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Types of Chemical Reactions and Solution Stoichiometry Chapter 4

Water – the common solvent A Bent polar molecule

Hydration –positive and negative ends of water attracted to reciprocal ions -Ionic compounds dissociate when they dissolve.Hydration

Water can also dissolve non-ionic compounds if they are “like”

Solution Concentration Molarity (M) = moles of solute per volume of solution in liters:

Calculate Molarity A solution contains 1.5 moles of NaCl in 500 ml of water. What is the molar concentration of salt in the solution? 1.5 mol NaCl = 3M NaCl 0.5 L

Solution Concentration terms Stock - routinely used solutions prepared in concentrated form. Concentrated - relatively large ratio of solute to solvent. (5.0 M NaCl) Dilute - relatively small ratio of solute to solvent. (0.01 M NaCl)

Calculating Concentrations of Solutions M 1 V 1 = M 2 V 2 Where M  molarity Where V  volume Useful equations for dilutions use given volume to calculate new Molarity Calculate how much volume to dilute a stock solution to get a desired concentration for an experiment. Example: Calculate the final concentration of a solution of NaCl where 25mL of a stock concentration of 5.0M has been diluted into 2.0L. (5.0M) (0.025L) = M 2 (2.0L) M 2 = 0.063M

Aqueous solutions - electrolytes Electrolyte – solution that conducts electricity Strong electrolytes NaCl, HCl, NaOH Weak Electrolyte NH 3, CH 3 COOH Nonelectrolyte C 6 H 12 O 6

Classes of Strong Electrolyes Soluble Ionic Compounds – dissociate in water into anions and cations Strong acids – acids produce H+ ions when dissolved in water (Arrhenius); strong acid – completely ionizes in aqueous solutions Like HCl, HBr, HI, HNO 3, HClO 4, H 2 SO 4 *HCl Strong bases – soluble ionic compound containing hydroxide Like LiOH, NaOH, KOH, Ba(OH) 2, Sr(OH) 2

Strong electrolytes

Weak Electrolytes Weak electrolytes dissociate only to a small extent in aqueous solutions Weak acids (HC 2 H 3 O 2 ) Weak bases ( NH 4 OH ) Dissociation – each ion is surrounded by a shell of water molecules Ionic compounds dissociate while molecular compounds do not dissociate Acids are an exception. Weak acids are molecular compounds that dissociate.

WeakWeak electrolytes

Identifying electrolytes Which of the following are strong electrolytes? NaCl, C 6 H 12 O 6, HCl, HC 2 H 3 O 2, NH 4 OH, KOH, KNO 3

Types of Solution Reactions 4 Precipitation reactions AgNO 3 (aq) + NaCl(aq)  AgCl(s) + NaNO 3 (aq) 4 Acid-base reactions NaOH(aq) + HCl(aq)  NaCl(aq) + H 2 O(l) 4 Oxidation-reduction reactions FeCl 2 (aq) + Mg(s)  Fe(s) + MgCl 2 (aq)

Precipitation Reactions Ba(NO 3 ) 2 (aq) + K 2 CrO 4 (aq)  2 KNO 3 (aq) + BaCrO 4 (s)

Ppt continued

Rules for Solubility RuleApplies to:Exceptions Group I and ammonium compounds are soluble Li +, Na +, K +, NH 4 + - “Rule 1” Acetates and nitrates are soluble C 2 H 3 O 2 -, NO 3 - - Most chlorides, bromides and iodides are soluble Cl -, Br -, I - Ag +, Hg 2 2+, Pb 2+ Most sulfates are solubleSO 4 2- Sr 2+, Ba 2+, Hg 2 2+, Pb 2+ Most carbonates and phosphate are insoluble CO 3 2-, PO 4 3- See Rule 1 Most sulfides and hydroxides are insoluble S 2-, OH - See Rule 1, and Ca 2+, Sr 2+, Ba 2+ Only learn rules in red

Revised Table for Solubility RuleApplies to:Exceptions AcetatesC2H3O2-,C2H3O2-, Most chlorides, bromides and iodides are soluble Cl -, Br -, I - Ag +, Hg 2 2+, Pb 2+ Most sulfates are solubleSO 4 2- Sr 2+, Ba 2+, Hg 2 2+, Pb 2+ Most carbonates and phosphate are insoluble CO 3 2-, PO 4 3- Most sulfides and hydroxides are insoluble S 2-, OH - Ca 2+, Sr 2+, Ba 2+ Missing Red Rules – Available to You Essentially the Rules show Ksp <0.01mol/L

Describing equations 1.Molecular equation (reactants and products as compounds) AgNO 3 (aq) + KCl(aq)  AgCl(s) + KNO 3 (aq) 2.Complete ionic equation (all strong electrolytes shown as ions) Ag + (aq) + NO 3  (aq) + K + (aq) + Cl  (aq)  AgCl(s) + K + (aq) + NO 3  (aq)

Describing Equations continued 3.Net ionic equation (show only components that actually react) Ag + (aq) + Cl  (aq)  AgCl(s) K + and NO 3  are spectator ions – do not react

Net Ionic – simple rules Soluble ionic compounds in solution are written as ions Strong acids and bases are written as ions Weak acids and bases are written in “molecular form” Any solid, liquid or gas is written in “molecular form” Reaction occurs if new compounds form that must be written in molecular form.

Predicting precipitation reactions (a) Write the complete ionic and net ionic chemical equation that forms when solutions of BaCl 2 and K 2 SO 4 are mixed. (b) Write the complete ionic and net ionic chemical equation that forms when solutions of Fe 2 (SO 4 ) 3 and LiOH are mixed? (c) Will a precipitate form when solutions of Ba(NO 3 ) 2 and KOH are mixed? No. both products are soluble. No chemical reaction Ba 2+ + Cl -1 + K + + SO 4 -2  BaSO 4 + 2K + + 2Cl - Fe 2 (SO 4 ) 3 + 6LiOH  2Fe(OH) 3 + 3Li 2 SO 4 2Fe +3 + 3SO 4 -2 + 6Li +1 +6 OH -1  2Fe(OH) 3 + 3Li +1 +3SO 4 -2 2Fe +3 + 6 OH -1  2Fe(OH) 3 (proper net ionic)

Conclusion Water is common solvent that dissolves ionic compounds and polar covalent molecules Strong electrolytes dissociate in aqueous solutions while weak electrolytes do not. There are three types of solution reactions: precipitation, acid-base, and oxidation-reduction Equations can be written in one of three ways – molecular, complete ionic, net ionic

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