+ IO 3 + 8I - 4. What is the concentration of I -, if 7.50 ml of a M solution of KI was diluted to a final volume of ml?

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1 Study Guide SCHM 109 for Vinegar titration, Kinetics, Equilibrium, Enzyme kinetics, & DNA I A. Review all pre-lab questions, reports and post-lab questions. B. Work the sample questions. Remember that all possible types of questions may not be represented. SHOW ALL WORK! Remember to use proper s.f. and units. Titration of Fake Vinegar In general: Be able to perform the four steps for the calculation of a titration. Review the experiment and your results. Know what was in the buret, what was in the titrating flask, the color of the indicator and in general how the titration was performed. 1. During a titration of a ml sample of acetic acid (CH 3 COOH), the endpoint was reached after adding ml of M NaOH. a) Write a balanced equation for this titration. b) How many moles of NaOH were added? c) How many moles of CH 3 COOH were present in the sample? d) What was the concentration of the CH 3 COOH in the sample? Kinetics: 1. Based on the following results for the reaction: A + B C Trial [A] (in M) [B] (in M) Average Rate (M s -1 ) Std. Dev E E E E E E E E E E E E-10 a) Write a general rate law for the reaction b) Calculate the order (n & m) of the reaction with respect to each reactant. c) Calculate k for the rate law using trial 1. d) Propose a specific rate law for this reaction. 2. For the reaction we studied: 6H IO 3 + 8I I 3 + 3H 2 O a) Which was the species used to follow the progress of the reaction? Why? b) Using Beer s Law (A = a b c) calc. the concen., c, (in M) for a sample reading A 353 = (a = 26,400 cm -1 M -1, b = 1.08 cm) 3. Given the following plot of concentration of I - 3 versus reaction time, determine the rate of the reaction. 1.80E-04 Production of I 3 - versus Time 1.60E E-04 y = 1.48E-06x E-06 R 2 = 9.96E E E-04 [I 3 - ] 8.00E E E E E Time (s) 4. What is the concentration of I -, if 7.50 ml of a M solution of KI was diluted to a final volume of ml?

2 Equilibrium: Review all the equilibria studied. Remember that heating and cooling can affect an equilibrium. Do you remember what exothermic and endothermic mean? 2-1. Given the following equilibrium: 2CrO 4 + 2H + 2- Cr 2 O 7 + H 2 O a) Adding sulfuric acid (H 2 SO 4 ) to the yellow chromate solution (CrO 2-4 ) results in a persisting orange color; explain the observed change. b) Write the equilibrium constant expression in terms of concentration of reactants and products. 2. Given the following data for the equilibrium: Fe 3+ + SCN - Fe(SCN) 2+ tube A 456 [Fe(SCN) 2+ ] Total [Fe 3+ ] Free [Fe 3+ ] Free [SCN - ] K eq E E E E-04 NA E E E E-04 a) Write the expression for the equilibrium constant K eq b) Find the values for the equilibrium constant for tube 2. Enzyme Kinetics Given information: A = abc b = 1.08 cm a =10,300 M -1 cm -1 (for benzoq. ) A = abc Student data for enzymatic conversion of catechol to benzoquinone by catechol oxidase. A, Absorbance values for given time Rate Tube Catechol Conc. 30 s 60 s 90 s 120 s (M/s) 1 10 mm mm E mm, no enzyme E mm, boiled enzyme E mm, with inhibitor E For the 10 mm sample, calculate the concentration of benzoquinone for each of the four time points. 2. Using the 30 s and 90 s data from the 10 mm catechol assay, calculate the approximate Rate (or [benzoquinone]/ t). Express your rate in [benzoquinone]/sec. 3. Calculate the relative % activity of your boiled enzyme. 4. Explain the results of question 3 in terms of protein structure. 5(a) Determine the maximum velocity of the enzyme from the graph. (b) At what catechol concentration was half-maximal activity obtained? Show the lines on graph that help in this determination. Reaction Rate (M/s) Enzyme Activity vs Catechol Concentration 3.50E E E E E E E E Catechol Concentration (mm)

3 6. Using the data from the accompanying graph, approximately how long of a boiling time was required to reduce enzyme activity to 20% of its original value? Show the lines on graph that help in this determination. Rate (M/s) 4.0E E E E E+00 Effect of Boiling on Enzyme Activity Time (s) DNA I 1. You should be able to draw or interpret a pedigree (family tree), especially as related to hemophilia. For example: what shape is used to represent a female? A male? A individual affect by a disease? 2. What places in a cell contain DNA? In each case, from whom is that DNA inherited? 3. What disease did Alexei of the Romanovs suffer from? What kind of protein does not function properly in individuals with this disease? 4. You should be able to determine some aspects of family relationships by comparing sets of sequences. For example, the table below contains bases from specific regions of mitochondrial DNA from Fred Genetico and four other people. Which people shown do not share the same maternal ancestor with Fred (a great grandmother of Fred s)? Explain. Comparing Bases Present in Particular Locations sample location 1 location 2 location 3 location 4 location 5 Philip T C C A T person 1 T C C A T person 2 T A G T C person 3 A G G C T person 4 T C C A T Some Answers! Titration of Fake Vinegar 1. During a titration of a ml sample of acetic acid (CH 3 COOH), the endpoint was reached after adding ml of M NaOH. a) Write a balanced equation for this titration CH 3 COOH + NaOH Na + CH 3 COO - + H 2 O Note: ratio or reactants is 1:1. b) How many moles of NaOH were added? (0.100 mol/l )( ml) ( ) = mol, rounds to mol NaOH c) How many moles of CH 3 COOH were present in the sample? mol NaOH) ( ) = mol, rounds to mol CH 3COOH d) What was the concentration of the CH 3 COOH in the sample? ( mol) / L = M, rounds to M CH 3 COOH

4 Kinetics: 1. Based on the following results for the reaction: A + B C a)write a general rate law for the reaction Rate = k[a] m [B] n b) Calculate the order (m,n) of the reaction with respect to each reactant. For determining m, compare trials 3 and 1. You must show the full work and find that m = 1. For determining n, compare trials 2 and 1. You must show the full work and find that n = 2. c) Calculate k for the rate law using trial E-08 = k(1.72e-03)( 1.38E-02) 2 Solve for k. The value for k = 5.95 x10-2 M -2 s -1 d) Propose a specific rate law for this reaction. Rate = 5.95x10-2 M -2 s -1 [A] [B] 2 2. b) Using Beer s Law (A = a b c) calc. the concen., c, (in M) for a sample reading A 353 = (a = cm -1 M -1, b = 1.08 cm) A = abc so c = A/(a x b) c = 0.042/ (26,400 x 1.08) = 1.5E-6 4. What is the concentration of I -, if 7.50 ml of a M solution of KI was diluted to a final volume of ml? Use M 1 V 1 = M 2 V 2 Answer is M Equilibrium: 2-1. Given the following equilibrium: 2CrO 4 + 2H + 2- Cr 2 O 7 + H 2 O a) Adding sulfuric acid (H 2 SO 4 ) to the yellow chromate solution (CrO 2-4 ) results in a persisting orange color; explain the observed change. H 2 SO 4 H HSO 4 This increases the concentration of H +. The collision rate between H + and CrO 2-4 increases. The rate of the forward reaction increases and the reaction shifts to the right. 2. Given the following data for the equilibrium: Fe 3+ + SCN - Fe(SCN) 2+ a) Write the expression for the equilibrium constant K eq K eq = [Fe(SCN) 2+ ] / ([Fe 3+ ][SCN - ]) b) Find the values for the equilibrium constant for tube 2. K eq = [1.97x10-6 ] / ([4.8x10-5 ][1.98x10-4 ]) = 207 Enzyme Kinetics 1. For the 10 mm sample, calculate the concentration of benzoquinone for each of the four time points. For the 30 s point, c =A/(ab) = 0.172/(10,300*1.08) = 1.55E-05 M For the 90 s point, c =A/(ab) = 0.564/(10,300*1.08) = 5.07E-05 M 2. Using the 30 s and 90 s data from the 10 mm catechol assay, calculate the approximate Rate (or [benzoquinone]/ t). Express your rate in [benzoquinone]/sec. Rate = (5.07E-05 M E-05 M)/(90 s -30 s) = 3.52E-05 M/60 s = 5.87E-07 M/s 3. Calculate the relative % activity of your boiled enzyme. Part/whole x100% 1.31E-07/7.22E-07 x 100% = 18.1% 4. Explain the results of question 3 in terms of protein structure. See answers to Enz. Kinetics post-lab question Using the data from the accompanying graph, approximately how long of a boiling time was required to reduce enzyme activity to 20% of its original value? Show the lines on graph that help in this determination.

5 Take the unboiled sample activity, 2.94E-07 and find 20% of that value or 5.88E-08. Locate that value on the y-axis and draw a horizontal line over to the graph line, then drop a vertical line to the x-axis and read the value. Should be ~14 seconds. DNA I 1. For example, what shape is used to represent a female? Circle 2. DNA is located in the nucleus and mitochondria. 3. What disease did Alexei of the Romanovs suffer from? hemophilia What kind of protein does not function properly in individuals with this disease? clotting factors 4. The table below contains bases from specific regions of mitochondrial DNA from Fred Genetico and four other people. Which people shown do not share the same maternal ancestor with Fred (a great grandmother of Fred s)? Explain. Comparing Bases Present in Particular Locations sample location 1 location 2 location 3 location 4 location 5 Fred T C C A T person 1 T C C A T person 2 T C G T T person 3 A C G C T person 4 T C C A T Persons 2 and 3 are not related to Fred Genetico. Their sequence differs from his at 2 or 3 locations. It would be seriously unlikely to have mutations at so many locations in a short stretch of mitochondrial DNA over a few generations time.