1. Precipitation
A reaction is which a solid
(precipitate) is formed.
Objective: What you need to know is how to
work out which chemical is the precipitate/the
solid.

2. Question
When sodium carbonate solution is mixed with calcium
chloride solution, a precipitate is formed. What is it?
Calcium chloride

3. Step 1: Write out the word equation
When sodium carbonate solution is mixed with calcium
chloride solution, a precipitate is formed. What is it?
sodium carbonate + calcium chloride  sodium chloride + calcium carbonate
Explanations:
When the solutions are mixed, the ions swap partner (displacement).
AB + CD  AD + BC

4. Step 2: Add state symbols
When sodium carbonate solution is mixed with calcium
chloride solution, a precipitate is formed. What is it?
sodium carbonate + calcium chloride  sodium chloride + calcium carbonate
(aq) (aq) (aq) (s)
Explanations:
Use the solubility data from the table above.
• Sodium carbonate (aqueous) – soluble in water therefore will remain dissolved
• Calcium carbonate (solid) – insoluble in water therefore will be seen as a solid

5. Answer
When sodium carbonate solution is mixed with calcium chloride
solution, a precipitate is formed. What is it?
sodium carbonate + calcium chloride  sodium chloride + calcium carbonate
(aq) (aq) (aq) (s)
The precipitate formed is calcium carbonate (white solid).
Calcium chloride