Chapter 7 · Chemical Reactions
7.6Precipitation Reactions
11 min · two checks
Predict
What happens when aqueous AgNO₃ meets aqueous NaCl?
The idea
- Predict whether two solutions produce a precipitate.
- Write the formulas of the possible products by swapping ions.
In a double-replacement precipitation, the cations trade partners. AB + CD → AD + CB, with charges rebuilt properly, not letters swapped blindly. AgNO₃ + NaCl can become AgCl and NaNO₃. Then consult solubility. AgCl is insoluble, NaNO₃ is soluble, so a solid forms. If both possible products are soluble, as in NaCl + KNO₃, there is no reaction of this type; you just have a mixture of ions.
Write the solid with (s) and the remaining soluble salt as (aq), or leave the spectator ions out entirely in the next section. Check that formulas are charge-balanced before you declare a product. Pb(NO₃)₂ with KI gives PbI₂, not PbI, because lead(II) is 2+ and iodide is 1−.
Keep these
- Swap cations, rebuild formulas from charges, then apply solubility.
- One insoluble product means a precipitation reaction.
- Two soluble products means no precipitate.