Salt analysis is a systematic method used to detect the cation and anion present in a given salt using dry and wet tests.

METHODS OF SALT ANALYSIS

1. Dry Tests

• Flame test
• Borax bead test
• Charcoal cavity test
• Cobalt nitrate test
• Heating test

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2. Wet Tests

• Preliminary test (solubility test)
• Anion analysis (acid radical tests)
• Cation analysis (group analysis)
• Confirmatory tests

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3. Special Tests

• Brown ring test
• Lime water test
• Chromyl chloride test
• Lead acetate test
• Nessler’s test

CATION GROUPS (Basic Radicals)

Group I (Dilute HCl group)

• Ag⁺
• Pb²⁺
• Hg₂²⁺

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Group II (H₂S in acidic medium)

Group II A (Copper group)

• Cu²⁺
• Cd²⁺
• Hg²⁺
• Pb²⁺
• Bi³⁺

Group II B (Arsenic group)

• As³⁺ / As⁵⁺
• Sb³⁺ / Sb⁵⁺
• Sn²⁺ / Sn⁴⁺

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Group III (NH₄Cl + NH₄OH group)

• Fe³⁺
• Al³⁺
• Cr³⁺

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Group IV (H₂S in basic medium)

• Zn²⁺
• Mn²⁺
• Ni²⁺
• Co²⁺

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Group V ((NH₄)₂CO₃ group)

• Ba²⁺
• Sr²⁺
• Ca²⁺

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Group VI (No group reagent)

• Mg²⁺
• Na⁺
• K⁺
• NH₄⁺

What is a Group Reagent?

A group reagent is a chemical reagent used in salt analysis to precipitate a specific group of cations together based on their similar properties.

Do anions have groups in salt analysis?

No, anions do not have a fixed “group system” like cations.

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Why not?

• Cations are grouped based on systematic precipitation using group reagents
• Anions do not show such uniform precipitation behavior
• Different anions require different specific tests

In qualitative analysis, dry tests are performed without dissolving the salt in solution. In a flame test, the salt (usually converted to its chloride) is directly heated in a flame, so it falls under dry tests. Flame test is done by heating a salt (on a clean wire loop with HCl) in a non-luminous flame and observing the characteristic color.

COMPLETE FLAME TEST LIST

1. Alkali Metals (Group 1) — Very important

• Li⁺ (Lithium) → Crimson red
• Na⁺ (Sodium) → Intense golden yellow
• K⁺ (Potassium) → Lilac / pale violet (seen through cobalt glass)
• Rb⁺ (Rubidium) → Red-violet
• Cs⁺ (Caesium) → Blue-violet

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2. Alkaline Earth Metals (Group 2)

• Be²⁺ (Beryllium) → No colour
• Mg²⁺ (Magnesium) → No colour
• Ca²⁺ (Calcium) → Brick red (orange-red)
• Sr²⁺ (Strontium) → Crimson red
• Ba²⁺ (Barium) → Apple green

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3. Transition & Post-Transition Metals

• Cu⁺ / Cu²⁺ (Copper) → Bluish green
• Pb²⁺ (Lead) → Bluish white (faint)
• Tl⁺ (Thallium) → Bright green

Most others do NOT give a characteristic flame colour:

• Fe²⁺ / Fe³⁺ → No colour
• Co²⁺ → No colour
• Ni²⁺ → No colour
• Zn²⁺ → No colour
• Mn²⁺ → No colour
• Al³⁺ → No colour

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4. Ions Showing NO Flame Colour (Important for elimination)

• Be²⁺, Mg²⁺, Al³⁺
• Zn²⁺, Fe²⁺/Fe³⁺, Co²⁺, Ni²⁺, Mn²⁺
  Reason: emission not in visible region / weak excitation

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IMPORTANT EXAM FACTS

1. Sodium Interference

• Na⁺ gives very intense yellow
• Masks all other colours

Solution: Use cobalt glass to detect K⁺

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2. Why flame colour appears?

• Due to electronic excitation and emission spectrum

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3. Best observed for:

• Volatile salts (usually chlorides)

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What is a Wet Test?

A wet test is a method in salt analysis where the substance is first dissolved in a solvent (usually water or acid) and then tested using chemical reactions.

COLOURS OF CATION RADICALS

1. Coloured Ions (VERY IMPORTANT)

• Cu²⁺ (Copper) → Blue solution
• Fe²⁺ (Ferrous) → Pale green
• Fe³⁺ (Ferric) → Yellow / brown
• Ni²⁺ (Nickel) → Green
• Co²⁺ (Cobalt) → Pink
• Cr³⁺ (Chromium) → Green / violet
• Mn²⁺ (Manganese) → Very pale pink
• V³⁺ (Vanadium) → Green
• Ti³⁺ (Titanium) → Purple

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2. Colourless Ions (VERY COMMON MCQ)

• Na⁺
• K⁺
• NH₄⁺
• Mg²⁺
• Ca²⁺
• Ba²⁺
• Sr²⁺
• Al³⁺
• Zn²⁺

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3. Characteristic Precipitate Colours (IMPORTANT)

• Ag⁺ → White ppt (AgCl)
• Pb²⁺ → White ppt
• Fe³⁺ → Reddish-brown ppt (Fe(OH)₃)
• Fe²⁺ → Dirty green ppt (Fe(OH)₂)
• Cu²⁺ → Blue ppt (Cu(OH)₂)
• Ni²⁺ → Green ppt
• Co²⁺ → Blue ppt (on heating)
• Zn²⁺ → White ppt (Zn(OH)₂)
• Al³⁺ → White gelatinous ppt

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IMPORTANT EXAM POINTS

• Colour is due to d–d transitions (transition metals)
• d⁰ and d¹⁰ ions → colourless (Zn²⁺, Al³⁺ etc.)
• Cu²⁺ always → blue solution (very important)

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MOST ASKED

• Blue solution → Cu²⁺
• Green solution → Ni²⁺ / Fe²⁺ (trap!)
• Pink → Co²⁺
• Yellow/brown → Fe³⁺

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SPECIAL REAGENTS – DETAILS

1. Nessler’s Reagent

Used for: Detection of NH₄⁺ (ammonium ion)

Composition

• Alkaline solution of K₂HgI₄ (potassium mercuric iodide)

Observation

• Brown colour / brown precipitate → NH₄⁺ present

Reaction idea

• NH₃ (from NH₄⁺) reacts with Nessler’s reagent → coloured complex

One-line (viva)

Nessler’s reagent gives brown colour with ammonium ions.

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2. FeSO₄ (Ferrous sulphate) – Brown Ring Test

Used for: Detection of NO₃⁻ (nitrate ion)

Reagents used

• Fresh FeSO₄ solution
• Concentrated H₂SO₄

Observation

• Brown ring at junction of two layers

Key concept

• Formation of nitrosyl complex

$$[Fe(H_2O)_5NO]^{2+}$$

Important conditions

• FeSO₄ must be fresh
• H₂SO₄ added slowly along test tube wall

One-line (viva)

Brown ring test confirms presence of nitrate ion.

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3. Copper Turnings Test

Used for: Detection of NO₃⁻ (nitrate ion)

Reagents used

• Copper metal + conc. H₂SO₄

Observation

• Brown fumes of NO₂ gas

Reaction idea

• Nitrate gets reduced → NO₂ gas evolves

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TEST FOR NICKEL (Ni²⁺) – KEY FACTS

1. Group Information

• Group IV cation
• Precipitated as NiS (black ppt) in basic medium (H₂S + NH₄OH)

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2. Most Important Confirmatory Test

Dimethylglyoxime (DMG) Test

• Reagent: Dimethylglyoxime (DMG) + NH₄OH
• Observation: Bright red / rose-red precipitate
• Compound formed: Nickel dimethylglyoxime complex

Very specific test for Ni²⁺

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3. Reaction Idea

• Ni²⁺ + DMG → Red complex (insoluble)

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4. Other Supporting Facts

• Ni²⁺ solution → Green colour
• With NaOH → Green ppt (Ni(OH)₂)
• With NH₄OH → forms complex (no ppt in excess)

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What is Lake Test?

Lake test is used to detect Al³⁺ (aluminium ion) in salt analysis.

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Principle

• A lake is a coloured complex (dye + metal hydroxide) formed when a dye gets adsorbed on a gelatinous precipitate.

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Procedure (short)

• Add NH₄OH → forms Al(OH)₃ (white gelatinous ppt)
• Add a dye (like alizarin / litmus)

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Observation

• Formation of a coloured “lake” (red/blue coloured ppt)

This confirms Al³⁺

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Iodide of Millon’s base is involved in the Nessler’s reagent test.

In the test for NH4+ (ammonium ion), iodide of Millon’s base is involved in the Nessler’s reagent test.

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Nessler’s Reagent (used for $NH_4^+$​ detection):

• It contains alkaline solution of potassium tetraiodomercurate(II)

$$K_2[HgI_4]$$ This is prepared using:

• Mercury salts
• Potassium iodide (KI)
• KOH

During preparation, iodide of Millon’s base type species are formed.

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Reaction with $NH_4^+$​:

When ammonium ion is present:$$NH_4^+ + 2[HgI_4]^{2-} + 4OH^- \rightarrow HgO \cdot Hg(NH_2)I \downarrow + 7I^- + 3H_2O$$

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Observation:

• Brown precipitate forms
  This precipitate is called:

Iodide of Millon’s base$$HgO \cdot Hg(NH_2)I$$

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Charcoal Cavity Test (CCT)

The charcoal cavity test is a dry test in qualitative inorganic analysis used to detect certain metal ions (cations) by heating them in a small cavity made in charcoal.

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Procedure:

• A small cavity (hole) is made in a piece of charcoal
• A pinch of the salt is placed in it
• Heated strongly using a blowpipe flame
• Sometimes mixed with sodium carbonate (Na₂CO₃)

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Principle:

• Charcoal acts as a reducing agent
• On heating, metal compounds are reduced to metal or metal oxide
• Different metals give characteristic residues / coatings

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Observations (Important for exams):

Metal ion	Observation
Zn²⁺	Yellow when hot, white when cold (ZnO coating)
Pb²⁺	Yellow coating (PbO)
Cu²⁺	Red metallic bead (Cu)
Ag⁺	Shiny white metallic bead
Bi³⁺	Yellow coating

Borax Bead Test — Full Concept for JEE / NEET

This is one of the most important dry tests in qualitative analysis to identify transition metal ions.

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What is Borax?

Borax = Sodium tetraborate

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Principle (CORE CONCEPT)

On heating, borax decomposes to form boric anhydride which reacts with metal oxides:

Step 1: Heating borax

$$Na_2B_4O_7 \rightarrow 2NaBO_2 + B_2O_3$$

$B_2O_3$ = boric anhydride (glassy mass)

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Step 2: Reaction with metal oxide

$$B_2O_3 + MO \rightarrow M(BO_2)_2$$

Forms colored metaborate bead

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Why color appears?

• Due to transition metal ions
• Caused by d–d electronic transitions

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Flame Types (VERY IMPORTANT)

Flame type	Nature	Use
Oxidizing flame (O.F.)	Excess oxygen	Metal in higher oxidation state
Reducing flame (R.F.)	Less oxygen	Metal in lower oxidation state

Same metal → different color in OF & RF

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Important Colors (JEE/NEET GOLD)

Metal ion	Oxidizing Flame	Reducing Flame
Cu²⁺	Blue-green	Red (Cu₂O / Cu)
Co²⁺	Deep blue	Deep blue
Cr³⁺	Green	Green
Fe³⁺	Yellow-brown	Bottle green
Mn²⁺	Amethyst (purple)	Colorless
Ni²⁺	Brown	Grey
V	Yellow	Green

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Procedure (Short)

1. Take a platinum wire loop
2. Dip in borax → heat → forms colorless bead
3. Add salt → heat in O.F. & R.F.
4. Observe color

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Key Points (Exam Focus)

• Works mainly for transition metals
• Bead = transparent glassy mass
• Color depends on:
  • Metal ion
  • Oxidation state
  • Flame type
• Cobalt always gives blue → very important MCQ

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Common Mistakes Students Make

• Ignoring reducing flame colors
• Confusing Cu and Cr colors
• Forgetting Mn becomes colorless in R.F.

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Different Zones of Flame (very important for JEE/NEET)

1. Inner Zone (Dark Zone)

• Location: Innermost part near burner
• Color: Dark / almost invisible
• Temperature: Lowest
• Nature: Unburnt gases present (no combustion)

Contains mixture of fuel gas + air
No practical use in tests

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2. Middle Zone (Luminous Zone)

• Color: Yellow / bright
• Temperature: Moderate
• Nature: Reducing zone (incomplete combustion)

Contains glowing carbon particles
Gives sooty flame

Used in:

• Reduction reactions
• Sometimes in charcoal cavity test

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3. Outer Zone (Non-luminous Zone)

• Color: Blue
• Temperature: Highest
• Nature: Oxidizing zone (complete combustion)

Contains excess oxygen
Clean flame (no soot)

Used in:

• Borax bead test (oxidizing flame)
• Flame test
• Most heating purposes

Brown Ring Test — for Nitrate
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Reagents Used:

Fresh **Ferrous sulfate solution

Concentrated Sulfuric acid

Procedure:

Take the salt solution (suspected NO3−NO_3^-NO3−​)

Add freshly prepared FeSO₄ solution

Carefully pour conc. H₂SO₄ along the side of the test tube

Two layers form

Observation:
A brown ring appears at the junction of the two layers
Confirms presence of nitrate ion

⚙️Principle (CORE CONCEPT):
Step 1: Reduction of nitrate
NO3−+3Fe2++4H+→NO+3Fe3++2H2ONO_3^- + 3Fe^{2+} + 4H^+ \rightarrow NO + 3Fe^{3+} + 2H_2ONO3−​+3Fe2++4H+→NO+3Fe3++2H2​O
Nitrate is reduced to nitric oxide (NO)

Step 2: Formation of brown complex
[Fe(H2O)5(NO)]2+[Fe(H_2O)_5(NO)]^{2+}[Fe(H2​O)5​(NO)]2+
is nitrosyl complex gives the brown color

Key Points (Exam Focus):

Test confirms NO₃ ^–​ (not nitrite)

Fresh FeSO₄ is essential

Brown ring forms at junction, not throughout solution

Complex contains NO (nitric oxide) ligand

Common Mistakes:

Shaking the test tube → destroys layers

Using old FeSO₄ → no result

Confusing with nitrite rick:
“Nitrate → NO → Brown complex ring”