Acid-Base and Buffer ChemistryExam Study Questions Chemistry 20L Spring 2005 During the exam you will be allowed to use a calculator, your lab notebook, your lecture guides and any hand-written materials that you want. Printed study questions and/or answers are not allowed. Review the pre-lab study questions even if they were not assigned. You should be able to answer all these questions now. Review the sidebar questions in the experiments. Review the experimental procedures. Error Analysis 1. Calculate the percent error for the following quantities (a) (20.54 ± 0.02)(0.254 ± 0.003)3.21± 0.05 (b) (30.078 ± 0.003) - (20.174 ± 0.001) + (9.813 ± 005) (c) [(0.642 ± 0.002) (2.413 ± 0.004)] - (0.501 ± 0.002) (d) 12.635± 0.005(5.967± 0.003) + (0.478 ± 0.004) 2. Calculate the absolute errors for the quantities in question 1. 3. Calculate the percent relative average deviation for the following set of data: 20.96, 20.85, 20.89, 20.92 Concentrations 4. Define the concentration terms molarity, normality, weight percent (w/w and w/v), PPM, pH. 5. When would it be appropriate to use each of the concentrations in question 1. What limitations are there with any of these concentrations? 6. An ethanol (C2H5O in water) solution was labeled as 1.00 x 10-3 M. What is this concentration in PPM, weight %, volume %? (Assume the density of water is 1.00 g/1.00 mL and the density of ethanol is 0.880 g/1.00 mL.) 7. A sulfuric acid solution was prepared by transferring 0.0196g of acid to a 1-L volumetric flask and diluting the solution to the mark. Calculate the concentration of acid in the solution. in all of the units in question 5. (Assume the sulfuric acid dissociates completely.) 8. A sodium hydroxide solution was prepared by transferring 0.4063g to a 100-mL volumetric flask and diluting the solution to the mark. A 10-mL aliquot of this solution was transferredto a 50-mL volumetric flask and the solution we diluted to the mark. Calculate the concentration of the final sodium hydroxide solution in all of the units in question 5. (Pay attention to significant figures. Remember the name of the flask does not designate its precision.) 9. A student made a standard solution by transferring 0.1037g of CuSO4.5H2O into a 100-mL volumetric flask, dissolving the salt and diluting to the mark. He then withdrew a 5-mL aliquot with a volumetric pipet and transferred it to a 100-mL volumetric flask. The solution was diluted to the mark and mixed well. Calculate the concentration of copper in parts per million. Since this is an aqueous solution you can assume a mL of solution weighs 1g. 10. If the tolerance of the balance is ±0.2 mg, the volumetric flask is ± 0.08 mL, and the pipet is ±0.01 mL, calculate the percent inherent error in the final diluted solution. Beer’s Law 11. Beer's Law is summarized by the equation A = εbc Name and define each of the symbols in this equation. 12. Calculate the percent transmittance of a solution if its absorbance is 0.352. 13. The following set of data was obtained for the calibration curve for a Beer’s Law experiment. Molarity Absorbance blank solution 0.0 9.80 x 10-5 0.240 1.96 x 10-4 0.475 3.10 x 10-4 0.741 Plot the data. (a) Calculate the slope of the line. (b) Calculate the inherent error in the slope of this line by determining the error bars on one of the points that was used to draw the line. Assume the error in the concentration is consistent with the rules outlined in Sec. III.1a and the error in the meter reading is ±1% (absolute) transmittance.(c) Calculate the concentration of a solution of this same compound if its absorbance were 0.500. (d) Calculate the inherent error in the concentration determined in (c) by considering the range of possible slopes from (b) above and the error in the meter reading for the measured absorbance of the unknown. Definitions 14. Define the following terms being careful to identify any differences or relationships between them. (a) End point and equivalence point (b) Volumetric and non-volumetric glassware (c) “Weak” coffee and “weak” acid (d) Absorbance and transmittance (e) Accuracy and precision Techniques 15, Briefly write a procedure for - preparing a 100-mL volumetric solution that contains 1.500 g of a primary standard. - transferring a 5-mL aliquot of a solution using a volumetric pipet. - reading a buret. - calibrating a pH meter Acid-Base and Buffer Chemistry 16. How many milliliters of 0.0400 M Ba(OH)2 are required to reach the equivalence point with 15.0 mL of 0.100 HCl? 17. What volume of 0.250 M H2SO4 is required to reach the equivalence point with 38.40 mL of 0.200 M NaOH? 18. What volume of 0.120 N H2SO4 is required to reach the equivalence point with 24.0 mL of 0.200 N NaOH?19. How many grams of barium hydroxide are contained in 250 mL of 0.0800 N Ba(OH)2 solution? 20. What weight of NaOH is required to neutralize 250 mL of 0.050 M HCl? 21. A sample of an organic acid weighing 0.3446 g was titrated to a penolphthalein end point with 41.51 mL of 0.1000 N NaOH. Calculate the equivalent weight of the acid. 22. Calculate [H+], pH, [OH-], and pOH in 0.030 M HCl. 23. Calculate [H+] and pH for each of the following solutions, and list the color that would be imparted to the solution by one drop of (i)bromocresol green, (ii) phenolphthalein. (a) 0.05 M HCl (b) 1.2 x 10-4 M HCl (c) 250 ppm HCl 24. Calculate [H+] and pH for each of the following solutions, and list the color that would be imparted to the solution by one drop of (i) methyl red, (ii) phenolphthalein. (a) 0.05 M NaOH (b) 1.3 M NaOH (c) freshly boiled water 25. What indicators would you select to produce a color change over each of the following ranges of [H+]? (a) from 1 x 10-3 to 5 x 10-6 (b) from 7 x 10-5 to 6 x
View Full Document
Unlocking...