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Unit 3: Chemical Equations and Stoichiometry

Unit 3: Chemical Equations and Stoichiometry. Net Ionic Equations. Net Ionic Equations. For reactions taking place in water many substances dissociate (break apart) into ions Spectator ions: ions that do not actually participate in the reaction

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Unit 3: Chemical Equations and Stoichiometry

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  1. Unit 3: Chemical Equations and Stoichiometry Net Ionic Equations

  2. Net Ionic Equations For reactions taking place in water many substances dissociate (break apart) into ions Spectator ions: ions that do not actually participate in the reaction To write a net ionic equation you must determine what compounds dissociate and which do not

  3. Net Ionic Rules Which molecules dissociate??? • Rule 1 – Solids, liquids, and gases • Do NOT dissociate (break apart) • Rule 2 – Acids: • Strong acids dissociate (break apart): HCl, HBr, HI, H2SO4, HNO3, & HClO4 • Weak acids stay together • Rule 3 – Bases: • Strong bases dissociate (break apart): Group 1 and 2 hydroxides (but NOT beryllium hydroxide): LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 • Weak bases stay together

  4. Net Ionic Rules Which molecules dissociate??? • Rule 4 – Ionic Compounds: • If soluble: dissociate • If insoluble: stay together **Use the table on p. 125 in your textbook or the chart on your periodic table

  5. Net Ionic Practice • Determine whether the following compounds dissociate in water or not: • H2SO4 • FeS • KOH • Ca(NO3)2 • Cu3(PO4)2

  6. Steps to Writing Net Ionic Equations Example: Hydrochloric acid solution and sodium hydroxide solution yield water and dissolved sodium chloride Step 1 – Write and balance the molecular form: HCl (aq) + NaOH (aq) H2O (l) + NaCl (aq) Step 2 – Determine which molecules dissociate and rewrite in ionic form:H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) H2O(l) + Cl-(aq) + Na+(aq) Spectator ions Step 3 – Cancel ions that appear on both sides: H+(aq) + OH-(aq) H2O (l)

  7. Net Ionic Example – WS #1 Sodium metal + water  sodium hydroxide + hydrogen gas

  8. Net Ionic Decision Making Tree

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