9.1 Net Ionic Equations and Qualitative Analysis Learning Goals … … write an ionic and net ionic equation … use qualitative analysis (flame test, solution colour and solubility) to identify ions in a solution

Let’s take a closer look at the reaction between NaCl (aq) + AgNO 3 (aq)  NaNO 3 (aq) + AgCl (s)

A chemical equation written without the spectator ions is called a net ionic equation. A net ionic equation includes only those ions or compounds that undergo chemical change. What actually happened? Cl - (aq) + Ag + (aq)  AgCl (s) The Na + and NO 3 - are still in the solution SPECTATOR IONS

TYPES OF EQUATIONS i.Balanced Chemical equation ii.Ionic equation iii.Net ionic equation Zinc + sodium  chloride phosphate i. ii. iii. Spectator ions: zinc + sodium phosphate chloride ZnCl 2 (aq) + 3Zn +2 (aq) + 6Cl - (aq) 3Zn +2 (aq) + 2PO 4 -3 (aq)  Zn 3 (PO 4 ) 2(s) Na + and Cl Na 3 PO 4(aq)  Zn 3 (PO 4 ) 2 (s) +NaCl (aq) 6Na + (aq) + 6Cl - (aq) + 6Na + (aq) + 2PO 4 -3 (aq)  Zn 3 (PO 4 ) 2(s) +

Now you try one … Lead (II) + sodium  nitrate sulfide i. ii. iii. Spectator ions: Lead (II) + sodium sulfide nitrate Pb(NO 3 ) 2 (aq) + Pb +2 (aq) + 2 NO 3 - (aq) Pb +2 (aq) + S -2 (aq)  PbS (s) Na + and NO 3 - 2Na 2 S (aq)  PbS (s) + NaNO 3(aq) 2Na + (aq) + 2NO 3 - (aq) + 2Na + (aq) + S -2 (aq)  PbS (s) +

Qualitative Analysis Qualitative Analysis identifies a substance in a sample by observation of physical and chemical properties. You can often identify whether a cation ion is in a sample by observing one or more of the following: Flame Test results solution colour precipitates formed with select aqueous solutions. Qualitative analysis can tell you what ions are present in a solution.

IonColour Li + Crimson Red Na + Yellow-orange K+K+ Purple Cs + Blue Ca 2+ Red-orange Sr 2+ Bright red Cu 2+ Bluish-green Pb 2+ Bluish-white Flame Colours of Some Metals 1.Flame Test Uses the colour that a sample produces in a flame to identify the metal ion in the sample

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IonColour Cr 2+ Cu 2+ blue Cr 3+ Cu + Fe 2+ Ni 2+ green Fe 3+ Pale yellow Co 2+ Mn 2+ Pink Pb 2+ Bluish-white 2.Colours of Ions in Solution Uses the colour of a solution to identify the metal ion in the sample

3. Precipitate Formation Uses the solubility properties of ions to identify an unknown ion. We can add a known reactant to a solution and observe whether a precipitate forms. Let’s say we wanted to precipitate Pb 2+ out of a water sample… Let’s look at our Solubility Table …Solubility Table … Lead (II) ions can be precipitated with sulfate ions to yield solid lead (II) sulfate. Pb 2+ + SO 4 2-  PbSO 4 (s) We can filter off the precipitate and separate it out of the solution. SO 4 2- could be obtained from a solution of Na 2 SO 4 (we would need a nonreactive cation)

Ex)An ion in solution forms a yellow precipitate when sodium iodide, NaI (aq), is added to the solution. The precipitate produces a blue-white colour when it is heated in a flame. What metal ion might be present in the solution? According to the Solubility Rules,Solubility Rules iodides are soluble except if it contains Pb 2+, Ag +, and Hg + and Hg So the ion must be one of these four. We can then look to the flame test results to narrow the ion down. flame test Pb 2+ has a blue-white flame so this must be the ion present.

HOMEWORK p410 #5-10 p414 #12-14 CAN I … … write an ionic and net ionic equation … use qualitative analysis (flame test and solubility) to identify ions in a solution

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IonColour Li + Crimson Red Na + Yellow-orange K+K+ Purple Cs + Blue Ca 2+ Red-orange Sr 2+ Bright red Cu 2+ Bluish-green Pb 2+ Bluish-white Flame Colours of Some Metals back