Name: Quiz name: Equilibria + Acids/Bases Date: 1. 2. At 450 C, 2.0 moles each of H 2(g), I 2(g), and HI are combined in a 1.0 L rigid container. The value of K c at 450 C is 50. Which of the following will occur as the system moves toward equilbrium? H 2(g) + I 2(g) <> 2HI (g) A More hydrogen gas and iodine gas will form. B More HI will form. C The total pressure will increase D No net reaction will occur, because the number of molecules is the same on both sides of the equation. H 2 (aq) + H 2 O (l) <> H 3 O + (aq) + H (aq) H O 4 (aq) + H 2 O (l) <> H 3 O+ (aq) + O 4 (aq) H 2 O (l) + H 2 O (l) <> H 3 O + (aq) + OH All the reactions represented above occur in an aqueous solution of (aq) oxalic acid. Which of the following represent a BronstedLowry conjugate acidbase pair? A H 2 and B H and C2 C H and H2 O D H 3 O + and OH 3. As the reaction rate progresses toward equilibrium, the rate of the forward reaction A increases until it becomes the same as the reverse reaction rate at equilibrium. B stays constant before and after equilibrium is reached C decreases to become a constant nonzero rate at equilibrium D decreases to become zero at equilibrium 4. Which of the following statements about K p, the equilibrium constant for the reaction, is correct? A K p > 1 B K p < 1 C K p = 1 D It can not be determiend without additional information. 5. For which acid is the value of the acid dissociation constant, K a, the smallest? A Acid 1 D Acid 4 6. Which of the four acids listed in the table is hydrochloric acid? Page 1 of 5
A Acid 1 D Acid 4 7. A OH B H 3 O + C Acid 1 Of the following species, which has the greatest concentration in a 1.0 M solution of acid 1 at equilibrium? D The conjugate base of acid 1 8. If equal volumes of the four acids at a concentration of 0.50 M are each titrated with a strong base, which will require the greatest volume to reach the equivalence point? A Acid 1 D All the acids will require the same volume of base to reach the equivalence point. 9. A 25 ml sample of a 1.0 M solution of acid 1 is mixed with 25 ml of 0.50 M NaOH. Which of the following best explains what happens to the ph of the mixture when a few drops of 1.0 M HNO 3 are added? A The ph of the mixture increases sharply, because HNO 3 is a strong acid. B The ph of the mixture decreases sharply because H 3 O + ions were added. C The ph of the mixture stays about the same, because the conjugate base of acid 1 reacts with the added H 3 O + ions. D The ph of the mixture stays about the same, because the OHions in the solution react with the added H 3 O + ions. 10. The table shows the values of K a for four weak acids. Which of the following pairs of chemical speceis, when combined in equimolar amounts, results in a buffer with ph closest to 7.5? A HN and N B HC 3 and C 3 C HClO and ClO D C 6 OH and C 6 O 11. A 0.040 COCl 2 (g) <> CO (g) + Cl 2(g) COCl 2 decomposes according to the equation above. When pure COCl 2 is injected into a rigid, previously evacuated flask at 690 K, the pressure in the flask is initially 1.0 atm. After the reaction reaches equilibrium at 690 K, the total pressure in the flask is 1.2 atm. What is the value of K p for the reaction at 690 K? Page 2 of 5
B 0.050 C 0.80 D 1.0 12. During which of the following titrations, using 0.10 M aqueous solutions, would conductivity of the solution increase to become greatest at the equivalence point? A HCl and KOH B H 2 S and Ba(OH) 2 C H H 3 and NH 3 D HCl and Ba(OH) 2 13. Which of the following ions is likely to have the highest K b value? A ClO 3 B Cl C BrO 3 D Br For the reaction HS (aq) + F (aq) <> SO 4 (aq) + HF (aq), K = 18. It is evident from the eq 14. information above that the strongest of the following BronstedLowry bases is A HS B F C S D H 2 S 15. CO (g) is added to a reaction vessel to a pressure of 2.0 atm. H 2(g) is added until the total pressure reaches 5.0 atm. The reaction CO (g) + 2H 2(g) <> CH 3 OH (g) occurs, and reaches equilibrium at a total pressure of 3.0 atm, while the temperature is kept constant. What is the initial pressure of the hydrogen gas, before the reaction takes place? A 2.0 atm B 3.0 atm C 5.0 atm D 7.0 atm 16. A 1.0 B 0.020 5 D 50 CO(g) is added to a reaction vessel to a pressure of 2.0 atm. H2(g) is added until the total pressure reaches 5.0 atm. The reaction CO(g) + 2H2(g) <> CH3OH(g) occurs, and reaches equilibrium at a total pressure of 3.0 atm, while the temperature is kept constant. What is the value of K p for the reaction at that temperature? 17. A CO 3 CO 3 has a Kb of 1.8x104. In a 1.0 M aqueous solution of K 2 CO 3, which of the following ions is present in the greatest concentration? B HCO 3 C OH D H 3 O + Page 3 of 5
18. A student is attempting to standardize an NaOH solution with a 0.500 M solution of H 2. The net ionic equation for the reaction is H 2 (aq) + 2OH (aq) > O 4 (aq) + 2H 2 O The student (l) prepares three 20.0 ml samples of the 0.500 M acid solution, adding phenolphthalein to each sample. He thoroughly rinses a burette with distilled water, adds the NaOH solution to the burette, and titrates each of the three samples, refilling the burette after each. The student finds his results are inconsistent. It is most likely that the determined concentration of NaOH would be A lower in the first run than in the other two B higher in the first run than in the other two C the same in the first two runs, but lower in the third D the same in the first two runs, but higher in the third 19. From the list of indicators shown, choose one that is suitable for this reaction A phenolphthalein B bromophenol blue C bromocresol green D any indicator can be used and an accurate result will be obtained 20. Select the correct combination of descriptors of the titration and the data A Ethanoic acid is the titrant and ph is plotted on the xaxis of the titration curve B Sodium hydroxide is the titrant and ph is plotted on the xaxis of the titration curve C Ethanoic acid is the titrant and ph is plotted on the yaxis of the curve D Sodium hydroxide is the titrant and ph is plotted on the yaxis of the titration curve. 21. A buffer solution exists when the volume of titrant added is A 0.00 ml B At any point between 0.01 ml adn 24.9 ml 5.0 ml D At any point greater than 25.0 ml 22. The ph of the solution when the buffer solution in the flask contains equal concentrations of weak acid and conjugate base is A 2.86 B 4.75 C 8.77 D 12.01 23. The ph of 8.77 tht is recorded after 25.0 ml of titrant has been added, can be best described as being caused by which equation? Page 4 of 5
A NaOH > Na + + OH B CH 3 COO + H 2 O > CH 3 COOH + OH C CH 3 COOH + H 2 O > CH 3 COO + H 2 O D CH 3 COOH + NaOH > CH 3 COONa + H 2 O Page 5 of 5