Ionic Equilibrium PDF

# Ionic Equilibrium ## Topics: * Electrolyte * Acid-Base Theories * Ionic Product of Water * Degree of Dissociation (α) * Factors affecting α * pH and pH scale * Measurement of pH * WA, WB, SA, SB, Mixture * Hydrolysis of Salts * Buffer Solutions * Solubility and Solubility Product ## Farada...

# Ionic Equilibrium ## Topics: * Electrolyte * Acid-Base Theories * Ionic Product of Water * Degree of Dissociation (α) * Factors affecting α * pH and pH scale * Measurement of pH * WA, WB, SA, SB, Mixture * Hydrolysis of Salts * Buffer Solutions * Solubility and Solubility Product ## Faraday Classification Faraday classified molecules into two categories: * **Electrolyte:** * In presence of solvent, dissociate (H₂O) into ions * Eg: HCl, NaOH, NaI, H₂SO₄ * **Non-Electrolyte:** * Do not give ions in solvent * Eg: Urea (NH₂)₂, Glucose (C₆H₁₂O₆) ## Electrolyte ### Electrolyte types: * **Strong Electrolyte:** * Complete dissociation in solvent. * α = 1 or α = 100% * Non-Eqbm bcoz Irreversible. * Eg: HCl, H₂SO₄, HNO₃, NaOH, NaCl, Ba(OH)₂ * **Weak Electrolyte:** * Do not dissociate completely * α < 1 or α < 100% * Eqbm exists bcoz (< 100%, Reversible) * Eg: HCN, HCOOH, Zn(OH)₂, AgCl, AgBr ## W.E AB(aq) A+(aq) + BCq HCOOH HCOO- + H+ ## SE CD(aq) C+(aq) + D(aq) NaOH (aq) Na+(aq) + OH-(aq) ## Acid- Base Theories ### 1. Arrhenius Theory **(Sour) Acid:** Give H+ in Water **(Bitter) Base:** Give OH- in Water * **Acid:** * H₂O (aq) H+(aq) + Cl- (aq) * H₂O + H₂O H₃O+ + OH- * **Note:** H+ does not exist independently but combines with H₂O to form H₃O+ * **Base:** * BOH(aq) B+(aq) + OH-(aq) * OH- + H₂O H₃O₂- * H+ + H₂O H₃O+ * GF → H₂n+1O_n * H₃O₂^- (H₅O₂+ * H₂O * H₇O₃ * OH- + H₂O H₃O₂- * GF → H₂n-1O_n * H₅O₃ * H₂O * H₇O₄- ### 2. Bronsted- Lowry Theory * **Acid:** Proton Donors (H+) * **Base:** Proton Acceptor * **Proton Acceptor:** * NH₃ + H₂O NH₄+(aq) + OH-(aq) * Base Acid SB * Proton lose (Donor) * **Proton Donor:** * HX + H₂O X- + H₃O+ * Acid Base * Conjugate Base Conjugate Acid ### Forward Reaction: Acid H+ Base H₂O ### Backward Reaction: Acid H₃O+ Base X- ### Applying the theory to examples * NH₂, NH₃, NH₄+ * H₃O+, H₅O₂+, H₂O * H₂SO₄, SO₄^2- * H₂SO₄ H+ + HSO₄^- * H₃SO₄ HSO₄^- * **Note:** In above mentioned, make Acid-C-B, Base-C.A Pairs. * NH₃ NH₂- + H+ A CB * NH₄⁺ NH₃ Base CA * NH₂- + 2H+ NH₃ Base CA * **Note:** Conjugate Acid-Base Pairs only differ by 1 Proton(H+) ### 3. Lewis Acid-Lewis Base * **LA:** Accept lone pair of electrons * **LB:** Lone Pair Donor * **LA:** * **a) Electron deficient:** * eg: H+, Ca²⁺, Mg²⁺, Na+ * **b) Vacant orbital and e deficiency:** * **Eg:** BF₃ ( 6e- in outermost shell) * **Note:** AlCl₃ (Vacant d) * **Note:** PuCl₃ (Vacant d) * **Note:** FeBr₃ (Vacant d) * **LB:** NH₃, (CH₃)₂O, NH₂^-, PH₃, H₂S * **Examples:** * NH₃ + H+ NH₄+(aq) LB LA * NH₃ + BF₃ NH₃.BF₃ LB LA ## Ionic Product of Water * H₂O(l) H+ + OH- * (UE) 10^-7M 10^-7M * K = [H+] [OH-] / [H₂O] * **Note:** [H₂O] is a constant * Kx [H₂O] = [H+] [OH-] * Kw = [H+] [OH-] * **Note:** [H+] = [OH-] = 10^-7M * **At T = 25^o C**: * Kw = 10^-14 mol² L^-2 * **Note:** Ionic Product of Water * 10^-7 is very small * Dissociation is very less * H₂O is W.E ## Finding α for H₂O at 25^o C * **Note:** α = Dissociated moles/Ionic initial moles/Ionic * H₂O H+ + OH- * C – Cα Cα Cα * **Note:** Cα = 10^-7 * (10^-7) * **Note:** 55.55 = 0.0000000001 /55.55 * α = 10^-7/55.55 * α = 1.8 x 10^-9 * √α = 1.8 x 10^-7 ## Density and Molar Mass at 25^o C * Density of water = 1000 g/L * Molar mass = 18 g/mol * (C)_H2O = M = D / MM = 1000 g/L / 18 g/mol = 55.55 mol/L ## Effect of Dilution on α * HX H+ + X- * C 0 0 * C - Cα Cα Cα * Ka = (Cα)² / (C - Cα) * Ka = (Cα)² / (C - Cα) * α = √Ka / C * ** Note:** α α √Ka / C * **Note:** α > α' if C > C' , or ν1, α' α 1 * **Note:** If we say α <<< 1 (1 - α = 1) * α << √5/c * **Note:** α ≈ 0.05 ## Dilution and Concentration * **Note:** This is not applicable for S.E * α = 1 or α = 100% * SE → Irreversible ## Applying the theory to examples * H₂O H+ + OH- * Keq = 10^-7 x 10^-7 / 55.55 * Kw = [H+][OH-] * -logKw = -log[H+] - log[OH-] * pKw = pH + pOH * **Note:** pKw = 7 + 7 = 14 at 25^oC ## Effect of Temperature on α * T α α * HX H+ + X-, △H = +vc * **Note:** Dissociation of Electrolytes is Endothermic. * T↑ , △H↑ , α↑ * log Ke = △H / 2.303R (T₁ - T₂ / T₁T₂) * △H = +ve, T↑, K₂>K₁ ## Effect of Solvent * Polarity of Solvent α Degree of Dissociation * (More Polar) * CH₃COOH + H₂O CH₃COO- + H₃O+, α₁ * (Less Polar) * CH₃COOH + CH₃OH CH₃COO- + H+, α₂ * α₁ > α₂ ## Applying logarithmic formulas * px = -logx * pKw = -logKw * pH = -logpH * logab = loga + logb * log a/b = loga - logb * loga^b = bloga * ln = 2.303log¹⁰ ## pH and pH scale * pH = -log[H+] * **Note:** HCL H+ + Cl- * **Note:** H₂SO₄ 2H+ + SO₄^2- * **Note:** HNO₃ H+ + NO₃^- ## Finding pH of 5 x 10^-3 M H₂SO₄ solⁿ * H₂SO₄ 2H+ + SO₄^2- * 5 x 10^-3 2 x 5 x 10^-3 * **Note:** 2 x 5 x 10^-3 = 10^-2 * [H+] = 10^-6 * pH = -log[10^-6] * **Note:** pH = 6log¹⁰ (log₁₀10 =1) * pH = 6 ## Calculating pH from [H+] * **Note:** [H+]= 5 x 10^-6 * pH = ? * pH = -log(5 x 10^-6) * **Note:** -(log 5 - log3 + log 10^-6) * **Note:** -(0.70 - 0.48 - 6) * pH = +5.78 ## pH scale * **Note:** pH scale is from 1-14, with 7 being neutral, less than 7 being acidic, and more than 7 being basic at 25^oC. ## Effect of Temperature on pH Scale * H2O = H+ + OH-, at 25^oC * 10^-7 10^-7 * pKw = 14 * pH scale = 1 to 14 * Neutral = 7 * H2O = H+ + OH-, at 90^oC * 10^-6 10^-6 * pH scale = 1 to 12 * Neutral = 6 * **Note:** at 90^oC, pKw = pH + pOH (H₂O) * **Note:** pKw = 6+6 * **Note:** pKw = 12 ## Relating pH and pOH * [H+] = [OH-] → Neutral * [H+] > [OH-] → Acidic * [OH-] > [H+] → Basic * **Note:** pOH = 14-pH at 25^o * pOH = -log[OH-] * **Note:** 14 = pH + pOH = pKw ## pH Measurement * **Note:** pH measurement is covered tomorrow.