Application of Co-ordination compounds Questions in English

(N/A) $(i)$ Biological systems: Chlorophyll,the pigment responsible for photosynthesis,is a coordination compound of magnesium. Haemoglobin,the oxygen-carrier in human blood,is a coordination compound of iron.
$(ii)$ Medicinal chemistry: Coordination compounds like $cis-platin$ (a platinum complex) are used as anti-cancer agents to inhibit the growth of tumours.
$(iii)$ Analytical chemistry: Coordination compounds are used in the detection of metal ions during salt analysis. For example,$Ni^{2+}$ ions are detected by the formation of a red precipitate with dimethylglyoxime $(DMG)$.
$(iv)$ Extraction/metallurgy of metals: Metals are extracted from their ores via complex formation. For example,gold is extracted from its ore by forming a cyano-complex $[Au(CN)_2]^-$,from which gold is later recovered by displacement with zinc.

(N/A) Coordination compounds are widely used in qualitative and quantitative chemical analysis. The color-producing reactions of metal ions with various ligands are a result of the formation of coordination complexes. Such reagents include $EDTA$,$DMG$ (dimethylglyoxime),$\alpha$-nitroso,$\beta$-naphthol,cupron,etc.
Water hardness is estimated by titration with $Na_{2}[EDTA]$. $Ca^{2+}$ and $Mg^{2+}$ ions form stable complexes with $EDTA$. Selective estimation of these ions can be done due to the difference in the stability constants of their $Ca$ and $Mg$ complexes.
Complex formation is used in the extraction of metals (e.g.,gold and silver). For example,gold combines with cyanide in the presence of oxygen and water to form the complex $[Au(CN)_{2}]^{-}$. Gold can then be recovered from this solution by adding $Zn$.
Purification of metals can be achieved through the formation and subsequent decomposition of coordination compounds. For example,impure $Ni$ is converted to $[Ni(CO)_{4}]$ and then decomposed to obtain pure $Ni$.
In biological systems,chlorophyll,the pigment responsible for photosynthesis,is a coordination compound of magnesium.
Hemoglobin,the red pigment of blood that acts as an oxygen carrier,is a coordination compound of iron. Vitamin $B_{12}$ (cyanocobalamin),an anti-pernicious anemia factor,is a coordination compound of cobalt.
Important metal-coordinated enzymes include carboxypeptidase-$A$ and carbonic anhydrase.
Coordination compounds are used as catalysts in many industrial processes. For example,the rhodium complex $[(Ph_{3}P)_{3}RhCl]$,known as Wilkinson's catalyst,is used in the hydrogenation of alkenes.
Electroplating of silver and gold can be done using complex solutions like $[Ag(CN)_{2}]^{-}$ and $[Au(CN)_{2}]^{-}$,which provide a more uniform coating than simple metal ion solutions.
In black and white photography,developed films are fixed by washing with hypo solution,which dissolves unreacted $AgBr$ by forming the complex $[Ag(S_{2}O_{3})_{2}]^{3-}$.
In medicinal chemistry,they are used in chelation therapy to treat metal poisoning in plants and animals. Excess copper and iron can be removed by chelation with ligands like $D$-penicillamine and desferrioxime-$B$. $EDTA$ is used in the treatment of lead poisoning.
Certain coordination compounds of $Pt$ effectively inhibit tumor growth,such as cis-platin.

(A) The calcium-disodium salt of $EDTA$ (Ethylenediaminetetraacetic acid) is used in the treatment of lead poisoning.
It acts as a chelating agent that binds to lead ions in the body to form a stable,water-soluble complex that can be excreted through urine.

(N/A) In black and white photography,the developed film is fixed by washing it with a solution of sodium thiosulphate $(Na_2S_2O_3)$.
This process involves the formation of a soluble coordination complex between the unreacted silver bromide $(AgBr)$ and the thiosulphate ions $(S_2O_3^{2-})$.
The chemical reaction is: $AgBr(s) + 2Na_2S_2O_3(aq) \rightarrow Na_3[Ag(S_2O_3)_2](aq) + NaBr(aq)$.
The complex formed,sodium dithiosulphatoargentate$(I)$,is water-soluble and is washed away,leaving behind the metallic silver image.

(N/A) Coordination compounds play a crucial role in the extraction and purification of metals.
$1$. Extraction of Gold and Silver: Gold and silver are extracted by leaching them with a dilute solution of $NaCN$ or $KCN$ in the presence of air (for $O_2$),which forms a soluble coordination complex: $4Au(s) + 8CN^-(aq) + 2H_2O(aq) + O_2(g) \rightarrow 4[Au(CN)_2]^-(aq) + 4OH^-(aq)$. The metal is then recovered from this complex by displacement with a more electropositive metal like zinc.
$2$. Purification of Nickel: The Mond process is used for the purification of nickel. Nickel reacts with carbon monoxide to form a volatile coordination complex,tetracarbonylnickel$(0)$,which is then decomposed at higher temperatures to yield pure nickel: $Ni(s) + 4CO(g)$ $\rightarrow [Ni(CO)_4](g)$ $\rightarrow Ni(s) + 4CO(g)$.

(N/A) In electroplating,coordination compounds are used to ensure a smooth and uniform deposition of metal. For example,articles can be electroplated with silver and gold much more smoothly and evenly from solutions of the complexes $[Ag(CN)_{2}]^{-}$ and $[Au(CN)_{2}]^{-}$ than from a simple solution of metal ions.

(N/A) Industrial processes: Coordination compounds are used as catalysts for many industrial processes. For example,the Wilkinson catalyst,$[(Ph_{3}P)_{3}RhCl]$,is used for the hydrogenation of alkenes.
Biological systems:
$1$. Chlorophyll,the green pigment responsible for photosynthesis,is a coordination compound of magnesium.
$2$. Haemoglobin,the red pigment of blood that acts as an oxygen carrier,is a coordination compound of iron.
$3$. Vitamin $B_{12}$ (cyanocobalamin),the anti-pernicious anaemia factor,is a coordination compound of cobalt.
$4$. Carboxypeptidase-$A$ and carbonic anhydrase are essential metalloenzymes of zinc that act as catalysts in biological systems.

(N/A) In black and white photography,the developed film is fixed by washing it with a hypo solution (sodium thiosulphate). The hypo solution dissolves the undecomposed $AgBr$ to form a soluble complex ion,$[Ag(S_2O_3)_2]^{3-}$,which can be washed away. The reaction is: $AgBr(s) + 2Na_2S_2O_3(aq) \rightarrow Na_3[Ag(S_2O_3)_2](aq) + NaBr(aq)$.

(N/A) Metallurgical processes: Some important extraction processes of metals,such as those of $Ag$ and $Au$,utilize complex formation.
$1$. Extraction: Gold $(Au)$ combines with cyanide in the presence of oxygen and water to form the coordination entity $[Au(CN)_2]^-$ in aqueous solution. Gold can be separated in metallic form from this solution by the addition of zinc.
$2$. Purification: Purification of metals can be achieved through the formation and subsequent decomposition of their coordination compounds. For example,impure nickel is converted to $[Ni(CO)_4]$,which is decomposed to yield pure nickel.

(N/A) In medicine,coordination compounds are used in chelate therapy to treat problems caused by the presence of toxic levels of metals in plants and animals.
For example,an excess of $Cu$ and $Fe$ is removed by chelating agents such as $D$-penicillamine and desferrioxime $B$ through the formation of stable coordination compounds.
$EDTA$ is used in the treatment of $Pb$ poisoning.
Cis-platin and its related compounds are effectively used to inhibit the growth of tumors.

(N/A) $PCl_5$ acts as a chlorinating agent and oxidizes finely divided silver $(Ag)$ to silver chloride $(AgCl)$.
$PCl_5 + 2Ag \rightarrow 2AgCl + PCl_3$
The white precipitate of $AgCl$ dissolves in excess aqueous $NH_3$ due to the formation of a soluble diamminesilver$(I)$ chloride complex.
$AgCl + 2NH_3 \rightarrow [Ag(NH_3)_2]Cl$
(white precipitate) $\quad$ (soluble complex)

(N/A) The reactions are as follows:
$1. \text{ Decomposition of } CuCO_3: CuCO_3 \xrightarrow{\Delta} CuO + CO_2 \uparrow (D)$
$2. \text{ Self-reduction of copper: } 2CuO + CuS \xrightarrow{\Delta} 3Cu (A) + SO_2 \uparrow$
$3. \text{ Reaction with conc. } HNO_3: Cu (A) + 4HNO_3 \text{ (conc.)} \to Cu(NO_3)_2 (B) + 2NO_2 + 2H_2O$
$4. \text{ Formation of blue complex: } Cu^{2+} + 4NH_3 \to [Cu(NH_3)_4]^{2+} (C)$
$5. \text{ Test for } CO_2: CO_2 (D) + Ca(OH)_2 \to CaCO_3 (E) \text{ (Milky)} + H_2O$
$6. \text{ Formation of clear solution: } CaCO_3 (E) + CO_2 + H_2O \to Ca(HCO_3)_2 \text{ (Clear solution)}$
Therefore,the identities are:
$(A) = Cu$
$(B) = Cu(NO_3)_2$
$(C) = [Cu(NH_3)_4]^{2+}$
$(D) = CO_2$
$(E) = CaCO_3$

(B) Chlorophyll is a coordination compound of magnesium $(a-iv)$.
Vitamin $B_{12}$ (cyanocobalamin) is a coordination compound of cobalt $(b-iii)$.
Cisplatin is used as an anti-cancer drug and is a coordination compound of platinum $(c-ii)$.
Grubbs catalyst is a complex of ruthenium $(d-i)$.
Therefore,the correct matching is $a-iv, b-iii, c-ii, d-i$.

(D) When $FeCl_{3}$ reacts with an excess of $K_{4}[Fe(CN)_{6}]$,the reaction is as follows:
$Fe^{3+} + K^{+} + [Fe(CN)_{6}]^{4-} \rightarrow KFe[Fe(CN)_{6}]$
This product,$KFe[Fe(CN)_{6}]$,is a soluble complex that forms a Prussian blue coloured colloidal solution.
Therefore,the correct option is $D$.

(D) The reaction between potassium ferrocyanide and ferric chloride is as follows:
$3K_{4}[Fe(CN)_{6}] + 4FeCl_{3} \rightarrow Fe_{4}[Fe(CN)_{6}]_{3} + 12KCl$
The product $Fe_{4}[Fe(CN)_{6}]_{3}$ is known as Prussian blue,which is a deep blue pigment.

(D) The reaction between $Fe^{3+}$ ions and potassium ferrocyanide,$K_4[Fe(CN)_6]$,leads to the formation of ferric ferrocyanide,which is known as Prussian blue.
The balanced chemical equation is:
$4Fe^{3+} + 3[Fe(CN)_6]^{4-} \longrightarrow Fe_4[Fe(CN)_6]_3$ (Prussian blue).

(C)
Aqueous solution of silver nitrate $(X = AgNO_3)$ reacts with $NH_4OH$ to form a brown precipitate of silver oxide $(Y = Ag_2O)$.
$2AgNO_3 + 2NH_4OH \longrightarrow Ag_2O + 2NH_4NO_3 + H_2O$
This precipitate dissolves in excess $NH_4OH$ to form the diamminesilver$(I)$ complex,$[Ag(NH_3)_2]^+$,which is known as Tollen's reagent.
$Ag_2O + 4NH_3 + H_2O \longrightarrow 2[Ag(NH_3)_2]^+ + 2OH^-$
Tollen's reagent is reduced by acetaldehyde $(CH_3CHO)$ to deposit metallic silver $(Ag)$.
$CH_3CHO + 2[Ag(NH_3)_2]^+ + 3OH^- \longrightarrow CH_3COO^- + 2Ag + 4NH_3 + 2H_2O$

(D) Dimethylglyoxime $(DMG)$ is a specific chelating agent used for the detection of $Ni^{2+}$ ions.
In the presence of an ammoniacal solution,$Ni^{2+}$ reacts with $DMG$ to form a stable,brilliant red-colored complex,bis(dimethylglyoximato)nickel$(II)$.
The reaction is: $Ni^{2+} + 2C_4H_8N_2O_2 \xrightarrow{NH_3} [Ni(C_4H_7N_2O_2)_2] + 2H^+$.
Therefore,the metal ion is $Ni^{2+}$.

(A) $Cis-Platin$ is a coordination compound of $Pt$ used in chemotherapy to inhibit the growth of tumors.
Its chemical formula is $cis-[Pt(NH_3)_2Cl_2]$.
Therefore,both $B$ and $D$ are correct as $Cis-Platin$ is a specific type of coordination compound of $Pt$.

(D) The reaction between $FeCl_3$ and $K_4[Fe(CN)_6]$ is a standard test for $Fe^{3+}$ ions.
When $Fe^{3+}$ ions react with potassium ferrocyanide,$K_4[Fe(CN)_6]$,they form a deep blue complex known as Prussian blue.
The chemical reaction is: $4Fe^{3+} + 3[Fe(CN)_6]^{4-} \rightarrow Fe_4[Fe(CN)_6]_3$.
The resulting compound is ferric ferrocyanide,$Fe_4[Fe(CN)_6]_3$,which is responsible for the Prussian blue color.

(A) $A.$ Chlorophyll contains $Mg^{2+}$ ion,not $Co$. Thus,this is mismatched.
$B.$ $EDTA$ is used to estimate water hardness by forming a stable complex with $Ca^{2+}$ and $Mg^{2+}$ ions. This is a correct match.
$C.$ In black and white photography,the developed film is fixed by washing with hypo solution $(Na_2S_2O_3)$,which dissolves undecomposed $AgBr$ to form the complex ion $[Ag(S_2O_3)_2]^{3-}$,not $[Ag(CN)_2]^-$. Thus,this is mismatched.
$D.$ Wilkinson catalyst is $[(Ph_3P)_3RhCl]$. This is a correct match.
$E.$ $D^{-}$\text{Penicillamine} is a chelating ligand used to treat Wilson's disease by chelating excess copper. This is a correct match.
Therefore,the mismatched combinations are $A$ and $C$.

(D) The reagent used for the detection of $Ni^{2+}$ ions is dimethyl glyoxime $(dmg)$.
In the presence of an ammonium hydroxide $(NH_4OH)$ basic medium,$Ni^{2+}$ reacts with $dmg$ to form a complex,$Ni(dmg)_2$,which appears as a brilliant red precipitate.
The chemical reaction is: $Ni^{2+} + 2C_4H_8N_2O_2 \rightarrow [Ni(C_4H_7N_2O_2)_2] + 2H^+$.
Thus,the correct option is $D$.

(A) $Fe_4[Fe(CN)_6]_3 \cdot xH_2O$ is Prussian Blue.
$[Fe(CN)_5NOS]^{4-}$ is Violet.
$[Fe(SCN)]^{2+}$ is Blood Red.
$(NH_4)_3PO_4 \cdot 12MoO_3$ is Yellow.
Therefore,the correct matching is $A-III, B-I, C-II, D-IV$.

(A) The aqueous solution of $CuSO_4$ appears blue because it absorbs light in the orange-red region of the visible spectrum.
According to the complementary colour theory,the colour observed is complementary to the colour absorbed.

(C) The correct matches are:
$A$. Haber process uses $Fe$ as a catalyst for the synthesis of ammonia.
$B$. Wacker oxidation uses $PdCl_2$ as a catalyst for the oxidation of alkenes to aldehydes or ketones.
$C$. Wilkinson catalyst is $[(PPh_3)_3RhCl]$,used for the hydrogenation of alkenes.
$D$. Ziegler catalyst is $TiCl_4$ with $Al(CH_3)_3$ (or $Al(C_2H_5)_3$),used for the polymerization of ethene.
Therefore,the correct sequence is $A-I, B-II, C-III, D-IV$.

(D) Lead poisoning is treated using chelating agents that can form stable,water-soluble complexes with lead ions,allowing them to be excreted from the body.
$EDTA$ (Ethylenediaminetetraacetic acid) is commonly used for this purpose.
Specifically,the calcium complex of $EDTA$,which is $[Ca(EDTA)]^{2-}$,is administered.
In the body,the lead ions $(Pb^{2+})$ displace the calcium ions $(Ca^{2+})$ from the complex because the lead-$EDTA$ complex is more stable.
The resulting lead complex is then excreted through urine.

(A) The hardness of water is primarily due to the presence of $Ca^{2+}$ and $Mg^{2+}$ ions.
$EDTA$ (Ethylenediaminetetraacetic acid) is a hexadentate ligand that forms stable,water-soluble complexes with these metal ions.
Due to the difference in the stability constants of their $EDTA$ complexes,$Ca^{2+}$ and $Mg^{2+}$ ions can be selectively estimated using a titration method with $EDTA$.

(A) $EDTA$ (Ethylenediaminetetraacetic acid) is a chelating agent used in the treatment of lead $(Pb)$ poisoning because it forms stable,water-soluble complexes with $Pb^{2+}$ ions,which are then excreted from the body.

(B) $cis-[PtCl_2(NH_3)_2]$,commonly known as cisplatin,is used in the treatment of cancer.

(A) $EDTA$ (Ethylenediaminetetraacetate) is a hexadentate ligand that forms stable,water-soluble complexes with metal ions like lead $(Pb^{2+})$.
In chelate therapy,$EDTA$ is administered to bind with lead ions in the body,forming a stable complex that can be easily excreted through urine,thereby reducing the toxic effects of lead.

(D) Chlorophyll is a green pigment found in plants that plays a vital role in photosynthesis.
It is a porphyrin derivative containing a central metal ion.
The central metal ion in the chlorophyll molecule is $Mg^{2+}$ (Magnesium ion).
Therefore,chlorophyll is a coordination compound of Magnesium.

(D) The color of a coordination complex is complementary to the color of light absorbed.
For complex $I$,the observed color is pale blue,which corresponds to the absorption of orange light (wavelength range $\approx 600-650 \ nm$).
For complex $III$,the observed color is violet,which corresponds to the absorption of yellow light (wavelength range $\approx 530-580 \ nm$).
Comparing these with the given options,the wavelengths absorbed for $I$ and $III$ are approximately $600 \ nm$ and $535 \ nm$ respectively.

(D) According to the colour wheel,the colour observed is the complementary colour of the light absorbed.
When a metal complex absorbs orange light,it appears in its complementary colour,which is blue.

(D) The complex $[Ti(H_2O)_6]Cl_3$ contains $Ti^{3+}$ ion which has a $3d^1$ electronic configuration.
Due to the presence of one unpaired electron,it undergoes $d-d$ transition and exhibits a violet colour.
Upon heating at $250^{\circ} C$ in the presence of oxygen,it decomposes to form $TiO_2$ where titanium is in the $+4$ oxidation state $(Ti^{4+} : 3d^0)$.
Since $Ti^{4+}$ has no unpaired electrons,it does not undergo $d-d$ transition and is colourless.
Therefore,the colour change is from violet to colourless.

(D) Ferric salts (such as $FeCl_3$) react with potassium ferrocyanide to form Prussian blue,which is ferric ferrocyanide.
The chemical reaction is:
$4 FeCl_3 + 3 K_4[Fe(CN)_6] \longrightarrow Fe_4[Fe(CN)_6]_3 + 12 KCl$
The product $Fe_4[Fe(CN)_6]_3$ is known as Prussian blue.

(A) Hemoglobin is a complex protein found in red blood cells that is responsible for transporting oxygen throughout the body.
It contains a prosthetic group called heme,which consists of a porphyrin ring coordinated to a central iron ion.
In functional hemoglobin,this iron ion is in the ferrous state,represented as $Fe^{2+}$.

(D) The ferric ion $(Fe^{3+})$ reacts with potassium ferrocyanide $(K_4[Fe(CN)_6])$ to form a Prussian blue precipitate of ferric ferrocyanide,which is $Fe_4[Fe(CN)_6]_3$.
The chemical reaction is: $4Fe^{3+} + 3[Fe(CN)_6]^{4-} \rightarrow Fe_4[Fe(CN)_6]_3$.