Salt Analysis: Cations (Wet & Dry Tests) Why cation analysis matters In the lab, you rarely get a label on the salt. You use simple, low-cost tests to “read” ions from colors, flames, and precipitates. This skill is tested in NEET and is used in real labs for water testing, metallurgy, forensics, and pharma QC. We will build the logic from quick dry tests to the systematic wet group separation so you can narrow down and then confirm the cation with confidence. remember Forensic toxicology: Qualitative cation analysis helps flag heavy metal poisoning (e.g., Pb²⁺, Hg²⁺) in biological samples (blood, tissues), supporting diagnosis or legal investigation. The roadmap at a glance Flowchart: classical group separation scheme for cations (Groups I–VI). Follow arrows: add group reagent → observe precipitate → filter → proceed with filtrate to next group. Sequence you will follow Start: Note color and water of crystallization of dry salt. Perform dry tests: action of heat, flame test, charcoal-cavity with cobalt nitrate, borax-bead (if needed). Prepare clear aqueous solution (Original Solution, O.S.). Group I: Add dilute HCl → chlorides of Ag⁺, Pb²⁺, Hg2²⁺ precipitate. Group II: To filtrate, acidify and pass H2S → sulfides of Cu²⁺, Cd²⁺, Bi³⁺, Hg²⁺, Pb²⁺, As/Sb/Sn precipitate. Group III: Boil off H2S, then add NH4Cl + NH4OH → hydroxides of Al³⁺, Cr³⁺, Fe³⁺ (Fe²⁺ oxidizes to Fe³⁺) precipitate. Group IV: To filtrate, pass H2S in basic NH4OH/NH4Cl → ZnS, CoS, NiS, MnS precipitate. Group V: To filtrate, add (NH4)2CO3 in NH4OH/NH4Cl → CaCO3, SrCO3, BaCO3 precipitate. Group VI: In final filtrate test for Mg²⁺, Na⁺, K⁺, NH4⁺ using specific tests (no common group reagent). Preliminary dry tests — Color of the salt Color gives the first hint. Hydrated transition-metal salts are often colored. Do not jump to conclusions — use it only as a clue before wet tests. Copper(II) sulfate pentahydrate (blue vitriol), CuSO4·5H2O Blue crystals Iron(II) sulfate heptahydrate (green vitriol), FeSO4·7H2O Pale green crystals (turn brown on oxidation) Manganese(II) sulfate monohydrate, MnSO4·H2O (often listed as hepta for older samples) Very pale pink Nickel(II) sulfate hexahydrate, NiSO4·6H2O Green Cobalt(II) chloride hexahydrate, CoCl2·6H2O Pink (turns blue on dehydration/heat) Potassium permanganate, KMnO4 Deep purple Potassium dichromate, K2Cr2O7 Orange; in alkaline medium converts to yellow chromate ( CrO4 2− ) Salt (IUPAC; common name) Appearance (solid) Characteristic colors of some common salts tip Hydration matters: Cobalt(II) chloride is pink when hydrated and turns blue on heating (dehydration). Rehydrate to restore pink. Preliminary dry tests — Action of heat Observe color change and gases evolved Zinc oxide (from zinc salts on strong heating) turns yellow when hot and becomes white on cooling. Lead(II) oxide turns yellow when hot and becomes reddish on cooling. Carbonates on heating with acid release CO2 (effervescence; lime water turns milky due to CaCO3). Nitrates: Alkali metal nitrates often give O2 (and NO2 with some heavy-metal nitrates). Ammonium salts on heating with NaOH release NH3 (pungent smell; turns moist red litmus blue). neet-alert Always distinguish: CO2 is colorless and extinguishes a glowing splinter; NO2 is brown and irritating; NH3 is pungent and basic (blue litmus). Flame test — quick screen for alkali/alkaline earths gpt-image-2 2026-05-26T17:05:52.380Z Comparative flame-test chart: clean nichrome wire loop dipped in salt solutions producing colored flames. Side-by-side flames labeled: Na (golden yellow), K (pale lilac) with overlay cobalt-blue glass icon, Ca (brick red), Sr (crimson), Ba (apple green), Cu (blue-green), Pb (pale blue). Clean white background, vector style. Flame colors: Na yellow, K lilac/violet (use cobalt blue glass), Ca brick red, Sr crimson, Ba apple green, Cu blue-green, Pb pale blue. Flame-test colors (qualitative) Cation Flame color Note Na⁺ Golden yellow Very intense; masks others K⁺ Pale lilac/violet Observe through cobalt blue glass to filter Na Ca²⁺ Brick red Moderate intensity Sr²⁺ Crimson Deeper red than Ca Ba²⁺ Apple green Distinct green tinge Cu²⁺ (as volatile halide) Blue-green Best seen with HCl (forms CuCl vapors) Pb²⁺ Pale blue Weak and fleeting K and Na flames look similar to the eye. Sodium’s yellow is so strong it hides K’s lilac. Use cobalt-blue glass — it cuts the yellow and reveals K’s violet. neet-alert Charcoal-cavity and cobalt-nitrate test On a charcoal block, make a small cavity, mix a pinch of salt with sodium carbonate, and heat strongly (blowpipe/Bunsen). You get the oxide/incrustation. Then add a drop of cobalt(II) nitrate solution and reheat. Specific colored masses form due to mixed cobaltates/aluminates. Charcoal-cavity test: heat salt + Na2CO3 on charcoal, then add Co(NO3)2 and reheat to see diagnostic colors. 2026-05-26T17:05:52.475Z gpt-image-2 Diagram of charcoal-block cavity test: Panel 1 mixing salt with Na2CO3; Panel 2 strong heating with blowpipe; Panel 3 adding a drop of cobalt(II) nitrate and reheating; show resulting colored incrustations (Zn green, Al blue, Mg pink). Clear labels, vector schematic, white background. Zn²⁺ (ZnO) Yellow when hot → white on cooling; with Co²⁺ gives green mass Green due to cobalt zincate Al³⁺ (Al2O3) Deep blue mass Cobalt aluminate (Thenard’s blue) Mg²⁺ (MgO) Pink mass Characteristic pale pink Cation (as oxide after heating) Color after Co(NO3)2 test Note Cobalt-nitrate colors on charcoal Borax-bead test — colored beads for transition metals Heat a loop with borax (Na2B4O7·10H2O) to form a clear glassy bead (sodium metaborate/borate). Touch the hot bead to a trace of the sample and heat in oxidizing and reducing flames. Metal metaborates/oxides in the bead show characteristic colors. Borax-bead test: make a clear borax bead, pick sample, heat in oxidizing vs reducing flames to compare colors. Four-panel vector sequence: 1) Heat borax on loop to clear bead; 2) Touch bead to sample; 3) Heat in oxidizing flame; 4) Heat in reducing flame. Side labels: Cu (green→red), Cr (green), Fe (yellow-brown→green), Co (blue), Mn (violet→colorless), Ni (brown→gray). Clean textbook style. 2026-05-26T17:05:52.753Z gpt-image-2 Cation Oxidizing flame Reducing flame Borax-bead colors (Oxidizing vs Reducing flame) Cu²⁺ Green bead Red/opaque brown (Cu metal) Cr³⁺/Cr⁶⁺ (as chromate/chromic species) Green Green Fe³⁺/Fe²⁺ Yellow to brown Bottle-green Co²⁺ Deep blue Deep blue Mn²⁺/Mn³⁺ Violet (amethyst) Colorless Ni²⁺ Brown Gray (Ni metal) Wet analysis — the logic of group separation Selective precipitation: by controlling pH and common ions, we cross the Ksp of only one group at a time. Idea: At each step you add a reagent that precipitates only a subset of cations because their solubility products (Ksp) are very small under those conditions. For example, in acidic medium, [ S 2- ] is kept very low (H2S is suppressed), so only very insoluble sulfides (Group II) form. In alkaline medium, [ S 2- ] is high, so moderately insoluble sulfides (Group IV) also precipitate. Ammonium chloride provides a common-ion effect to control OH− (Group III) and CO3 2− (Group V). Group reagents overview (I to VI) Cation groups, reagents, and precipitate types Group Group reagent/medium Representative cations Group precipitate Typical color Dilute HCl Ag⁺, Pb²⁺, Hg2²⁺ Chlorides (AgCl, PbCl2, Hg2Cl2) White (PbCl2 partly soluble in hot water) II H2S in acidic medium Cu²⁺, Cd²⁺, Bi³⁺, Hg²⁺, Pb²⁺, As³⁺/Sb³⁺/Sn²⁺/Sn⁴⁺ Sulfides Black (CuS, PbS, HgS), Yellow (CdS, As2S3), Orange (Sb2S3) III NH4Cl + NH4OH (buffered basic) Al³⁺, Cr³⁺, Fe³⁺/Fe²⁺ Hydroxides (Al(OH)3, Cr(OH)3, Fe(OH)3) White gelatinous, green, reddish-brown IV H2S in basic NH4OH/NH4Cl Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺ Sulfides (ZnS, CoS, NiS, MnS) White (ZnS), Black (CoS/NiS), Pink-buff (MnS) (NH4)2CO3 in NH4OH/NH4Cl Ca²⁺, Sr²⁺, Ba²⁺ Carbonates (CaCO3, SrCO3, BaCO3) All white VI No common group reagent Mg²⁺, Na⁺, K⁺, NH4⁺ Specific tests See individual confirmatory tests Group precipitates in test tubes: yellow CdS (Group II), reddish-brown Fe(OH)3 (Group III), white BaCO3 (Group V). Core precipitation equations you must know Group I (chloride) Silver(I) chloride is a curdy white precipitate insoluble in cold water. Only very insoluble sulfides form in acidic medium (low [ S 2- ]). Group II (sulfide in acid) NH4Cl suppresses [OH−] just enough to precipitate Group III hydroxides selectively. Group III (hydroxide with NH4Cl/NH4OH) Group V forms white carbonates in ammoniacal medium. Group V (carbonate in ammoniacal medium) Selective precipitation uses Ksp and common-ion/pH control to separate ions stepwise. Group-wise highlights and confirmatory tests Group I — Ag⁺, Pb²⁺, Hg2²⁺ Group reagent: dilute HCl → white chlorides. AgCl: curdy white; dissolves in NH3 to [Ag(NH3)2]⁺, reprecipitates with acid. PbCl2: white; dissolves in hot water, reprecipitates on cooling/with chromate as yellow PbCrO4. Hg2Cl2: white; with NH3 turns black (due to formation of Hg°/HgNH2Cl). Black: CuS, PbS, HgS; Yellow: CdS, As2S3; Orange: Sb2S3. Cu²⁺: deep blue solution with excess NH3 due to [Cu(NH3)4] 2+ . Cd²⁺: yellow CdS precipitate; dissolves in hot dilute HCl to some extent (lab variation). Arsenic/antimony/tin: colored sulfides; further differentiation done in sub-groups (beyond NEET depth). Group II — Sulfides in acidic medium Group III — Hydroxides with NH4Cl/NH4OH Fe(OH)3: reddish-brown gelatinous ppt; Fe²⁺ is first oxidized to Fe³⁺ in air/acids. Al(OH)3: white gelatinous ppt; dissolves in excess NaOH (amphoteric). Cr(OH)3: green ppt; dissolves in excess NaOH/H2O2 to chromate (yellow) upon oxidation. Group IV — Sulfides in basic medium ZnS: white; MnS: pink-buff; CoS/NiS: black. Ni²⁺: confirmed by dimethylglyoxime (DMG) — rose-red Ni(DMG)2 ppt in ammoniacal medium. Co²⁺: blue borax bead; also forms complex [Co(SCN)4] 2− (deep blue) in presence of SCN− in acetone (advanced, lab note). Group V — Carbonates in ammoniacal medium All three (Ca²⁺, Sr²⁺, Ba²⁺) give white carbonates with (NH4)2CO3 in NH4OH/NH4Cl. Flame test: Ca (brick red), Sr (crimson), Ba (apple green). Further differentiation (typical lab): Ba²⁺ forms yellow BaCrO4 with K2CrO4; Ca²⁺ gives white CaC2O4 with ammonium oxalate. Group VI — No group reagent Mg²⁺: with Na2HPO4 in ammoniacal solution → white crystalline Mg(NH4)PO4·6H2O. Na⁺: intense yellow flame. K⁺: lilac flame (see through cobalt blue glass); also gives yellow ppt with sodium cobaltinitrite, Na3[Co(NO2)6], in acidic solution. NH4⁺: on heating with NaOH → NH3 gas (pungent, turns moist red litmus blue). Ni²⁺ confirmatory test: rose-red Ni(DMG)2 precipitate in ammoniacal solution. Close-up vector of a test tube with clear ammoniacal solution turning to a rose-red precipitate after adding DMG reagent. Label: Ni2+ + 2 DMG → Ni(DMG)2 (rose-red). Show a dropper adding DMG. Clean white lab style. gpt-image-2 2026-05-26T17:05:53.230Z Fe³⁺ + SCN⁻: blood-red complex in solution (intense color even at low concentration). gpt-image-2 2026-05-26T17:05:53.626Z Two side-by-side test tubes: left pale yellow Fe3+ solution, right deep blood-red after adding KSCN. Label the complex qualitatively as [Fe(SCN)]2+ (aq). Neutral vector style, white background. Prussian blue: Fe³⁺ + ferrocyanide gives deep blue precipitate (a classical hallmark). 2026-05-26T17:05:54.428Z gpt-image-2 Test tube forming a deep Prussian blue precipitate after adding K4[Fe(CN)6] to an Fe3+ solution. Include a small inset lattice icon to hint at the coordination solid. Vector schematic. High-yield confirmatory reactions (Fe²⁺/Fe³⁺/Ni²⁺) What to remember Ni²⁺ + dimethylglyoxime (DMG) in ammoniacal solution → rose-red Ni(DMG)2 (insoluble). Fe³⁺ + thiocyanate (SCN−) → blood-red complex (often written as [Fe(SCN)]2+ in dilute solution). Fe³⁺ + potassium ferrocyanide (K4[Fe(CN)6]) → Prussian blue (ferric ferrocyanide). Fe²⁺ + potassium ferricyanide (K3[Fe(CN)6]) → Turnbull blue (ferrous ferricyanide). Avoiding pitfalls: pH control and interferences Not true. Many sulfides are not black: CdS and As2S3 are yellow, Sb2S3 is orange, ZnS is white, MnS is buff. All sulfides are black, so any colored sulfide must be an impurity. K and Na flame tests look similar; you can always guess by eye without any filter. Sodium’s yellow is so strong it hides potassium’s lilac. Use cobalt-blue glass to filter out Na’s yellow and reveal K’s violet. A failed precipitation can also mean wrong conditions (e.g., pH not correct) or concentration too low. Recheck conditions and repeat. If the group reagent doesn’t give a precipitate, the group is absent. Group II needs acidic medium; otherwise Group IV sulfides may co-precipitate. Always acidify (dilute HCl) before passing H2S for Group II. Students often skip setting the solution acidic before passing H2S for Group II, so they think Group II is absent. They do. Phosphate, oxalate, tartrate can mask or carry down cations. Destroy organics/oxalate by boiling with concentrated HNO3; remove phosphate by precipitating as MgNH4PO4 (magnesia mixture), then filter before proceeding. Interfering radicals like phosphate or oxalate don’t matter in cation analysis. tip pH discipline: For Group II, keep solution acidic; for Group III, add NH4Cl first, then NH4OH; for Group IV, ensure ammoniacal/basic medium before passing H2S. NEET traps and memory aids Trap alerts ZnO hot–cold: yellow (hot) → white (cold). PbO: yellow (hot) → reddish (cold). Group II vs Group IV sulfides: medium decides. Acidic → Group II only; basic → Group IV also. AgCl dissolves in NH3; PbCl2 dissolves in hot water; Hg2Cl2 blackens with NH3. Borax bead: Mn violet (ox) → colorless (red); Fe yellow-brown (ox) → bottle-green (red); Co blue (both). Ni²⁺–DMG gives rose-red solid; Fe³⁺–SCN− gives blood-red solution; Fe³⁺ with ferrocyanide → Prussian blue; Fe²⁺ with ferricyanide → Turnbull blue. Key terms Identification of ions/compounds based on characteristic reactions (color, precipitate) without measuring amount. Qualitative analysis A reagent used to precipitate a specific set (group) of cations under controlled conditions. Group reagent Systematic separation Stepwise addition of group reagents to separate cations into groups for easier identification. Formation of metal sulfides on passing H2S; controlled by pH (affects [S2−]). Sulfide precipitation Formation of metal hydroxides by OH− (e.g., Group III with NH4Cl/NH4OH). Hydroxide precipitation Carbonate precipitation Formation of metal carbonates (Group V) using (NH4)2CO3 in ammoniacal medium. Characteristic emission colors of metal ions when heated in a flame. Flame test Charcoal cavity test Heating salt with Na2CO3 on charcoal to form oxides; then color tests (e.g., with Co(NO3)2). Cobalt nitrate test After forming the oxide on charcoal, adding Co(NO3)2 and reheating gives diagnostic colored masses for Zn, Al, Mg. Color test for transition metals using a fused borax bead in oxidizing/reducing flames. Borax-bead test An organic reagent that forms a rose-red chelate with Ni²⁺ in ammoniacal solution. Dimethylglyoxime (DMG) Prussian blue Deep blue ferric ferrocyanide formed when Fe³⁺ reacts with K4[Fe(CN)6]. Blue ferrous ferricyanide formed when Fe²⁺ reacts with K3[Fe(CN)6]. Turnbull blue The [Fe(CN)6] 4− complex ion; reagent in Prussian blue test. Ferrocyanide Ferricyanide The [Fe(CN)6] 3− complex ion; reagent in Turnbull blue test. A specific reaction that uniquely verifies the presence of a particular ion. Confirmatory test Memorizing the qualitative analysis scheme for practical-based questions. Cation Analysis Groups Qualitative Analysis Salt Analysis Inorganic Chemistry NEET Practical Group Nobody ( NH 4 + ) Hits ( HCl ) Small ( H 2 S ) Apples ( Al/Fe ) Since ( S 2- ) Candy ( CO 3 2- ) Melts ( Mg 2+ ) to remember the sequence of reagents and cations. REACTION VARIANTS Group Reagent Cations Precipitated Precipitate Color/Form Here are a few precise prompt options tailored for a high-quality, scientifically accurate generation. I have designed these to ensure the AI understands the hierarchical nature of the "Cation Analysis" table used in NEET preparation. Option 1: The Standard Vertical Schematic (Best for direct textbook accuracy) > Prompt: A professional educational vertical flowchart diagram illustrating the "Cation Analysis Scheme" (Qualitative Analysis of Basic Radicals). The chart flows from top to bottom on a pure white background. Style: Clean 2D vector graphics, high contrast black lines, textbook illustration style. Content: Top box labeled "Salt Mixture / Original Solution." The flow branches downwards into Groups I through VI. Each step shows an arrow labeled with the group reagent (e.g., "Dilute HCl," "H₂S + HCl," "NH₄OH + NH₄Cl"). Visuals: Differentiate between "Precipitate" (left side branches) and "Filtrate" (continuing downward arrow). Use distinct color coding for precipitates: White for Group I, Black/Yellow for Group II, Reddish-brown/Green for Group III. Text is crisp, sans-serif, and legible. Option 2: The "Reaction Variant" Focus (Best for showing chemical separation) > Prompt: A scientific vector infographic showing the separation of cations. Composition: Central vertical flow representing the filtrate passing through sequential filtration stages. At each stage, a side branch leads to a test tube icon representing the precipitate. Labels: Detailed chemical formulas clearly visible (Group I: Pb²⁺, Ag⁺; Group II: Cu²⁺, Cd²⁺; Group III: Fe³⁺, Al³⁺; Group IV: Zn²⁺, Ni²⁺; Group V: Ba²⁺, Ca²⁺; Group VI: Mg²⁺). Style: High-contrast technical drawing, flat design, minimal shading. Primary colors used only to highlight the reagents and precipitate colors. White background, ISO standard scientific symbols. Option 3: The Detailed Table Layout (Best for NEET study material) > Prompt: A structured scientific table formatted as a flowchart for "Classification of Cations." Layout: Organized into columns: "Group," "Reagent," and "Cations Precipitated." Style: High-definition vector art, educational textbook aesthetic. Details: Sharp typography. The visual flow connects Group 0 to Group VI logically. Arrows indicate the sequential addition of reagents. The design is clean, symmetrical, and uses a professional blue and black color palette on a white background. No photorealism, strictly schematic. Tips for Best Results: Aspect Ratio: Set your aspect ratio to 2:3 (Vertical) , as flowcharts for this topic are tall. Text Rendering: AI text generation is often gibberish. You may need to specify --no text if you plan to add the labels (Group I, Reagents, etc.) yourself in Photoshop/Canva later, or use a tool with strong OCR capabilities. If you need the AI to try the text, use Option 1 . Group 0: NaOH + Heat Primary cation: NH 4 + No precipitate; NH 3 gas evolved (Pungent odor, turns Nessler's reagent brown) Group I: Dilute HCl Precipitates: Pb 2+ , Ag + , Hg 2 2+ White precipitates: PbCl 2 , AgCl , Hg 2 Cl 2 Group II: H 2 S gas in dilute HCl ( low [S 2- ] ) Precipitates: Pb 2+ , Cu 2+ , Hg 2+ , Bi 3+ , Cd 2+ , As 3+ , Sb 3+ , Sn 2+ Black ( PbS , CuS , HgS , Bi 2 S 3 ); Yellow ( CdS , As 2 S 3 , SnS 2 ); Orange ( Sb 2 S 3 ) Group III: NH 4 OH in the presence of NH 4 Cl Precipitates: Fe 3+ , Al 3+ , Cr 3+ Reddish-Brown ( Fe(OH) 3 ); White gelatinous ( Al(OH) 3 ); Green ( Cr(OH) 3 ) Group IV: H 2 S gas in NH 4 OH ( high [S 2- ] ) Precipitates: Zn 2+ , Mn 2+ , Ni 2+ , Co 2+ White ( ZnS ); Buff/Flesh-colored ( MnS ); Black ( NiS , CoS ) Group V: (NH 4 ) 2 CO 3 in NH 4 Cl and NH 4 OH Precipitates: Ba 2+ , Sr 2+ , Ca 2+ White precipitates: BaCO 3 , SrCO 3 , CaCO 3 Group VI: Na 2 HPO 4 in presence of NH 4 OH Remaining cation: Mg 2+ White crystalline precipitate: Mg(NH 4 )PO 4 CONSTANTS Flame Color Through Blue Glass Metal Ion Salty Na is Gold, K is Lilac-Pink, Ca is Brick, Ba is Apple, and the Crimson twins Li and Sr glow bright. Flame Test Colors Inorganic Chemistry Qualitative Analysis S-Block Elements Flame Photometry Rapid identification of cations based on flame coloration. A scientific illustration or chart displaying flame test colors for different metal ions: Crimson (Lithium), Golden-Yellow (Sodium), Lilac (Potassium), Brick-Red (Calcium), Apple-Green (Barium), and Blue-Green (Copper) with chemical symbols. Na + Golden Yellow Invisible (Absorbed) K + Lilac (Violet) Pink / Crimson Ca 2+ Brick Red Light Green Ba 2+ Apple Green Bluish Green Li + Crimson Red Invisible Sr 2+ Crimson / Blood Red Purple Cu 2+ Greenish Blue Green