Forming A Precipitate

Students will combine two clear colorless solutions (baking soda solution and calcium chloride solution) and see the formation of a solid and a gas. Students will analyze the chemical equation for the reaction and see that all atoms in the reactants end up in the products. They will make the connection between the chemical equation and the real substances and see that the solid and gas produced in the actual reaction are also in the products of the equation.

Standards & Objectives

Learning objectives: 

Students will be able to explain that for a chemical reaction to take place, the reactants interact, bonds between certain atoms in the reactants are broken, the atoms rearrange, and new bonds between the atoms are formed to make the products. Students will also be able to explain that this definition applies to the production of a solid called a precipitate.

Essential and guiding questions: 

Would you consider adding a sodium carbonate solution to a magnesium sulfate solution a chemical reaction?  Why or Why not?

How do you know when a precipitate is formed in a chemical reaction?

What did you observe when you mixed the baking soda solution and the calcium chloride solution?

Did you observe a precipitate?

Do you think this was a chemical reaction?  Why?

What products of the reaction do you recognize?

Look at the product side of the chemical equation. What gas is produced in the chemical reaction?

What do you think is the precipitate?

How many of each type of atom is on the reactant side of the equation?

How many of each type of atom is on the product side of the chemical equation?

Is this a balanced chemical equation?  Why?

How do you think we could separate the precipitate from the other products?

Can you separate the calcium carbonate from the rest of the products?

What is the solid white substance on the paper?

Is filtering out the calcium carbonate and allowing the water to evaporate a chemical change or a physical change?  Why?

What evidence was there that a chemical reaction occurred when you combined baking soda solution and calcium chloride solution?

How could we compare the precipitate to the reactants to be sure that the precipitate is actually different from both of them?

Is the solubility of the precipitate different than the solubility of baking soda and calcium chloride?

How should we set up the solubility test?

Should we use the same amount of each substance?

Should we use the same amount of water?




Lesson Variations

Blooms taxonomy level: 
Extension suggestions: 

Do a demonstration to show students another example of a precipitate and a color change.

Helpful Hints

Materials for the Demonstrations:

  • Sodium carbonate
  • Epsom salt (magnesium sulfate)
  • 2 clear plastic cups
  • Test tube
  • Water
  • Copper II sulfate
  • Household ammonia
  • Hydrogen peroxide (3%)
  • Graduated cylinder
  • 2 droppers

Materials for Each Group

  • Baking soda
  • Calcium chloride
  • Water
  • Graduated cylinder
  • Measuring spoon (½ teaspoon) or balance
  • 2 clear plastic cups
  • Masking tape
  • Pen