Chemistry 101 Vandan Desai Chapter 5: Reactions Between Ions in Aqueous Solutions (Lecture Outline) --------------------------------------------------------------------------------------------------------------------------I. Special terminology applies to solutions A. Solution homogeneous mixture in which two or more components mix freely B. Solvent component present in the largest amount; medium into which the solutes are mixed or dissolved i. Water is a typical and very common solvent ii. Solvent can be in any physical state solid, liquid, or gas C. Solute any substance dissolved in the solvent; can be solid, liquid, or gas D. Concentration ratio of the amount of solute either to the amount of solvent of to the amount of solution (can be any units but grams is preferred) E. Percentage concentration ratio of grams of solute per 100 g of solution F. Relative amounts of solute and solvent are often given w/o specifying actual quantities i. Dilute solution ratio of solute to solvent is small; relative terms ii. Concentrated solution ratio of solute to solvent is large; relative terms G. Saturated solution at its present temp, solution that cannot dissolve any more solute H. Solubility described by the number of grams of solute that dissolve in 100 g of solvent at a given temperature to make a saturated solution i. Solubility to solute increases as the temperature increases ii. More solute can be dissolved by heating the mixture I. Unsaturated solution solution that contains less solute than required for saturation J. Supersaturated solution solution that contains more solute than required for saturation at a given temperature i. Unstable ii. Can only be prepared if there are no traces of undissolved solute left in contact with the solution iii. If even a tiny crystal of the solute is present or is added, the extra solute crystallizes K. Sometimes when a reaction is carried out in a solution, one of the products that forms has a low solubility in the solvent i. As this substance forms, the solution becomes highly supersaturated and the substance separates from the solution as a solid, which we call a precipitate ii. A reaction that produces a precipitate is called a precipitation reaction II. Ionic compounds conduct electricity when dissolved in water A. Many ionic compounds dissolve in water B. Solutes that produce ions in solution are called electrolytes b/c their solution can conduct electricity C. An ionic compound dissociates as it dissolves in water i. Ions separate from solid and become hydrated or surrounded by H2O molecules ii. Ions move freely and solution is able to conduct electricity D. Ionic compounds that dissolve completely are strong electrolytes E. Most solutions of molecular compounds do not conduct electricity and are called nonelectrolytes i. The molecules of a nonelectrolyte separate but stay intact ii. The solution is nonconducting because no ions are generated F. Some ionic compounds have low solubilities in water but are still strong electrolytes because what does dissolve is 100% dissociated G. The dissociation of ionic compounds may be described with chemical reactions Na 2 SO 4 ( s ) 2 Na + ( aq ) + SO 2- (aq ) 4 P age |1 Chemistry 101 Vandan Desai III. Equations for ionic reactions can be written in different ways A. Ionic compounds often react when their aqueous solutions combine B. When a solution of Pb(NO3)2 is mixed with a solution of KI the yellow precipitate PbI2 rapidly forms C. This rxn may be represented with a molecular, ionic, or net ionic equation: i. Molecular: Pb(NO3 ) 2 (aq) + 2KI(aq) PbI 2 ( s ) + 2KNO3 (aq) ii. Ionic: Pb 2 + (aq) + 2NO-3 (aq ) + 2K + (aq ) + 2I- (aq ) iii. Net Ionic: D. The most compact notion is the net ionic equation which eliminates all the nonreacting spectator ions from the equation E. Criteria for balanced ionic and net ionic equations: i. Material balance same number of each type of atoms on each side of arrow ii. Electrical balance the net electrical charge on the left side of the arrow must = the net electrical charge on the right side of the arrow F. Remember that charge on an ion must be included when it is not in a compound. Adding charges on all the ions on one side of the arrow gives net electrical charge 2+ PbI 2 ( s) + 2K + ( aq ) + 2NO3 (aq ) - Pb ( aq ) + 2I ( aq ) PbI 2 ( s ) IV. Reactions that produce precipitates can be predicted A. In the reaction of Pb(NO3)2 with KI the cations and anions changed partners B. This is an example of a metathesis or double replacement reaction C. Metathesis reactions in which precipitate forms sometimes called precipitation rxns D. Solubility rules allows the prediction of when a precipitation reaction will occur E. For many ionic compounds, the solubility rules correctly predict whether the ionic compound is soluble or insoluble Solubility Rules for Ionic Compounds in Water Soluble Compounds 1. All compounds of the alkali metals (Group IA) are soluble. 2. All salts containing NH4+, NO3-, ClO3-, ClO4-, and C2H3O2- are soluble. 3. All chlorides, bromides, and iodides are soluble except when combined with Ag+, Pb2+, and Hg22+. 4. All sulfates are soluble except those of Pb2+, Ca2+, Sr2+, Hg22+, and Ba2+. Insoluble Compounds 5. All metal hydroxides and all metal oxides are insoluble except those of Group IA and Ca2+, Sr2+, and Ba2+. 6. All salts that contain C2O42-, PO43-, CO32-, and SO32- are insoluble except those of Group IA and NH4+. 7. All salts that contain S2- are insoluble except those of Group IA and NH4+ and Ca2+, Sr2+ and Ba2+. F. A knowledge of these rules will allow you to predict a large number of precipitation reactions P age |2 Chemistry 101 Vandan Desai V. Acids and bases are classes of compounds with special properties A. Acids and bases are another important class of compounds Bases Have a bitter taste Turn litmus paper blue Slippery; Have a soapy &quot;feel&quot; Some are dangerous (Sodium Hydroxide in lye) Others help with indigestion/upset stomach (Milk of Magnesia) Acids Have a tart (sour) taste Turn litmus paper (acid-base indicator) to red Corrode many metals Some are dangerous (Sulfuric Acid in batteries Others are necessary for well-being (Ascorbic Acid found in Vitamin C) B. First comprehensive theory of acids, bases, and electrical conductivity by Arrhenius i. Proposed that ions form directly when salts dissolve in water ii. Theorized that all acids release hydrogen ions (H+) in water and all bases release <a href="/keyword/hydroxide-ion/" >hydroxide ion</a> s (OH-) C. Characteristic reaction between acids and bases is neutralization: i. HCl(aq) + aOH(aq) aCl(aq) + H2O(l) ii. In general, reaction of an acid and a base produces water and a salt iii. Salt any ionic compound that doesn't contain either <a href="/keyword/hydroxide-ion/" >hydroxide ion</a> /oxide ion D. Arrhenius Definition of Acids and Bases i. An acid is a substance that reacts with water to produce hydronium ion (H3O+) ii. A base is a substance that produces <a href="/keyword/hydroxide-ion/" >hydroxide ion</a> (OH-) in water E. Substances that are acids i. Acids are molecular compounds that react with water to produce ions ii. This is called ionization reaction: HCl(g) + H2O H3O+(aq) + Cl-(aq) iii. It is common to encounter the hydrogen ion (H+) instead of the hydronium ion 2O iv. The previous ionization is also written as: HCl( g ) H H + (aq ) + Cl - (aq ) v. Monoprotic acids are capable of furnishing only one hydrogen ion per molecule (Examples: HCl, HNO3, and HC2H3O2) vi. Acid that can furnish more than one hydrogen ion per molecule are called polyprotic acids vii. Some nonmetal oxides react with water to produce acids They are called acidic anhydrides (anhydride means without water) Examples: SO3, CO2, N2O5 viii. General Acid Formula: HA + H2O H3O+ + A F. Substances that are bases i. Ionic compounds that contain OH- or O2ii. Molecular compounds that react with water to give <a href="/keyword/hydroxide-ion/" >hydroxide ion</a> s iii. Soluble metal oxides are basic anhydrides because they react with water to form the <a href="/keyword/hydroxide-ion/" >hydroxide ion</a> as one of the products For example: CaO(s) + H2O Ca(OH)2(aq) iv. Ammonia gas ionizes in water producing <a href="/keyword/hydroxide-ion/" >hydroxide ion</a> s It is an example of a molecular base v. Many molecules that contain nitrogen can act as a base For example: NH3(aq) + H2O NH4+(aq) + OH-(aq) vi. General Base Formula: B + H2O BH+ + OH P a ge |3 Chemistry 101 Vandan Desai VI. aming acids and bases follows a system A. Binary compounds of many nonmetals and hydrogen are acidic B. In water solution these are referred to as binary acids i. They are named by adding the prefix hydro- and the suffix ic to the stem of the nonmetal name, followed by the word acid ii. For example: HCl(aq): hydrochloric acid &amp; H2S(aq): hydrosulfuric acid C. Only the aqueous solutions of binary compounds are named as acids D. Acids that contain hydrogen, oxygen, plus another element are called oxoacids i. They are named according to the number of oxygen atoms in the molecule and do not take the prefix hydroii. When there are two oxoacids, the one with the larger number of oxygens takes the suffix ic and one with the fewer oxygens takes the suffix ous iii. For example: H2SO4 (Sulfuric Acid) &amp; H2SO3 (Sulfurous Acid) HNO3 (Nitric Acid) &amp; HNO2 (Nitrous Acid) iv. The halogens can occur with up to four different oxoacids The oxoacids with the most oxygens has the prefix per The one with the least has the prefix hypov. For example: HClO (Hypochlorous Acid) &amp; HClO2 (Chlorous Acid) HClO3 (Chloric Acid) &amp; HClO4 (Perchloric Acid) vi. Anions are produced when oxoacids are neutralized vii. Simple relationship b/w the name of the polyatomic ion and the parent acid -ic acids give ate ions -ous acids give ite ions viii. Naming polyatomic anions, prefixes per- &amp; hypo- carry over from parent acid E. Polyprotic acids can be neutralized i. An acidic salt contains an anion that is capable of furnishing additional hydrogen ions ii. The number of hydrogens that can still be neutralized is also indicated NaHSO4 = sodium hydrogen sulfate Na2HPO4 = sodium hydrogen phosphate NaH2PO4 = sodium dihydrogen phosphate F. Naming bases is much less complicated i. Ionic compounds containing metal ions are named like any other ionic compound ii. Molecular bases are specified by giving the name of the molecule Acids and bases are classified as strong or weak A. Acids and bases can be classified as strong or weak, so as strong or weak electrolytes B. Strong acids are strong electrolytes C. Most common strong acids: i. HClO4(aq) perchloric acid ii. HCl(aq) hydrochloric acid iii. HBr(aq) hydrobromic acid iv. HI(aq) hydroiodic acid nitric acid v. HNO3(aq) vi. H2SO4(aq) sulfuric acid D. Strong bases are the soluble metal hydroxides E. Most common strong bases: hydroxides o Group 1A metals, &amp; Ca, Ba, and Sr F. Weak acids and bases are weak electrolytes b/c &lt; 100% of the molecules ionize P a ge |4 VII. Chemistry 101 Vandan Desai G. Weak acids and bases are in dynamic equilibrium in solution H. Two opposing reactions occur in solution: i. The ionization of the acid, called the forward reaction ii. The recombination of ions into molecules, called the reverse reaction I. Chemical or dynamic equilibrium results when the rate of the forward and reverse reactions are equal J. USE double arrows when describing what happens when weak acids/bases are ionized K. DO OT use double arrows when describing what happens when strong acids/bases are ionized VIII. eutralization occurs when acids and bases react A. Neutralization of a strong acid with strong base gives a salt and water: i. Molecular: HCl(aq) + KOH(aq) KCl(aq) + H2O ii. Ionic: H+(aq) + Cl-(aq) + K+(aq) + OH-(aq) H2O + K+(aq) + Cl-(aq) iii. et Ionic: H+(aq) + OH-(aq) H2O B. This net ionic equation applies only to strong acids and bases C. Neutralization of a weak acid with a strong base involves a strong and weak electrolyte (For example: neutralization of acetic acid w/ NaOH) i. Molecular: HC2H3O2(aq) + NaOH(aq) NaC2H3O2(aq) + H2O ii. Ionic: HC2H3O2(aq) + Na+(aq) + OH-(aq) Na+(aq) + C2H3O2-(aq) + H2O iii. et Ionic: HC2H3O2(aq) + OH-(aq) C2H3O2-(aq) + H2O D. Note that in ionic equations the formulas of weak electrolytes are written in &quot;molecular&quot; form E. The situation is similar when a strong acid reacts with a weak base F. For ammonia and HCl the net ionic equation is: OR i. NH3(aq) + H+(aq) NH4+(aq) + + ii. NH3(aq) + H3O (aq) NH4 (aq) + H2O G. Note that water only appears as a product if the hydronium ion is used H. Solutions of weak acids and bases becomes strong conductor of electricity i. Molecular: HC2H3O2(aq) + NH3(aq) NH4C2H3O2(aq) ii. Ionic &amp; et Ionic: HC2H3O2(aq) + NH3(aq) NH4+(aq) + C2H3O2-(aq) I. Both strong and weak acids react with insoluble hydroxides and oxides J. The driving force is the formation of water K. Magnesium hydroxide has a low solubility in water, but reacts with strong acid i. et Ionic: Mg(OH) 2 ( s ) + 2 H + (aq ) Mg 2 + (aq ) + 2H 2 O ii. Magnesium hydroxide is written as a solid b/c it is insoluble L. A number of metal oxides also dissolve in acids i. Molecular: Fe 2 O 3 ( s ) + 6HCl(aq ) 2FeCl3 (aq ) + 3H 2 O ii. et Ionic: Fe 2 O 3 ( s ) + 6H + ( aq ) 2Fe 3+ ( aq ) + 3H 2 O P a ge |5 Chemistry 101 Vandan Desai IX. Gases are formed in some metathesis reactions A. Some reactions with acids or bases produce a gas B. The reactions are driven to completion b/c gas escapes and is unavailable for back rxn Gas Compounds Net Ionic Equation H 2 S Sulfides HCN Cyanides CO 2 SO 2 Carbonates Sulfites Hydrogen Sulfites 2H + + S 2- H 2 S H + + CN - HCN 2 2H + + CO 3 - CO 2 + H 2 O Hydrogen Carbonates H + + HCO 3 CO 2 + H 2 O 2 2H + + SO 3 - SO 2 + H 2 O 2 H + + HSO 3 - SO 2 + H 2 O + NH 3 Ammonium Salts NH 4 + OH - NH 3 + H 2 O C. (CO2 and SO2 are produced by the decomposition of H2CO3 and H2SO3, respectfully) X. Predicting metathesis reactions--A summary A. A net ionic equation will exist when: i. A precipitate forms from a solution of soluble reactants If both products are soluble, strong electrolytes no net ionic equation b/c no reaction will occur ii. Water forms in the reaction of an acid and a base Formation of water is a very strong driving force iii. A weak electrolyte forms from a solution of strong electrolytes General driving force for ionic reactions formation of a weak electrolyte from reactants that are strong electrolytes iv. A gas is formed that escapes from the reaction mixture Gas is formed from a reaction and it leaves the solution, which serves as the driving force for the reaction B. To predict whether an ionic reaction will occur between a pair of reactants: i. Begin by writing a molecular equation in the form of a metathesis reaction. Exchanging anions between the two cations ii. Translate the molecular equation into an ionic equation iii. Cancel any spectator ions C. If net ionic equation remains = net reaction does occur D. If no net ionic equation = no net reaction The composition of a solution is described by its concentration A. Solutions are characterizes by their concentration B. The molar concentration or molarity (M) is defined as i. Molarity (M) = moles of solute/liters of solution C. The molarity of a solution gives an equivalence relation between the moles of solute and volume of solution D. Solution of high concentration can be diluted to make solutions of lower concentration E. Conservation of solute mass requires: i. Vdil M dil = Vconcd M concd F. Where dil labels the diluted and concd the concentrated solution XI. P a ge |6 Chemistry 101 Vandan Desai XII. Molarity is used for problems in solution stoichiometry A. Stoichiometry problems often require working with volumes and molarity B. Concentration of a particular ion equals the concentration of the salt multiplied by the number of ions of that kind in one formula unit of salt C. Limiting reagent problems are also common Chemical analysis and titration are applications of solution stoichiometry A. Titration is a technique used to make quantitative measurements of the amounts of solutions B. The end-point is often determined visually C. The long tube is called the buret. The valve at the bottom of the buret is called the stopcock. The titration is complete when the indicator changes color. XIII. D. Paths for working stoichiometry problems may be summarized with a flowchart: P a ge |7