Reactions to Identify Cations - PDF

## Reactions to identify cations and element groups ### Confirmation of the action of the first element group ### Test for $Ag^+$ 1. Diluted hydrochloric acid precipitates $Ag^+$ ions forming a white precipitate, $AgCl$. * $AgCl$ is sensitive to light and turns black. * Concentrated $H...

## Reactions to identify cations and element groups ### Confirmation of the action of the first element group ### Test for $Ag^+$ 1. Diluted hydrochloric acid precipitates $Ag^+$ ions forming a white precipitate, $AgCl$. * $AgCl$ is sensitive to light and turns black. * Concentrated $HCl$ dissolves $AgCl$ to form the complex $[AgCl_2]^- $. * It dissolves completely in complexing substances, such as colorless complexes. * For example, using $NH_3$: $Ag^+ + Cl^- \longrightarrow AgCl$ $AgCl + NH_3 \longrightarrow [Ag(NH_3)_2]Cl \longrightarrow [Ag(NH_3)_2]^+$ * The addition of $KI$ to $2[Ag(NH_3)_2]^+$ precipitates $Ag^+$ as yellow $AgI$. 2. Alkaline Chromates/Dichromates form a red-brown precipitate of $Ag_2CrO_4$ or $Ag_2Cr_2O_7$. * The precipitate is soluble in $HNO_3$, $NH_4OH$ and all complexing substances that form complexes with $Ag^+$. * Confirmation is disrupted by $Cu^{2+}$, $Pb^{2+}$, $Hg^{2+}$, $Hg_2^{2+}$ and $Bi^{3+}$. * $K_2CrO_4 + 2Ag^+ \longrightarrow Ag_2CrO_4+2K^+$ 3. Argenton I with the formula $H_2N-CS-SH$ in a neutral medium (alcohol or acetone) is a light yellow precipitate. * It can be used to form a blood-orange precipitate. * Confirmation can be disrupted by $Hg_2^{2+}$, $Pb^{2+}$, $Bi^{3+}$. ### Confirmation of the action of $Hg_2^{2+}$ 1. Diluted hydrochloric acid precipitates $Hg_2^{2+}$ and forms a white precipitate. * $Hg_2Cl_2$ (calomel) turns black upon the addition of $NH_3$ * The dichloride di-mercury reaction (calomel): $Hg_2^{2+} + 2HCI \longrightarrow Hg_2 Cl_2 + H^+$ $Hg_2Cl_2 + NH_3 \longrightarrow Hg_2 NH_2Cl + HCI$ $Hg_2 NH_2Cl \longrightarrow Hg NH_2 Cl + Hg \enspace(black - releases\enspace Hg^0)$ 2. $KI$ precipitates $Hg_2^{2+}$ as a green precipitate $Hg_2 I_2$. * In excess, it dissolves to produce $K_2[HgI_4]$, emits $Hg^0$ and turns black. 3. Alkaline chromates/dichromates form red-brown $Hg_2, CrO_4$ $K_2CrO_4 + Hg_2^{2+} \longrightarrow Hg_2 CrO_4 +2k^+$ ### Test for $Pb^{2+}$ 4. $KI + Pb^{2+} \longrightarrow$ forms a yellow precipitate $Pb I_2$ *(honeycombed)* * Soluble in water, releasing golden crystals * In-excess of $KI$, $K_2[P5I_4]$ is formed. 5. Chromates $+ Pb^{2+} \longrightarrow$ yellow $PbCrO_4$ * Soluble in $HNO_3$, alkali hydroxides differing from $Ag^+$ and $Bi^{3+}$. * $K_2CrO_4 + Pb^{2+} \longrightarrow Pb CrO_4 +2k^+$ 6. $Na_2SO_4$ precipitates from neutral or weakly ammoniacal solutions $Pb^{2+}$ * White amorphous $PbSO_4$ (lead sulfate) is present. * Confirms $Pb^{2+}$ in drinking water. * Other cations do not disrupt the $Pb^{2+}$ confirmation. 7. Dithizone in chloroform (green solution) $+ Pb^{2+} \longrightarrow$ red complex * $Zn^{2+}$ also reacts similarly. * The reaction is only selective in the presence of $KCN$, otherwise all heavy ions disrupt the confirmation! * Chemical structures of dithizone ($Diphenylthiocarbazone$) * Isomers are listed as: $C_{13}H_{12}N_4S$ #### Reactions to identify cations of the second element group ### Test for $Hg^{2+}$ 1. $KI$ precipitates $Hg^{2+}$ as a red precipitate $HgI_k$ * In excess $KI \longrightarrow K_2[HgI_4]$ * With the presence of $CuI_2 \longrightarrow $ orange-red $Cu_2[Holy]$ in a basic environment. * $K_2[Hals] + CuI_2 \longrightarrow Cu_2 [Holy] + 2 KI $ $Cu^{2+} + I^- \longrightarrow Cu_2l_2 + I_2$ 2. Alkaline hydroxides in excess hydroxide $\longrightarrow$ yellow $HgO$, soluble with acids. $NaOH + Hg^{2+} \longrightarrow HgO + H^+$ ### Test for $Cu^{2+}$ 1. $NH_3 + Cu^{2+} \longrightarrow$ violet-blue $[Cu(NH_3)_6]^{2+}$, * With concenrated $HCI$ (chloride), a green $[CuCl_2]^2$ is formed. * Slow addition of $NH_3 \longrightarrow$ medium-green to violet blue. * Complex $[Cu(NH_3)_4]^{2+}$ can be decomposed with mineral acids. 2. $K_4[Fe(CN)_6]$ precipitates from neutral/weakly acidic solutions $Cu^{2+}$ with a red-brown precipitate. *red-brown precipitate* *small amount of $Cu^{2+} \longrightarrow K_2 \{Cu[Fe(CN)_6]\}$ *the excess $Cu^{2+} \longrightarrow Cu \{Cu [Fe(CN)_6]\}$ - dissolves in alkaline hydroxides- the jasnomodry $Cu(OH)_v$ in excess $NH_3$ for modry roztok $[Cu(NH_3)_4]^+$ $K_y [Fe(CN)] + c^{2+} \longrightarrow K, \{ Cu[Fe(CN)6] \} + K^+$ $K_z \{ Cu [Fe(CN)6] \} + Cu^{2+} \longrightarrow Cu \{ Cu [Fe(CN)6] \} + K^+$ $NaOH + Cu \{Cu [Fe(CN)6] \} \longrightarrow Cu(OH)_2$ - On oxidation of $Cu(OH)_2$, with HNO3, red-brown $K_2\{Cu[Fe(CN)_6]\}$ will precipitate back. - The disruptive influence if $Fe^{3+}$ can be removed by adding $NH_3 \longrightarrow$ hnedárazanina $Fe(OH)_3$ -after settling remove the staining, wash -Jony $Fe^{3+} 2. Montegulino skimming agent in the presence of $Zn^{2+} \longrightarrow$ modrofialove crystals. $Zn [Hg(SCN)_⁴ ] a Cu [Hy(SCN)₄] 2+ $ -the concentration of if Cat is hysoia nez zn²* venlihie zelene lyslaly Dokaz Cd²+ + A. sulfate 14,5 zada 20 sabokysleho pros/redis elly CDS 1. Concentrated KSCN s neutr. / shabo kysl's roztokom mody komplex $\longleftarrow_{2}[Co(SCN)4 – dokáz nisia Fe** “mosbuje sa pridaním fluidov 2. KSCNowy 3. The disruptive influence if Fest can be removed by adding 14, - huedárazanina Fe(OH), . – The destructive impact if can be remoned by adding 14,-The destructive impact if can be removed by adding NH, – huedárazan ### Confirmation of the action of 3 elements groups ### Proof $Co^{2+}$ 1. $HCI + Co^{2+}$ has a blue complex. chemical formula 2. concentrated KSCNs neut. /slabo kystim roztokom mody komplex Ki [Co(SCN);] ### **Test for Cd2+** 1. Sulfide H₂S zráża 20 sabokyslého prostredia illy CdS. 2. Concentrated KSCN s neutr. / shabo kyslom roztokom mody komplex $\longleftarrow_{2}[Co(SCN)4 – dokáz nisia Fe* *" mosbuje sa pridaním fluidov ### Test for $Bi^{3+}$ 1. $KI + Bi^{3+} \longrightarrow$ brown-red to black precipitate Biiz nadbytekt Kl-žilly rozlok [Bily]" dokáz nisia Cu * *, Hgt" a Pb 2. concentrated as 3. Sulfide H₂S zada 20 sabokysleeho pros/redia illy CDS.