💧 DAT Solubility Rules & Precipitation Reactions: What Dissolves and What Doesn’t

You’ll often face DAT questions asking:

• Whether a precipitate forms

• How to write complete vs. net ionic equations

• Which salts are soluble in water

These are quick-win questions—if you memorize the rules.

📋 Core Solubility Rules to Know

Compound Type	Solubility in Water	Exceptions
Group 1 ions & NH₄⁺	Always soluble	—
NO₃⁻, ClO₄⁻, C₂H₃O₂⁻	Always soluble	Ag⁺, Pb²⁺, Hg₂²⁺
Cl⁻, Br⁻, I⁻	Soluble	Ba²⁺, Pb²⁺, Hg₂²⁺, Ca²⁺
SO₄²⁻	Insoluble	Group 1, NH₄⁺, Ba²⁺, Sr²⁺, Ca²⁺
CO₃²⁻, PO₄³⁻	Insoluble	Group 1, NH₄⁺
OH⁻, S²⁻	Insoluble	Group 1, NH₄⁺, Ba²⁺, Sr²⁺, Ca²⁺

🔎 How to Predict Precipitation on the DAT

Precipitation reactions occur when two soluble salts react to form an insoluble product (the precipitate). Use the solubility rules to identify which product is solid.

Example:

What forms when AgNO₃ is mixed with NaCl?

Answer:

• Ag⁺ + Cl⁻ → AgCl (s) (precipitate)

• Na⁺ + NO₃⁻ → NaNO₃ (aqueous)

⚖️ How to Write Net Ionic Equations

1. Write balanced molecular equation

2. Break apart soluble strong electrolytes

3. Cancel spectator ions

4. Write the net ionic reaction

Example:

Molecular:

AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq)

Net Ionic:

Ag⁺ (aq) + Cl⁻ (aq) → AgCl (s)

🧠 DAT Tips for Solubility & Reactions

• Group 1 and NH₄⁺ = always soluble

• Ag⁺, Pb²⁺, and Hg₂²⁺ = often form precipitates

• Use the (aq) vs (s) labels to determine reaction type

• Watch for double displacement reactions and lab-style setups

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✅ Summary

• Know solubility rules and key exceptions cold

• Use them to quickly identify precipitate products

• Practice net ionic equations regularly

• Visual memory tools make this fast and permanent

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Frequently Asked Questions (FAQs)

• How many hours should I study for the MCAT each day?

  Aim for 4-6 focused hours, ensuring you incorporate breaks to avoid burnout.

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