{"id":5996,"date":"2020-10-13T12:17:41","date_gmt":"2020-10-13T06:47:41","guid":{"rendered":"http:\/\/astan.lk\/al_virtualclassroom\/?p=5996"},"modified":"2020-10-13T12:17:50","modified_gmt":"2020-10-13T06:47:50","slug":"qualitative-analysis-cations","status":"publish","type":"post","link":"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/","title":{"rendered":"Qualitative analysis – Cations"},"content":{"rendered":"

\u2022 Almost all cations form atoms in a flame test. The colour of the flame in the flame test is associated with elements possessing low energy gaps.<\/p>\n

\"\"<\/a><\/p>\n

 <\/p>\n

Cations identified by precipitation<\/h3>\n

\u2022 The precipitates of the cations having d7<\/sup>, d8<\/sup>, d9<\/sup> and d10<\/sup> electronic configurations are soluble in excess ammonia and form the respective stable complex ions.
\nM2+<\/sup>(aq) + X2-<\/sup>(aq) \u2192 MX(s)<\/p>\n

(d7<\/sup>) [Co(NH3<\/sub>)6<\/sub>]2+<\/sup> – Yellow brown<\/p>\n

(d8<\/sup>) [Ni(NH3<\/sub>)6<\/sub>]2+<\/sup> – Deep blue<\/p>\n

(d9<\/sup>) [Cu(NH3<\/sub>)4<\/sub>]2+<\/sup> – deep blue<\/p>\n

(d10<\/sup>) [Zn(NH3<\/sub>)4<\/sub>]2+<\/sup> – colourless<\/p>\n

(d10<\/sup>) [Ag(NH3<\/sub>)2<\/sub>]+<\/sup> – colourless<\/p>\n

(d10<\/sup>) [Cd(NH3<\/sub>)4<\/sub>]2+<\/sup> – colourless<\/p>\n

 <\/p>\n

Identification of NH4<\/sub>+<\/h4>\n

\u2022 Ammonium salts give ammonia gas with solutions of alkali(NaOH, KOH, Ca(OH)2<\/sub> etc).
\neg. NH4<\/sub>Cl(s) + NaOH(aq) \u2192 NH3<\/sub>(g) + Na+<\/sup>(aq) + Cl–<\/sup>(aq) + H2<\/sub>O(l)<\/p>\n

The evolved NH3<\/sub> gas can be tested with Nessler’s reagent or moist red litmus paper.
\nNH3<\/sub>(g) + Nerssler’s reagent \u2192\u00a0brown precipitate\/colouration<\/p>\n

 <\/p>\n

Separation procedure of a mixture of cations<\/h4>\n

\u2022 Qualitative analysis of a mixture of cations involves the separation of them to five groups. The scheme of qualitative analysis is based on the principle of selective precipitation. The precipitation of cations from a solution one at a time is called selective precipitation.<\/p>\n

Group I<\/strong>
\n\u2022 Cold, excess dilute HCl is added to a solution containing a mixture of cations. Only Ag+<\/sup>, Pb2+<\/sup> and Hg2<\/sub> 2+<\/sup> will be precipitated as insoluble chlorides (AgCl, PbCl2<\/sub>, Hg2<\/sub>Cl2<\/sub>).<\/p>\n

 <\/p>\n

Group II<\/strong>
\n\u2022 After the separation of the insoluble chlorides in Group I, the filtrate is still acidic. When H2<\/sub>S is passed through the solution, only insoluble sulphides get precipitated.
\n\"\"<\/a>\u2022 The concentration of sulphide ion is relatively low because of the higher concentration of H+<\/sup> \u00a0ions. Other cations such as Mn2+<\/sup> , Zn2+<\/sup> , Ni2+<\/sup> and Co2+<\/sup> with higher Ksp values of their respective sulphides will remain in the solution.<\/p>\n

 <\/p>\n

Group III<\/strong>
\n\u2022 The filtrate from Group II is boiled for a few minutes to expel all the dissolved H2<\/sub>S. Then boil the filtrate for a few minutes with conc.HNO3<\/sub> to oxidise Fe2+<\/sup> to Fe3+<\/sup> . The solution is treated with NH4<\/sub>Cl and NH4<\/sub>OH.
\nFe3+<\/sup> (aq) \u2192 Fe(OH)3<\/sub>(s) (reddish brown)
\nAl3+<\/sup> (aq) \u2192 Al(OH)3<\/sub>(s) (white gelatinous)
\nCr3+<\/sup> (aq) \u2192 Cr(OH)3<\/sub>(s) (green)<\/p>\n

 <\/p>\n

Group IV<\/strong>
\n\u2022 The filtrate from Group III contains OH–<\/sup> ions and is basic. H2<\/sub>S\u00a0is passed through this solution in the presence of OH–<\/sup> ions. Then H+<\/sup> ions produced from H2<\/sub>S\u00a0are neutralised by hydroxyl ions.<\/p>\n

\"\"<\/a><\/p>\n

\u2022 The above equilibrium shifts to the right and the concentration of S2-<\/sup> ions increases<\/p>\n

\"\"<\/a><\/p>\n

 <\/p>\n

Group V<\/strong>
\n\u2022 Boils off H2<\/sub>S\u00a0from Group IV filtrate and add a little amount of NH4<\/sub>Cl and NH4<\/sup>OH in excess. Heat the solution, then add (NH4<\/sub>)2<\/sub>CO3<\/sub> solution. Here Ca2+<\/sup>, Sr2+<\/sup> and Ba2+<\/sup> ions are precipitated as carbonates.<\/p>\n

\"\"<\/a><\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

\u2022 Almost all cations form atoms in a flame test. The colour of the flame in the flame test is associated with elements possessing low energy gaps.   Cations identified by precipitation \u2022 The precipitates of the cations having d7, d8, d9 and d10 electronic configurations are soluble in excess ammonia and form the respective […]<\/p>\n","protected":false},"author":842,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[14,1662],"tags":[],"class_list":["post-5996","post","type-post","status-publish","format-standard","hentry","category-chemistry","category-unit-06"],"acf":[],"yoast_head":"\nQualitative analysis - Cations - Learning & Education Portal<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Qualitative analysis - Cations - Learning & Education Portal\" \/>\n<meta property=\"og:description\" content=\"\u2022 Almost all cations form atoms in a flame test. The colour of the flame in the flame test is associated with elements possessing low energy gaps.   Cations identified by precipitation \u2022 The precipitates of the cations having d7, d8, d9 and d10 electronic configurations are soluble in excess ammonia and form the respective […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/\" \/>\n<meta property=\"og:site_name\" content=\"Learning & Education Portal\" \/>\n<meta property=\"article:published_time\" content=\"2020-10-13T06:47:41+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2020-10-13T06:47:50+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/astan.lk\/al_virtualclassroom\/wp-content\/uploads\/2017\/01\/cn-300x114.png\" \/>\n<meta name=\"author\" content=\"Admin\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Admin\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"2 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/\"},\"author\":{\"name\":\"Admin\",\"@id\":\"https:\/\/astan.lk\/al_virtualclassroom\/#\/schema\/person\/ffb0504e2cfb71518790b2fffd668c59\"},\"headline\":\"Qualitative analysis – Cations\",\"datePublished\":\"2020-10-13T06:47:41+00:00\",\"dateModified\":\"2020-10-13T06:47:50+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/\"},\"wordCount\":470,\"commentCount\":1,\"publisher\":{\"@id\":\"https:\/\/astan.lk\/al_virtualclassroom\/#organization\"},\"image\":{\"@id\":\"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/#primaryimage\"},\"thumbnailUrl\":\"http:\/\/astan.lk\/al_virtualclassroom\/wp-content\/uploads\/2017\/01\/cn-300x114.png\",\"articleSection\":[\"Chemistry\",\"Unit 06\"],\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/\",\"url\":\"https:\/\/astan.lk\/al_virtualclassroom\/qualitative-analysis-cations\/\",\"name\":\"Qualitative analysis - 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