A double replacement reaction is a type of aqueous reaction where two ionic compounds are dissolved in water allowing the aqueous ions from one compound to react with the aqueous ions from the other compound.
These reactions are beautiful, but they are toxic and silver is expensive. I show these reactions to my intro chemistry class as a demonstration. This minimizes waste, expense, and the handling of these chemicals by my students with limited laboratory experience. I do let my advanced chemistry students do this in a predicting chemical reaction laboratory activity as a review for the AP test. It helps them remember the colors, which they had a hard time doing when I did this same lab early in the year.
In this video Potassium Chromate and Silver Nitrate are mixed, producing red Silver Cromate. In the second reaction Potassium Iodide and Lead (II) Nitrate is mixed, producing a yellow Lead Iodide. To predict these reactions, you have to use your solubility rules. Remember that all Nitrates and alkali metals (such as potassium) are soluble. The nitrate and alkali metals are considered spectator ions in the reaction.
Double replacement reactions:
Reaction 1: Potassium Chromate and Silver Nitrate
K2CrO4(aq) + 2AgNO3(aq) <==> Ag2CrO4(s) + 2KNO3(aq)
Reaction 2: Potassium Iodide and Lead (II) Nitrate
2KI(aq) + Pb(NO3)2(aq) <==> PbI2(s) + 2KNO3(aq)