DPP-47 to 48 English Physical chemistry PC

DAILY PRACTICE PROBLEMS (DPP) Subject : Physical/Inorg.Chemistry Date : DPP No. 47 to 48 Class : XIII Course : DPP No.47 DPP No.1 Total Marks : 45 Max. Time : 45 min. Single choice Objective ('–1' negative marking) Q.1 to Q.3 (3 marks 3 min.) [9, 9] Multiple choice objective ('–1' negative marking) Q.4 (4 marks 4 min.) [4, 4] Subjective Questions ('–1' negative marking) Q.5 to Q.12 (4 marks 4 min.) [32, 32] 1. Calculate the change in pH when a 0.1 M solution of CH3COOH in water at 25ºC is diluted to a final concentration of 0.01 M. [Ka = 1.85 × 10–5] (1) +0.5 (2) +0.4 (3) +0.7 (4) +0.6 2. At 25ºC , the dissociation constants of CH3COOH and NH4OH in an aqueous solution are almost the same. The pH of a solution of 0.01 N CH3COOH is 4 at 25ºC. The pH of 0.01 N NH4OH solution at the same temperature would be : (1) 4 (2) 3 (3) 10 (4) 11 3. The acid dissociation constants of H S and HS– are 10–7 and 10–13 respectively. The pH of 0.1M aqueous solution of H2S will be : (1) 2 (2) 2 (3) 4 (4) 5 4. Which of the following increase with dilution at a given temperature? (1) pH of 103M acetic acid solution (2) pH of 103 M aniline solution (3) degree of dissociation of 103M acetic acid (4) degree of dissociation of 10–3M aniline 5. How much water must be added to 300 mL of a 0.2 M solution of CH3COOH for the degree of dissociation of the acid to double ? (Assume Ka of acetic acid is of order of 10–5 M) 6. Saccharin (K = 2  10 12) is a weak acid represented by formula HSac. A 4  10 4 mole amount of saccharin is dissolved in 200 cm3 solution of pH 3 . Assuming no change in volume , calculate the concentration of Sac  ions in the resulting solution at equilibrium. 7. Find [OH–] in a solution made by dissolving 0.005 mol each of NH (K = 1.8 × 10–5) and pyridine (K =1.5×10–9) 3 b b in enough water to make up 1 L of the solution. What are the concentration of ammonium and pyridinium ions. 8. What is the concentration of acetic acid which can be added to 0.5 M formic acid so that the % dissociation of neither acid is changed by the addition. K for acetic acid is 2 × 10-5, K for formic acid = 2.4 × 10-4. 9. Hydrazine, N2H4, can interact with water in two stages. N H (aq) + H O(l) N H + (aq) + OH–(aq) K = 8.1 × 10–7 N H + (aq) + H O (l) N H 2+ (aq) + OH–(aq) K = 9 × 10–16 2 5 2 2 6 b2 (i) What are the concentrations of OH–, N H + and N H 2+ in a 0.010 M aqueous solution of hydrazine ? 2 5 2 6 (ii) What is pH of the 0.010 M solution of hydrazine? Integer Answer Type This section contains 3 questions. The answer to each of the questions is a single digit integer, ranging from 0 to 9. 10. In what ratio should a 15% solution of acetic acid be mixed with a 3% solution of the acid to prepare a 12% solution(all percentages are mass/mass percentages) : 11. 2 mole PCl5, 1 mole Cl2 and 1 mole PCl3 are taken in 1 lt flask. When equilibrium is set up, PCl5 is found to be 50% dissociated into the products. Then, find KC for the reaction PCl5(g) PCl3(g) + Cl2(g). 12. Consider the following reversible reactions : A + B P ; KC = 6 2B + C 2D ; KC = 4 Hence, what will be the KC for the reaction, C A + D P + 2 DPP No.48 DPP No.2 Total Marks : 42 Max. Time : 42 min. Single choice Objective ('–1' negative marking) Q.1 to Q.2 (3 marks 3 min.) [6, 6] Subjective Questions ('–1' negative marking) Q.3 to Q.11 1.(a) Which of the following salts is alkaline in water? (4 marks 4 min.) [36, 36] (1) CuSO4 . 5H2O (2) K2SO4 (3) NaNO3 (4) Na2B4O7 . 10H2O (b) Which of the following salts undergoes anionic hydrolysis? (1) CuSO4 (2) NH4Cl (3) FeCl3 (4) Na2CO3 2.(a) The pH value will be highest for the aqueous solution of (1) NaCl (2) Na2CO3 (3) NH4Cl (4) NaHCO3 (b) Which of the following salts does not undergo hydrolysis? (1) NH4NO3 (2) FeCl3 . 6H2O (3) KCl (4) KCN 3. Find the concentration of H+ , HCO  & CO 2 in a 0.01 M solution of H CO if the pH of this is 4.1. 3 K (H CO ) = 4  10 7 ; K 3 2 3 (HCO ) = 4.8  10 11 . a 2 3 a 3 4.(a) Potassium Cyanide is the deadliest poison known. Calculate the percent hydrolysis in a 0.06 M solution of KCN. [K (HCN) = 6 × 10-10] (b) Calculate the degree of hydrolysis of 0.1 M sodium acetate solution if pH is 8.9 . 5. A solution contains 0.10 M H S and 0.25 M HCl. Calculate the concentration of [ S 2 ] and [ HS  ] ions in the solution. For H2S, Ka1 = 1.0 ×10–7 , Ka2 = 1.3 × 10–13 6. Determine the [S2] in a saturated (0.1M) H S solution to which enough HCl has been added to produce a [H+] of 2 x 104 . K = 107 , K = 1014. 7. Ka for butyric acid is 2.0  10 . Calculate pH and hydroxyl ion concentration of 0.02 M aqueous solution of 6 sodium butyrate . 8. Calculate the mass of NH4Cl required to be dissolved in 500 ml water to have pH = 4.5, if Kb for NH OH is 10 –6 . 9. Calculate hydrolysis constants for each of the following salt solutions. Compute also the pH of the solution and the percentage of hydrolysis. (i) 0.05 M NaAc ; K (HAc) = 2 × 10–5. (ii) 0.008 M NH4 Cl ; Kb (NH ) = 2 × 10 . –5 (iii) 0.5 M Na S ; K (HS—) = 1.0 × 10–15 [ log (0.475) = - 0.32 ]. 2 a (iv) 0.64 M KCN : Ka (HCN) = 4.0 × 10–10. Integer Answer Type This section contains 2 questions. The answer to each of the questions is a single digit integer, ranging from 0 to 9. 10. For the equilibrium AB(g) A(g) + B(g) at a given temperature, the pressure at which one-third of AB is dissociated is numerically equal to how many times of KP ? 11. How many moles of KMnO4 are needed to oxidise 50 moles of Fe0.9O in acidic medium ? ANSWER KEY DPP No.-45 1. 1 2. 1 3. 2 4. 2 7. (1) to the left (2) to the right 9. 2 10. 3 11. 2 DPP No.-46 1. 2 2. 2 3. 3 4. 2 5. 1 6. 3 7. Kb [CN–] = 2 × 10–5 8. Ka = 1.56 × 10–10 9. 1.8 × 10–5 . 10. 1.8 × 10–5 11. [OH–] = 5 × 10–9 M 13. 5 14. 6

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