Aqueous solutions Types of reactions Chapter 4 Aqueous solutions Types of reactions

solution mixture homogeneous heterogeneous solvent Solute(s) two phases oil/water milk one phase Tab water solution solvent Solute(s) more abundant component of mixture water in tab water Less abundant or other component(s) of mixture salts in tab water Water always solvent even in 98% H2SO4

Solute undergoes Dissociation solutes Non-electrolytes Electrolytes Solute undergoes Dissociation Sugar / H2O strong weak complete dissociation partial dissociation NaCl / H2O HCl / H2O HAc / H2O

Hydration of Solid Solute At edges, fewer oppositely charged ions around H2O can come in; Ion-dipole forces; Remove ion New ion at surface Process continues until all ions in solution Hydration of ions Completely surrounded by solvent

Molecular Compounds In Water When molecules dissolve in water Solute particles are surrounded by water Molecules are not dissociated Fig 5.6

Electrical conductivity of electrolyte solutions Weak acids and bases Ex. Acetic acid (HC2H3O2), ammonia (NH3) Ionic compounds Strong acids and bases Ex. NaBr, KNO3, HClO4, HCl, KOH Ex. Sugar, alcohol

Learning Check Write the equations that illustrate the dissociation of the following salts: Na3PO4(aq) → Al2(SO4)3(aq) → CaCl2(aq) → Ca(MnO4)2(aq) → 3 Na+(aq) + PO43(aq) Ca2+(aq) + 2 Cl(aq)

Solubility Maximum amount of a substance that can be dissolved in a given amount of solvent at a given temperature. Usually g/100 mL. Saturated solution: Solution in which no more solute can be dissolved at a given temperature Unsaturated solution: Solution containing less solute than max. amount; Able to dissolve more solute

Solubilities of Some Common Substances Formula Solubility (g/100 g water) Sodium chloride NaCl 35.7 at 0°C 39.1 at 100°C Sodium hydroxide NaOH 42 at 0°C 347 at 100°C Calcium carbonate CaCO3 0.0015 at 25°C

“Like dissolves Like” polar ↔ polar Ethanol (C2H5OH) dissolves in water: polar ↔ polar Glucose (C6H12O6) and sucrose (C12H22O11) dissolve in water: polar ↔ polar Oil doesn’t dissolve in water: nonpolar ↔ polar Oil dissolves in benzene: nonpolar ↔ nonpolar

Water unable to separate Ag+ from Cl- Interaction very strong Salts are polar. soluble insoluble AgCl NaCl Water unable to separate Ag+ from Cl- Interaction very strong

Relative Concentration Solute-to-solvent ratio Dilute solution Small solute to solvent ratio Ex. Eyedrops Concentrated solution Large solute to solvent ratio Ex. Pickle brine Dilute solution contains less solute per unit volume than more concentrated solution Figure 5.2 Eyedrops = Low concentration of NaCl in water Pickle brine = high concentration ofNaCl in water

Molarity quantitatively abbreviated M 1 M = 1 mol solute / 1 liter solution

Preparing Solution of Known Molarity a b c d e Weigh solid and transfer to volumetric flask Add part of the water Dissolve solute completely Add water to reach etched line Stopper flask and invert to mix thoroughly Fig 5.24

Concentration of each type of ions in 0.50 M Co(NO3)2(aq)? 1 mol 1 mol 2 mol In 1.00 L 0.50 mol 0.50 mol 1.00 mol Molarity 0.50 M 0.50 M 1.00 M Concentration of each type of ions in 0.50 M Fe(ClO4)3(aq)? Molarity 0.50 M 0.50 M 1.50 M

Moles of Cl- 1.75 L of 1.0×10-3 M ZnCl2(aq)? 1 2 1.75×10-3 mol ?

Practice How many grams of HCl would be required to make 50.0 mL of a 2.7 M solution? What would the concentration be if you used 27g of CaCl2 to make 500. mL of solution? What is the concentration of each ion? Describe how to make 1.00 L of a 0.200 M K2CrO4 solution. Describe how to make 250. mL of an 2.0 M copper (II) sulfate dihydrate solution. Calculate the concentration of a solution made by dissolving 45.6 g of Fe2(SO4)3 to 475 mL. What is the concentration of each ion?

Describe how to make 1.00 L of a 0.200 M K2CrO4 solution.

No solid K2CrO4 available in the lab . But 2.00 M K2CrO4 solution is available .

Dilution

Prepare 150 mL of 0.100 M H2SO4 from 16.0 M solution. What volume of a 1.7 M solution is needed to make 250 mL of a 0.50 M solution? 18.5 mL of 2.3 M HCl is added to 250 mL of water. What is the concentration of the solution? You have a 4.0 M stock solution. Describe how to make 1.0 L of a 0.75 M solution.

Types of Chemical Reactions Reduction-Oxidation Metathesis Double Replacement Electron transfer AB + CD  AD + CB precipitation reaction Acid-Base Reaction a solid is formed from solution precipitate Formation of a weak electrolyte Formation of a gas

Precipitation reactions

Net ionic equation: describes what really happens. Molecular equation Ionic equation Net ionic equation: describes what really happens. Spectator ions: A reaction takes place if it has a net ionic equation

Solubility Rules All nitrates and acetates are soluble Salts of alkali metals ions and NH4+ ions are soluble. Chlorides, bromides and iodides (salts of Cl-, Br- and I-) are soluble except those of Ag+, Pb2+, and Hg22+. Most sulfates are soluble, except those of Pb2+, Ba2+, Hg2+, and Ca2+. Most hydroxides are slightly soluble (insoluble) except those of alkali metals (Ba(OH)2, Sr(OH)2 and Ca(OH)2 are marginally soluble). Sulfides (S2-), carbonates (CO32-), chromates (CrO42-) and phosphates (PO43-), are insoluble except those of alkali metals and NH4+.

Does the following mixing process involve a chemical reaction?

Precipitation reactions NaOH(aq) + FeCl3(aq) ® ?? NaOH(aq) + FeCl3(aq) ® NaCl + Fe(OH)3 NaOH(aq) + FeCl3(aq) ® NaCl(aq) + Fe(OH)3(s) Na+(aq)+OH-(aq) + Fe3+ (aq) + Cl-(aq) ® Na+ (aq) + Cl- (aq) + Fe(OH)3(s) OH-(aq) + Fe3+ (aq) ® Fe(OH)3(s)

Precipitation reactions BaCl2(aq) + KNO3(aq) ® ?? BaCl2(aq) + KNO3(aq) ® KCl + Ba(NO3)2 BaCl2(aq) + KNO3(aq) ® KCl(aq) + Ba(NO3)2(aq) Ba2+(aq)+2 Cl-(aq) + K+ (aq) + NO3-(aq) ® K+ (aq) + Cl- (aq) + Ba2+(aq)+ 2 NO3-(aq) No net ionic equation No reaction

Practice iron (III) sulfate and potassium sulfide Lead (II) nitrate and sulfuric acid. solutions of NaOH and NiCl2 are mixed.

1 1 0.15 mol ?

1. 25 L of 0. 0500 M Pb(NO3)2 mixed with 2. 0 L of 0. 0250 M Na2SO4 1.25 L of 0.0500 M Pb(NO3)2 mixed with 2.0 L of 0.0250 M Na2SO4. Calculate the mass of precipitate. 1 1 0.0625 mol ? 1 1 0.0500 mol ?

Stoichiometry of Precipitation What mass of solid is formed when 100.00 mL of 0.100 M Barium chloride is mixed with 100.00 mL of 0.100 M sodium hydroxide? What volume of 0.204 M HCl is needed to precipitate the silver from 50.0 ml of 0.0500 M silver nitrate solution ? 25 mL 0.67 M of H2SO4 is added to 35 mL of 0.40 M CaCl2 . What mass CaSO4 Is formed?

HC2H3O2(aq) + H2O  H3O+(aq) + C2H3O2−(aq) Arrhenius Acid Substance that reacts with water to produce the hydronium ion, H3O+ Acid + H2O  Anion + H3O+ HA + H2O  A– + H3O+ HC2H3O2(aq) + H2O  H3O+(aq) + C2H3O2−(aq)  HCl(g) + H2O Cl–(aq) + H3O+(aq) Fig 5.10 Note for organic acids In general, only hydrogen written first in formula transfers to H2O to give H3O+. Bronsted-Lowry Acid: H+ donor

Bronsted Base: H+ acceptor Arrhenius Bases Substance that reacts with water to give OH–. Metal Hydroxides NaOH(s)  Na+(aq) + OH–(aq) Mg(OH)2(s)  Mg2+(aq) + 2OH–(aq) Basic Anhydrides CaO(s) + H2O  Ca(OH)2(aq) Ca(OH)2(aq)  Ca2+(aq) + 2OH–(aq) c. Molecular bases: NH3(aq)+H2O  NH4+(aq)+ OH-(aq) Bronsted Base: H+ acceptor

Acid-Base Reactions Ionic equation Weak electrolyte: H2O + H2O  H3O+(aq)+ OH-(aq) Net ionic equation: Any strong acid + strong base

HAc + H2O  H3O+(aq)+ Ac-(aq) Formation of Weak electrolyte: HAc + H2O  H3O+(aq)+ Ac-(aq) Acid - Base Reactions are often called neutralization reaction Because the acid neutralizes the base.

Volume of 0.100 M HCl needed to neutralize 25.0 mL of 0.350 M NaOH ? 1 1 ? 8.75×10-3

28.0 mL of 0.250 M HNO3 mixed with 53.0 mL of 0.320 M KOH; Amount of water formed Concentrations of H+ and OH- at the end of rct 1 1 7.0 mmol ?  1 1 17.0 mmol ?

HNO3 is Limiting reactant: reacts completely No HNO3 left HNO3 → H+ + NO3- No H+ at the end of reaction How much remains from KOH? KOH → K+ + OH- 10 → 10 mmol

Volumetric analysis: Titration Controlled addition of 1 reactant to another until rxn is complete. Acid-Base Titration: Very common type of titration Ex. Analysis of citric acid in orange juice by neutralization with NaOH

Acid (Base) added equivalent to base (acid) present An indicator is needed: organic substance that changes color according to solution acidity Where the indicator changes color is the endpoint. Endpoint must be very close to the equivalence point. Acid (Base) added equivalent to base (acid) present Phenolphthalein Acidic Basic

Standardization of NaOH solution Know the exact concentration! Its weight is inaccurate . NaOH is hygroscopic and it absorbs CO2. Cannot be used to prepare solutions with exactly known M. Not a primary standard. KHP is a primary standard: high purity, no weighing problems, Potassium hydrogen phthalate: KHC8H4O4. Monoprotic! 41.2 mL of NaOH solution is needed to react exactly with 1.300 g of KHP (M=204.22 g/mol). MNaOH=?

practice 75 mL of 0.25M HCl is mixed with 225 mL of 0.055 M Ba(OH)2 . What is the concentration of the excess H+ or OH- ? A 50.00 mL sample of aqueous Ca(OH)2 requires 34.66 mL of 0.0980 M Nitric acid for neutralization. What is [Ca(OH)2 ]?