JEE Main & Advanced Chemistry The d-and f-Block Elements / d तथा f ब्लॉक के तत्व Copper and its Compounds

(1) Ores :  Copper pyrites (chalcopyrite) \[CuFe{{S}_{2}},\] Cuprite (ruby copper) \[C{{u}_{2}}O,\] Copper glance \[(C{{u}_{2}}S)\], Malachite \[[Cu{{(OH)}_{2}}.\,CuC{{O}_{3}}],\] Azurite \[[Cu{{(OH)}_{2}}.\,2CuC{{O}_{3}}]\]

(2) Extraction :  Most of the copper (about 75%) is extracted from its sulphide ore, copper pyrites.

Concentration of ore : Froth floatation process.

Roasting : Main reaction : 

\[2CuFe{{S}_{2}}+{{O}_{2}}\to C{{u}_{2}}S+2FeS+S{{O}_{2}}\].

Side reaction : \[2C{{u}_{2}}S+3{{O}_{2}}\to 2C{{u}_{2}}O+2S{{O}_{2}}\]

\[2FeS+3{{O}_{2}}\to 2FeO+2S{{O}_{2}}\].

Smelting : \[FeO+Si{{O}_{2}}\to FeSi{{O}_{3}}(\text{slag)}\] 

\[C{{u}_{2}}O+FeS\to FeO+C{{u}_{2}}S\]

The mixture of copper and iron sulphides melt together to form 'matte' \[(C{{u}_{2}}S+FeS)\] and the slag floats on its surface.

Conversion of matte into Blister copper (Bessemerisation) : Silica is added to matte and a hot blast of air is passed \[FeO+Si{{O}_{2}}\to FeSi{{O}_{3}}(\text{slag})\]. Slag is removed. By this time most of iron sulphide is removed.  \[C{{u}_{2}}S+2C{{u}_{2}}O\to 6Cu+S{{O}_{2}}\]

Blister copper : Which contain about 98% pure copper and 2% impurities (Ag, Au, Ni, Zn etc.)

Properties of copper : It has reddish brown colour. It is highly malleable and ductile. It has high electrical conductivity and high thermal conductivity. Copper is second most useful metal (first being iron). It undergoes displacement reactions with lesser reactive metals e.g. with Ag. It can displace Ag from \[AgN{{O}_{3}}\]. The finally divided Ag so obtained is black in colour.

Copper shows oxidation states of +1 and +2. Whereas copper (I) salts are colourless, copper (II) salts are blue in colour. Cu (I) salts are less stable and hence are easily oxidised to Cu (II) salts \[(2C{{u}^{+}}\to C{{u}^{2+}}+Cu)\]. This reaction is called disproportionation.

(1) In presence of atmospheric \[C{{O}_{2}}\] and moisture, copper gets covered with a green layer of basic copper carbonate (green layer) which protects the rest of the metal from further acton.

\[Cu+{{O}_{2}}+C{{O}_{2}}+{{H}_{2}}O\to \underset{\text{(green layer)}}{\mathop{Cu{{(OH)}_{2}}CuC{{O}_{3}}}}\,\]

(2) In presence of oxygen or air, copper when heated to redness (below 1370K) first forms red cuprous oxide which changes to black cupric oxide on further heating. If the temperature is too high, cupric oxide changes back to cuprous oxide

\[4Cu+{{O}_{2}}\xrightarrow{\text{Below 1370}\,\text{K}}\underset{\text{(Red)}}{\mathop{2C{{u}_{2}}O}}\,\underset{\text{Above 1370 }K}{\mathop{\xrightarrow{{{\text{O}}_{\text{2}}}}}}\,\underset{\text{(Black)}}{\mathop{4CuO}}\,\]

\[CuO+Cu\]\[\xrightarrow{\text{High temp}\text{.}}\]\[C{{u}_{2}}O\]

(3) Action of acids. Non oxidising dil. acids such as \[HCl,{{H}_{2}}S{{O}_{4}}\] have no action on copper. However, copper dissolves in these acids in presence of air.

\[Cu+2HCl+\frac{1}{2}{{\text{O}}_{\text{2}}}\text{(air)}\to CuC{{l}_{2}}+{{H}_{2}}O\]

With dil. \[HN{{O}_{3}}\], \[Cu\] liberates \[NO\] (nitric oxide)

\[3Cu+8HN{{O}_{3}}\to 3Cu{{(N{{O}_{3}})}_{2}}+2NO+4{{H}_{2}}O\]

With conc. \[HN{{O}_{3}}\], copper gives \[N{{O}_{2}}\]

\[Cu+4HN{{O}_{3}}\to Cu{{(N{{O}_{3}})}_{2}}+2N{{O}_{2}}+2{{H}_{2}}O\]

With hot conc. \[{{H}_{2}}S{{O}_{4}}\], copper gives \[S{{O}_{2}}\]

\[Cu+2{{H}_{2}}S{{O}_{4}}\to CuS{{O}_{4}}+S{{O}_{2}}+2{{H}_{2}}O\]

Compounds of Copper

(1) Halides of copper : Copper (II) chloride, \[CuC{{l}_{2}}\] is prepared by passing chlorine over heated copper. Concentrated aqueous solution of \[CuC{{l}_{2}}\] is dark brown but changes first to green and then to blue on dilution.

On heating, it disproportionates to copper (I) chloride and chlorine

\[2CuC{{l}_{2}}\xrightarrow{\text{Heat}}2CuCl+C{{l}_{2}}\]

It is used as a catalyst in the Daecon’s process for the manufacture of chlorine.

Copper (I) chloride, \[CuCl\] is a white solid insoluble in water. It is obtained by boiling a solution of \[CuC{{l}_{2}}\] with excess of copper turnings and conc. \[HCl\].

\[CuC{{l}_{2}}+Cu\xrightarrow{\text{HCl}}2CuCl\]

It dissolves in conc. \[HCl\] due to the formation of complex \[H[CuC{{l}_{2}}]\]

\[CuCl+HCl\to H[CuC{{l}_{2}}]\]

It is used as a catalyst alongwith \[N{{H}_{4}}Cl\] in the preparation of synthetic rubber.

(2) Cuprous oxide \[C{{u}_{2}}O\]: It is a reddish brown powder insoluble in water but soluble in ammonia solution, where it forms diammine copper (I) ion. \[C{{u}^{+}}+2N{{H}_{3}}\to {{[Cu{{(N{{H}_{3}})}_{2}}]}^{+}}\]. It is used to impart red colour to glass in glass industry. 

(3) Cupric oxide \[CuO\] : It is dark black, hygroscopic powder  which is reduced to \[Cu\] by hydrogen, CO etc. It is used to impart light blue colour to glass. It is prepared by heating copper nitrate.

\[2Cu{{(N{{O}_{3}})}_{2}}\xrightarrow{\Delta }2CuO+\,4N{{O}_{2}}+{{O}_{2}}\]

(4) Copper sulphate \[CuS{{O}_{4}}.\,5{{H}_{2}}O\] (Blue vitriol) : It is prepared by action  of dil \[{{H}_{2}}S{{O}_{4}}\] on copper scrap in presence of air. 

\[2Cu+2{{H}_{2}}S{{O}_{4}}\underset{\,\,\,(\text{air})}{\mathop{+{{O}_{2}}}}\,\to CuS{{O}_{4}}+2{{H}_{2}}O\]

(i) On heating this blue salt becomes white due to loss of water of crystallization.

\[CuS{{O}_{4}}.\,\underset{\text{Blue }}{\mathop{5{{H}_{2}}O}}\,\xrightarrow{503K}\underset{\text{White}}{\mathop{CuS{{O}_{4}}}}\,+5{{H}_{2}}O\]

At about 1000 K, \[CuS{{O}_{4}}\]decomposes to give \[CuO\] and \[S{{O}_{3}}.\]

\[CuS{{O}_{4}}\]\[\xrightarrow{1000K}CuO+S{{O}_{3}}\]

(ii) It gives a deep blue solution of tetrammine copper (II) sulphate with \[N{{H}_{4}}OH.\]

\[C{{u}_{2}}S{{O}_{4}}+4N{{H}_{4}}OH,\to \underset{\text{Blue colour}}{\mathop{[Cu{{(N{{H}_{3}})}_{4}}]S{{O}_{4}}}}\,+4{{H}_{2}}O\]

(iii) With \[KCN\] it first gives yellow precipitate of \[CuCN\] which decomposes of give \[C{{u}_{2}}{{(CN)}_{2}}.\] \[C{{u}_{2}}{{(CN)}_{2}}\] dissolves in excess of \[KCN\] to give \[{{K}_{3}}[Cu{{(CN)}_{4}}]\]

\[2CuS{{O}_{4}}+4KCN\to C{{u}_{2}}{{(CN)}_{2}}+2{{K}_{2}}S{{O}_{4}}+{{(CN)}_{2}}\]

(iv) With \[KI\] it gives white ppt. of \[C{{u}_{2}}{{I}_{2}}\]

\[4KI+2CuS{{O}_{4}}\to 2{{K}_{2}}S{{O}_{4}}+\underset{\text{White ppt}\text{.}}{\mathop{C{{u}_{2}}{{I}_{2}}}}\,+{{I}_{2}}\]

(v) With \[{{K}_{4}}[Fe{{(CN)}_{6}}],CuS{{O}_{4}}\] gives a reddish brown ppt. of \[C{{u}_{2}}[Fe{{(CN)}_{6}}]\]

\[2CuS{{O}_{4}}+{{K}_{4}}[Fe{{(CN)}_{6}}]\to \underset{\text{Reddish brown ppt}\text{.}}{\mathop{C{{u}_{2}}[Fe{{(CN)}_{6}}]}}\,+2{{K}_{2}}S{{O}_{4}}\]

Uses : For electroplating and electrorefining of copper. As a mordant in dyeing. For making Bordeaux mixture (11 parts lime as milk of lime + 16 parts copper sulphate in 1,000 parts of water). It is an excellent fungicide. For making green pigments containing copper carbonate and other compounds of copper.  Like Verdigris which is \[Cu{{(C{{H}_{3}}COO)}_{2}}Cu{{(OH)}_{2}}\] i.e. basic copper acetate  and is used as a green pigment in paints. As a fungicide in starch paste for book binding work.

(5) Cupric sulphide \[CuS:\] It is prepared as follows : \[Cu{{(N{{O}_{3}})}_{2}}+{{H}_{2}}S\to \underset{\text{Black}\,\text{ppt}\text{.}}{\mathop{CuS+}}\,2HN{{O}_{3}}\].

(6) Basic copper carbonates : Because of lower solubility of the hydroxide, the normal carbonate does not exist. Two basic copper carbonates occur in nature viz malachite \[CuC{{O}_{3}}.Cu{{(OH)}_{2}}\] which has a fine green colour, and azurite, \[2CuC{{O}_{3}},Cu{{(OH)}_{2}}\] which is deep blue in colour.

Malachite is prepared by heating a mixture of \[CuS{{O}_{4}}\] solution and limestone in a sealed tube at 423 – 443 K

\[2CuS{{O}_{4}}+2CaC{{O}_{3}}+{{H}_{2}}O\]\[\xrightarrow{\text{423-443K}}\]\[\underset{\text{Malachite}}{\mathop{CuC{{O}_{3}}Cu{{(OH)}_{2}}}}\,\]\[+2CaS{{O}_{4}}+C{{O}_{2}}\]

 At lower temperature azurite is formed 

\[3CuS{{O}_{4}}+3CaC{{O}_{3}}+{{H}_{2}}O\xrightarrow{<423\,K}\]\[\underset{\text{Azurite}}{\mathop{2CuC{{O}_{3}}.Cu}}\,\]\[{{(OH)}_{2}}\]\[+3CaS{{O}_{4}}+C{{O}_{2}}\] 

On heating, both decompose to give black cupric oxide, water and \[C{{O}_{2}}\].

They are used as green and blue painter’s pigments under the name ‘malachite green’ and azurite blue’.

Silver and its Compounds

(1) Ores : Argentite (silver glance) \[A{{g}_{2}}S,\] Horn silver \[(AgCl),\] Ruby silver (Pyrargyrite) \[3A{{g}_{2}}S.\,S{{b}_{2}}{{S}_{3}}\].

(2) Extraction : Cyanide process  or Mac Arthus-Forrest cyanide process : This method depends on the fact that silver, its sulphide or chloride, forms soluble complex with alkali cyanides in the silver. This implies that silver compounds will dissolve in solution of alkali cyanides in the presence of blast of air.

\[4Ag+8NaCN+2{{H}_{2}}O+\underset{\text{air}}{\mathop{{{O}_{2}}}}\,\]\[\rightleftharpoons \]\[4Na[Ag{{(CN)}_{2}}]+4NaOH\]

or             \[4Ag+8C{{N}^{-}}+2{{H}_{2}}O+{{O}_{2}}\]\[\rightleftharpoons \] \[4{{[Ag{{(CN)}_{2}}]}^{-}}+4O{{H}^{-}}\]

\[A{{g}_{2}}S+4NaCN\]\[\rightleftharpoons \] \[2Na[Ag{{(CN)}_{2}}]+N{{a}_{2}}S\]

\[AgCl+2NaCN\]\[\rightleftharpoons \]\[Na[Ag{{(CN)}_{2}}]+NaCl.\]

The reaction with the sulphide is reversible and accumulation of \[N{{a}_{2}}S\] must be prevented. A free excess of air is continuously passed through the solution which oxidizes \[N{{a}_{2}}S\] into sulphate and thiosulphate.

\[2N{{a}_{2}}+2{{O}_{2}}+{{H}_{2}}O\to N{{a}_{2}}{{S}_{2}}{{O}_{3}}+2NaOH\]

\[N{{a}_{2}}{{S}_{2}}{{O}_{3}}+2NaOH+2{{O}_{2}}\to 2N{{a}_{2}}S{{O}_{4}}+{{H}_{2}}O\]              

\[2Na[Ag{{(CN)}_{2}}]+4NaOH+Zn\to N{{a}_{2}}Zn{{O}_{2}}+\]

\[4NaCN+2{{H}_{2}}O+2Ag\] 

(3) Extraction of Ag from argentiferrous lead (PbS + Ag₂S)– Parke’s Process : It is based upon the following facts (i) Molten Zn and Pb are immiscible, zinc forms the upper layer (ii) Ag is more soluble in molten Zn (iii) Zn-Ag alloy solidifies earlier than molten Pb (IV) Zn being volatile can be separated from Ag by distillation. Ag is purified by cupellation.

Properties of Silver:  Silver is a white lustrous metal, best conductor of heat and electricity. Being soft, it is alloyed. The silver alloy used for making jewellery contain 80% Ag and 20% Cu. The composition of a silver alloy is expressed as its purity i.e. the amount of Ag present in 1000 parts of the alloy Ag does not react with dilute HCl or dil. \[{{H}_{2}}S{{O}_{4}}\] and aqua regia but reacts with dil. \[HN{{O}_{3}}\] and conc. \[HN{{O}_{3}}\] forming \[NO\] and \[N{{O}_{2}}\] respectively. Chlorine also reacts with \[Ag\] to form \[AgCl\].

\[2\,Ag+C{{l}_{2}}\to 2\,AgCl\]

Hot conc. \[{{H}_{2}}S{{O}_{4}}\] reacts with \[Ag\] forming \[S{{O}_{2}}\] like \[Cu\]

Compounds of Silver:

(1) Silver oxide \[(A{{g}_{2}}O)\]: It is unstable and decomposes into \[Ag\] and \[{{O}_{2}}\] on slow heating.

\[2\,A{{g}_{2}}O\to 4\,Ag+{{O}_{2}}\]

(2) Silver halides (AgF, AgCl, AgBr and Agl) : Only AgF is soluble in \[{{H}_{2}}O\]. \[AgCl\] is insoluble in \[{{H}_{2}}O\] but dissolves in \[N{{H}_{4}}OH\],\[N{{a}_{2}}{{S}_{2}}{{O}_{3}}\] and \[KCN\] solutions. AgBr is partly soluble whereas \[Agl\]is completely insoluble in \[N{{H}_{4}}OH\]. Except \[AgF\], all the remaining three silver halides are photosensitive.

\[AgCl+2N{{H}_{4}}OH\to \underset{\text{Diamine silver (I) chloride}}{\mathop{[Ag{{(N{{H}_{3}})}_{2}}]Cl+2{{H}_{2}}O}}\,\] \[\]

\[AgCl+2KCN\to \underset{\text{Pot}\text{. Dicyano argentate (I)}}{\mathop{K[Ag{{(CN)}_{2}}]+KCl}}\,\]

\[AgCl+2N{{a}_{2}}{{S}_{2}}{{O}_{3}}\to \underset{\text{Sod}\text{. Dithiosulphato argentate (I)}}{\mathop{N{{a}_{3}}[Ag{{({{S}_{2}}{{O}_{3}})}_{2}}]+NaCl}}\,\]

(3) Silver nitrate (AgNO₃) : Silver nitrate \[(AgN{{O}_{3}})\] is called lunar caustic silver nitrate on heating above its m.p. (485 K) decomposes to silver nitrite but on heating to red heat gives silver.

\[2\,\,AgN{{O}_{3}}\xrightarrow{\text{Above 485 K}}2\,AgN{{O}_{2}}+{{O}_{2}}\]

\[2\,\,AgN{{O}_{3}}\xrightarrow{\text{Red heat}}2\,Ag+2N{{O}_{2}}+{{O}_{2}}\]

When treated with alkali, \[AgN{{O}_{3}}\] forms silver oxide which in case of \[N{{H}_{4}}OH\] dissolves to form complex ion.

\[2\,AgN{{O}_{3}}+2NaOH\to A{{g}_{2}}O+2NaN{{O}_{3}}+{{H}_{2}}O\]

\[2\,AgN{{O}_{3}}+2N{{H}_{4}}OH\to A{{g}_{2}}O+2N{{H}_{4}}N{{O}_{3}}+{{H}_{2}}O\]

\[A{{g}_{2}}O+4N{{H}_{4}}OH\to \underset{\text{Diamine silver hydroxide}}{\mathop{2[Ag{{(N{{H}_{3}})}_{2}}]OH}}\,+3{{H}_{2}}O\]

\[AgN{{O}_{3}}\] reacts with iodine in two ways

\[6\,AgN{{O}_{3}}\] (excess) +\[3{{l}_{2}}+3{{H}_{2}}O\to \]\[Agl{{O}_{3}}+5AgI+6HN{{O}_{3}}\]

\[5\,AgN{{O}_{3}}+3{{l}_{2}}\] (excess) +\[3{{H}_{2}}O\to HI{{O}_{3}}+5Agl+5HN{{O}_{3}}\]

In contact with organic matter (skin, cloth, paper etc.) \[AgN{{O}_{3}}\] is reduced to metallic silver (black)

\[2\,AgN{{O}_{3}}+{{H}_{2}}O\to 2\,Ag+2HN{{O}_{3}}+[O]\to \]oxidises organic matter

\[AgN{{O}_{3}}\] gives different coloured ppt. with different anions like \[C{{l}^{-}},B{{r}^{-}},{{I}^{-}},{{S}^{2-}},{{S}_{2}}O_{3}^{2-},CrO_{4}^{2-},PO_{4}^{3-}\] etc.

\[AgN{{O}_{3}}\] is used in the preparation of ink and hair dyes.

Photography : The photographic plate is coated with a colloidal gelatinised solution of \[AgBr\]. During exposure, AgBr is reduced to metallic silver.

\[2\,AgBr\to 2\,Ag+B{{r}_{2}}\]

The exposed film is developed. The developer used is an alkaline solution of hydroquinone or quinol which reduces some of the exposed AgBr to black silver.

\[\underset{\text{Quinol}}{\mathop{{{C}_{6}}{{H}_{4}}{{(OH)}_{2}}}}\,+2\,AgBr\to 2\,Ag+\underset{\text{Quinone}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}{\mathop{{{C}_{6}}{{H}_{4}}{{O}_{2}}+2\,HBr}}\,\]

The film is finally fixed by dipping in a solution of sodium thiosulphate or hypo which removes unchanged AgBr as complex ion.

\[AgBr+2N{{a}_{2}}{{S}_{2}}{{O}_{3}}\to N{{a}_{3}}[Ag{{({{S}_{2}}{{O}_{3}})}_{2}}]+NaBr\]

After taking a print of the photograph it is finally toned by dipping in a dilute solution of gold chloride to impart a beautiful golden colour or it is dipped in potassium chloro platinate \[{{K}_{2}}PtC{{l}_{6}}\] solution to get a shining grey tinge.

\[AuC{{l}_{3}}+3Ag\to 3AgCl+Au\]