Equilibrium PDF

"@ BG Sir Classes ; 9932024007" FAST TRACK : QUICK REVISION  Equilibrium : It is a state in a process when two opposing processes (forward and reverse) occur simultaneously at the same rate. The free energy change at equilibrium state is zero i.e., ∆G = 0.  Equilibrium constan...

"@ BG Sir Classes ; 9932024007" FAST TRACK : QUICK REVISION  Equilibrium : It is a state in a process when two opposing processes (forward and reverse) occur simultaneously at the same rate. The free energy change at equilibrium state is zero i.e., ∆G = 0.  Equilibrium constant : For a general reaction : aA + bB    cC + dD Kc = and Kp =  Relationship between Kp and Kc : Kp = Kc (RT)∆ng ∆ng = np(g) – nr (g)  Magnitude of equilibrium constant depends upon the way in which a reaction is written : Chemical equation Equilibrium constant aA + bB    cC + dD K cC + dD    aA + bB K1 = naA + nbB    ncC + ndD K2 = K n 1 1 1 1 aA + bB   cC + dD n n n n K3 = K1/n Equilibrium 105 "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007"  Predicting the direction of reaction : If Qc = Kc The reaction is in a state of equilibrium. Q c > Kc The reaction proceeds in reverse direction. Q c < Kc The reaction proceeds in forward direction.  Ostwald’s dilution law : Degree of dissociation of weak electrolyte, =  Ionic Product of water (Kw) = [H3O+] [OH–] = 10–14 at 298K  Le-Chatelier’s Principle : When a system of equilibrium is subjected to a change in temperature, pressure or concentration, the equilibrium shifts itself in such a way so as to undo or nullify the effect of change.  Outcomes of Le-Chatelier’s Principle Change at equilibrium Shift in equilibrium Increase in temperature Endothermic direction Decrease in temperature Exothermic direction Increase in pressure Towards lesser gaseous moles Decrease in pressure Towards greater gaseous moles Increase in Conc. of reactants Forward direction Increase in Conc. of products Reverse direction  Con ugate Acid or Base : Acid base pair hich di er by H+ ion. Species – H+ = Conjugate base Species + H+ = Conjugate acid  pH of solution : pH = –log [H3O+] or [H+] = 10–pH , pOH = –log [OH–] pH + pOH = pKw = 14 at 298K  Common ion e ect : The depression of ionisation of weak electrolyte by the presence of common ion from a strong electrolyte is called common ion effect. For example degree of dissociation of NH4OH decreases in the presence of strong electrolyte NH4Cl. 106 Chemistry Class XI "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" +  Hydrolysis of salts and pH of their solutions : Hydrolysis of salt is defined as the reaction of cation or anion with water as a result of which the pH of water changes. 1. Salts of strong and strong bases (e.g., NaCl) do not hydrolyse. The solution pH will be 7. 2. Salts of weak acids and strong bases (e.g., CH3COONa) hydrolyse, pH >7 (The anion acts as a base). X– + H 2O    HX + OH– (Weak acid) (Weak base) pH = (pKa + log C) 3. Salt of strong acids and weak bases (e.g., NH4Cl) hydrolyse, pH < 7. (The cation acts as an acid). M + + H 2O    MOH + H+ pH = (pKb + logC) 4. Salt of weak acids and weak base (e.g., CH3COONH4) hydrolyse. The cation acts as an acid and anion as a base but whether the solution is acidic or basic depends upon the relative values of Ka and Kb for these ions. M + + X – + H 2O    MOH + HX pH = (pKa – pKb)  Bu er solutions : The solutions, which resist the change in pH on dilution or addition of small amounts of acid or base, are called buffer solutions.  Basic bu er : Solution of weak base and its salt with strong acid, For e.g., NH4OH NH4Cl  Acidic bu er : Solution of weak acid and its salt with strong base, For e.g., CH3COOH + CH3COONa.  Henderson Hasselbalch E uation for the pH of Bu er solution pH = pKa + log (for acidic buffer) pOH = pKa + log (for basic buffer) "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007"  Solubility Product ( sp) : The equilibrium constant that represent the equilibrium between undissolved salt (solute) and its ions in a saturated solution is called solubility product constant (Ksp). For AxBy xAy+ + yBx– Ksp = [Ay+]x [Bx–]y = (xs)x (ys)y = xx. yx. s(x+y) where s = Molar solubility If ionic product < Ksp ; salt remain dissolve. If ionic product > Ksp ; salt will be precipitated.  elationship bet een solubility (s) and solubility product ( sp). Ksp = xx.yy. sx + y For binary salts (e.g., AgCl, AgBr, AgI) Ksp = s2 For Ternary salts (e.g., PbI2) Ksp = 4s3 "@ BG Sir Classes ; 9932024007"  MIND MAP : EQUILIBRIUM Effect of Pressure Equilibrium Constant EQUILIBRIUM !ng = 0 No effect aA + bB ! cC + dD !ng > 0 On increasing pressure c d [C] [D] Non Ionic Ionic Entities backward reaction favoured Kc = a b Entities and vice-versa [A] [B] Ionic Equilibrium c d !ng < 0 On increasing pressure [PC] [PD] backward reaction favoured Kc = a b Chemical [PA] [PB] Equilibrium and vice-versa K p = Kc(R5) and !ng = (c + d) + (a + b) Effect of Concentration Gaseous component A, B, C & D Le-Chatlier If reactant concentration increases or Principle product decreases then forward reaction forward and vice-versa Reaction Quotent c d [C] [D] Qc = a b Effect of Volume (Opposite ‘P’ Effect) [A] [B] !n = 0 No effect Q c = Kc Reaction is at equilbrium !n > 0 On increasing pressure Q c < Kc Forward reaction favoured backward reaction favoured Q c > Kc Backward reaction fovoured till and vice-versa new equilibrium is re-establish !n < 0 On increasing pressure backward reaction favoured and vice-versa Effect of Temperature Effect of Inert Gas (N2, Xe, Kr, etc.) "@ BG Sir Classes ; 9932024007" "@ BG Sir Classes ; 9932024007" !H K2 1 1 If inter gas is added at constant condition then log = = R ( – ) no effect is observed K1 2.303 T1 T1 If inter gas is added at constant pressure then For endothermic reaction !H is + at !ng = 0 No effect If T increases, forward reaction favoure !ng > 0 Forward reaction fovoured and otherwise backward reaction If T decreases, For Exothermic opposite effect !ng < 0 Forward reaction fovoured "@ BG Sir Classes ; 9932024007" "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" MULTIPLE CHOICE QUESTION (MCQ) 1. For the hypothetical reactions, the equilibrium constant (k) values are given A B : k1 = 2 B C: K2 = 4 C D : K3 = 8 The equilibrium constant (K) for the reaction A D is (a) 48 (b) 24 (c) 12 (d) 64 2. The equilibrium constant for the reaction 1 SO2(g) + O (g) SO3(g) is 5 × 10–2 atm–1/2 2 2 The equilibrium constant for the reaction 2SO3(g) 2SO2(g) + O2(g) would be (a) 100 atm (b) 25×10–4 atm (c) 400 atm (d) 125 ×19-6 atm–3/2 3. A(g) + 3B(g) 4C(g) initial concentration of A is equal to that of B. The equilibrium concentrations of A and C are equal. What is the equilibrium constant for 4C(g) A(g) + 3B (g) (a) 4 (b) 1/8 (c) B (d) 16 4. The equilibrium reaction that is not affected by volume change at constant temperature is (a) H2(g) + Cl2(g) 2HCl(g) (b) N2(g) + 3H2(g) 2NH3(g) (c) PCl5(g) PCl3(g) + C12(g) (d) H2(l) + CO2(g) H2CO3(l) 5. For the reaction CO(g) + Cl2 (g) COCl2(g), the value of Kc/Kp is equal to (a) RT (b) RT (c) 1/RT (d) 1.0 6. At 90°C pure water has Kw = 10–12. The solution with pH value 6.5 is (a) Acidic (b) Basic (c) Amphoteric (d) Data insufficient "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 7. 40 ml of 0.1 M NH4OH is mixed with 20 mL of 0.1 M HCl. What is the pH of the mixture? (pKb of ammonia solution = 4.74) (a) 4.74 (b) 2.26 (c) 9.26 (d) 5 8. Identify Bronsted Lowry Acids in the reaction [Al(H2Ol6]3– + HCO3 [Al(H2O)5(OH)]2+ + H2CO3 (X) (Y) (P) (Q) (a) X, Y (b) Y, P (c) P, Q (d) X, Q 9. The pKa of weak acid HA is 4.80 and pKb of a weak base BOH is 4.78. The pH of an aqueous solutions of corresponding salt BA will be (a) 7.01 (b) 4.79 (c) 9.22 (d) 10.0 10 If ‘P’ M is the solubility of KAl(SO4)2, then Ksp is equal to (a) p3 (b) 4p4 (c) p4 (d) 4p3 TRUE AND FALSE TYPE QUESTIONS 1. Equilibrium state can be achieved if a reversible reaction is carried out in closed or open container. 2. For a reaction 2A(g) B (g) Qc > K if ‘A’ is added maintaining Qc > K, the reaction will move in backward direction. 3. For the reaction at equilibrium CaCO3 CaO(s) + CO2(g) What CaO(s) is removed reaction moves in forward direction. 4. For a reaction aA + bB cC + dD at eqilibrium G = 0 always. 5. For a reaction at equilibrium H2(g) + Cl2(g) 2HCl(g) 2 K b [HCl] K = 4, the value of is 1. K f [H 2 ][Cl2 ] 6. For the electrolyte A2B if Ksp is solubility product then its solubling ‘S’ M is [Ksp] 4. 7. HCO–3 is conjugate base of H2CO3. 8. H2O can act as acid as well as base. 9. The pH of buffer solution remain same when any amount of dilution is done. "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 10. For a salt AB2(s) solution if Ionic product (I.P) > Ksp, then precipitation will take place. Ans. 1. False 2. True 3. False 4. False 5. True 6. True 7. True 8. True 9. False 10. True FILL IN THE BLANKS 1. At equilibrium rate of forward reaction is always equal to.................. 2. Kp & Kc are....... for reaction at equilibrium of type H2(g) + Br2(g) 2HBr(g). 3. If Kc for reaction CH3COOH(l) + C2H5OH CH3COOC2H5(l) + H2O(l) is 4. Then Qc and Kc are................. 4. If A+B –70J/mol D, reaction temperature is increased then reaction moves in............... direction. 5. Presence of catalyst will...... the equilibrium constant. 6. The conjugate acid of H2O is.............. 7. On dilution, the degree of dissociation of acetic acid will.............. 8. The presence of NH4Cl in NH4OH solution will............. the degree of dissociation of NH4OH. 9. If Ionic product (IP) < Ksp for a salt solution of AB, then addition of AB further........... lead to precipitation initially. 10. Kp is always equal to Kc if ∆ ng is............ Ans. 1. rate of backward reaction, 2. equal, 3. equal, 4. forward, 5. not change, 6. H3O+, 7. increase, 8. decrease, 9. will not, 10. zero MATCH THE COLUMNS 1. Column-I Column-II A) Na(g) 3H2(g) 2NH3(g); ∆H = - ve P) K increases with increase in temp B) 2N (g) + 2O (g) 4 NO(g) : ∆H = +ve Q) K decreases with increase in tem- 2 2 perature C) X(g) 2Y(g) ∆H = +ve R) Pressure has no effect D) PC1 (g) PC13 + Cl2 ; ∆H = +ve S) Product moles increases due to 5 addition of inert gast at constant pressure. Ans. (A) Q (B) P, R (C) P, S (D) P, S "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 2. Coloumn-I Column-II A) Salt of weak acid and weak base P) pH = ½ (pKw + pKa + logc) B) Salt of weak Acid and strong Base Q) pH = ½ (pKw + pKa – pkb) C) Salt of strong acid and strong base R) pH = ½ (pKw – pKb – logc) D) Salt of strong acid and weak base S) pH = ½ (pKw) Ans. (A) Q (B) P (C) S (D) R ASSERTION - REASON TYPE QUESTION Each question contains statement-1 (assertion) and Statement-2 (Reason) Examine the statements carefully and mark the correct answer according to the instruction given below : A. If both the statements are true and statement -2 is the correct explanation of statement-I B. If both the statements are true but statement-2 is not the correct explanation of statement-I C. If statement-I is true and statement-2 is false D. If statement-I is false and statement-2 is true. 1. Statement-1 : The endothermic reactions are favoured at lower temperature and the exothermic reactions are favoured at higher temperature. Statement-2 : when a system in equilibrium is disturbed by changing the temperature, it will tend to adjust itself so as to overcome the effect of change. 2. Statement-1 : The melting point of ice decreases with increase of pressure Statement-2 : Ice contracts on melting. 3. Statement -1 : The gas phase reaction PCl3(g) + Cl2(g) PCl5(g) shifts to the right on increasing pressure. Statement-2 : When pressure increase, equilibrium shifts towards more number of moles. 4. Statement-1 : The physical equilibrium is not static but dynamic in nature. Statement-2: The physical equilibrium is a state in which two opposing process are proceeding at the same rate. 5. Statement-1 : The catalyst does not after the equilibrium constant. Statement-2 : Because for the catalysed reaction and uncatalysed reaction ∆H remains same and equilibrium constant depends on ∆H. "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 6. Statement-1 : If water is heated to 59°C, the pH will increase. Statement-2 : Kw increases with increase in temperature. 7. Statement-1: Addition of HCl(aq.) to CH3COOH (aq.) decrease the ionisation of CH3COOH (aq.). Statement-2 : Due to common ion effect H+, ionisation of CH3COOH decreases. 8. Statement-1: Sparingly soluble salts AB and XY2 with the same solubility product, will have different solubility. Statement 2: Solubility of sparingly soluble salts depends upon solubility product. 9. Statement-1 : The ionisation constants of weak diprotic acid are in the order of Ka1 > Ka2. Statement-2 : Removal of H+ from anion is difficult as compared to neutral atom. 10. Statement-1 : In a titration of weak acid with strong base, the pH at the half equivalence point is pKa. Statement-2 : At half equivalence point, it will form acidic buffer at its maximum capacity where [Acid] = [Salt]. Ans.: 1. D, 2. A, 3. C, 4. A, 5. A, 6. D, 7. A, 8. B, 9. A, 10. A ONE WORD ANSWER TYPE QUESTIONS 1. What is sum of pH + pOH at 25ºC? [Ans. 14] 2. Write the Henderson Hasselbalch equation for acidic buffer [SALT] Ans. pH = pka + l0g [ACID] 3. How is degree of dissociation related with concentration terms and Ka, for weak electrolyte. Ans. = Ka / c 4. How NH3 is defined as Lewis base? [Ans. It contain Lone paid of electrons] 5. How are Kp and Kc related? [Ans. Kp = Kc (RT)∆n] 6. How does K affected for endothermic reaction if temperature is increased? [Ans. K get decreased] 7. What is the effect of catalyst on K? Ans. K remains unaffected 8. How is pH scale affected by increasing temperature? [Ans. pH scale gets contracted] 9. What is the conjugate base of HCO3– ? [Ans. CO32–] 10. What is the nature of CH3COOH in conc. HCl solution? [Ans. Bronsted Base] "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 1-MARK QUESTIONS 1. Define physical equilibrium. Give an example also. 2. Fizz is observed when soda water bottle is opened. Why ? 3. Justify the statement : ‘Both physical and chemical equilibrium are dynamic in nature’ 4. State Henry’s law. 5. In a reversible reaction, the two substances are in equilibrium. If the concentration of each one is reduced to half, then what is the effect on the equilibrium constant ? 6. K1 and K2 are equilibrium constant for reactions (1) and (2) (i) N2(g) + O2(g) 2 NO(g) (ii) NO(g) 1 2 N2(g) + 1/2 O2(g) Calculate the relation between K1 and K2. 7. Write the equilibrium constant expression for the following reaction : 3 Fe(s) + 4 H2O(g) Fe3O4(s) + 4 H2(g) 8. Classify the equilibrium as homogeneous or heterogeneous : CH3COOC2H5(aq.) + H2O(1) CH3COOH(aq.) + C2H5OH (aq.) (PNH3 ) 9. Kp = 3 1 (PH2 ) 2 (PN2 ) 2 Write the balanced chemical equation corresponding to the above expression. 10. Give the direction in which the reaction would proceed if Qc > Kc. 11. Hb(s) + O2(g) HbO2(s) Predict the direction in which equilibrium gets shifted if partial pressure of O2(g) is lowered. 12. Discuss the position of equilibrium if the following reaction is carried out in the presence of catalyst. 2SO2(g) + O2(g) 2SO3(g) 13. Which of the following are Lewis acids ? H2O, BF3, H+, NH4+ "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 14. Write the conjugate acids for the following Bronsted bases. C6H5OH, H2O 15. Write the conjugate bases for the following Bronsted acids. H2O, CH3COOH. 16. Which of the following are Lewis acids ? (a) H2O (b) AlCl3 (c) NH4+ 17. Define Ostwald’s dilution law. 18. SO32– is Bronsted base or acid and why ? 19. Why pH of our blood remains almost constant at 7.4 though we quite often eat spicy food ? 20. pH of black coffee is 5.0 at 25 C. Is black coffee acidic or basic ? [Ans. Acidic] 21. What will be the value of (pKa + pKb) at 25ºC. 22. What will be the pH of 1 M KNO3 solutions at 25ºC? 23. CaCl2(s) + H2O(l) CaCl2(aq.) + Heat Discuss the solubility of CaCl2 if temperature is increased. 24. Why does the solubility of CO2 decrease with rise in temperature ? 25. The solubility of A2 X3 is y mol dm–3. Calculate its solubility product. 26. Write the Ksp expression for Al (OH)3. 27. What is the condition for precipitation of a salt ? 28. Pridict whether the solution is acidic, basic or natural when NH4NO3 undergo hydrolysis. 29. Explain why pure NaCl precipitates out when HCl gas is passed through the solution of NaCl ? 30. Give the Henderson’s Hasselbalch equation for an acidic buffer solution. 31. On which of the factors the equilibrium depend : Temperature, nature of reactant and product, initial concentration and pressure of the reactants. 32. Arrange the following in increasing acidic strength HCl, HBr, HF, HI [Ans. HF < HCl < HBr < HI] "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 33. Arrange the following in increasing Lewis base strange NH3, BiH3, PH3, AsH3, SbH3 [Ans. BiH3< SbH3 < ASH3< PH3 NH3] 34. Arrange following in increasing pH value 0.1M CH3COOH, 0.1 M NaCl, 0.1MHCl, 0.1MNaOH, 0.1MNH4OH [Ans. 0.1MHCl < 0.1M CH3COOH 0.1M NaCl 0.1 NH4OH 0.1M NaOH 35. Arrange following in increasing order of degree of hydrolysis. 0.1M NH4OH, 0.01 M NH4OH, 10-5 M NH4OH, 10-3 M NH4OH, 10-6 M NH4OH [Ans. 0.1M NH4OH < 10-2 M NH4OH, 10-3M NH4OH< 10-5MNH4OH < 10-6 M NH4OH] 36. Arrange following in increasing order of acidic strengh CH3COOH, HCOOH, CH3CH2COOH, C6H5COOH, CH2COOH [Ans. CH3COOH < C6H5COOH < HCOOH < CH2FCOOH] 37. Arrange following in increasing order of basic strength in gas phase NH3, (CH3)2NH, (CH3)3N, CH3NH2 [Ans. NH3 NH3NH2 < (CH3)2NH (CH3)3N 38. Arrange the following pkb in increasing order [Ans. pK2 < pK1 < pK4 < pK3] 39. Arrange the basic strength of following F–, Br–, Cl–, I– [Ans. I– < Br– < Cl– < F–] 40. Arrange the following in increasing base strength CH3–, NH2–, OH–, F– [Ans. F– < OH– NH2 < CH3] "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 2-MARKS QUESTIONS 1. The standard Gibbs energy change at 300 k for the reaction 2A B+ C is 2494. 2 J. At a given temperature, and time. the composition of the reaction mixture is [A] = ½, [B] = 2, [C] = ½. The reaction proceed in the (R = 8.314J/K/mo1, = 2.718) [Ans. Reverse direction] 2. The equilibrium constant for N2(g) + O2(g) 2NO(g) is K, then calculate equilibrium constant for N2(g) + ½O2(g) NO(g). Ans. K] 3. For the reversible reaction N2(g) + 3H2(g) 2NH3(g) at 500°C, the –5 –2 value of Kp is 1.44×10 atn. Find the Kc value. [Ans. 1.44 × 10–5 / (0.082 × 773)–2] 4. The equilibrium constant at 298 K for the reaction A + B C + D is 100. If the initial concentration of all the four species were 1M each, then equilibrium concentration of D will be [Ans. 1.818] 5. For the reaction NH4COO NH2(g) 2NH3(g) + CO2(g) If equilibrium pressure is 3 atm. Find the value of Kp [Ans. 4] 6. A buffer solution with pH 9 is to be prepared by mixing NH4Cl that should be added to one litre of 1.0m NH4OH kb 1.8 × 10-5 [Ans. NH4Cl = 1.8 M] 7. Calculate the solubility of silver chloride in water at room temperature if the Ksp of AgCl is 1.6×10-10. [Ans. 1.26 × 10-5M] 8. Calculate the molar solubility of Ni(OH)2 in 0.10m NaOH. The ionic product of Ni(OH)2 is 2.0 × 10-15. [Ans. 2.0 × 10-13M] 9. Calculate the pH of 10-8 M HCl solution. [Ans. 6.96] 10. How many grams of NaOH must be dissolved in IL of the solution to give it a pH value of L2? [Ans. 0.4g] "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 3-MARKS QUESTIONS 1. The equilibrium constant for the reaction H2(g) + Br2(g) 2HBr(g) at 1024 K is 1.6×105. Find the equilibrium pressure of all gases if 10.0 bar of HBr is introduced into a sealed container at 1024K. [Ans. 10 bar] 2. For the reaction 2BrCl(g) Br2(g) + Cl2(g) Kc is 32 at 500 K. If initially pure BrCl is present at a concentration of 3.30 ×10-3 M, what is its molar concentration in the mixture at equilibrium? [Ans. 3.0 × 10-4 M] 3. What is the equilibrium constant Kp and Kc for the reaction PCl5(g) PCl3(g) + Cl2(g) if the pressure is 1.0 atm in 8.0L container at equilibrium. [Ans. Kc = 0.04 Kp = 1.77] 4. The Kp for the reaction, N2O4(g) NO2(g) is 640 mm at 775 K. Calculate the percentage dissociation of N2O4 at equilibrium pressure of 160mm. At what pressure the dissociation will be 50%. [Ans. 70.7%, P = 480 mm] 5. Show that degree of dissociation ( ) for the dissociation of PCl5 into PCl3 1/ 2 Kp and Cl2 at pressure P is given by = P + kp 6. How much of 0.3M NH4OH should be mixed with 30 mL of 0.2m solution of NH4Cl to give a buffer solution of pH 10. pkb for NH4OH is 4.75. [Ans. V = 112.5 mL] 7. Predict whether a precipitate will be formed or not on mixing 20 mL of 0.001 N NaCl solution with 80 mL of 0.01 M AgNO3 solution. Ksp for AgCl is 1.5 × 10-10. [Ans. Yes, ppt will formed.] 8. The values of Ksp of two sparingly soluble salts Ni(OH)2 and AgCN are 2.0 × 10-15 and 6.0 × 10-17 respectively. Which salt is more soluble. Explain [Ans. SNi(OH) = 5.8 × 10-5M : S(Ag CN) = 7.8×10-9M. Ni(OH)2 2 is more soluble] 9. The ionization constant of propanoic acid is 1.32×10-15. Calculate the degree of ionization if its solution is 0.05 M. What will be its degree of ionization if the solution is 0.01 M in HCl solution. [Ans. 1.62 × 10-2, 1.32 × 10-3] 10. Calculate the pH of a solution obtained by mixing 50ml of 0.2M HCl with 49.9 mL of 0.2m NaOH solution. Ans. 3.699] "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" HOTS QUESTIONS 1. The molar solubility of Cd(OH)2 is 1.84 × 10-5M. Calculate the expected solubility of Cd(OH)2 in a buffer solution of pH = 12. 2+ — Ans. Cd(OH) 2  Cd (aq.) + 2OH (aq.) S 10–2 2.49 × 10-14 = S(10-2)2 S = 2.49 × 10-10M 2. An aqueous solution contains an unknown concentration of Ba2+. When 50 ml of a 1M solution of Na2SO4 is added. BaSO4 just begins to precipitate. The final volume is 500ml. The solubility product of BaSO4 is 1×10-10. Find the original concentration. 50 1 Ans. K sp = Ba 2+ SO 42— = Ba 2+ = 10 —9 500 500 Ba2+ = 10–9 M 10–9 × 500 = 450 × M M = 1.11 × 10–9M 3. An aqueous solution contains 0.10 M H 2S and 0.20 M HCl. If the equilibrium constants for the formation of HS– from H2S is 1.0 ×10–7 and that of S2– from 4S– ions is 1.2×10–13, then find the concentration of S–2 ions in aqueous solution. Ans. H2S(aq.) 2H+ + S2– (0.1 – x) (2x + 0.29) x Ka = Ka × Ka = 1.2 × 10–20 1 2 2 0.2 S2— 1.2 × 10–20 = , [S2–] = 3 × 10–20 0.1 4. How many litres of water must be added to 1 litre of an aqueous solution of HCl with a pH of 1 to create an aqueous solution with pH of 2? Ans. 0.1 × 1 = (1 + v) (0.01) v = 9L 5. A certain buffer solution contains equal concentration of – and HX. The Kb for X– is 10–10. Find the pH of the buffer. 10 —14 Ans. ka.kb = 10–14 ka = = 10 —4 10 —10 [x — ] pH = pka + log [Hx] 1 pH = 4 + log = 4 pH = 4 1 "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" 6. The yield of Ammonia as a function of time in the reaction N2(g) + 3H2(g) 2NH3(g), ∆H < O at (P, T) is given below: If this reaction is conducted at T2 > T1, then plot the yield of NH3 as a function of time on same graph T1 Ans. Initially on increasing temperature the T2 rate of reaction increases, however since the % reaction is exothermic therefore yield of NH3 (yield) get decreased overall after a certain interval of time. Time 7. Consider the reaction NH4COONH2(s) 2NH3(g) + CO2(g) at a certain temperature, the equilibrium pressure of the system is 0.318 atm. Find Kp of the decomposition of ammonium carbonate. Ans. Ptotal = 3P P = 0.318/3 = 0.106 Kp = 4P3 = 4.76 × 10–3 8. The equilibrium constant for the reaction CO(g) + H2O(g) CO2(g) + H2(g) is 5. How many moles of CO2 must be added to 1 litre container already containing 3 moles each of CO and H2O to make 2M equilibrium concentration of CO? Ans. CO + H2O CO2 + H2 t=0 3 2 x 0 At equilibrium 2 2 x+1 1 x +1 S= x = 19 4 9. At constant temperature, the equilibrium constant Kp N 2O 4 2NO2 is given by 2 4x P kp = where, P = Pressure and X = Extent of reaction 1— x "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" How does the value of Kp change on following changes (a) ‘P’ increases (b) X changes (c) ‘P’ decreases Ans. Kp is equilibrium constant which does not change on changing the P, x.Kp depends on temperature. 10. When two reactants A and B are mixed to give product 'c' and 'p' the reaction quotient 'Q' at the initial stages of the reaction will be? Ans. In the beginning of the reaction Q = 0. As the reaction proceeds in the forward direction Q starts increasing. At chemical equilibrium Q = K "@ BG Sir Classes ; 9932024007"  "@ BG Sir Classes ; 9932024007" UNIT TEST Time Allowed: 1 hr Maximum Marks : 20 General Instructions: (i) All questions are compulsory. (ii) Maximum marks carried by each question are indicated against it. 1. What is the pH 10–3 M HCl solution ? (a) 1 (b) 11 (c) 3 (d) 14 2. Which one can act as Arrhenius Acid ? (a) NH3 (b) H2O (c) HCl (d) C6H5OH 3. Write the conjugate base of CH3COOH + H2. 4. Write the relation between Kp and Kc. 5. What is the nature of following reaction Exothermic or endothermic A + B – 70J —→ C 6. The pKa of CH3COOH and pKb of NH4OH are 4.76 and 4.75 respectively. Calculate the pH of CH3COONH4. 7. What is a buffer solution. Calculate the pH of the solution obtained by adding 4mol of CH3COOH with 3 mol of NaOH in 1 litre container. 2 pKa, CH3COOH = 4.74 log2 = 0.3010 log3 = 0.4771 8. Calculate the molar solubility of Ni(OH)2 in 0.1M KOH solution. The Ksp for Ni(OH)2 is 2.0×10–15. 9. Kp = 0.04 atm at 899 K for the equilibrium shown below. What is the equilibrium concentration of 2H6 when it is placed in a flask at 4.0 atm pressure and allowed to come to equilibrium. C2H6(g) C2H4(g) + H2(g) 10. Ionization constant of Benzoic acid is 6.46×10-5 and Ksp for silver benzoate is 2.5 × 10-13. How many times is silver ben oate more soluble in buffer of pH 3.19 compared to its solubility in pure water. [H+] = 6.46 ×10–4 ***** "@ BG Sir Classes ; 9932024007"