Example: Write the overall reaction and the rate law for the reaction that occurs in the following two steps. The second step is the rate determining step. I 2 k 1 k -1 2 I H 2 + 2 I k 2 2 HI
Example. Consider all possible mechanisms for 2 NO 2 + O 3 N 2 O 5 + O 2 rate law is rate = k[no 2 ][O 3 ]
Propose mechanism consistent with given rate law: 3 NO N2O + NO2 Rate Law: rate = k[no]2 t-bubr + OH - tbuoh + Br Rate law: rate = k[tbubr]
SN1 Substitution nucleophilic unimolecular CH3I + NaBr CH3Br + NaI (Me)(Et)CHBr + Cl- (Me)(Et)CHCl + Br- rate = k[ch3i] rate = k[(me)(et)chbr] SN2 Substitution nucleophilic bimolecular (Me)(Et)CHBr + HS - (Me)(Et)CHSH + Br - rate = k[(me)(et)chbr][hs - ]
7 1. Dinitrogen tetroxide (N2O4) is introduced into an empty container at an initial pressure of 1.00 atm. After the reaction is established, the total pressure in the container is found to be 1.62 atm. Calculate the pressure-based equilibrium constant, KP for this reaction. N 2 O 4 (g) 2 NO 2 (g) 2. For the following reaction, KC = 8.0 at a certain temperature. What is concentration of NOCl must be put into an empty reaction vessel in order to have an equilibrium concentration of NOCl of 1.00 M? 2 NOCl (g) 2 NO (g) + Cl 2 (g)
8 3. For the reactio below, the equilibrium constant at 700 C, K c is 0.534. Calculate the number of moles of H2 that are present at equilibrium if a mixture of 0.300 mole of CO and 0.300 mole of H2O is heated to 700 C in a 10.0 L container. H2 (g) + CO 2 (g) H 2O (g) + CO (g) 4. The equilibrium constant K c for the reaction below, is 2.18 x 10 6 at 730 C. Starting with 3.20 moles of HBr in a 12.0 L reaction vessel, calculate the concentrations of H 2, Br 2 and HBr at equilibrium. H 2 (g) + Br 2 (g) 2 HBr (g)
9 5. At a certain temperature, the equilibrium constant Kc for the decomposition of phosgene, COCl 2 is 5.6 x 10-6. Calculate the equilibrium concentrations of CO, Cl2, and COCl2 if 2.0 moles of COCl2 is placed in a 1.0 L container. COCl2 (g) Cl 2 (g) + CO (g) 6. The equilibrium constant, K c for the following reaction is 3.5 x 10 6 at a certain temperature. Calculate the amount of each gas present at equilibrium if a 1 mole of SO 2 and 1 mole of O 2 are placed in a 1.0 L container. 2 SO 2 (g) + O 2 2 SO 3 (g)
Chapter 15. Acids and Bases 15.1 Brønsted Acids and Bases Explain that C2H5OH is not a base. Need to get a recognizable ion/polyatomic ion with loss of OH Example What is the ph of a solution that is 0.00250 M HNO2 (aq)? The K a 10-4. is 7.2 x Percent Ionization - the more dilute the solution, the greater the % ionization; system responds to dilution by forming more ions. Thus cannot assume "x" is small here. more H2O pushes equilibrium to right (Le Chatelier's principle) HA (aq) + H 2 O H 3 O+ (aq) + A- (aq)
Example What is the ph of a 0.25 M solution of NH3?
Example The pkb value for cyanide ion, CN -, is 4.80. What molar concentration of NaCN is required to make a solution with a ph of 11.75? [answer: 2.0 M NaCN] 15.7 Relationship Between Ionization Constants of Acids and Their Conjugate Bases KaKb = Kw
15.8 Diprotic and Polyprotic Acids Example Ascorbic acid (vitamin C), H2C6H2O6, is an example of a diprotic acid with Ka 1 = 7.9 x 10-5 and Ka 2 = 1.6 x 10-12. For a 0.10 M solution of ascorbic acid, determine the ph and the concentrations of the mono anion, HC6H2O6 -, and the dianion, C 6 H 2 O 6 2-. (Let A -2 = C 6 H 2 O 6 2-, etc. ) H 2 A HA - + H + K a1 = [HA - ] [H + ] / [H 2 A] HA - A 2- + H + K a2 = [A 2- ] [H + ] / [HA - ] based on the first equilibrium: (details will be shown on blackboard) x = [H + ] [HA - ] and [H 2 A] = 0.10 - x 0.10 K a1 = 7.9 x 10-5 x 2 / (0.10) x 2.8 x 10-3 so, ph = 2.55 must use the 2nd equilibrium to find [A 2- ]: K a2 = [A 2- ] [H + ] / [HA - ] but, from above [H + ] [HA - ] K a2 [A 2- ] (a general result for H 2 A!) [A 2- ] 1.6 x 10-12
Give dual equation of H2CO3 dissociation to CO2 H2O vs acidity 1. (a) The conjugate acid of HPO3 2- (aq) is. (b) The conjugate base of HPO3 2- (aq) is. (c) The conjugate base of H2CF2 in nonaqueous solution is. 2. Write the reaction that occurs when the following are placed in water. (CH3)2NH2Cl C6H5COOH KClO2 3. Which of the above are acidic, basic, or neutral? 4. At 40 C, the ion product for water is K w = 2.92 x 10-14. Determine the ph of a 0.0035 M KOH solution at this temperature. Include a balanced chemical equation for the relevant equilibrium reaction.
5. (#50 Chapter 15) (a) Calculate the percent ionization of a 0.20 M solution of the monoprotic acetylsalicylic acid (aspirin), for which Ka = 3.0 x 10-4. (b) The ph of gastric juice in the stomach of a certain individual is 1.00. After a few aspirin tablets have been swallowed, the concentration of acetylsalicylic acid in the stomach is 0.20 M. Calculate the percent ionization of the acid under these conditions.
6. Write a balanced chemical equation to illustrate how the anion NO2 - acts as a weak base in aqueous solution. 7. Calculate the ph of a 1.00 L solution containing 0.150 mole CH 3 COOH and 0.100 mole HCl. 8. Among the following, circle the strongest Brønsted acid. HClO HClO 2 HClO 3 HBrO HBrO 2 HBrO 3 9. Among the following, circle the weakest Brønsted base. HS - HO - HSe - Br - F - Cl -
10. What is the ph of a 0.40 M solution of NH4CH3COO? 11. Is a solution of NaHCO3 acidic, basic or neutral? 12. Calculate the concentration of all the species in a 0.100 M Na2CO3 solution.
13. Is NH4NO2 acidic, basic, or neutral? Justify your answer with chemical reactions. Ka(HNO2, 4.5 x 10-4 ), Kb NH3, 1.8 x 10-5 )? 14. In the following reaction, write complete Lewis electron dot formulas for all reactants and products. Clearly indicate which reactant is the Lewis acid and which is the Lewis base. Use arrows to illustrate the formation and breaking of any bonds as the reaction goes from left to right. CH 3 SH + HOCN CH 3 SH 2 + + OCN -
Problems 1. (a) The pka of HF is 3.17. Calculate the ph of a 1.00-L solution that is 1.00 M HF and 1.50 M NaF. (b) What is the ph of this solution after addition of 50.0 ml of 10.0 M HCl?
2. What mass of solid NaCN must be added to 500 ml of 0.50 M HCN to prepare a buffer solution with a ph of 9.50? pka for HCN is 9.21.
Example Calculate the Ksp for calcium sulfate given that the solubility is 0.67g/L. CaSO 4 (s) Ca+2 (aq) + SO 4-2 (aq) Ksp = [Ca +2 ][ SO4-2 ] 0.67 g/ L x 1 mol CaSO 4 / 136.2 g = 4.9 x 10-3 mole/l K sp = [4.9 x 10-3 ][ 4.9 x 10-3 ] = 2.4 x 10-5 Example Given that the K sp for Ag 2 CO 3 is 8.1 x 10-12, determine the molar solubility. let x = molar solubility = moles Ag 2 CO 3 dissolved / liter Ag 2 CO 3 (s) 2 Ag + (aq) + CO 3 2- (aq)
Example C. Predicting Precipitation Reactions If 1.00 ml of 0.200 M NaOH is added to 1.00 L of 0.100 M CaCl2, will precipitation occur? (Ksp Ca(OH) 2 = 8.0 x 10-6)
16.8 Common Ion Effect Example (a) What is molar solubility of Ag2 CO 3 in 0.10 M Na 2 CO 3 given that Ksp for Ag2CO3 is 8.1 x 10-12? (b) What is the solubility in g/l?
1. Assuming equal concentrations of each of the following pairs of reagents, which one of the following mixtures is suitable for making a buffer solution with an optimum ph of 4.6 to 4.9. a. CH 3 COOH / CH 3 COONa (K a = 1.8 x 10-5 ) b. NH 3 / NH 4 Cl (K b = 1.8 x 10-5 ) c. HNO 2 / NaNO 2 (K a = 4.5 x 10-4 ) d. HOCl/ NaOCl (K a = 3.2 x 10-8 ) e. C 5 H 5 N / [C 5 H 5 NH]Cl (K b 1.7 x 10-9 ) f. any of these will satisfy the ph requirement 2. Assuming that equal volumes of each of the following solutions are mixed, which one forms a buffer solution? a. 0.50 M H 2 CO 3 and 1.00 M NaOH b. 0.50 M H 2 CO 3 and 1.50 M NaOH c. 1.00 M CH 3 NH 2 and 0.50 M KOH d. 0.50 M NaOH and 1.00 M HClO 2 e. 1.50 M Ba(OH) 2 and 3.00 M HF f. 1.50 M NaOH and 0.50 M HCl 3. SHOW ALL WORK. Calculate the ph of each of the following solutions. Include balanced chemical equations for any equilibrium reactions and clearly state any assumptions where appropriate. [Note: The K a value of HNO 2 is 7.1 x 10-4 ] a. Solution A: 1.25 M Ba(NO 2 ) 2 [ Note: This is barium nitrite! ] b. Solution B: 0.85 M HCl
c. Solution C: A mixture of 1.00 L solution A and 1.00 L of solution B.
4. Assume you are a TA for General Chemistry next fall and the instructor asks you to help with the lab prep. One of your first assignments is to make a buffer solution with a ph of 4.20. You are told to make approximately 1 liter of solution and that this can be done by mixing 500 ml of two reagents that are already available in the lab. Among these are the following: 1.0 M benzoic acid, C 6 H 5 COOH 1.0 M sodium chloride, NaCl 0.50 M sodium hydroxide, NaOH 0.5 M ammonia, NH 3 0.50 M sodium acetate, CH 3 COONa solid calcium hydroxide, Ca(OH) 2 Some useful information is the following: K sp Ca(OH) 2 = 1.3 x 10-6 ; K a, CH 3 COOH = 1.8 x 10-5 ; K a, C 6 H 5 COOH = 6.3 x 10-5 ; K b, NH 3 = 1.8 x 10-5 Which two solutions would you use? Use an equilibrium equation, an equilibrium expression, a concentration table, and simple calculations to fully and clearly justify your answer.
5. # 62. A volume of 75 ml of 0.06 M NaF is mixed with 25 ml of 0.15 M Sr(NO 3 ) 2. Calculate the concentration of NO 2 -, Na +, Sr 2+, and F - in the final solution.
6. Clearly state and justify any assumptions that you make. Calculate the molar solubility of CaF 2 in each of the following solutions. Note that these two parts can be worked independently. The answer for part a is not needed to solve part b. Given: K sp for CaF 2 = 1.7 x 10-10 K f for AlF 6 3- = 6.7 x 10 19 a. in H 2 O b. in 2.00 M Al(NO) 3
7. Many metal sulfides such as Ag 2 S (K sp = 6.0 x 10-51 ) are extremely insoluble. Silver ion, however, forms a variety of stable complex ions, including Ag(SCN) 4 3- (K f = 1.2 x 10 10 ). Calculate the molar solubility of Ag 2 S in a 1.50 M KSCN solution.
8. the K sp for Fe(OH) 2 is 7.9 x 10-16. The Fe 2+ ion forms the complex ion, [Fe(CN) 6 ] 4- with cyanide ion (K f = 1.0 x 10 24 ). What is the molar solubility of Fe(OH) 2 a. in H 2 O b. 3.0 M NaOH c. 3.0 M NaCN
Problem #145. Using the titration curve above which represents the titration of H 2 A with NaOH,identify the major species present at the marked points and estimate the pk a1 and pk a2.
1. Which of the following pairs are the same or which are enantiomers (nonsuperimposable mirror images)? H H H H H 3 C HO C Cl HO C Cl CH 3 CH 3 CH 2 CH 3 C Cl Cl C CH 3 CH 2 CH 3 2. In each of the boxes, indicate whether the compounds are the same CH 3 CH 2 CH CH 3 CH 2 CH 3 CH 3 CH 2 CH CH 2 CH 3 CH 3 CH 3 CH 3 CH CH 2 CH 3 O CH 2 CH 3 CH 3 CH 2 CH 2 O CH 2 CH 2 3. Name the following compounds. CH 3 CH 3 CH CH2 CH CH CH 3 CH3 CH 2 CH 2 CH 3 CH3 C O O O C CH 2 CH 2 CH 2 CH 3 O
H 3 C H 3 C CH CH CH CH C CH 3 CH 3 NH 2 O O CH 3 CH 2 CH CH C H O C CH 2 CH 3 CH 3 4. Write complete, specific structural formulas for all of the organic reactants and products in each of the following reactions. (a) aniline + 2-methylbutanoic acid an amide H (b) 2-phenylpropanal 2 H an alcohol + an alkene (reduction) (c) t-butyl acetate + NaOH two products O CH 3 O CH 3 H 3 C C O C CH 3 H 3 C C O Na + + H O C CH 3 CH 3 CH 3
5. A student in the second semester Organic Chemistry lab has tentatively identified her first unknown as a secondary alcohol. More specifically, she thinks it is 2,5-dimethylcyclo-pentanol, C 7 H 14 O (compound A). In order to confirm its structure, she carries out a series of chemical reactions to produce compounds B - G as summarized in the scheme below. (Note: The molecular formula of each compound is given.) A C 7 H 14 O H + H 2 O [O] No Reaction [O] HBr B C 7 H 12 HBr C C 7 H 14 O (an isomer of A) HBr E C 7 H 13 Br D C 7 H 12 O H 2 F C 7 H 13 Br (an isomer of E) A C 7 H 14 O acetic acid G (smells like an ester) C 9 H 16 O 2
6. Consider the molecule on the right from the viewpoint of bonding and structure concepts. The numbers below the formula refer to the individual carbon atoms in the following questions......... O Cl CH 2 C 1 2 3 (a) In the structure above, insert any lone electron pairs that are not shown. (b) What is the hybridization at each of the following atoms? C 1 sp 3 C 2 sp 2 C 3 sp 2 (c) What are the approximate bond angles around each of the following centers? C 1 109 C 2 120 C 3 120 (d) Are there any chiral centers in this molecule? If so, please list them. There are no chiral centers. 7. Complete the following reactions by giving the structural formula for the missing polymer or monomer. Indicate what type of polymerization is involved in each reaction. H 2 C C H type of polymerization: O CH 2 ring opening O CH 2 CH CH 2 n (b) CH 2 H C C N H C H H C C n N type of polymerization: addition (c) HO O C + C O OH H 2 N NH 2 O O C C N H N H n
8. Draw structural formulas in the appropriate boxes for the products of each the following reactions. OH H 2 C CH 2 CH 2 CH 3 H + + H 2 O [O] A B [O] D [O] C + NaOH E - H 2 O G + CH 3 OH + NaOH - CH 3 OH F
type of polymerization: condensation 1. Write the complete, systematic name of each of the following. (9 points) H 3 C CH CH C CH 3 H 3 C CH CH CH 3 2,4-dimethy-2,5-heptadiene O O C CH 2 CH 3 phenyl propanoate CH 3 CH 2 NH 2 O CH CH C H CH 3 3-amino-2-methylpentanal