Objectives To learn more about some of the results of chemical reactions To learn to predict the solid that forms in a precipitation reaction To learn to write molecular, complete ionic, and net ionic equations

A. Common Results of a Reaction Four common events accompany chemical reactions. These often occur when a reaction happens Formation of a solid Formation of water Formation of a gas Transfer of electrons Can you give examples of each of these?

B. Precipitation Reactions What Happens When an Ionic Compound Dissolves in Water? H2O NaCl (s) NaCl (aq) But what does NaCl (aq) mean? Na+ and Cl- ions in water ? NaCl molecules in water ? Na and Cl atoms in water?

B. Precipitation Reactions What Happens When an Ionic Compound Dissolves in Water? The ions separate and move around independently – a strong electrolyte

B. A Reaction in Which a Solid Forms A reaction in which a solid is formed from a solution is called a precipitation reaction Solid = precipitate = insoluble When positive and negative ions form a precipitate the net charge of the precipitate is zero Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)

Stalactites in Yosemite Ca(HCO3)2(aq) → CaCO3(s) + H2O(l) + CO2(aq)

B. Precipitation Reactions What Happens When Two Ionic Compounds Dissolve in Water? K2CrO4(aq) + Ba(NO3)2(aq)  Products

B. Precipitation Reactions How to Decide What Products Form Determine the possible products from the ions in the reactants. In our example K2CrO4(aq) + Ba(NO3)2(aq)  Products The possible ion combinations are

What are the potential products in the reactions between the following aqueous solutions? – Write balanced equations for each NaOH + CaCl2 CuBr2 + (NH4)2CO3 K2SO4 + Fe(NO3)3

B. Precipitation Reactions How Would We Decide What Product Has Formed? What is most likely to be the yellow solid formed in the following reaction? K2CrO4(aq) + Ba(NO3)2(aq) The possible product combinations are KNO3 and BaCrO4 KNO3 white solid BaCrO4 yellow solid

B. Precipitation Reactions – Solubility Rules

B. Precipitation Reactions Using Solubility Rules Predicting Precipitates Soluble solid Insoluble solid (Slightly soluble solid) Why are some compounds soluble and others not?

Solubility Rules – Are These Compounds Soluble or Insoluble? Barium Nitrate Potassium Carbonate Sodium Sulfate Copper (II) Hydroxide Mercury (I) Chloride Ammonium Phosphate Chromium (III) Sulfide Lead (II) Sulfate

B. Precipitation Reactions Let’s try some predictions: WOC P271 Q10

C. Describing Precipitation Reactions in Aqueous Solutions Three types of equations: Molecular (formula) equation  complete formulas of all reactants and products Complete ionic equation  all strong electrolytes are shown as ions Net ionic equation  only those components of the solution that undergo a change Spectator ion (those that remain unchanged)  not shown in the net ionic equation

C. Describing Precipitation Reactions in Aqueous Solutions Molecular Equation Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq) Complete Ionic Equation Pb2+(aq) + 2NO3-(aq) + 2Na+(aq) + 2I-(aq) PbI2(s) + 2Na+(aq) + 2NO3-(aq)

C. Describing Precipitation Reactions in Aqueous Solutions Net Ionic Equation Pb2+(aq) + 2I-(aq) PbI2(s) What are the spectator ions in this reaction? A solution of sodium chloride in water reacts with aqueous silver nitrate to give a precipitate of silver chloride – write down the three equations that describe this reaction and identify the spectator ions (P272 Q14 – all three equations and identify spectators)