PACS Elimination Questions I. Analytical Chemistry 1. A 516.7-mg sample containing a mixture of K2SO4 and (NH4)2SO4 was dissolved in water and treated with BaCl2, precipitating the SO42–as BaSO4. The resulting precipitate was isolated by filtration, rinsed free of impurities, and dried to a constant weight, yielding 863.5 mg of BaSO 4. What is the %w/w K2SO4 in the sample? 2. Chloride in a brine solution is determined by the Volhard method. A 10.00-mL aliquot of the solution is treated with 15.00 mL of standard 0.1182 M AgNO3 solution. The excess silver is titrated with standard 0.101 M KSCN solution, requiring 2.38 mL to reach the red Fe(SCN)2+ end point. Calculate the concentration of chloride in the brine solution, in g/L 3. The Phosphorus content in urine can be determined by treating the sample with a Mo +6 salt and then reducing the phosphomolybdate by reacting it to aminonaphtholsulfonic acid to give the characteristic blue color attributed to molybdenum-phosphorus complex. This absorbs at 690 nm. A patient with kidney problems attributed to elevated phosphates levels in the body excreted 1270 mL urine in the span of a day, and the pH of the urine was 6.5. A 1.00-mL aliquot of the urine sample was treated with molybdate reagent and aminonaphtholsulfonic acid and was diluted to a volume of 50.0 mL. A series of phosphate standards was prepared and treated similary. The absorbance of the solutions at 690 nm, measured against a blank, were as follows: Solution Absorbance 1.00 ppm P 0.205 2.00 ppm P 0.410 3.00 ppm P 0.615 4.00 ppm P 0.820 Urine sample 0.625 Determine the amount of phosphorous content excreted per day. II. Organic Chemistry 1. Draw the rotational energy diagram for the rotation of 3-methyl pentane around the C2-C3 bond. 2. Provide a mechanism for the following aldol reaction. 3. For each reaction shown below, indicate which energy level is used to predict the stereochemical outcome by shading the appropriate lobes of the entire orbital array. (The methyl groups are omitted for clarity; you do not have to draw them.) In the box under each reaction arrow, write conrotatory or disrotatory, as appropriate. In the box to the right of each reaction arrow, draw the major product of the reaction, clearly indicating the relative stereochemistry III. Biochemistry 1. The genetic data below is the DNA sequence of part of a theoretical fungal genome. a. Which strand of DNA shown is the template strand? b. What is the sequence of the mRNA produced from this gene? Label the 5’ and 3’ ends c. What is the sequence of the peptide produced from the mRNA in (b)? d. A mutation develops wherein a T/A (top/bottom) base pair were added immediately after the T/A base pair shown in bold, what would be the sequence of the mRNA? What would be the sequence of the peptide? 2. a. From 1c, what is the one letter symbol of the peptide? b. Will this give a positive result in the xanthoproteic test? c. Will this give a positive result in the Millon’s test? d. Will this give a positive result in the Hopkins-Cole test? e. Will this give a positive result in the reduced sulfur test? IV. Physical Chemistry 1. A sample consisting of 1 mol of perfect gas atoms (for which CV =32R) is taken through the cycle shown below. (a) Determine the temperature at the points 1, 2, and 3. (b) Calculate q, w, ∆U, and ∆H for each step and for the overall cycle. If a numerical answer cannot be obtained from the information given, then write in +, −, 0, or ? as appropriate. 2. Show that the work for the Van der Waals gas is W = −nRT lnV2 − nb V1 − nb – n2aV1 − V2 V2V1 3. A singly positively charged cation is involved in the activated complex of a reaction. Deduce the charge of the anion from the following data: I kr/kr0 0.005 0.995 0.01 0.925 0.015 0.875 0.02 0.835 0.025 0.800 0.03 0.770 V. Inorganic Chemistry 1. An irregularly shaped metal part made from a particular alloy was galvanized with zinc using a Zn(NO3)2 solution. When a current of 2.599 A was used, it took exactly 1 hour to deposit a 0.01123-mm layer of zinc on the part. What was the total surface area of the part? The density of zinc is 7.140 g/cm3. 2. Three drops of 0.20M KI are added to 100mL of 0.01M Pb(NO3)2. Will a precipitate of lead (II) iodide form? (Assume 1 drop = 0.05 mL) PbI2(s) ⇌ Pb2+(aq) + 2I-(aq) Ksp = 7.1x10-9 3. Determine the point group of the following molecules: a.
