Making Chalk

This demo shows how a precipitation reaction works. The precipitate formed is a common ingredient in chalk.
CaCl2 (aq) + Na2CO3 (aq) → NaCl (aq) + CaCO3 (s)

precipitate reactions
double replacement reactions
chemical change

– 1M CaCl2
– 1M Na2CO3
– petri dish
– disposable pipets

1. Add a pipet full of CaCl2 to the petri dish
2. Add a pipet full of Na2CO3  to the petri dish

This demo would work great on a document camera, just put a piece of colored paper under the petri dish to help the students see. Food coloring can also be added to help see. If only a small amount of liquid is used, the reaction can be wiped up with a paper towel. If not it can be poured down the drain.

Safety goggles should always be worn.

“Demo: Precipitation of Chalk.” Educational Web Labs. Accessed 29 Jun 2010.


This problem set practices writing molecular, total ionic, and net ionic equations for a reaction, as well as identifying spectator ions and precipitates. Concentration calculations and using Avogadro’s number are also practiced.

This lesson plan‘s topic is precipitate reactions: writing balanced molecular, total ionic, and net ionic reactions; identifying spectator ions and precipitates, all using solubility rules. Making Chalk is used as the hook in this lesson. The practice problems provide more problems to go with the lesson.

This lesson plan‘s topic is the Evidences of Chemical Reactions. Students learn the various evidences, then they get a change to practice identifying them with a hands on activity. Making Chalk is used in the notes portion of this lesson.