Interactive Lesson7.3.1 Core
The Solubility Rules
Club Aqueous: Who gets dissolved, and who gets precipitated out?
Imagine Club Aqueous — the most exclusive water club in chemistry. Every ionic compound wants to get in (dissolve). The bouncer uses a strict rulebook: VIPs always enter, most chlorides and sulfates get in, but carbonates and hydroxides are on the banned list — unless they arrive with a VIP!
⭐ THE VIP RULE (Most Important!)
If the compound contains Na⁺, K⁺, or NH₄⁺, it is always soluble — no exceptions. Likewise, ALL nitrates (NO₃⁻) are soluble. These are the VIPs of chemistry.
⭐VIPs (Always Soluble)
✅ Na⁺ salts
✅ K⁺ salts
✅ NH₄⁺ salts
✅ ALL Nitrates (NO₃⁻)
🟢Chlorides
✅ Most Chlorides → SOLUBLE
Exceptions:
❌ AgCl (s)
❌ PbCl₂ (s)
🟢Sulfates
✅ Most Sulfates → SOLUBLE
Exceptions:
❌ BaSO₄ (s)
❌ PbSO₄ (s)
❌ CaSO₄ (slightly s)
🔴Carbonates
❌ INSOLUBLE
Exceptions:
✅ Na₂CO₃ (aq)
✅ K₂CO₃ (aq)
✅ (NH₄)₂CO₃ (aq)
🔴Hydroxides
❌ INSOLUBLE
Exceptions:
✅ NaOH (aq)
✅ KOH (aq)
✅ Ca(OH)₂ (slightly s)
⚠️ EXAMINER TRAPS
- • CaSO₄ is technically "slightly soluble" — most mark schemes accept it as (s)
- • Ca(OH)₂ is "slightly soluble" — write (aq) for dilute limewater
- • Never say "doesn't dissolve" — say "forms a precipitate" or "is insoluble"
- • State symbols are mandatory in equations — missing them loses marks!
🔑 Quick Reference Card
Always Soluble (aq)
• Na⁺, K⁺, NH₄⁺ — all salts
• ALL nitrates NO₃⁻
• Most chlorides
• Most sulfates
• NaOH, KOH, Ca(OH)₂
Usually Insoluble (s)
• AgCl, PbCl₂
• BaSO₄, PbSO₄
• Most carbonates CO₃²⁻
• Most hydroxides OH⁻
• (except VIP companions!)
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