽŶ ƌĞĚƵĐƟŽŶ ŵĞƚŚŽĚ ĐĂŶŶŽƚ Reduction with carbon and carbon monoxide
ďĞ ƵƐĞĚ ĨŽƌ ƌĞĚƵĐŝŶŐ ƚŚĞ ŽdžŝĚĞƐ ŽĨ The oxides of moderately reactive metals, such as iron (Fe), zinc (Zn),
ŚŝŐŚůLJ ƌĞĂĐƟǀĞ ;ŚŝŐŚůLJ ĞůĞĐƚƌŽƉŽƐŝƟǀĞͿ copper (Cu), nickel (Ni), and tin (Sn), which appear in the middle of the
ŵĞƚĂůƐ͕ ƐƵĐŚ ĂƐ ƐŽĚŝƵŵ͕ ƉŽƚĂƐƐŝƵŵ͕ reactivity series, can be reduced by heating with carbon (coke) at a higher
ĐĂůĐŝƵŵ͕ ŵĂŐŶĞƐŝƵŵ͕ ĂůƵŵŝŶŝƵŵ͕ ĞƚĐ͘ temperature.
dŚŝƐ ŝƐ ďĞĐĂƵƐĞ ƚŚĞƐĞ ŵĞƚĂůƐ ŚĂǀĞ heat, high T
ŐƌĞĂƚĞƌ ĂĸŶŝƚLJ ĨŽƌ ŽdžLJŐĞŶ ƚŚĂŶ ĨŽƌ MO(s) + C(s) o M + CO(g)
ĐĂƌďŽŶ͘ metal oxide carbon in the
form of coke
(reducing agent)
The CO(g) so produced may also act as a reducing agent. For example,
'
PbO + C o Pb + CO
lead oxide lead
'
/Ŷ ĐĞƌƚĂŝŶ ĐĂƐĞƐ͕ hydrogen ŵĂLJ ĂůƐŽ ďĞ PbO + CO o Pb + CO
ƵƐĞĚ ĨŽƌ ƌĞĚƵĐŝŶŐ ŵĞƚĂů ŽdžŝĚĞƐ͕ Ğ͘Ő͘ lead(II) oxide carbon monoxide lead 2
' > 980 K
&Ğ O н ϯ, ;gͿ o Ϯ&Ğ н ϯ, K;gͿ Fe O 3 + 3C o 2Fe + 3CO
2
Ϯ ϯ
Ϯ
Ϯ
' ferric oxide iron
ƵK н , ;gͿ o Ƶ н , O
Ϯ
Ϯ
< 980 K
' Fe O + 3CO o 2Fe + 3CO
WďK н , ;gͿ o Wď н , O 2 3 2
Ϯ
Ϯ
ferric oxide iron
'
ZnO + C o Zn + CO
zinc oxide zinc
'
SnO 2 + 2C o Sn + 2CO
tin oxide tin
ůƵŵŝŶŝƵŵ ƌĞĚƵĐƟŽŶ ŵĞƚŚŽĚ ŝƐ ĂůƐŽ Reduction with aluminium
ĐĂůůĞĚ alumino-thermic process Žƌ
thermite process͘ ^ƵĐŚ ƌĞĂĐƟŽŶƐ Certain metals cannot be obtained by carbon reduction method. Oxides of
ĂƌĞ ŚŝŐŚůLJ ĞdžŽƚŚĞƌŵŝĐ ĂŶĚ ƚŚĞ ŵĞƚĂů such metals can be reduced by aluminium powder.
ƐŽ ĨŽƌŵĞĚ ŝƐ ŽďƚĂŝŶĞĚ ŝŶ ƚŚĞ ŵŽůƚĞŶ For example, aluminium reduces manganese dioxide (MnO ) to
ĨŽƌŵ͘ dŚĞƌĞĨŽƌĞ͕ ƚŚŝƐ ƉƌŽĐĞƐƐ ĐĂŶ ďĞ 2
ƵƐĞĚ ĨŽƌ ǁĞůĚŝŶŐ ƉƵƌƉŽƐĞƐ ĂůƐŽ͘ manganese (Mn), iron oxide (Fe O ) to iron (Fe), and chromium oxide
2
3
(Cr O ) to chromium (Cr).
2
3