Chem 1 Chemistry in Solutions: Chapter 4 Atoms, Molecules, and Ions Solutions: • Homogeneous mixtures of two or more pure substances. • The solvent is present in greatest abundance. • All other substances are solutes. • Water is the most common solvent. If solvent is not specified, presume it is water. Atoms, Molecules, and Ions Solubility • Solids can be soluble is water (like sugar or sodium chloride) and insoluble (like silicon dioxide, sand, and calcium carbonate, chalk). Atoms, Molecules, and Ions Dissociation • When an ionic substance dissolves in water, the solvent interacts with the individual ions from the crystal and solvates them. • This process is called dissociation. • Some molecular compounds may also Atoms, undergo dissociation (ionization) in Molecules, and Ions aqueous solution. Solubility • Liquids can be soluble in water (like ethanol) and insoluble (like gasoline, a mixture of hydrocarbons). Soluble liquids are miscible, and mutually insoluble liquids are immiscible. Atoms, Molecules, and Ions Solubility • Ammonia gas (NH3) and hydrogen chloride gas (HCl) are very well soluble in water, while oxygen and nitrogen gases (O2 and N2) are only poorly soluble. Atoms, Molecules, and Ions Electrolytes An electrolyte is a substance that dissolves in water and dissociates into ions. Its solution conducts electricity. Atoms, Molecules, and Ions Non-Electrolytes A nonelectrolyte does not dissociate into ions. A nonelectrolyte solution does not conduct electricity. . Insoluble chemicals are considered non-electrolytes in Chem 1. Atoms, Molecules, and Ions Strong and Weak Electrolytes A strong electrolyte will completely dissolve in water, dissociating into ions A weak electrolyte will partially dissolve in water, or partially ionize. ~110% ionization. Solution will contain both ions and molecules of the electrolyte. Atoms, Molecules, and Ions Electrolytes and Nonelectrolytes Table 4.3 Soluble ionic compounds are all electrolytes: NaCl(aq) Na+(aq) + Cl-(aq) Atoms, Molecules, and Ions Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes. Example: CH3OH (methanol) Exceptions: acids, NH3 Atoms, Molecules, and Ions Strong and Weak Electrolytes • A weak electrolyte only partially dissociates when dissolved in water. NH3 + H2O NH4+ + OH- ammonia CH3COOH acetic acid CH3COO- + H+ Some equilibrium is established, net concentrations of the reactants and products will not change. Atoms, Molecules, and Ions Strong and Weak Electrolytes • A strong electrolyte dissociates completely when dissolved in water. HCl(aq) H+(aq) + Cl-(aq) NaOH(aq) Na+(aq) + OH-(aq) Atoms, Molecules, and Ions Strong Electrolytes Are… 1) Seven common strong acids Most other acids are weak Atoms, Molecules, and Ions Acids: Arrhenius defined acids as substances that produce H+(aq) when dissolved in water. Lewis defined acids as electron acceptors Strong acids ionize in water completely: HCl(aq) H+(aq) + Cl-(aq) Weak acids ionize only partially: H(C2H3O2)(aq) ⇄ H+(aq) + C2H3O2-(aq) Atoms, Molecules, and Ions Acids There are seven common strong acids: Hydrochloric, HCl(aq) Hydrobromic, HBr(aq) Hydriodic, HI(aq) Nitric (HNO3) Sulfuric, (H2SO4) Chloric (HClO3) Perchloric (HClO4) All other common acids are weak (HF, H2S, HClO, HClO2, H2CO3, H3PO4, all organic acids, etc.) Atoms, Molecules, and Ions Strong Electrolytes Are… 2) Eight strong bases Other metal hydroxides are insoluble weak bases. Ammonia (NH3) is a soluble weak base. Atoms, Molecules, and Ions Bases: Arrhenius defined bases as substances that produce OH−(aq) when dissolved in water. Lewis defined bases as electron donors + NaOH(aq) Na (aq) + OH-(aq) strong base NH3(aq) + H2O(l) ⇄ NH4+(aq) + OH -(aq) weak base Atoms, Molecules, and Ions Strong Bases The 8 strong bases are the soluble ionic compounds with the hydroxide anion, OH− • Alkali metals (Li, Na, K, Rb, Cs): MOH • Heavy alkali earth metals (Ca, Sr, Ba): M(OH)2 Atoms, Molecules, and Ions Weak Bases Common inorganic weak bases include: • Ammonia (NH3): NH3(aq) + H2O(l) ⇄ NH4+(aq) + OH (aq) - • Poorly soluble metal hydroxides: Mg(OH)2(s) ⇄ Mg2+(aq) + 2OH-(aq) Al(OH)3(s) ⇄ Al3+(aq) + 3OH-(aq) magnesium and aluminum hydroxides Atoms, Molecules, and Ions Strong Electrolytes Are… 3) Soluble ionic compounds Atoms, Molecules, and Ions Practice Problem Classify the following soluble compounds as strong electrolytes, weak electrolytes, or non-electrolytes. Write ionization reactions in water (where applicable). 1) HNO3 = 2) KOH = 3) C2H5OH = 4) HCOOH = 5)NH3 = 6) N2 = Atoms, Molecules, and Ions Practice Problem Classify the following soluble compounds as strong electrolytes, weak electrolytes, or non-electrolytes. Write ionization reactions in water (where applicable). 1) 2) 3) 4) HNO3 = strong acid, HNO3(aq) → H+(aq) + NO3-(aq) KOH = strong base, KOH(aq) → K+(aq) + OH-(aq) C2H5OH = molecular compound, non-electrolyte HCOOH = weak acid, HCOOH(aq) ⇄ HCOO-(aq) + H+(aq) 5) NH3 = weak base, NH3(aq) + H 2O(l) ⇄ NH 4+(aq) + OH-(aq) 6) N2 = molecular species, non-electrolyte Atoms, Molecules, and Ions Precipitation Reactions When ions are mixed together and form insoluble compounds (as predicted by the solubility guidelines), a precipitate is formed. Silver chloride (AgCl) is insoluble; mixing of solutions containing Ag+(aq) and Cl-(aq) will result in the precipitation of AgCl(s). Atoms, Molecules, and Ions Exchange (Metathesis) Reactions • Metathesis comes from a Greek word that means “totranspose” AgNO3 (aq) + KCl (aq) Atoms, Molecules, and Ions Exchange (Metathesis) Reactions • Metathesis comes from a Greek word that means “totranspose” • The reactants exchange, or transpose, ions AgNO3 (aq) + KCl (aq) Atoms, Molecules, and Ions Exchange (Metathesis) Reactions • Metathesis comes from a Greek word that means “totranspose” • The reactants exchange, or transpose, ions AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Atoms, Molecules, and Ions Molecular Equation This “molecular” equation lists the reactants and products as full formulas. AgNO3 (aq) + KCl (aq) AgCl (s) +KNO3 (aq) Atoms, Molecules, and Ions Full Ionic Equation • In the ionic equation all strong soluble electrolytes (strong acids, strong bases, and soluble salts) are dissociated into their ions. • This is a more accurate reflection of the species found in the solution. AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) AgCl (s) + K+ (aq) + NO3- (aq) Atoms, Molecules, and Ions Net Ionic Equation • To form the net ionic equation, cross out any species that are present in the same form on the reactant and product side of the equation. Ag+(aq) + NO 3-(aq) + K+(aq) + Cl-(aq) AgCl (s) + K+(aq) + NO3-(aq) Atoms, Molecules, and Ions Net Ionic Equation • To form the net ionic equation, cross out any species that are present in the same form on the reactant and product side of the equation. • The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Ag+(aq) + NO 3-(aq) + K+(aq) + Cl-(aq) AgCl (s) + K+(aq) + NO3-(aq) Ag+(aq) + Cl-(aq) AgCl (s) Atoms, Molecules, and Ions Net Ionic Equation • To form the net ionic equation, cross out any species that are present in the same form on the reactant and product side of the equation. • The only things left in the equation are those things that change (i.e., react) during the course of the reaction. • Those things that didn’t change are called spectator ions. Ag+(aq) + NO -(aq) + K+ 3 (aq) + Cl-(aq) AgCl (s) + K+(aq) + NO3-(aq) Atoms, Molecules, and Ions Precipitation Reactions 1. 2. 3. 4. 5. 6. If two soluble ionic species (two soluble salts) are mixed, there is the possibility a precipitate may form. Predict the formulas of the possible products of the exchange reaction of the two starting species. If both products are soluble, there will be no chemical reaction (NR). Instead, physical mixing of the solutions will occur. If one or both products of the exchange is/are insoluble, there will be a precipitation chemical reaction. To write the full ionic equation, dissociate all strong electrolytes into ions. Leave weak electrolytes, nonelectrolytes, and insoluble compounds in molecular form. To obtain the net ionic equation, cross out spectator ions (which are dissociated on each side of the equation). Check if the coefficients in the net ionic equation Atoms, Molecules, can be simplified. and Ions Practice Problem Predict the products (if any) of the following reactions and write balanced equations in molecular, full ionic, and net ionic form where applicable: 1) NaBr(aq) + Al(NO3)3(aq) 2) CaI2(aq) + AgNO3(aq) Atoms, Molecules, and Ions Practice Problem Predict the products (if any) of the following reactions and write balanced equations in molecular, full ionic, and net ionic form where applicable: 1) NaBr(aq) + Al(NO3)3(aq) NR Exchange rxn results in soluble ionic compound 2) CaI2(aq) + AgNO3(aq) Ca+(aq) + 2I- (aq) + 2Ag+(aq) + NO 3- (aq) NO3- (aq) + Ca+(aq) + 2AgI (s) Ag+(aq) + I-(aq) AgI(s) Atoms, Molecules, and Ions Solubility Rules Atoms, Molecules, and Ions Solubility Rules Atoms, Molecules, and Ions Practice Problem A solution containing 4.73 g of BaCl2 is mixed with a solution containing 5.88 g of MgSO4. a) How many grams of precipitate will form? Name the precipitate. b) Which reagent will be left over and how many grams? A: (a) 6.47 g BaSO4 (Barium sulfate) (b) 2.54 g MgSO4 Atoms, Molecules, and Ions ICE Reaction Tables ▪ Some reactions have stoichiometric coefficients that are all ones (which appears like no coefficients at all): Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s) ▪ Stoichiometric calculations for such a reaction may be simplified by using a so called ICE reaction table. ▪ In such a table, three lines below the reaction equation list moles of chemicals that are Initial, Change, and End amounts. Atoms, Molecules, and Ions ICE Reaction Tables How many moles of products will be obtained from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)? What will be left over and how much? Atoms, Molecules, and Ions ICE Reaction Tables How many moles of products will be obtained from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)? What will be left over and how much? Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s) Atoms, Molecules, and Ions ICE Reaction Tables How many moles of products will be obtained from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)? What will be left over and how much? Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s) 0 0 Ini. 2.55 mol 1.20 mol Atoms, Molecules, and Ions ICE Reaction Tables How many moles of products will be obtained from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)? What will be left over and how much? Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s) Ini. 2.55 mol 1.20 mol 0 0 Ch. -1.20 mol -1.20 mol +1.20 mol +1.20 mol Atoms, Molecules, and Ions ICE Reaction Tables How many moles of products will be obtained from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)? What will be left over and how much? Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s) Ini. 2.55 mol 1.20 mol 0 0 Ch. -1.20 mol -1.20 mol +1.20 mol +1.20 mol End 1.35 mol 0 1.20 mol 1.20 mol Atoms, Molecules, and Ions ICE Reaction Tables How many moles of products will be obtained from 2.55 mol Na2S(aq) and 1.20 mol FeSO4(aq)? What will be left over and how much? Na2S(aq) + FeSO4(aq) → Na2SO4(aq) + FeS(s) Ini. 2.55 mol 1.20 mol 0 0 Ch. -1.20 mol -1.20 mol +1.20 mol +1.20 mol End 1.35 mol 0 1.20 mol 1.20 mol Answer: 1.20 mol Na2SO4 and 1.20 mol FeS will be obtained, and 1.35 mol Na2S will be left over. Atoms, Molecules, and Ions Acids&Bases Arrhenius defined acids as substances that produce H+(aq) when dissolved in water. Arrhenius defined bases as substances that produce OH−(aq) when dissolved in water. Strong acids ionize in water completely: HCl(aq) H+(aq) + Cl-(aq) NaOH(aq) Na+(aq) + OH-(aq) strong base Weak acids ionize only partially: H(C2H3O2)(aq) ⇄ H +(aq) + C 2H 3O 2-(aq) NH3(aq) + H 2O(l) ⇄ NH 4+(aq) + OH-(aq) weak base Atoms, Molecules, and Ions Acid-Base Reactions An acid reacts with a base to form a salt and, usually, water. HCl + NaOH NaCl + H2O Atoms, Molecules, and Ions Acid-Base Reactions An acid reacts with a base to form a salt and, usually, water. HCl + NaOH NaCl + H2O 3H2SO4 + 2Al(OH)3 Al2(SO4)3 + 6H2O Atoms, Molecules, and Ions Acid-Base Reactions An acid reacts with a base to form a salt and, usually, water. HCl + NaOH NaCl + H2O 3H2SO4 + 2Al(OH)3 Al2(SO4)3 + 6H2O CH3COOH + NH3 (NH4)(CH3COO) ammonium acetate and no water Atoms, Molecules, and Ions Acid-Base Reactions An acid reacts with a base to form a salt and, usually, water. HCl + NaOH NaCl + H2O 3H2SO4 + 2Al(OH)3 Al2(SO4)3 + 6H2O CH3COOH + NH3 (NH4)(CH3COO) ammonium acetate and no water Acid-base reactions are also called neutralization reactions because salts are generally neutral. Atoms, Molecules, and Ions Salts Salt is any ionic compound other than metal oxide or hydroxide. (Metal oxides and hydroxides are bases.) Atoms, Molecules, and Ions Salts Salt is any ionic compound other than metal oxide or hydroxide. (Metal oxides and hydroxides are bases.) A salt can be derived from an acid and a base. The base provides the cation of the salt, and the acid provides the anion of the salt. Atoms, Molecules, and Ions Salts Salt is any ionic compound other than metal oxide or hydroxide. (Metal oxides and hydroxides are bases.) A salt can be derived from an acid and a base. The base provides the cation of the salt, and the acid provides the anion of the salt. Examples: NaCl is a salt of NaOH and HCl Atoms, Molecules, and Ions Salts Salt is any ionic compound other than metal oxide or hydroxide. (Metal oxides and hydroxides are bases.) A salt can be derived from an acid and a base. The base provides the cation of the salt, and the acid provides the anion of the salt. Examples: NaCl is a salt of NaOH and HCl Pb(NO3)2 is a salt of Pb(OH)2 and HNO3 Atoms, Molecules, and Ions Salts Salt is any ionic compound other than metal oxide or hydroxide. (Metal oxides and hydroxides are bases.) A salt can be derived from an acid and a base. The base provides the cation of the salt, and the acid provides the anion of the salt. Examples: NaCl is a salt of NaOH and HCl Pb(NO3)2 is a salt of Pb(OH)2 and HNO3 (NH4)3PO4 is a salt of NH3 and H3PO4 Atoms, Molecules, and Ions Strong Acid + Strong Base HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) acid base salt water H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) → Na+(aq) + Cl-(aq) + H2O(l) {Full ionic equation} H+(aq) + OH-(aq) → H2O(l) (This net ionic equation is realized for the reaction of any strong acid with any strong base.) Atoms, Molecules, and Ions Strong Acid + Strong Base HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) acid base salt water H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) → Na+(aq) + Cl-(aq) + H2O(l) {Full ionic equation} H+(aq) + OH-(aq) → H2O(l) (This net ionic equation is realized for the reaction of any strong acid with any strong base.) Atoms, Molecules, and Ions Ionic Equations with Weak Electrolytes When writing ionic equations, we leave weak electrolytes, non-electrolytes, and insoluble compounds in molecular form. 2HNO3(aq) + Mg(OH)2(s) → Mg(NO3)2(aq) + 2H2O(l) Atoms, Molecules, and Ions Strong Acids & Solubility… There are seven common strong acids: Hydrochloric, HCl(aq) Hydrobromic, HBr(aq) Hydriodic, HI(aq) Nitric (HNO3) Sulfuric, (H2SO4) Chloric (HClO3) Perchloric (HClO4) Atoms, Molecules, and Ions Ionic Equations with Weak Electrolytes When writing ionic equations, we leave weak electrolytes, non-electrolytes, and insoluble compounds in molecular form. (In this example we are looking at a weak base) 2HNO3(aq) + Mg(OH)2(s) → Mg(NO3)2(aq) + H2O(l) 2H+(aq) + 2NO3-(aq) + Mg(OH)2(s) → Mg2+(aq) + 2NO3-(aq) + H2O(l) 2H+(aq) + Mg(OH)2(s) → Mg2+(aq) + 2H2O(l) Atoms, Molecules, and Ions insoluble Practice Problem Predict the products of the following reactions and write balanced equations in the molecular, full ionic, and net ionic forms. a) H2S (aq) + NaOH (aq) b) Zn(OH)2(s) + H3PO4(aq) c) NH3(aq) + CH3COOH(aq) Atoms, Molecules, and Ions Practice Problem Predict the products of the following reactions and write balanced equations in the molecular, full ionic, and net ionic forms. a) H2S (aq) + NaOH (aq) Molecular equation: H2S (aq) + NaOH (aq) Na2S(aq) + 2H2O(l) Full ionic equation: H2S (aq) + 2Na+ + 2OH- (aq) 2Na+(aq) + S2-(aq) + 2H2O(l) Net ionic equation: H2S (aq) + 2OH- (aq) S2-(aq) + 2H2O(l) Atoms, Molecules, and Ions Practice Problem Predict the products of the following reactions and write balanced equations in the molecular, full ionic, and net ionic forms. b) Zn(OH)2(s) + H3PO4(aq) Molecular equation: 3Zn(OH)2(s) + 2H3PO4(aq) Zn3(PO4)2(s) + 6H2O(l) There is no ionic equation here, because all reactants and products are either weak electrolytes or insoluble substances. Atoms, Molecules, and Ions Practice Problem Predict the products of the following reactions and write balanced equations in the molecular, full ionic, and net ionic forms. c) NH3(aq) + CH3COOH(aq) Molecular Equation: NH3(aq) + CH3COOH(aq) (NH4)(CH3COO)(aq) Atoms, Molecules, and Ions Strong Acid + Salt of Weak Acid Product is the salt of the strong acid and the weak acid of the salt (The strong acid “forces”the weak acid from its salt). NaF(aq) + HCl(aq) → NaCl(aq) + HF(aq) salt of HF strong acid salt of HCl weak acid Atoms, Molecules, and Ions Strong Acid + Salt of Weak Acid Product is the salt of the strong acid and the weak acid of the salt (The strong acid “forces”the weak acid from its salt). NaF(aq) + HCl(aq) → NaCl(aq) + HF(aq) salt of HF strong acid salt of HCl weak acid Na+(aq)+F-(aq)+ H+(aq)+Cl-(aq) → Na+(aq)+Cl-(aq) + HF (aq) Atoms, Molecules, and Ions Strong Acid + Salt of Weak Acid Product is the salt of the strong acid and the weak acid of the salt (The strong acid “forces”the weak acid from its salt). NaF(aq) + HCl(aq) → NaCl(aq) + HF(aq) salt of HF strong acid salt of HCl weak acid Na+(aq)+F-(aq)+ H+(aq)+Cl-(aq) → Na+(aq)+Cl-(aq) + HF(aq) F-(aq) + H+(aq) → HF(aq) {Net ionic equation} (association of ions to make weak acid) Atoms, Molecules, and Ions Gas-Forming Reactions • Carbonates (salts with CO32-) react with strong acids to form a weak carbonic acid (H2CO3): CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2CO3(aq) Atoms, Molecules, and Ions Gas-Forming Reactions • Carbonates (salts with CO32-) react with strong acids to form the weak carbonic acid (H2CO3): CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2CO3(aq) • Carbonic acid is not only weak, but also unstable: H2CO3(aq) CO2 (g) + H2O (l) Atoms, Molecules, and Ions Gas-Forming Reactions • Carbonates (salts with CO32-) react with strong acids to form the weak carbonic acid (H2CO3): CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2CO3(aq) • Carbonic acid is not only weak, but also unstable: H2CO3(aq) CO2 (g) + H2O (l) • The overall reaction is CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) Atoms, Molecules, and Ions Gas-Forming Reactions • Carbonates (salts with CO32-) react with strong acids to form the weak carbonic acid (H2CO3): CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2CO3(aq) • Carbonic acid is not only weak, but also unstable: H2CO3(aq) CO2 (g) + H2O (l) • The overall reaction is CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) • Sulfites (salts with SO32-) similarly produce SO 2(g) and sulfides (with S2-) produce H2S(g): FeS(s) + 2 HI (aq) FeI2 (aq) + H2S(g) Atoms, Molecules, and Ions Strong Base + Salt of Weak Base Product is the salt of the strong base and the weak base of the salt 2NH4Br + Ca(OH)2 2NH3 salt of NH3 strong base weak base + CaBr2 + 2H2O salt of Ca(OH)2 Atoms, Molecules, and Ions Strong Base + Salt of Weak Base Product is the salt of the strong base and the weak base of the salt 2NH4Br + Ca(OH)2 2NH3 salt of NH3 strong base + weak base CaBr2 + 2H2O salt of Ca(OH)2 MgSO4(aq) + 2KOH(aq) Mg(OH)2(s) + K2SO4(aq) salt of Mg(OH)2 strong base weak base salt of KOH Atoms, Molecules, and Ions Strong Base + Salt of Weak Base Product is the salt of the strong base and the weak base of the salt 2NH4Br + Ca(OH)2 2NH3 salt of NH3 strong base + weak base CaBr2 + 2H2O salt of Ca(OH)2 MgSO4(aq) + 2KOH(aq) Mg(OH)2(s) + K2SO4(aq) salt of Mg(OH)2 strong base weak base salt of KOH The last reaction can also be understood as precipitation: Mg2+(aq) + 2OH–(aq) Mg(OH)2(s) Atoms, Molecules, and Ions Practice Problem Predict the products of the following reactions and write balanced equations in molecular form: a) Li2SO3 (aq) + H2SO4 (aq) • Li2SO3 (aq) + H2SO4 (aq) Li2SO4(aq) + H2SO3(aq) b) NaOH (aq) + Fe(NO3)3 (aq) • NaOH (aq) + Fe(NO3)3 (aq) Fe(OH)3(s) + 3NaNO3(aq) c) Mg(OH)2 (s) + KNO3 (aq) • Mg(OH)2 (s) + KNO3 (aq) NR Atoms, Molecules, and Ions Strong Acids & Solubility… There are seven common strong acids: Hydrochloric, HCl(aq) Hydrobromic, HBr(aq) Hydriodic, HI(aq) Nitric (HNO3) Sulfuric, (H2SO4) Chloric (HClO3) Perchloric (HClO4) Atoms, Molecules, and Ions Polyprotic Acids Many acids contain several acidic hydrogens. Such acids are called polyprotic. Most of them are weak. Polyprotic acids in water dissociate in steps. Step 1: H3PO4 (aq) ⇄ H + (aq) + H2PO4- (aq) Step 2: H2PO4- (aq) ⇄ H + (aq) + HPO42- (aq) Step 3: HPO42- (aq) ⇄ H + (aq) + PO43- (aq) Dissociation of all weak acids in water is incomplete. Atoms, Molecules, and Ions Polyprotic Acids If a strong base is gradually added to a polyprotic acid, the acid is neutralized in steps. Step 1: H3PO4 + KOH KH2PO4 + H2O Step 2: KH2PO4 + KOH K2HPO4 + H2O Step 3: K2HPO4 + KOH K3PO4 + H2O Neutralization reactions are one-sided (complete) unlike the dissociation of weak electrolytes ⇄ The addition of a strong base makes Atoms, Molecules, the neutralization reaction complete. and Ions Nomenclature of Salts of Polyprotic Acids KH2PO4 , K2HPO4 , and K3PO4 are three salts formed form triprotic acid H3PO4 and base KOH. KH2PO4 = potassium dihydrogen phosphate K2HPO4 = potassium hydrogen phosphate K3PO4 = potassium phosphate H2PO4- = dihydrogen phosphate anion HPO42- = hydrogen phosphate anion PO43- = phosphate anion Atoms, Molecules, and Ions Dissociation of Salts of Polyprotic Acids In the salts of polyprotic acids with remaining H, only metal (and NH4 ) dissociate completely in water: + KH2PO4 (aq) K+(aq) + H2PO4- (aq) K2HPO4 (aq) 2K+(aq) + HPO42- (aq) K3PO4 (aq) 3K+(aq) + PO43- (aq) H2PO4- and HPO42- are very weak acids and their own dissociation is negligible Atoms, Molecules, and Ions Sequential Reactions If the product of one reaction is a reactant for another reaction, we refer to the reactions as sequential and theycan be added to give an overall reaction equation. Step 1: H3PO4 + KOH KH2PO4 + H2O Step 2: KH2PO4 + KOH K2HPO4 + H2O Step 3: K2HPO4 + KOH K3PO4 + H2O Overall: H3PO4 + 3KOH K3PO4 + 3H2O Atoms, Molecules, and Ions Stoichiometry in Steps In a stoichiometric problem with sequential reactions, we consider the first step first – we find the limiting and excess reactants for the 1st step, the amounts of products formed, and the amount leftover after the 1st step. Then, if the chemicals needed for the 2nd step are present after the completion of the 1st step, the 2nd step may start, etc. A reaction sequence may stop at any step depending on the initial amounts of reactants. Atoms, Molecules, and Ions Practice Problem i) What salts can be formed from a reaction of H2CO3 and NaOH? ii) Calculate the moles of each salt after the reaction of the following: a) 0.25 mol H2CO3 and 0.25 mol NaOH b) 0.25 mol H2CO3 and 0.34 mol NaOH c) 0.25 mol H2CO3 and 0.60 mol NaOH Atoms, Molecules, and Ions Oxidation-Reduction Reactions • An oxidation occurs when an atom or ion loses electrons: Zn → Zn2+ + 2e- OIL RIG • A reduction occurs when an atom or ion gains electrons: Cu2+ + 2e- → Cu • One cannot occur without the other: Zn + Cu2+ → Cu + Zn2+ Atoms, Molecules, and Ions Redox Reactions Oxidationreduction reactions are referred to as redox reactions. Atoms, Molecules, and Ions Redox Reactions • CuSO4 in solution (blue hue). • Submerge Zn strip. • Zinc metal has less of an affinity for its electrons than metallic copper does. • Zinc slowly etched from surface (in sol’n) and metallic Cu plates Atoms, onto the strip. Molecules, and Ions Oxidation Numbers In order to keep track of what loses electrons and what gains them, we assign oxidation numbers (oxidation states) to elements: Zn + Cu2+ → Cu + Zn2+ Atoms, Molecules, and Ions Assigning Oxidation Numbers 1. Atoms or molecules in elemental form always have an oxidation number of 0. 2. For any monatomic ion, the oxidation number equals the charge of the ion. 3. Non-metals usually have negative oxidation numbers, but can be positive: a) O is usually -2; (exception – peroxides of H, alkali and alkaline earth metals, where O is -1); b) H is +1 when bonded to non-metals and -1 when bonded to metals and metalloids; c) F is always -1; d) Cl, Br, I are usually -1 (exceptions: compounds with F and O, where Cl, Br, I are positive). Atoms, Molecules, and Ions Assigning Oxidation Numbers 4a. The sum of the oxidation numbers in a neutral compound is 0. 4b. The sum of the oxidation numbers in a polyatomic ion is the charge on the ion. 5. Metals always have positive oxidation numbers in compounds: i) +1 for group 1 (Li, Na, K, Rb, Cs) and Ag ii) +2 for group 2 (Be, Mg, Ca, Sr, Ba) and Zn. iii) +3 for groups 3 and 13 (Al, Sc, lanthanides, actinides). iv) Oxidation numbers are variable for transition metals, but not more than the group number and commonly +2 &+3. 6. The first element in a formula is usually electropositive, and the last is electronegative. Exceptions: NH3, organic compounds. Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: Zn H2 NO2 H 2 O2 NH3 CaH2 Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0. H2 NO2 H 2 O2 NH3 CaH2 Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0. H2 1. Atoms or molecules in elemental form always have an oxidation number of 0. NO2 H 2 O2 NH3 CaH2 Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0. H2 1. Atoms or molecules in elemental form always have an oxidation number of 0. NO2 a) O is usually -2; (exception – peroxides of H, alkali and alkaline earth metals, where O is -1) H2O2 NH3 CaH2 Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0. H2 1. Atoms or molecules in elemental form always have an oxidation number of 0. NO2 a) O is usually -2; (exception – peroxides of H, alkali and alkaline earth metals, where O is -1) H2O2 exception – peroxides of H, alkali and alkaline earth metals, where O is -1 NH3 CaH2 Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0. H2 1. Atoms or molecules in elemental form always have an oxidation number of 0. NO2 a) O is usually -2; (exception – peroxides of H, alkali and alkaline earth metals, where O is -1) H2O2 exception – peroxides of H, alkali and alkaline earth metals, where O is -1 NH3 H is +1 when bonded to non-metals CaH2 Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: Zn 1. Atoms or molecules in elemental form always have an oxidation number of 0. H2 1. Atoms or molecules in elemental form always have an oxidation number of 0. NO2 a) O is usually -2; (exception – peroxides of H, alkali and alkaline earth metals, where O is -1) H2O2 exception – peroxides of H, alkali and alkaline earth metals, where O is -1 NH3 H is +1 when bonded to non-metals Atoms, Molecules, a n d Ions CaH2 H is +1 when bonded to non-metals and -1 when bonded to metals and metallo i d s Lecture Problem Determine the oxidation numbers for all elements in the following species: OF2 Cl2O P4O6 Cr2O72Ti2(SO4)3 CH2O Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: OF2 F is always -1 Cl2O P4O6 Cr2O72Ti2(SO4)3 CH2O Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: OF2 F is always -1 Cl2O Cl, Br, I are usually -1 (exceptions: compounds with F and O, where Cl, Br, I are positive) P4O6 Cr2O72Ti2(SO4)3 CH2O Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: OF2 F is always -1 Cl2O Cl, Br, I are usually -1 (exceptions: compounds with F and O, where Cl, Br, I are positive) P4O6 The sum of the oxidation numbers in a neutral compound is 0. Cr2O72Ti2(SO4)3 CH2O Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: OF2 F is always -1 Cl2O Cl, Br, I are usually -1 (exceptions: compounds with F and O, where Cl, Br, I are positive) P4O6 The sum of the oxidation numbers in a neutral compound is 0. Cr2O72- The sum of the oxidation numbers in a polyatomic ion is the charge on the ion. Ti2(SO4)3 CH2O Atoms, Molecules, and Ions Lecture Problem Determine the oxidation numbers for all elements in the following species: OF2 F is always -1 Cl2O Cl, Br, I are usually -1 (exceptions: compounds with F and O, where Cl, Br, I are positive) P4O6 The sum of the oxidation numbers in a neutral compound is 0. Cr2O72- The sum of the oxidation numbers in a polyatomic ion is the charge on the ion. Ti2(SO4)3 CH2O The sum of the oxidation numbers in a polyatomic ion is the charge on the ion. Atoms, Molecules, and Ions Oxidation of Metals Metals can be oxidized by non-metals in combination reactions: 2Ca + O2 → 2CaO 2Ca(s) + O2(g) 2Ca0 + O02 → 2Ca2+O2- 2CaO(s) Atoms, Molecules, and Ions Metals can also be oxidized by the H+ cations from acids: Mg(s) + 2HCl(aq) → MgCl2 (aq) + H2(g) {molecular} Mg(s) + 2H+(aq) + 2Cl-(aq) → Mg2+(aq) + 2Cl-(aq) + H2(g) {full ionic} Mg(s) + 2H+(aq) → Mg2+(aq) + H2(g) {net ionic equation} This is a displacemnet (substitution) reaction: Mg displaces (substitues) H in a compound with Cl as it is oxidized. As a result, magnesium metal chemically dissolves Atoms, in acid. Molecules, and Ions Metals can also be oxidized by aqueous solutions of other salts: Cu(s) + 2AgNO3(aq) → Cu(NO3)2 (aq) + 2Ag(g) {molecular} Cu(s) + 2Ag+(aq) + 2NO3-(aq) → 2Ag(s) + Cu2+(aq) + 2NO3-(aq) {full ionic} Cu(s) + 2Ag+(aq) → 2Ag(s) + Cu2+(aq) {net ionic equation} In this reaction, silver ions oxidize copper metal. Atoms, Molecules, and Ions Activity Series Based on the ease of oxidation, metals and hydrogen are ranked in an activity series. Metals that are easily oxidized are chemically more reactive and found at the top (ACTIVE); less reactive metals are at the bottom. Atoms, Molecules, and Ions Where would Zn and Cu be relative to each other? Atoms, Molecules, and Ions Activity Series • Easily oxidized metals prefer to be cations; less reactive metals prefer to be neutral. • Any metal on the list can be oxidized by the ions of elements below it. Cu2+Zn • Only metals that are above hydrogen in the list will react with H+(aq) and thus chemically dissolve in acid. • Copper, silver, and mercury may be dissolved in HNO3(aq). However this is due to the oxidation number of N in the ion (N is +5). • Platinum and gold may be dissolved in a mixtureAtoomfs, HNO3(aq) + HCl(aq)Molecules, and Ions Practice Problem… • Predict the outcome: a) Al(s) + Pb2+(aq) b) Mn(s) + CH3COOH(aq) c) Hg(l) + H2SO4(aq) Atoms, Molecules, and Ions Lecture Problem 25.00 mL of a solution of oxalic acid (H2C2O4) is titrated with 0.1000 M NaOH(aq) until all acidic hydrogens are neutralized. The solution of acid with some phenolphthalein is colorless; the solution turns pink immediately after the addition of 38.56 mL of the base solution. Calculate the molarity of H2C2O4 in the starting solution assuming that oxalic acid is diprotic. Atoms, Molecules, and Ions Solve it yourself… Problem. A 0.500-g sample of a mixture of NaBr(s) and Na2CO3(s) was dissolved in water. To precipitate all bromide and carbonate ions from this solution, 71.5 mL of 0.100 M AgNO3(aq) were required. Calculate the mass percentage of sodium bromide in the starting solid mixture. A: 50% NaBr Atoms, Molecules, and Ions Atoms, Molecules, and Ions