Solubility and Net Ionic Equations

Solubility Is a measurement of how a compound will break apart (dissociate) in a solution. Depends on many factors, compound size, bond length, polarity. Etc. We will use a chart to determine if a compound is soluble in water.

3. Compounds containing Fluoride (F-) Mg+2, Ca+2, Sr+2, Ba+2, Pb+2 SOLUBLE COMPOUNDS EXCEPTIONS 1. Salts of Na+, K+ and NH4+ none 2. Chlorides (Cl-), Bromides (Br-), and Iodides (I-) [so these are Halide Salts] Ag+, Hg2+2, Pb+2 3. Compounds containing Fluoride (F-) Mg+2, Ca+2, Sr+2, Ba+2, Pb+2 4. Nitrates (NO3-), Chlorates (ClO3-), Perchlorates, (ClO4-), Acetates (C2H3O2-) Acetates of Ag+ and Hg2 +2 only moderately soluble 5. Sulfates (SO4-2) Sr+2, Ba+2, Pb+2 (Ca+2 & Ag+1 moderately soluble) INSOLUBLE (OR POORLY SOLUBLE) 6. All carbonates (CO3-2), Phosphates (PO4-3), Chromates (CrO4-2), Oxalates (C2O4-2) Na+, K+, NH4+ 7. All sulfides (S-2) Group 1 and 2 cations and NH4+ 8. All hydroxides (OH-) and oxides (O-2) Group 1 and NH4+; (Ca+2, Sr+2 and Ba+2 are only moderately soluble)

Practice Problems Determine if the following compounds are soluble: Aluminum Sulfide Insoluble Barium Iodide Soluble Ammonium Carbonate Soluble Silver (I) Nitrate Soluble

Net Ionic Equations… Whenever chemicals are combined, they don’t always react together. And even when they do react, not all elements are involved in creating new compounds. Net Ionic Equations help us predict if a reaction will occur, and how we identify what elements are involved in a reaction.

+ Net Ionic Equation Na2CO3 + Ca(NO3)2  ??? Clear Na2CO3 Clear Ca(NO3)2 + Cloudy solution But caused it? We need to determine what made the solution cloudy. We need to look at what the reaction produced: Na2CO3 + Ca(NO3)2  ???

3 Parts of a Net Ionic Equation 1) Molecular Equation Regular Balanced Equation 2) Total ionic equation All Ions are written that can dissociate 3) Net ionic equation Cancel out Spectator Ions: Compounds that do not change

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) Molecular Equation: A balanced chemical equation in which all the reactants and products are given by their chemical formula. For Example: AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) Soluble species are indicated by placing “(aq)” after the formula. Precipitates are indicated by placing “(s)” after the formula. This way of expressing the reaction is used whenever we want to indicate the chemical formula of the reactants and products.

Determining the Molecular Equation Na2CO3 + Ca(NO3)2  NaNO3 + CaCO3 Make sure the Equation is Balanced! Na2CO3 + Ca(NO3)2  2 NaNO3 + CaCO3 Determine which compounds will dissociate Na2CO3 + Ca(NO3)2  2 NaNO3 + CaCO3 (Soluble) (Soluble)  (Soluble) (Insoluble)

Total or Complete Ionic Equation Shows all the soluble ionic species broken up into their respective ions. For Example: Ag+(aq)+ NO3-(aq)+ Na+(aq)+ Cl-(aq) → AgCl(s)+ Na+(aq)+ NO3-(aq) This method is not frequently used because it is cumbersome to write out. It is used to emphasize the situation which exists before and after the reaction. Spectator ions: Ions that remain unchanged during a reaction and do not participate in the reaction. The spectator ions in the above equation are NO3-(aq) and Na+(aq) NEVER write a total ionic equation until you have first written a balanced formula equation. If you proceed directly to a total ionic equation the result may be balanced but still may not represent the actual situation.

Determining the Total Ionic Equation Any compound that is soluble will dissociate into its ions. Write each ion including charges. Pay attention to coefficients and subscripts. Na2CO3(aq)+Ca(NO3)2(aq)  2 NaNO3(aq)+CaCO3(s) R: 2 Na1+ + CO32- + Ca2+ + 2 NO31-  P: 2 Na1+ + 2 NO31- + CaCO3 (insoluble solids can’t dissociate)

Net Ionic Equation: Shows only the reacting species (species which are actively involved in the reaction…the one making the PPT) in the equation. The net ionic equation is formed by omitting the spectator ions from the total ionic equation. For Example: We had: AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) then: Ag+(aq)+ NO3-(aq)+ Na+(aq)+ Cl-(aq) → AgCl(s)+ Na+(aq)+ NO3-(aq) Canceling out spectator ions, we get: Ag+(aq)+ Cl-(aq) → AgCl(s)

Determining the Net Ionic Equation Cancel out any spectator ion. Spectator ions do not change in the course of the reaction. The same in the reactants as the products. R: 2 Na1+ + CO32- + Ca2+ + 2 NO31-  P: 2 Na1+ + 2 NO31- + CaCO3 Whatever is not a spectator ion represents the Net Ionic equation. They indicate what caused the observed change.

Determining the Net Ionic Equation CO32- + Ca2+  CaCO3 The Net Ionic Equation should balance both in number of atoms and in total charge.

Single Replacement Example Chlorine gas is bubbled through a solution of sodium fluoride. Balanced Molecular Formula: F2(g) + 2 NaCl(aq)  Cl2(g) + 2 NaF(aq) Only aqueous compounds are capable of dissociating. Gas, solid, pure liquids will not split apart.

Total Ionic Equation Net Ionic Equation Dissociate everything that can dissociate: R: F2(g) + 2 Na+(aq) + 2 Cl¯(aq)  P: Cl2(g) + 2 Na+(aq) + 2 F¯(aq) Net Ionic Equation Cancel out spectator ions. They must be exact! F2(g) + 2 Cl¯(aq)  Cl2(g) + 2 F¯(aq) The ions are not the same as the elements

Watch for: Occasionally there are no spectator species. Then the total and the net are the same. Occasionally all species in the total ionic equation are spectators! Everything cancels. What does this mean?