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Chapter 7. Reactions in Aqueous Solutions. 7.1 Predicting Whether a Reaction Will Occur?. Driving Forces Formation of solid Formation of water Transfer of electrons Formation of a gas. 7.2 Reactions in Which a Solid Forms?. Driving forces Precipitation – formation of solid
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Chapter 7 Reactions in Aqueous Solutions
7.1 Predicting Whether a Reaction Will Occur? • Driving Forces • Formation of solid • Formation of water • Transfer of electrons • Formation of a gas
7.2 Reactions in Which a Solid Forms? • Driving forces • Precipitation – formation of solid E.g Ba(NO3)2(aq) + K2CrO4(aq) yellow solid yellow sol. colorless
What happens When an Ionic Compound Dissolves in Water? • Ba(NO3)2(aq) => barium nitrate (white solid) has been dissolved in water • Containing Ba2+ (aq) and 2 NO3-(aq) ions • Strong electrolytes: A unit of substance that dissolves in water produces separate ions • E.g K2CrO4(aq) contains K+, K+ and CrO42- ions • => strong electrolyte
Strong Electrolytes • Ba(NO3)2(aq) + K2CrO4(aq) yellow solid
Write out all possible formula that can be formed How to Decide What Products Form
Using Solubility Rules • General Rules for Solubility of ionic compounds (salts) in water at 25oC • Most nitrate (NO3-) salts are soluble • Most salts of Na+, K+ and NH4+ are soluble • Most chloride, bromide, iodide (Cl-, Br- and I-) salts are soluble. Notable exceptions are AgCl, PbCl2 and Hg2Cl2. • Most sulfate salts are soluble. Notable exceptions are BaSO4, PbSO4 and CaSO4 • Most hydroxide (-OH) compounds are slightly soluble. The important exception are NaOH and KOH. Ba(OH)2 and Ca(OH)2 are only moderately soluble • Most sulfide (S2-), carbonate (CO32-) and phosphate (PO43-) salts are slightly soluble * The term insoluble and slightly soluble really mean the same thing
Identifying Precipitates in Reactions Where a Solid Forms • Step 1: Write the reactants as they actually exist before any reaction occurs • Step 2: Consider the various solids that could form. • Step 3: use solubility rules to decide whether a solid forms E.g AgNO3(aq) + KCl(aq) white solid
Examples • Using solubility rules to predict the product of Reactions • KNO3(aq) + BaCl2(g) • Na2S(aq) + Cu(NO3)2(aq) • KOH(aq) + Fe(NO3)2(aq)
Describing Reactions in Aqueous Solutions • Molecular equation: shows overall reaction but not necessary the actual forms of the reactants and products in solution • Complete ionic equation: represents all reactants and products that are strong electrolytes as ions. All reactants and products are included. • The net ionic equation includes only those components that undergoes a change. Spectator ions are not included
Examples • For each of the following reactions, write molecular equation, the complete ionic equation and the net ionic equation • Aqueous sodium chloride is added to aqueous silver nitrate to form solid silver chloride plus aqueous sodium nitrate • Aqueous nickel (II) nitrate is added to aqueous potassium carbonate to form solid nickel (II) carbonate and aqueous potassium nitrate
7.4 Reactions That Form Water: Acids and Bases • Arrhenius acids: a substance that produces H+ ions (protons) when it dissolved in water • Strong acids: strong electrolytes • Common strong acids: HCl, HBr, HI, H2SO4, HClO4, HNO3 dissolved in H2O HCl(aq) -------------- H+(aq) + Cl-(aq)
7.4 Reactions That Form Water: Acids and Bases • Arrhenius Bases: substance that produces –OH ion (hydroxide ions) in water • Strong bases: Strong electrolytes • Common strong bases: KOH, LiOH, NaOH, Ba(OH)2 and Sr(OH)2 dissolved in H2O NaOH(aq) ----------------- Na+(aq) + -OH(aq)
Writing Equations for Acid-Base Reactions • Nitric acid is a strong acid. Write the molecular, complete ionic and net ion equations for the reaction of aqueous nitric acid and aqueous potassium hydroxide. • Hydrobromic acid is a strong acid. Write the molecular, complete ionic and net ion equations for the reaction of aqueous hydrobromic acid and aqueous barium hydroxide
7.5 Reactions of Metals with Nonmetals (Oxidation Reduction) • Oxidation – Reduction or Redox reaction: process of transferring electrons from one to the other • Step in determination Redox Reaction • Determine the charges of each atom • Oxidation: loss of electron(s); charge becomes more positive • Reduction: gain of electron(s); charge becomes less positive • E.g 2 Na(s) + Cl2(g) 2 NaCl(s)
Examples • For each of the following reactions, show how electrons are gained and lost • 2 Al(s) + 3 I2(g) 2 AlI3(s) • 2 Cs(s) + F2(g) 2 CsF(s) • 2SO2(g) + O2(g) 2SO3(g)
7.6 Ways to Classify Reactions • Consider the driving forces • Formation of solid • Precipitation reaction • Double replacement • Formation of water • Acid – base reaction • Transfer of electrons • Oxidation – Reduction reaction
7.7 Other Ways to Classify Reactions • Combustion • Organic Compound + O2(g) + heat CO2(g) + H2O(g) • Combination • Element + element compound • Decomposition • Compound element + element
Examples • Classify each of the following reactions in as many ways as possible • 2 K(s) + Cl2(g) 2 KCl(s) • BaCl2 (aq) + Na2SO4(aq) BaSO4 (s) + 2 NaCl(aq) • HNO3(aq) + NaOH(aq) H2O(l) + NaNO3(aq) • 2C2H2 (g) + 5O2 (g) 4 CO2 (g) + 2H2O(l) • PbO2 (s) Pb(s) + O2 (g) • Fe2O3(s) + 2 Al(s) Al2O3(s) + 2 Fe(s)