Precipitation Reactions and Ionic Equations

Overview

• Focus on precipitation reactions and writing ionic equations.
• Precipitation reactions are double replacement reactions.
• Silver nitrate reacts with calcium chloride.

Determining Products

• Silver (Ag) has a +1 charge; nitrate (NO3) has a -1 charge.
• Chloride (Cl) has a -1 charge, common to halogens (F, Cl, Br, I).
• Use the crisscross method for formula determination:
  • AgCl (silver chloride)
  • Ca(NO3)2 (calcium nitrate)

Balancing the Equation

1. Determine the need for balancing based on ion counts:
   • Two nitrates on the right; put a 2 in front of AgNO3.
   • Two chlorides on the left; put a 2 in front of AgCl.
2. Ensure the equation is balanced.

Phase Determination

• Silver nitrate (AgNO3) is aqueous (NO3 always soluble).
• Calcium chloride (CaCl2) is aqueous.
• Silver chloride (AgCl) is insoluble (exceptions: Ag, Hg, Pb).

Total Ionic Equation

• Separate aqueous substances into ions:
  • AgNO3: Ag⁺ + NO3⁻ (2 of each)
  • CaCl2: Ca²⁺ + 2 Cl⁻
• AgCl stays as it is (solid).
• Ca(NO3)2: Ca²⁺ + 2 NO3⁻

Spectator Ions

• Nitrate (NO3⁻) and Calcium (Ca²⁺) are spectator ions.

Net Ionic Equation

• Ag⁺ + Cl⁻ → AgCl (solid)

Example 2: Lead Nitrate and Sodium Bromide

1. Product Prediction:

   • Pb pairs with Br; Charge on Pb: +2; Br: -1.
   • Use crisscross: PbBr2.
   • Na pairs with NO3; Charges: Na⁺, NO3⁻; NaNO3.

2. Balancing:

   • Two nitrates on the left; put a 2 in front of NaNO3.
   • Two bromines on the right; put a 2 in front of NaBr.

3. Phases:

   • NaNO3: Aqueous (soluble).
   • PbBr2: Solid (insoluble exception with Pb).

4. Ionic Equation:

   • Break down aqueous:
     • Pb(NO3)2: Pb²⁺ + 2 NO3⁻
     • 2 NaBr: 2 Na⁺ + 2 Br⁻
   • PbBr2 solid remains unchanged.

Spectator Ions

• Sodium (Na⁺) and Nitrate (NO3⁻)

Final Net Ionic Equation

• Pb²⁺ + 2 Br⁻ → PbBr2 (solid)

• Importance: Understanding solubility rules and charge balance.
• Application in predicting reactions and writing chemical equations.