Precipitation Reaction Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Precipitation Reaction.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A type of double displacement reaction in which two aqueous ionic solutions are mixed and the exchange of ions produces at least one insoluble ionic.

Mix two clear solutions and a solid appears 'out of nowhere' — the ions combine to form a compound that won't dissolve.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Use solubility rules to predict which combinations of ions will form an insoluble precipitate.

Common stuck point: The precipitate is the product that is insoluble — use solubility rules to predict it before doing the experiment.

Sense of Study hint: When predicting precipitation reactions, swap the cations and check solubility. First write the formulas of the two reactants and identify their ions. Then swap the cations to form two new potential products. Finally, check solubility rules for each product — if either is insoluble, a precipitate forms and the reaction proceeds.

Worked Examples

Example 1

easy
Define a precipitation reaction. When solutions of \text{AgNO}_3 and \text{NaCl} are mixed, a white solid forms. Identify the precipitate and write the balanced equation.

Solution

  1. 1
    A precipitation reaction occurs when two aqueous solutions are mixed and an insoluble solid (precipitate) forms.
  2. 2
    Exchange the cations: \text{Ag}^+ pairs with \text{Cl}^- to form \text{AgCl}, and \text{Na}^+ pairs with \text{NO}_3^- to form \text{NaNO}_3.
  3. 3
    AgCl is insoluble (per solubility rules) and precipitates out. Balanced equation: \text{AgNO}_3\text{(aq)} + \text{NaCl(aq)} \rightarrow \text{AgCl(s)}\downarrow + \text{NaNO}_3\text{(aq)}.

Answer

\text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl}\downarrow + \text{NaNO}_3
Precipitation reactions are a type of double displacement reaction driven by the formation of an insoluble product. Solubility rules help predict which ionic compounds are insoluble and will precipitate.

Example 2

medium
Predict whether a precipitate forms when solutions of \text{Pb(NO}_3)_2 and \text{KI} are mixed. If so, identify the precipitate and write the balanced equation. Use solubility rules: most iodides are soluble, but \text{PbI}_2 is insoluble.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
Will a precipitate form when \text{Na}_2\text{SO}_4\text{(aq)} is mixed with \text{BaCl}_2\text{(aq)}? Write the equation if a reaction occurs. (Solubility rule: \text{BaSO}_4 is insoluble.)

Example 2

hard
A forensic chemist tests a solution suspected of containing \text{Pb}^{2+} ions by adding \text{Na}_2\text{CrO}_4 solution. A yellow precipitate forms. Write the balanced molecular equation, identify the precipitate, and explain how this confirms the presence of lead ions.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

double displacementsolubility