Essentials of Chemistry Topic 38-39 PDF

Essentials of Chemistry Topic 38.-39. (Topic List) Emma Lang Fall Semester 2024-2025 Week 10. Hydrolysis of salts Acid-base titration, Indicators Buffers Biologically important buffer systems  Hydroly...

Essentials of Chemistry Topic 38.-39. (Topic List) Emma Lang Fall Semester 2024-2025 Week 10. Hydrolysis of salts Acid-base titration, Indicators Buffers Biologically important buffer systems  Hydrolysis of salts Hydrolysis: any chemical reaction in which one of the reactants is water Salt: an ionic compound composed of cation(s) and anion(s); Types of salts: 1. Salt of a strong acid and a strong base 2. Salt of a strong acid and a weak base 3. Salt of a weak acid and a strong base 4. Salt of a weak acid and a weak base 2  Hydrolysis of salts Aqueos solutions of salts Upon dissolution a salt dissociates into ions and the ions get hydrated Some of the hydrated ions may react with water and as a result If [H3O+] > [OH-] → acidic solution can be formed If [H3O+] < [OH-] → basic solution can be formed A salt hydrolysis reaction is the chemical reaction of a salt with water to produce hydronium ion or hydroxide ion. 3  Hydrolysis of salts 1. Neutral salts: salts of strong acids and strong bases Aqueous solutions of salts of strong acids and strong bases NaCl(aq) pKa(HCl) = -7 4  Hydrolysis of salts 2. Acidic salts: salts of strong acids and weak bases Aqueous solutions of salts of strong acids and weak bases pKa(HNO3) = -1.3 NH4NO3(aq) pKb(NH3) = 4.75 5  Hydrolysis of salts 3. Basic salts: salts of weak acids and strong bases Aqueous solutions of salts of weak acids and strong bases CH3COONa(aq) pKa(CH3COOH) = 4.75 6  Hydrolysis of salts 4. Aqueous solutions of salts of weak acids and weak bases pKb(NH3) = 4.75 0.1 M NH4NO2(aq) pH = 6.3 pKa(HNO2) = 3.30 pKb(NH3) = 4.75 0.1 M CH3COONH4(aq) pH = 7.0 pKa(CH3COOH) = 4.75 pKb(NH3) = 4.75 0.1 M NH4HCO3(aq) pH = 7.8 pKa(H2CO3) = 6.35 7  Formation of complexes FeSO4(aq) Fe2+(aq) + 6 H2O(l) [Fe(H2O)6]2+(aq) Complex ion: a metal ion with Lewis bases attached to it through coordinate covalent bonds. Complex (or coordination) compound: molecule that has one or multiple metal centers (metal atom(s) or metal ion(s), (a Lewis acid)) that is bound to ligands: atoms, ions, or molecules (Lewis bases) that donate electrons to the metal. 8  Formation of complexes [M(H2O)6]n+ ions with M = Sc3+(d0), Cr3+(d3), Co2+(d7), Ni2+(d8), Cu2+(d9), and Zn2+(d10). https://opentextbc.ca/chemistry/chapter/19-2-coordination-chemistry-of-transition-metals/ Coordination number: the total number of bonds the metal atom/ion forms with ligands. Monodental ligand: a ligand that bonds to the the metal atom/ion through one atom of the ligand Polydental ligand: a ligand that bonds through two or more atoms to the metal atom/ion EDTA Chelate: stable complex formed by polydentate ligands 9  Hydrolysis of salts Hydrolysis of salts of transition metals and some p-field metals (Al, Sn, Pb) in aqueous solutions [Fe(H2O)62+](aq) + H2O(l) [Fe(H2O)5OH]+(aq) + H3O+(aq) 2+ + Fe Fe 10  Hydrolysis of salts Hydrolysis of salts of transition metals and some p-field metals (Al, Sn, Pb) in aqueous solutions Al(NO3)3(aq) 11 Predict if the solutions of the following salts are acidic, neutral, or basic! KBr(aq); NaHCO3(aq); CuSO4(aq); LiClO4(aq); NH4F (aq); Na2HPO4(aq); NH4I(aq); CH3COOK(aq); Pb(NO3)2(aq) ; Ca(NO3)2(aq); Na3PO4(aq) pKa(H2CO3) = 6.35 pKa(HCO3-) = 10.3 pH < 7 pH = 7 pH > 7 pKa(HF) = 3.20 pKa(H3PO4) = 2.16 pKa(H2PO4-) = 7.20 pKa(HPO42-) = 12.38 pKb(NH3) = 4.75 12  Acid-base titration Titration is a volumetric analysis used to determine the concentration of an unknown solution Acid-base titration is a procedure for determining the amount of acid (or base) in a solution by measuring the volume of base (or acid) of known concentration that will completely react with it. 25.0 mL ~0.100 M HCl(aq) titrated with 0.100 M NaOH(aq) (analyte) (titrant) 13  Acid-base titration 25.0 mL ~0.100 M HCl(aq) titrated with 0.100 M NaOH(aq) Equivalence point: is the point in a titration when a stoichiometric Titration curve amount of reactant has been added. pH meter 14  Acid-base indicators An acid-base indicator is a substance that displays different colors when in the presence of an acid or a base HIn(aq) H+(aq) + In-(aq) Methyl orange Phenolphthalein Litmus paper 15  Acid-base indicators Universal indicator: a mixture of indicators 16  Acid-base titration 23.9 mL of 0.100 M sodium hydroxide solution was needed to neutralize 25.0 mL of hydrochloric acid solution. What is the molarity of the hydrochloric acid solution? 17  Buffers A buffer is an aqueous solution containing substances that prevent (resist) major changes in solution pH when small amounts of acid or base are added to it. Buffers are used to maintain optimum pH conditions for chemical reactions : a buffer system maintains blood’s pH at a value close to 7.4, an optimum pH for oxygen transport. A buffer system can be made of - a weak acid and the salt of the conjugate base of the weak acid - a weak base and the salt of the conjugate acid of the weak base 18  Buffers Buffers contain two active chemical species: a) an acidic substance to react with and remove added base and b) a basic substance to react with and remove added acid. 1) CH3COOH(aq)/CH3COONa(aq) 2) NH3(aq)/NH4Cl(aq) 19  pH calculation of buffer solutions 0.1 M CH3COOH(aq)/0.1 M CH3COONa(aq) CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq) CH3COO− ex[H3O+]e Ka = [CH3COOH]e CH3COO-(aq) + H2O(l) CH3COOH(aq) + OH-(aq) Common ion effect: the shift in equilibrium position that occurs because of the addition of an ion already involved in the equilibrium reaction. 20  pH calculation of buffer solutions 0.1 M CH3COOH(aq)/0.1 M CH3COONa(aq) [CH3COOH]e ~ 0.1 M [CH3COO-]e ~ 0.1 M CH3COO− x[H3O+] Ka = [CH3COOH] Henderson-Hasselbach equation [H3O+] in the buffer solution: 𝐬𝐚𝐥𝐭 pH = pKa + lg [𝐚𝐜𝐢𝐝] CH3COOH [H3O+] = Ka x [CH3COO−] CH3COOH -lg [H3O+] = -lg(Ka x ) [CH3COO−] 0.1 M pH = pKa + lg = pKa CH3COOH 0.1 M pH = pKa - lg [CH3COO−] Buffers work best within about ± 1 pH point of the pKa of CH3COO− the weak acid or pKb of the weak base of the buffer system. pH = pKa + lg [CH3COOH] 21  Buffer capacity quantifies the resistance of a buffer solution to changes in pH after the addition of acid or base the moles of an acid or base necessary to change the pH of a (1 L) solution by 1 unit 22 Which of the followings are buffer systems? H2SO4/KHSO4 NH3/NH4Cl H2CO3/Na2CO3 NaHCO3/Na2CO3 HCl/NaCl NaH2PO4/Na2HPO4 NH3/NaOH HCN/NaCN Write a net ionic chemical equation for the reaction which describes the neutralization of a) some KOH(aq) by an NH3/(NH4)2SO4 buffer solution b) some HNO3(aq) by an NH3/(NH4)2SO4 buffer solution 23  Biologically important buffer systems H2CO3(aq)/HCO3-(aq) buffer system in blood CO2(g) + H2O(l) H2CO3(aq) H+(aq) + HCO3-(aq) hypoventillation (asthma) hyperventillation (high fever, anxiety) high intensity exercise prolonged vomiting 24  Biologically important buffer systems Intracellular buffer system: H2PO4-(aq)/HPO42-(aq) pKa(H2PO4-) = 7.20 pKa(HPO42-) = 12.38 1. If extra hydroxide ions enter the cellular fluid, they are neutralised by 2. If extra hydrogen ions enter the cellular fluid, then they are neutralised by 25 a) 12.5 mL sodium hydroxide solution was needed to neutralize 15.0 mL of 0.02 M sulfuric acid solution. What is the molarity of the sodium hydroxide solution? 26 b) What is the pH of a solution which is made by mixing 15 mL of 0.010 M nitric acid solution and 15 mL of 0.010 M calcium hydroxide solution? 27