Solubility Rules — Inorganic Chemistry Mnemonic
Target: mnemonic for solubility rules inorganic chemistry
Why is this hard to memorize?
Solubility rules tell you which ionic compounds dissolve in water and which form precipitates. For NEET and JEE, you need these for predicting precipitation reactions, salt analysis, and ionic equilibrium problems. The rules follow a pattern: all nitrates are soluble, all Na/K/NH₄ salts are soluble, most chlorides are soluble (except AgCl, PbCl₂, Hg₂Cl₂), most sulphates are soluble (except BaSO₄, PbSO₄, CaSO₄), most hydroxides are insoluble (except NaOH, KOH, Ba(OH)₂). Learning the exceptions to the "mostly soluble" and "mostly insoluble" rules is the key skill.
Classic mnemonics you should know
"NAK = Always Soluble (Nitrates, Alkali metals, K-ammonium)"
Three categories that are ALWAYS soluble: all Nitrates (NO₃⁻), all Alkali metal (Na⁺, K⁺, Li⁺) salts, and all ammonium (NH₄⁺) salts. If you see any of these, the compound dissolves. Period.
"Chlorides soluble EXCEPT Silver, Lead, Mercury(I) — "SLiM exceptions""
S(Silver=AgCl), L(Lead=PbCl₂), M(Mercury=Hg₂Cl₂). Same logic for sulphates: "BaPS" = BaSO₄, PbSO₄, SrSO₄ are insoluble.
"Carbonates, Phosphates, Sulphides = Insoluble (except NAK)"
CO₃²⁻, PO₄³⁻, S²⁻ salts are generally INSOLUBLE unless paired with Na⁺, K⁺, or NH₄⁺. Same for hydroxides (OH⁻) — insoluble except NaOH, KOH, Ca(OH)₂ sparingly, Ba(OH)₂.
The complete list
- All nitrates (NO₃⁻) are soluble
- All Na⁺/K⁺/NH₄⁺ salts are soluble
- Most Cl⁻ soluble (except AgCl, PbCl₂, Hg₂Cl₂)
- Most SO₄²⁻ soluble (except BaSO₄, PbSO₄, CaSO₄)
- Most OH⁻ insoluble (except NaOH, KOH, Ba(OH)₂)
- Most CO₃²⁻ insoluble (except Na₂CO₃, K₂CO₃)
- Most PO₄³⁻ insoluble (except Na₃PO₄, K₃PO₄)
- Most S²⁻ insoluble (except Na₂S, K₂S)
Frequently asked questions
What is the fastest way to check solubility in an exam?
Step 1: Is the cation Na⁺, K⁺, or NH₄⁺? → SOLUBLE. Step 2: Is the anion NO₃⁻? → SOLUBLE. Step 3: Check specific rules for the anion (Cl⁻, SO₄²⁻ = mostly soluble with exceptions; CO₃²⁻, PO₄³⁻, OH⁻, S²⁻ = mostly insoluble). This 3-step check handles 95% of exam questions.
Why is BaSO₄ insoluble but MgSO₄ is soluble?
Ba²⁺ is much larger than Mg²⁺. In BaSO₄, the lattice energy (energy holding the crystal together) is relatively high compared to the hydration energy (energy released when ions dissolve). For MgSO₄, the small Mg²⁺ has a very high hydration energy that overcomes the lattice energy, making it soluble.
Is PbCl₂ soluble in hot water?
Yes! PbCl₂ is insoluble in cold water but becomes soluble in hot water. This is a classic salt analysis test: dissolve in hot water, filter, and the filtrate gives a white precipitate of PbCl₂ on cooling. NEET has asked this multiple times.
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