The document discusses solubility and writing ionic equations. It defines a soluble substance as one that dissociates into ions in aqueous solution. It provides a 5-step process for writing ionic equations: 1) Write the balanced molecular equation, 2) Add state symbols, 3) Write out aqueous ions, 4) Cancel spectator ions on both sides, 5) Write the net ionic equation with only reactants and products. An example uses this process to derive the net ionic equation for the reaction of lead nitrate and potassium iodide.

1. Ionic Equation Na + Al 3+ S 2– 2Ca 2+ PO 4 3– 3Cl –

2. Recap on Soluble and solubility What is the meaning of the term “Soluble”? NaCl is soluble in water. Solid NaCl dissociates into Na + and Cl - ions in aqueous solution: NaCl (s )  Na + (aq) + Cl - (aq)

3. Insoluble product Pb(NO 3 ) 2 + 2NaI  PbI 2 + 2NaNO 3 (aq) (aq) (s) (aq)

4. 5 Basic steps & 2 rules The 2 rules are: 1) Water soluble substances are in aqueous state 2) Substances in solid, liquid or gaseous state do not form free ions

5. 5 Simple steps 1) Write the balanced chemical reaction between lead nitrate and potassium iodide. Pb(NO 3 ) 2 + 2KI -----> PbI 2 + 2KNO 3 2) Put in the state symbol Pb(NO 3 ) 2 (aq) + 2KI(aq) ------> PbI 2 (s) +2 KNO 3 (aq) 3) Write out the free ions in aqueous solution. Pb 2+ (aq) + 2NO 3 - (aq) + 2K + (aq) + 2I - (aq) ------> PbI 2 (s) + 2K + (aq) + 2NO 3 - *note that the precipitate does not dissociate to its ions.

6. 5 Simple steps (continued) 4) Cancel all the same ions that appears twice on the left and right side of the equation. Pb 2+ (aq) + 2NO 3 - (aq) + 2K + (aq) + 2I - (aq) ------> PbI 2 (s) + 2K + (aq) + 2NO 3 - (aq) *we call these repeated ions as spectator ions 5) Rewrite the uncancelled ions to give an ionic equation Pb 2+ (aq) + 2I - (aq) ------> PbI 2 (s)

7. More Example What is the Net Ionic Equation for the reaction: HCl(aq) + NaOH(aq) ?

8. HCl (aq) + NaOH (aq) H 2 O (l) + NaCl (aq) H + (aq) + OH - (aq) H 2 O (l)