Read Microsoft Word - key2.doc text version

CHEM 1212 Test II MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) At 1000 K, the equilibrium constant for the reaction is Kp = 0.013. 2NO (g) + Br2 (g) 2NOBr (g) Calculate Kp for the reverse reaction, 2NOBr (g) 2NO (g) + Br2 (g). A) 1.6 x 10-4 B) 0.013 C) 77 D) 0.99

E) 1.1

2)

Consider the following chemical reaction: H2 (g) + I2 (g) 2HI (g) At equilibrium in a particular experiment, the concentrations of H2, I2, and HI were 0.15 M, 0.033 M, and 0.55 M, respectively. The value of Keq for this reaction is __________. A) 6.1 B) 111 C) 61 D) 23 E) 9.0 x 10-3 The Keq for the equilibrium below is 7.52 x 10-2 at 480oC. 2Cl2 (g) + 2H2O (g) 4HCl (g) + O2 (g) What is the value of Keq at this temperature for the following reaction? 4HCl (g) + O2 (g) 2Cl2 (g) + 2H2O (g) A) 0.150 B) 0.0752 C) -0.0752 D) 5.66 x 10-3

3)

E) 13.3

4)

The following equilibrium is readily established: SO2 (g) + Cl2 (g) SO2Cl2 (g) At equilibrium at 373 K, a 1.00-L reaction vessel contains 0.0106 mol of SO2Cl2 and 0.0287 mol each of SO2 and Cl2. What is Keq for the reaction at 373 K? A) 0.0777 B) 2.72 C) 12.8 D) 2.39 E) 0.418 Acetic acid is a weak acid that dissociates into the acetate ion and a proton in aqueous solution: HC2H3O2 (aq) C2H3O2- (aq) + H+ (aq) At equilibrium at 25oC a 0.100 M solution of acetic acid has the following concentrations: [HC2H3O2] = 0.0990 M, [C2H3O2-] = 1.33 x 10-3 M, and [H+] = 1.33 x 10-3 M. The equilibrium constant, Keq, for the ionization of acetic acid at 25oC is __________. B) 0.100 C) 1.75 x 10-7 D) 1.79 x 10-5 E) 5.71 x 104 A) 5.71 x 106 The equilibrium constant for the interconversion of PCl5 and PCl3 is 0.0121: PCl5 (g) PCl3 (g) + Cl2 (g) A vessel is charged with PCl5, giving an initial pressure of 0.123 atm. At equilibrium, the partial pressure of PCl3 is __________ atm. A) 0.123 B) 0.078 C) 0.033 D) 0.090 E) 0.045 The reaction below is exothermic: 2SO2 (g) + O2 (g) 2SO3 (g) Le Chatelier's Principle predicts that __________ will result in an increase in the number of moles of SO3 (g) in the reaction container. A) removing some oxygen B) decreasing the pressure C) increasing the pressure D) increasing the volume of the container

5)

6)

7)

8)

According to the Arrhenius concept, an acid is a substance that __________. A) reacts with the solvent to form the cation formed by autoionization of that solvent B) tastes bitter C) causes an increase in the concentration of H+ in aqueous solutions D) can accept a pair of electrons to form a coordinate covalent bond A Bronsted-Lowry base is defined as a substance that __________. A) acts as a proton acceptor B) decreases [H+] when placed in H2O C)acts as a proton donor D) increases [OH-] when placed in H2O E) amphoteric E) H+

9)

10) A substance that is capable of acting as both an acid and as a base is __________. A) miscible B) autosomal C) autocratic D) conjugated 11) The conjugate acid of HSO4- is A) HSO3+ B) SO42C) HSO4+ D) H2SO4

12) The magnitude of Kw indicates that __________ . A) water autoionizes only to a very small extent C) the autoionization of water is exothermic E) water autoionizes very quickly 13) In basic solution, __________. A) [OH-] > 7.00 D) [H3O+] < [OH-]

B) water autoionizes very slowly D) the autoionization of water is endothermic

B) [H3O+] = 0 M

C) [H3O+] > [OH-] E) [H3O+] = [OH-]

14) What is the pH of an aqueous solution at 25oC that contains 3.98 x 10-9 M hydronium ion? A) 3.980 B) 8.400 C) 5.600 D) 9.000 E) 7.000 15) Calculate the concentration (in M) of hydronium ions in a solution at 25oC with a pOH of 4.223. A) 1.00 x 10-7 B) 1.67 x 10-10 C) 5.98 x 10-5 D) 5.99 x 10-19 E) 1.67 x 104 16) Nitric acid is a strong acid. This means that __________. A) HNO3 does not dissociate at all when it is dissolved in water B) HNO3 cannot be neutralized by a weak base C) HNO3 dissociates completely to H+(aq) and NO3-(aq) when it dissolves in water D) HNO3 produces a gaseous product when it is neutralized E) aqueous solutions of HNO3 contain equal concentrations of H+(aq) and OH-(aq) 17) Of the following, __________ is a weak acid. A) HF B) HCl C) HClO4 D) HBr E) HNO3 E) 4.3 x 10-8

18) The pH of a 0.10-M solution of a weak base is 9.82. What is the Kb for this base? B) 2.1 x 10-4 C) 2.0 x 10-5 D) 6.6 x 10-4 A) 8.8 x 10-8

19) The acid-dissociation constant, Ka, for gallic acid is 4.57 x 10-3. What is the base-dissociation constant, Kb, for the gallate ion? A) 4.57 x 10-3 B) 2.19 x 102 C) 5.43 x 10-5 D) 7.81 x 10-6 E) 2.19 x 10-12 20) Of the following, which is the strongest acid? A) HClO2 B) HIO C) HClO4 D) HClO3 E) HClO

21) An acid containing the -COOH group is called a __________. A) double oxoacid B) carbonaceous acid D) carbo-oxo acid 22) In the reaction BF3 + FBF4-

C) strong acid E) carboxylic acid

BF3 acts as a(n) __________ acid. A) Bronsted-Lowry C) Lewis D) Arrhenius

B) Arrhenius, Bronsted-Lowry, and Lewis E) Arrhenius and Bronsted-Lowry

23) The pH of a solution that contains 0.818 M acetic acid (Ka = 1.76 x 10-5) and 0.172 M sodium acetate is __________. The Ka of acetic acid is 1.76 x 10-5. A) 8.568 B) 8.370 C) 5.432 D) 9.922 E) 4.077 24) The addition of hydrofluoric acid and __________ to water produces a buffer solution. A) NaCl B) HCl C) NaF D) NaBr E) NaNO3

25) A 25.0-mL sample of an HCl solution is titrated with a 0.139 M NaOH solution. The equivalence point is reached with 15.4 mL of base. The concentration of HCl is __________ M. A) 0.267 B) 0.0856 C) 0.00214 D) 11.7 E) 0.139

Problems 1) (5 points) For the following reaction, C6H12O6(s) + 6 O2(g) 6 CO2(g) + 6 H2O(l) How is the equilibrium yield of C6H12O6 affected by: HOMEWORK!!! a) increasing PCO2 Increases C6H12O6 (to the right) b) removing CO2 Decreases C6H12O6 (to the left)

c) decreasing total pressure No change 2) (10 points) Codeine (C18H21NO3) is a weak organic base. A 5.0 x 10-3M solution of codeine has a pH of 9.95. Calculate the value of Kb for this substance. What is the pKb for this base? HOMEWORK!!! C18H21NO3 + H2O C18H21NO3H+ + OH-

5.0 x 10-3M Codeine, pH = 9.95 need pOH, so 14 = pH + pOH 14 = 9.95 ­ pOH by stoichiometry: [C18H21NO3H+] = [OH-] and [C18H21NO3]eq = 0.0050 - [OH-] initial equilibrium C18H21NO3 0.0050M 0.0050 -10-4.05 C18H21NO3H+ 0 10-4.05 OH0 10-4.05

calculating yields: initial equilibrium C18H21NO3 0.0050M 0.00491 C18H21NO3H+ 0 0.0000891 OH0 0.0000891

Kb = =

[C

18

[0.0000891][0.0000891] [0.00491]

H 21 NO 3 H + OH - [C18 H 21 NO3 ]

][

]

= 1.62 × 10 - 6 pK b =- log K b = - log(1.62 × 10 - 6 ) = 5.79

3) (10 points) A buffer consisting of H2PO4- and HPO42-, helps control the pH of physiological fluids. Many carbonated soft drinks also use this buffer system. What is the pH of a soft drink in which the buffer ingredients are 6.5g of NaH2PO4 and 8.0g of Na2HPO4 per 355 mL of solution? (Ka = 6.2 x 10-8) HOMEWORK!!! Calculate the concentration of each buffer component, and then use the HendersonHasselblock equation to determine the pH of the solution.

MH

- 2 PO4

8 .0 g 1 = 142 g / mol 0.355L = 0.159 M 6.5g 1 = 120 g / mol 0.355L = 0.153M

MH

2- 2 PO 4

[base] pH = pK a + log [acid ] 0.153 = - log(6.2 × 10 -8 ) + log 0.159 = 7.22

Information

Microsoft Word - key2.doc

5 pages

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate

827079


Notice: fwrite(): send of 206 bytes failed with errno=104 Connection reset by peer in /home/readbag.com/web/sphinxapi.php on line 531