Interpretation
Estimate the pK4 of the acid has to be calculated.
Concept introduction:
UV/vis spectroscopy: It is deal with information about various compounds that have conjugated double, the UV light and visible light have jest the right energy to cause an electronic transition in a molecule that is to promote an electron from one molecular orbital to another higher energy.
Henderson-Hesselbalch equation: The acid lose a proton in an aqueous solution depends on the both the
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EBK ORGANIC CHEMISTRY
- Estimate the Ka of a weak acid from the data given below. One gram quantities of the acid were dissolved in equal quantities of the various buffer solutions and all solutions were measured under the same conditions. The anion of the acid is the only species that absorbs at the wavelength used. pH: Abs: 4 0.0 5 0.0 6 0.06 7 0.39 8 0.95 9 1.13 10 11 1.18 1.18arrow_forwardThe un-ionized form of the weak acid HA does not absorb in the visible region. When it ionizes, its conjugate base (A-) absorbs light strongly at 510 nm. The following data were obtained by measuring the absorbance at 510 nm of solutions with a concen- tration of 1.0 x 104 M HA in different pH buffers. pH Absorbance 2.0 0.00 3.0 0.00 4.0 0.00 5.0 0.025 6.0 0.180 7.0 0.480 8.0 0.570 9.0 0.595 10.0 0.595 11.0 0.595 12.0 0.595 What is the approximate pK of HA?arrow_forwardWhat is the absorbance of a 2.33×10−4M2.33×10−4M solution of a compound with a molar absorptivity of 1.05×103M−1cm−11.05×103M−1cm−1 in a 1.00 cm cell?arrow_forward
- Fe+3 (aq) + SCN – (aq) FeSCN +2 (aq) She mixes 4.00 mL of 2.00 mM SCN– and 5.00 mL of 2.00 mM Fe+3 ions, then diluting with 1.00mL of water to give a total volume of 10.00mL. She measures the absorbance of the solution asbeing 0.210. If she has previously calculated the molar absorbtivity constant (ε) of the product tobe 2583 cm–1 M–1, what is her best estimate for the K value for this reaction?arrow_forwardThe standard curve was made by spectrophotographic analysis of equilibrated iron(III) thiocyanate solutions of known concentration. You are asked to analyze a Fe(SCN)2+ solution with an unknown concentration and an absorbance value of 0.392. The slope-intercept form of the equation of the line is y = 4538.1x +0.0077. The unknown was analyzed on the same instrument as the standard curve solutions at the same temperature. What is the Fe³+ concentration of the unknown solution? [Fe³+] = mol/L Absorbance Iron(III) thiocynate standard curve 1.0 V 0.5 0.0001 Fe³+ concentration (M) 0 0.0002arrow_forwardOne common way to determine phosphorus in urine is to treat the sample, after removing the protein, with Mo (VI) and then reducing the resulting 12-molybdophosphate complex with ascorbic acid to give an intense blue colored species called molybdenum blue. The absorbance of molybdenum blue can be measured at 650nm. A 24-hour urine sample was collected and the patient produced 1122mL in 24 hours. A 1.00mL aliquot of the sample was treated with Mo(VI) and ascorbic acid and diluted to a volume of 50.00mL. A calibration curve was prepared by treating 1.00mL aliquots of phosphate standard solutions in the same manner as the urine sample. The absorbances of the standards and the urine sample were obtained at 650nm and the following results obtained: Solution Absorbance at 650nm: 1ppm P0.2302ppm P0.4363ppm P0.6384ppm P0.848Urine sample 0.518 How many grams of phosphorus were eliminated per day by the patient?arrow_forward
- Suppose that a solution has an absorbance of 0.250 at a wavelength of 450 nm. If the concentration of the solution is 22 μM, what is the value of the molar absorptivity? The data were taken with a standard 1-cm cuvette. molar absorptivity in (L cm^−1 mol^-1):arrow_forwardThe emission of quinine is observed to increase as the pH increases from pH 2.5 to 3.75 but is then observed to decrease at pH > 3.75. Suggest what may be happening to the molecule to account for this observation. Comment on the concentration of quinine in terms of EU limits.arrow_forwardBlue Blue dye stock solution 0.293 M Absorbance at 630 nm 0.00265 Calibration curve y = 0.0833x A solution is prepared by diluting 2.81 mL of the blue dye stock solution to 25.00 mL. The measure absorbance for the prepared solution is listed in the data table. (a) What is the theoretical molar concentration? [Blue]theoretical | × 10 |M (b) What is the experimental molar concentration? [Bluelexperimental x 10 M (c) What is the percent error? Percent error (blue) =arrow_forward
- Choose the correct answer from choices givenarrow_forwardYou have two solutions of the same compound that are blue. one is very pale and the other is very intense. Absorbance of each solution was measured with a spectrophotometer at the same wave length at which the solution absorbs. (A) Which solution has the higher absorbance? (B) Which is the more concentrated solution?arrow_forwardAn aqueous solution of a triphosphate derivative of molar mass 502 g mol-1, was prepared by dissolving 17.2 mg in enough water to make 500 cm3 of solution and a sample was transferred to a cell of length 1.00 em. The absorbance was measured as 1.011. Calculate (a) the molar absorption coefficient;(b) the transmittance. expressed as a percentage.for a solution of twice the concentration.arrow_forward
- Macroscale and Microscale Organic ExperimentsChemistryISBN:9781305577190Author:Kenneth L. Williamson, Katherine M. MastersPublisher:Brooks ColePrinciples of Instrumental AnalysisChemistryISBN:9781305577213Author:Douglas A. Skoog, F. James Holler, Stanley R. CrouchPublisher:Cengage Learning