Tables of data and equations are on the last pages of the exam.

Transcription

1 Nae 4 August 2005 CHM 112 Final Exa (150 pts total) Tables of data and equations are on the last pages of the exa. (1.) Methanol (CH 3 OH) is anufactured by the reaction of carbon onoxide with hydrogen in the presence of a ZnO/Cr 2 O 3 catalyst: ZnO/Cr 2O 3 CO(g) + 2 H 2 (g) ¾ CH 3 OH (g) H o = -91 kj Does the aount of ethanol increase, decrease, or reain the sae when an equilibriu ixture of reactants and products is subjected to the following changes? (15 pts) (a) The teperature in increased (b) The volue is decreased (c) Heliu is added (d) The catalyst is reoved

2 2 (2.) Consider the list of acids: (10 pts.) Acid K a CH 3 COOH HNO CHCl 2 COOH HOCl Which acid has the strongest conjugate base? Write the Lewis structure for this base. Write the reaction of this base with water. Would the ph of this conjugate base be greater than or less than 7? What effect causes the third acid to be uch stronger than the first acid?

3 3 (3.) The solubility of silver chroate, Ag 2 CrO 4, is M. What is the equilibriu constant (or) solubility product) for dissolving silver chroate? (5 pts) (4.) What is the ph of a solution prepared fro 3.52 g of aniline (a weak base), C 6 H 5 NH 2, and 200 L of water? (15pts)

4 4 (5.) You ay have heard of the ozone hole in the atosphere. A echanis for the destruction of ozone (O 3 ) is: (15 pts) O 3 O + O 2 O 3 + Cl ClO + O 2 ClO + O Cl + O 2 slow fast fast Write the balanced equation for this echanis. Write the rate law. What are the interediates (if any)? What are the catalysts (if any)?

5 5 (6.) Which of the following solutions will have the lowest freezing point? Support your answer with a calculation. Assue the volues of the solutions are the sae. a. 1 NaCl (aq) (10pts.) b. 1 CaBr 2 (aq) c. 1 Al(NO 3 ) 3 (aq)

6 6 (7. ) Identify the types of interolecular forces that are present in each of the following substances and select the substance in each pair that has the higher boiling point. (10 pts) a. C 6 H 14 or C 8 H 18 b. C 3 H 8 or CH 3 OCH 3 c. CH 3 OH or CH 3 SH d. NH 2 NH 2 or CH 3 CH 3 (8.) g of an unknown enzye was dissolved in water to ake L of solution. The osotic pressure was deterined to be Hg at 37 o C. What is the olar ass of the enzye? (10 pts)

7 7 (9.) Consider the electrocheical cell shown below: (20pts) The standard reduction potential, E o, of Ag + to Ag etal is V, and the reduction potential, E o, of Au 3+ to Au etal is 1.52 V. 1. Write the half reactions and the balanced equation for the reaction between Au and Ag How any electrons are transferred in this reaction? 3. Is the reaction spontaneous as written? 4. Write the reaction in the direction of spontaneous change (the way it would really go).

8 8 Proble 9 cont. 5. Label the anode and cathode and the direction of electron flow. 6. Given that G o = nfe o, where n is the nuber of electrons transferred, and F is a constant, 96500, calculate G o for the reaction. The units work to give joules. Do your G o value and E o values predict the sae direction for spontaneous change?

9 1/[N 2 O] [N 2 O] ln [N 2 O] (10.) At elevated teperatures, nitrous oxide decoposes according to the equation: (15 pts) 2 N 2 O (g) 2 N 2 (g) + O 2 (g) y = e x y = x tie (sec) tie (sec) y = 4E-05x x (a) Use the plots to deterine the order, the value of k and the half-life (t 1/2 ) (b) Write the rate law for the reaction (c) What is the initial concentration of N 2 O? {given the answer to 4 decial places} tie (sec) Please use the reverse side of this page for your answer.

10 (11.) Foric acid (HCO 2 H) is an organic acid secreted by ants. Calculate the ph and the concentrations of all species present (HCO 2 H, HCO - 2, H 3 O +, and OH - ) in 0.20 M HCO 2 H. Also calculate the % dissociation. (10 pts) (12.) Calculate the ph of a solution that contains 0.20 M foric acid and 0.50 M sodiu forate. (5 pts)

11 (13.) Describe the three definitions of acids and bases (with exaples) (10 pts) (a) Arrhenius Acids & Bases (b) Brønsted-Lowry Acids & Bases (c) Lewis Acids and Bases

12 oles total i oles P P nrtm RTM nk T k T nk T k T i solv solv so b b b b f f ln T R E A k kt A A k t kt A A a o o 1 ln ln ] [ 1 ] [ 1 ln 2 ] ln[ ] ln[ v v D D ) ( 3 ) ( ol kg RT or ol g RT v RMV

13 G o = -RT ln K G o = -nfe o G o = H o TS o ph = -log[h 3 O + ] poh = -log[oh - ] ph + poh = 14 pka + pkb = 14 [H 3 O + ][OH - ] = ph pk a [ A ] log [ HA ] Acid Dissociation Constants* pka Aonia, NH 3 H + (aka NH + 4 ) 4.75 Aniline, C 6 H 5 NH 2 H Foric acid, HCO 2 H 3.74 * Each acid is written in its protonated for. The acidic protons are indicated in bold type. K f (H 2 O) = K/olal K b (H 2 O) = K/olal R = L at ol -1 K -1 R = J ol -1 K -1