The Reaction

The reaction you're describing is a precipitation reaction. When aqueous solutions of lead(II) nitrate (Pb(NO₃)₂) and sodium iodide (NaI) are mixed, a bright yellow solid, lead(II) iodide (PbI₂), precipitates out of solution.

The Balanced Equation

```

Pb(NO₃)₂(aq) + 2 NaI(aq) → PbI₂(s) + 2 NaNO₃(aq)

```

Explanation of Balancing

* Lead (Pb): There's one lead atom on each side of the equation.

* Nitrate (NO₃): There are two nitrate ions on the left side and two on the right side.

* Sodium (Na): There are two sodium atoms on each side.

* Iodine (I): There are two iodine atoms on each side.

Key Points

* (aq) indicates that the substance is dissolved in water (aqueous solution).

* (s) indicates that the substance is a solid (precipitate).

* The yellow precipitate formed is lead(II) iodide (PbI₂).

* The reaction is balanced because the number of atoms of each element is the same on both sides of the equation.

Why the Reaction Occurs

Lead(II) iodide (PbI₂) is very insoluble in water. When the solutions are mixed, the lead and iodide ions come together to form a solid that separates from the solution. This is a classic example of a double displacement reaction where the ions switch partners.