Chemistry 33: Sample Test #2

Transcription

1 Chemistry 33: Sample Test #2 NOTE: This sample is longer than the upcoming test. 1. Methanol can be synthesized according to the following reversible reaction: CO (g) + 2 H 2 (g) CH 3 OH (g) K c = 14.5 at 483 K. Determine hydrogen s equilibrium concentration if [CO] eq = 1.03 M and [CH 3 OH] eq = 1.56 M. 2. Sulfur trioxide can be formed according to the following reversible reaction: 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) K c 2.8 x 10 2 at 1000 K. H o rxn = kj Describe the effect that each of the following will have on the concentrations of the substances at equilibrium: (c) (d) (e) adding sulfur trioxide decreasing the volume of the reaction vessel adding inert argon gas heating the reaction vessel adding a catalyst 3. Dinitrogen tetroxide, used as a rocket fuel, partially dissociates into nitrogen dioxide. At 25 o C, 7.64 g N 2 O 4 (g) and 1.56 g NO 2 (g) are present in a 3.00 L container. Find K c. 4. At 900 K, g of sulfur trioxide is placed in an evacuated 1.52 L container. Find the equilibrium concentrations of sulfur dioxide and oxygen if K c = 3.1 x For the following reaction, identify the conjugate acid-base pairs: NH 3 (g) + H 2 O (l) NH 4 + (aq) + OH - (aq) 6. Acetic acid, HC 2 H 3 O 2 (aq), has a K a = 1.8 x What is the solution s ph? 7. What is the ph for a solution formed by adding 535 ml of gaseous HCl to enough water to make 625 ml of solution at 26.5 o C and kpa?

2 8. Acetylsalicylic acid, HC 9 H 7 O 4, is the active ingredient in aspirin. What is the ph of solution formed when two extra-strength aspirin tables (500 mg of acetylsalicylic acid each) are dissolved in 325 ml of water. K a = 3.3 x Describe the salt solutions formed from: strong acid and strong base weak acid and weak base 10. Describe and list an example substance for each of the three classes of acids and bases. (c) 11. What is the ph of a solution from when 25.5 g sodium acetate is mixed with M acetic acid to make a 500 ml solution? 12. What mass of sodium acetate must be dissolved in L of 0.25 M acetic acid to produce a solution with ph = 5.09? 13. Two L buffer solutions are M acetic acid and M sodium acetate. What is the effect to the ph when mol of HCl is added to one solution? mol of NaOH is added to the second solution? 14. Complete the following table: Solution [H + ] [OH - ] ph poh M H 2 SO M NaOH 15. What mass of barium hydroxide must be dissolved to prepare ml of a solution whose ph = 12.00?

3 16. During a laboratory exercise, a stock solution of sodium hydroxide was standardized using the weak acid primary standard, KHC 8 H 4 O 4, potassium hydrogen phthalate. Paper (g) Paper + KHC 8 H 4 O 4 (g) KHC 8 H 4 O 4 (g) mol KHC 8 H 4 O should be used as the acid-base indicator for the titration of KHC 8 H 4 O 4 with NaOH. During the titration, the student used the following amounts of NaOH: mol KHC 8 H 4 O 4 V NaOH (ml) is the NaOH solution s average molarity. Next, the NaOH solution is then used as a secondary standard to determine the molarity of a hydrochloric acid solution. should be used as the acid-base indicator for the titration of HCl with NaOH. HCl (ml) NaOH (ml) is the HCl solution s average molarity. Finally, the NaOH solution is used to titrate an acetic acid (CH 3 COOH (aq)) solution. should be used as the acid-base indicator for the titration of CH 3 COOH (aq) with NaOH. CH 3 COOH (aq) (ml) NaOH (ml) is the CH 3 COOH solution s average molarity.

4 17. What volume of M hydrochloric acid is required to precipitate all of the silver ions from 50.0 ml of a M of silver nitrate? 18. What mass of solid sodium hydroxide must be dissolved to prepare ml of a M NaOH solution? 19. If a g bottle of sodium hydroxide costs $22.05, and the distilled water is free, what is the cost of the solution you prepared in Problem 18? [NOTE: If you could not get an answer for Problem 18, use g (not the actual amount) as the mass needed.] 20. A bottle of commercial concentrated hydrochloric acid has a density of g/cm 3 and is 37.0% HCl by mass. What volume of concentrated hydrochloric acid is needed to prepare ml of a M hydrochloric acid solution? 21. If a L bottle of concentrated hydrochloric acid costs $25.15, and the distilled water is free, what is the cost of the solution you prepared in Problem 20? [NOTE: If you could not get an answer for Problem 20, use ml (not the actual amount) as the volume needed.] 22. After taking your Chemistry 31 Test, you decide to take a brief vacation in Seattle. On the return trip, while driving through Montana, you pull off the road to take a nap. After your nap, you walk around the car to stretch your legs before continuing the long drive back to Columbia. During your walk, you stumble over a large shiny rock (It has a mass of g.). You suspect it contains copper ore and decide to bring it home with you. While going through your mail after getting back to MU, you discover your large, and overdue, MasterCard credit card bill. You need money fast, so you check with your TA and she agrees to let you try to recover the copper from your rock, if you will pay for the chemicals that you use. Based on the solubility rules, you decide to dissolve the rock using the 3.50 L of M hydrochloric acid. Once again, you refer to the solubility rules and decide to add the 4.25 L of M sodium hydroxide to the solution in order to precipitate the dissociated copper ions as copper (II) hydroxide. After you decant the solution, you wash and dry the precipitate. Your efforts yielded g of copper hydroxide. What was the mass percent for copper in the rock? 23. The stockroom manager agreed to buy your copper (II) hydroxide at the going rate of $16.45 per g. After paying for the hydrochloric acid and sodium hydroxide that you used, what profit/loss did you have?

5 24. During a laboratory exercise, a stock solution of NaOH was standardized using the weak acid primary standard, (COOH) 2 2H 2 O, oxalic acid. Paper (g) Paper + (COOH) 2 2H 2 O (g) (COOH) 2 2H 2 O (g) mol (COOH) 2 2H 2 O At the titration s end-point, the phenolphthalein indicator changed color from to. During the titration, the student used the following amounts of NaOH: mol (COOH) 2 2H 2 O V NaOH (ml) M NaOH is the NaOH solution s molarity. The NaOH solution was then used as a secondary standard to determine the molarity of an vinegar -- acetic acid (CH 3 COOH (aq)) -- solution. CH 3 COOH (aq) (ml) M CH 3 COOH (aq) NaOH (aq) (ml) M NaOH (aq) is the CH 3 COOH solution s molarity. What is the mass percent of acetic acid in the vinegar? Assume the solution s density is 1.00 g/ml.