The solid that appears
Precipitate: a solid that forms from clear liquids.
Two clear liquids
Sodium sulphate solution is clear. Barium chloride solution is clear too. Both look like plain water. Now we pour them together.
What do you expect to see?
What this lesson covers
The idea
An insoluble substance formed in a reaction is a precipitate, and any reaction that produces a precipitate is a precipitation reaction.
Two clear liquids
Sodium sulphate solution is clear. Barium chloride solution is clear too. Both look like plain water. Now we pour them together.
What do you expect to see?
- A white solid appears, although both liquids were clear
- Nothing, because clear plus clear stays clear
- The liquid boils
Solid out of liquids
Mix the two solutions and tell the two experiments apart.
The white solid is barium sulphate. Its state symbol tells you it is a solid. Complete the equation.
Insoluble means it will not dissolve
An insoluble substance formed in a reaction is a precipitate. Any reaction that produces a precipitate is a precipitation reaction.
Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq) is a precipitation reaction.
- Product | In water | Symbol
- BaSO₄ (barium sulphate) | does not dissolve: precipitate | (s)
- NaCl (sodium chloride) | remains in the solution | (aq)
Notes
An insoluble substance formed in a reaction is a precipitate, and any reaction that produces a precipitate is a precipitation reaction.
Check yourself
In Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl, which product is the precipitate?
Zinc and dilute acid give bubbles of hydrogen. Is that a precipitation reaction?
What does every precipitation reaction produce?
- BaSO₄, the white solid — correct. Yes! It is insoluble in water.
- NaCl. Sodium chloride remains in the solution, dissolved.
- Both products. Only one of them is insoluble. The other stays dissolved.
- Yes, because something new is formed. Every reaction makes something new. A precipitation reaction makes an insoluble solid.
- No, a gas is formed, not an insoluble solid — correct. Yes! A precipitate must be an insoluble solid in the liquid.
- Yes, because the metal is solid. The zinc is a reactant. A precipitate is a product that does not dissolve.
- A gas that bubbles out. That is a different clue (evolution of a gas).
- A flame. Flames are not part of this idea.
- An insoluble substance — correct. Yes! That is what the name means.