Reaction Predictions

Precipitation Reactions

Precipitation Prediction

1) Write the reactants in ionic from o breakdown into ionic form if compounds are solubleo leave as molecules if insoluble

2) Determine the solubility of the products.o Use solubility Rules

Precipitation Predictions (cont.)

3) Check to see if one product is insoluble in water.o Product will fall out of solution, identified as precipitate

4) Write the net ionic equationo Displays which ions are directly involved in the reaction,

produce the precipitateo Ions existing on BOTH sides of the equation are “spectator

ions” (do NOT participate in precipitate formation)o Spectator ions are eliminated

Example 1: • Na2SO4 + MgCl2

• Write the net ionic equation. Will a precipitate form?

Example 2: • MgSO4 + KOH

• Write the net ionic equation. Will a precipitate form?

Example 3: YOU TRY!• KNO3 + MgSO4

• Write the net ionic equation. Will a precipitate form?

What is the purpose of precipitation reactions?

1) Production of a particular chemical compound

2) Sample analysis of a chemical compound o Use actual vs. theoretical yield to determine the % yield of a

producto Determine the amount of precipitate formed in the reactiono If the chemical source of an ion is KNOWN, determine the

quantity of that chemical source present for the reaction

Example 1: A 240 g sample of chicken broth combined with excess AgNO3 (aq) produces 4.302 g AgCl. If all Cl – ions originate from NaCl, how much salt is present in the chicken broth (in grams)?

Example 2: A white precipitate is formed when an unknown white solid is dissolved into a solution and reacted with Ba(NO3)2 . Arthur with the help of Merlin has narrowed the identity of the unknown solid to be 3 possibilities: MgCl2, MgSO4, or Mg(NO3)2 . Identify the unknown.