CHE311 Analytical Chemistry Quizzes Collection.pdf

Overall 1 The University of Southern Mississippi Department of Chemistry and Biochemistry CHE 311 Analytical Chemistry...

Overall 1 The University of Southern Mississippi Department of Chemistry and Biochemistry CHE 311 Analytical Chemistry Chapter Quizzes This set of quizzes of CHE 311-Analytical Chemistry are collected from the website associated with “Quantitative Chemical Analysis”, 8th Ed, Daniel C. Harris/W.H. Freeman. Each chapter comes with a number of multiple choice-type questions. Understanding each of these questions is crucial for this course, particularly for preparing the ACS standardized exams. You are strongly encouraged to work on ALL of them and use them to test your knowledge or guide you on reviewing specific chapters. A few of the same or similar questions might be chosen for the course examinations. 1  Department of Chemistry and Biochemistry Overall 2 University of Southern Mississippi CHE 311 Class Practice Chapter 00 -Analytical Process and Sampling 1 of 15 A chemical firm was hired to monitor a nearby lake for possible mercury contamination. Several samples were taken at different locations around the lake, including water samples, lake bottom samples, and plant samples. When the chemist returned to the laboratory, the water samples were the first to be analyzed. The analysis began by removing a number of aliquots. An aliquot is (a) a measure of the contamination of the lake water. (b) a combined measure of the contamination in the lake. (c) a precise liquid sample taken for analysis. 2 of 15 The sampling technique is very important when analyzing a large area or vast amounts of material because you cannot analyze everything. When preparing a composite sample, a chemist would (a) take several samples at random from pre-planned locations in the bulk sample and analyze each. (b) take representative samples from various areas of the bulk samples and combine them for analysis. (c) analyze as much of the bulk sample as possible. 3 of 15 The steps in a chemical analysis are (a) 1. Formulate the question. 2. Select the analytical procedure. 3. Sample. 4. Prepare the sample. 5. Make replicate measurements of the sample. (b) 1. Select the analytical procedure. 2. Sample. 3. Prepare the sample. 4. Make replicate measurements of the sample. 5. Make a clear and complete written report of your findings. (c) 1. Formulate the question. 2. Select the analytical procedure. 1  Overall 3 3. Sample. 4. Prepare the sample. 5. Make replicate measurements of the sample. 6. Make a clear and complete written report of your findings. 4 of 15 A chemist following a procedure carefully was asked to decant a solution. This means (a) stir the solution thoroughly to suspend the solids and pour the mixture into a filtering apparatus. (b) allow any solid material to settle to the bottom of the flask, and then pours off the liquid above the solution. (c) pour the solution from one flask to another. 5 of 15 A sample is said to be homogeneous if (a) the sample is the same throughout. (b) the sample has a different composition in different parts of the sample. (c) the sample can be separated into the individual components by filtering the sample. 6 of 15 When performing an analysis a chemist often uses a standard solution. What is a standard solution? (a) A solution that complies with standards established by the Environmental Protection Agency. (b) A solution that has a concentration of a chemical that is known to a high degree of certainty. (c) A solution that is prepared from a chemical that has been designated as a primary standard. 7 of 15 2  Overall 4 In discussing quantitative and qualitative analysis one could say (a) the two terms are commonly used interchangeably. (b) quantitative analysis deals with determining what materials may be present in a sample. (c) quantitative analysis deals with the quantity of a material present in a sample. 8 of 15 The term masking generally refers to (a) removing any material that may interfere with an analysis. (b) the transformation of an interfering species into a form that is not detected. (c) selecting samples from which the identity has been masked. This procedure prevents the analyst from prejudging the outcome of the analysis. 9 of 15 Interference occurs (a) when a species other than the analyte causes an analysis to be inaccurate. (b) when the analyte is precipitated from a non-homogeneous solution. (c) when two or more methods used for separating species interfere with each other. 10 of 15 Which of the following statements is incorrect? (a) A bulk sample is taken from a lot. (b) A bulk sample is taken from a laboratory sample. (c) A bulk sample is also called a gross sample. 11 of 15 A quantitative transfer is (a) a complete transfer of material. (b) a liquid transfer using a pipette. 3  Overall 5 (c) a powder transfer using a spatula. 12 of 15 A detector response may be different for analytes with equal concentrations; therefore, (a) quantitative analysis is impossible. (b) a calibration curve must be constructed. (c) more samples must be analyzed. 13 of 15 The uncertainty in the measurement is as important as the (a) samples selected. (b) as the samples procured. (c) measurement itself. 14 of 15 Analysis of an unknown sample is meaningless unless you have (a) collected the sample properly. (b) collected the sample properly, taken measures to ensure the reliability of the analytical method, and communicated your results clearly and completely. (c) collected the sample properly and taken measures to ensure the reliability of the analytical method. 15 of 15 In a random heterogeneous material, (a) differences in composition occur randomly and on a fine scale. (b) large regions have obviously different compositions. (c) samples are collected by taking portions from the desired number of segments chosen at random. 4 Keys: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 c b c b a b c b a b a b c b b  Overall 6 Department of Chemistry and Biochemistry University of Southern Mississippi CHE 311 Class Practice Answer Sheet: Name__________________________ USM ID________________________ Date___________________________ Q 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A 1  Department of Chemistry and Biochemistry University of Southern Mississippi Overall 7 CHE 311 Class Practice Chapter 01-Chemical Measurements 1 of 17 A chemist is beginning to prepare 100.0 mL of a solution to be labeled "0.900% (wt/vol) sodium chloride." To prepare this solution, the chemist would (a) weigh 0.900 grams of sodium chloride into a container and add 100.0 mL of water to dissolve the sodium chloride. (b) weigh 0.900 grams of sodium chloride into a container, add water to dissolve the sodium chloride, and then add water to produce 100.0 mL of solution. (c) weigh 9.00 grams of sodium chloride into a container, dissolve the sodium chloride in water, and then add water to produce 100.0 mL of solution. 2 of 17 A solution is prepared by dissolving 25.8 grams of magnesium chloride (MgCl 2) in water to produce 250.0 mL of solution. Calculate the molarity of the chloride ion in the solution. (a) 0.271 molar (b) 1.08 molar (c) 2.17 molar 3 of 17 The Great Salt Lake, located in the state of Utah, is approximately eight times saltier than the ocean. The salinity of the lake is said to occasionally be as high as 27 parts per thousand (ppt) sodium chloride. Calculate the molarity of the sodium ion in the Great Salt Lake. (a) 4.6 x 10-4 molar (b) 0.46 molar (c) 1.2 molar 4 of 17 The ethyl alcohol content of many beers produced in the United States is 4.05% (vol/vol). If the density of ethyl alcohol at room temperature is 0.7893 grams/mL, what is the percent of ethyl alcohol in beer expressed as percent (wt/vol)? (a) 3.20% ethyl alcohol (wt/vol) 5  Overall 8 (b) 5.13% ethyl alcohol (wt/vol) (c) 7.80% ethyl alcohol (wt/vol) 5 of 17 An analytical procedure required the preparation of a solution containing 100.0 ppm chromium. How many grams of potassium dichromate (K 2Cr2O7) would be required to prepare 1.000 liter of this solution? (a) 0.2829 grams (b) 0.1000 grams (c) 0.5658 grams 6 of 17 Calculate the formal concentration of a sodium acetate solution prepared by diluting 45.0 mL of a solution containing 25.0 ppm sodium acetate (NaC2H3O2) to a total of 0.500 liters of solution. (a) 6.10 x 10-4 molar (b) 1.37 x 10-6 molar (c) 2.75 x 10-5 molar 7 of 17 Certain chemical compounds are given the label strong electrolyte. This means (a) that the compound consists of atoms bonded together by bonds that are considered primarily covalent. (b) that the compounds, when dissolved in water, dissociate into ions that will strongly inhibit the conduction of electricity. (c) that the compounds dissociate into ions when dissolved in water and facilitate the conduction of electricity through the water. 8 of 17 When concentrated sulfuric acid is sold to the chemist, the label contains no mention of the molarity of the acid. Instead, the label normally lists the concentration of sulfuric acid as a 6  Overall 9 wt/wt percent and the density of the sulfuric acid solution. If the solution is 98.0 (wt/wt %) sulfuric acid and has a density of 1.80 g/mL, calculate the molarity of concentrated sulfuric acid. (a) 18.0 molar (b) 18.4 molar (c) 10.0 molar 9 of 17 The concentration term parts per million is defined as (a) (the weight of the solute/the volume of the solution) x 10 6. (b) (the weight of the solute/the weight of the solution) x 10 6. (c) (grams of the solute/liters of solution). 10 of 17 A solution was prepared by diluting 10.0 mL of a 1.00 x 10-3 molar solution of potassium dichromate to 100.0 mL. What is the concentration of chromium in the new solution in parts per million? (a) 10.4 ppm (b) 104 ppm (c) 5.20 ppm 11 of 17 During the late 1800's, hard rock miners replaced candles with carbide lamps for work in mine shafts. The lamps worked by dripping water onto calcium carbide that generated acetylene gas (H2C2) that was burned. If the reaction is CaC2 + 2H2O H2C2 + Ca(OH)2, how many liters of acetylene gas at 1.00 atm pressure and 0.00 °C are produced from 75.0 grams of calcium carbide (CaC2)? (a) 13.1 L (b) 26.2 L (c) 52.4 L 12 of 17 7  Overall 10 In the analysis of iron in a local water well, 500.0 mL of the water sample was poured through a Jones reductor to convert the iron present to the Fe2+ oxidation state. The resulting sample required 1.05 mL of 0.0110 molar KMnO4 to react with the iron present. What is the wt/vol % of iron in the well water? The reaction is 5Fe2+(aq) + MnO4-(aq) + 8 H+(aq) 5 Fe3+(aq) + Mn2+(aq) + 4 H2O. (a) 1.29 x 10-4 % (b) 6.45 % (c) 6.46 x 10-4 % 13 of 17 In a 0.001 M aqueous solution of NaCl, the solvent is (a) NaCl. (b) H2O (c) Not able to be determined from the information given. 14 of 17 A 250.0 mL sample is concentrated for analysis to 25.0 mL. What is the correct expression for the new concentration? (a) [sample] x (25.0 mL/250.0 mL) (b) [sample] x 100 (c) [sample] x (250.0mL/25.0 mL) 15 of 17 Anhydrous, primary standard sodium thiosulfate can be prepared from the pentahydrate, Na2S2O3 5H2O. How many grams of primary standard should be dissolved in 500.0 mL of water to make a 0.040 M solution? (a) 5.0 grams (b) 3.2 grams (c) 20 grams 16 of 17 8  Overall 11 Given the reaction below, how many grams of KI are needed to produce 1.0 g of the yellow solid PbI2 2KI + Pb(NO3)2 PbI2(s) + 2KNO3 (a) 5.5 grams (b) 0.36 grams (c) 0.72 grams 17 of 17 The Environmental Protection Agency (EPA) allowable amount of arsenic in US drinking water is 10 ppb. Express the ppb concentration in molarity. (a) 1.3 x 10-4 molar (b) 1.3 x 10-7 molar (c) 1.3 x 10-8 molar 9  Overall 12 Keys for Chapter 01 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 b c b a a c c a b a b c a c a c b  Overall 13 /// c Overall 14 Overall 15  Overall 16 ///// XX (C) NOT CORRECT Overall 17 Overall 18 Overall 19 Overall 20 Overall 21 Overall 22 Overall 23 Overall 24  Overall 25 Department of Chemistry and Biochemistry University of Southern Mississippi CHE 311 Class Practice Answer Sheet: Chapter____04___________ Name__________________________ USM ID________________________ Date___________________________ Q 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A 1  Overall 26 Chapter 04-Statistics 1 of 17 When an analytical chemist uses the word precision when referring to the data obtained from an analysis, the chemist is talking about (a) how close the mean obtained from a set of data is to the true value of the composition of the sample analyzed. (b) relative error calculated from the mean of a set of data. (c) how close the individual data points obtained from a set of data are to each other. 2 of 17 A government chemist has performed a gravimetric analysis for chloride ion on a sample submitted to the laboratory. The following results were obtained: Sample Percent Chloride Ion 1 27.46 2 27.52 3 27.48 4 27.10 When reporting the standard deviation, the analyst said that (a) approximately 68.3% of the data points lie between 27.19 and 27.59 percent chloride. (b) approximately 75% of the data points lie between 27.46 and 27.52 percent chloride. (c) approximately 68.3% of the data points lie between 27.29 and 27.49 percent chloride. 3 of 17 A government chemist has performed a gravimetric analysis for chloride ion on a sample submitted to the laboratory. The following results were obtained: 19  Overall 27 Given the following data: What is the 98% confidence interval for this set of data? (a) 27.39±0.37 (b) 27.39±0.52 (c) 27.39±0.45 4 of 17 The following data were collected when performing a spectrophotometric analysis for chromium: Analysis # mg Cr/Liter Absorbance 1 5.23 0.095 2 10.52 0.198 3 15.41 0.295 ? 0.265 Using the least squares method of linear regression, the following equation was determined to define the line generated by plotting concentration vs. absorbance: y = 0.0196x - 0.008 Which of the following statements is correct? (a) This equation represents the statistical best fit of a line drawn through the data points. (b) The amount of unknown in the sample may be determined by substituting the absorbance value of the unknown for x in the equation and solving for the y value. (c) The value 0.0196 represents the value on the y axis where the line crosses this axis. 5 of 17 The following data were collected when performing a spectrophotometric analysis for chromium: Analysis # mg Cr/Liter Absorbance 20  Overall 28 1 5.23 0.095 2 10.52 0.198 3 15.41 0.295 Unknown ? 0.265 Using the least squares method of linear regression, the following equation was determined to define the line generated by plotting concentration vs. absorbance: y = 0.0196x - 0.008. The concentration of chromium in the sample was found to be (a) 13.11 mg Cr/L. (b) 2.81 mg Cr/L. (c) 13.93 mg Cr/L. 6 of 17 If one has a Gaussian distribution of data points, (a) approximately two thirds of the data points lie above the mean, and one third of the data points lie below the mean accounting for all of the data points. (b) approximately 2/3 of the data points lie within plus or minus two standard deviations of the mean. (c) Approximately 2/3 of the data points lie within plus or minus one standard deviation of the mean. 7 of 17 A Gaussian distribution of data is symmetric if (a) 4.5% of measurements lie outside the range defined by 2 standard deviations above the mean, and two standard deviations below the mean. (b) 4.5% of measurements lie outside the range defined by 2 standard deviations above the mean, and two standard deviations below the mean with 2.25% of the values above 2 standard deviations from the mean and 2.25% of the values below 2 standard deviations from the mean. (c) 68.3% of the measurements lie within plus or minus one standard deviation from the mean. 8 of 17 21  Overall 29 The degrees of freedom used to calculate the confidence interval are (a) the number of data points which are being evaluated. (b) the number of data points - 1. (c) the value associated with the number of data points used to determine the value of t. 9 of 17 A spectrometer was used to measure the light absorbed by three standard solutions containing different concentrations of K2Cr2O7. The following data were obtained: The equation of the straight line generated using the method of least squares is (a) y = 0.0331x - 0.0079 (b) y = 30.24x + 0.242 (c) y = -0.0079x + 0.0331 10 of 17 A spectrometer was used to measure the light absorbed by three standard solutions containing different concentrations of K2Cr2O7. The following data was obtained: The equation of the straight line generated using the method of least squares is y = 0.0331x - 0.0086. Use this information to find the standard deviation of the slope of the line expressed to the proper number of significant figures. (a) m = 0.033(± 0.0004) (b) m = 0.0331(± 0.0045) (c) m = 0.0331(± 0.0001) 11 of 17 22  Overall 30 The following standardization curve was prepared by plotting light absorbed on the y axis and ppm Cr on the x axis. You have 100 mL of an unknown sample of solution containing K 2Cr2O7. You remove 2.00 mL and dilute it to 100 mL with 0.5 M H2SO4. You further dilute this mixture, 10 to 100 mL with the same H2SO4 solution. The resulting solution had an absorbance of 0.20. How many milligrams of chromium were in your original unknown sample? (a) 100 ppm Cr (b) 5000 mg Cr (c) 500 mg Cr 12 of 17 When analyzing the iron content of a well drilled for use in a new housing development, water from the well was analyzed on three different days. The following data were obtained: The pooled estimate of the standard deviation of the analysis is (a) 0.14 mg Fe/L. (b) 0.072 mg Fe/L. (c) 0.076 mg Fe/L. 13 of 17 23  Overall 31 Given the following titration data, correctly report the average and standard deviation for the volume of NaOH: (Trial 1) 25.60 mL, (Trial 2) 25.75 mL, and (Trial 3) 25.85 mL. (a) 25.73 ± 0.1 mL (b) 25.7 ± 0.13 mL (c) 25.7 ± 0.1 mL 14 of 17 Police have a hit-and-run case and need to identify the brand of red auto paint. What statistical test might they perform? (a) Q test (b) t test (c) F test 15 of 17 Police have a hit-and-run case and need to identify the brand of red auto paint. The percentage of iron oxide, which gives paint its red color, found during analysis is as follows: 43.15, 43.81, 45.71, 43.23, 42.99, and 43.56%. What is the average percentage of the iron oxide in the paint sample? (Hint: use a 90% confidence level) (a) 43.35% (b) 43.74% (c) 43.90% 16 of 17 Police have a hit-and-run case and need to identify the brand of red auto paint. The percentage of iron oxide, which gives paint its red color, was determined to be 43.3 5 ± 0.33% by one method of analysis using five measurements. The color reference provided by the automotive manufacturer is 44.21%. What can you conclude about whether the sample matches the reference at a 95% confidence level? (a) The sample matches the reference. (b) The sample does not match the reference. (c) There are an insufficient number of trials to determine if the sample is a match. 24  Overall 32 17 of 17 Police have a hit-and-run case and need to identify the brand of red auto paint. The percentage of iron oxide, which gives paint its red color, was analyzed by two different methods. The results were 43.3 ± 0.33% and 43.6 ± 0.14% with five measurements each. Are the standard deviations "significantly" different from each other a 95% confidence level? (a) Yes (b) No (c) Possibly 25  Overall 33 Department of Chemistry and Biochemistry University of Southern Mississippi CHE 311 Class Practice Answer Sheet: Chapter______05_________ Name__________________________ USM ID________________________ Date___________________________ Q 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A 1  Overall 34 Chapter 05-Quality Assurance and Calibration Methods 1 of 19 Often the analyst will compare known quantities of analyte to unknown quantities of the material to be analyzed. This may be done in one of three ways: use calibration curves; use standard additions; or use internal standards. The method of standard additions would be used when (a) the standard solutions and the unknown solution all have similar characteristics and are unaffected by the other material in the sample. (b) the quantity of sample analyzed or the instrument response varies from run to run. (c) the sample composition is unknown or complex and affects the analytical signal. 2 of 19 Which of the following is true regarding the matrix effect? (a) The matrix effect is normally minimized when a careful calibration curve is prepared. (b) The matrix effect is defined as the change in the analytical signal caused by the sample and the analyte. (c) The matrix effect may be minimized by using the method of standard additions. 3 of 19 An analysis for iron was done using an atomic absorption spectrophotometer and the method of standard additions. When the concentration of added iron (in ppm) was plotted on the x axis and the light absorbed was plotted on the y axis, the following graph was obtained: The concentration of iron in the unknown is (a) -4.00 ppm iron (b) 0.100 ppm iron 26  Overall 35 (c) 4.00 ppm iron 4 of 19 The content of manganese in steel was found using atomic absorption and the method of standard additions. A standard solution of manganese containing 95.5 ppm Mn was prepared for the analysis. The steel sample was dissolved in dilute nitric acid, placed in a volumetric flask, and diluted to 100.0 mL. When this sample was introduced into the spectrophotometer, the light absorbed was indicated by an absorbance of 0.185. A second sample for analysis was prepared by pipeting 5.00 mL of the standard Mn solution and 50.0 mL of the steel sample into a 100.0 mL volumetric flask and diluting to 100.0 mL. The light absorbed by this sample was indicated by an absorbance of 0.248. Calculate the concentration of manganese in the original 100.0 mL of the dissolved steel. (a) 5.68 ppm Mn (b) 9.55 ppm Mn (c) 140 ppm Mn 5 of 19 A solution was prepared by mixing 5.00 mL of an unknown solution containing Fe3+ with 5.00 mL of standard K2Cr2O7 containing 9.50 ppm Cr and diluting to 50.0 mL. When the absorption by the Cr and Fe present were measured with an atomic absorption instrument, the light absorbed by the Fe was recorded as 1.15 and the Cr was recorded as 0.93. Because the iron was being analyzed by adding an internal standard, a second experiment was required where known quantities of Fe and Cr were analyzed. In this experiment it was found that the ratio of Fe light absorbed to Cr light absorbed was 0.86. The ratio of the Fe concentration to Cr concentration was 1.34. Find the concentration of Fe in the unknown. (a) 18.3 ppm Fe (b) 1.43 ppm Fe (c) 36.6 ppm Fe 6 of 19 A solution containing 1-pentanol was sent to the laboratory to be analyzed utilizing a high performance liquid chromatograph. The analyst decided to use the method of internal standards for the analysis, with 1-hexanol as the internal standard. The first solution contained a ratio of 2.54:1 pentanol to hexanol. When the chromatogram was run, the peak area of the pentanol was found to be 4,320, and the peak area of the hexanol was found to be 4,156. When the unknown was run, a solution containing 1.00 mL of the unknown pentanol was mixed with 5.00 mL of 1.42 mM hexanol, and the resulting solution was 27  Overall 36 diluted to 10.0 mL. The area of the pentanol peak was found to be 2,250 and the hexanol 5,450. Calculate the concentration of pentanol in the unknown. (a) 7.16 mM pentanol (b) 1.43 mM pentanol (c) 0.120 mM hexanol 7 of 19 Which of the following in untrue regarding a blank solution? (a) Solutions containing known concentrations of analyte are called blank solutions. (b) A solution containing all of the reagents and solvents used in the analysis and not deliberately added analyte is called a blank solution. (c) A blank solution measures the response of the analytical procedure to impurities or interfering species in the reagents. 8 of 19 Fractional factorial experimental design and simplex optimization are complex techniques enabling the chemist involved in methods development to (a) statistically determine which method of analysis to select among several approved methods when a specific goal has been specified. (b) optimize the parameters of a method by varying one parameter at a time while keeping everything else constant. (c) efficiently optimize a method by varying more than one parameter at a time. 9 of 19 Which of the following is not included in a method validation? (a) linearity (b) chain of custody (c) robustness 10 of 19 28  Overall 37 When method validation is considered, linearity measures how well a graph of analytical response versus concentration of analyte follows a straight line. Which of the following is not a measure of linearity? (a) the square of the correlation coefficient (b) the correlation coefficient (c) The vertical deviations of the data points from the least-squares line 11 of 19 Which of the following responses best illustrates ways to demonstrate the accuracy of a method? (a) Analyze a standard reference material, compare results from two or more different analytical methods, analyze a spiked sample, or add standard additions of analyte to an unknown. (b) Analyze a standard reference material or compare results from two or more different analytical methods. (c) Analyze a standard reference material, compare results from two or more different analytical methods, or analyze a spiked sample. 12 of 19 The minimum detectable concentration may be found by (a) multiplying the student t value for at least 6 degrees of freedom times the standard deviation of at least 7 measurements of a sample whose concentration is 1 to 5 times the detection limit, and dividing by the mean value of the measurement of the sample minus the mean value of the measurement of the blank. (b) adding the mean value of the measurement of the blank to the product of the student t value with at least 6 degrees of freedom and the standard deviation of the measurements of the sample. (c) multiplying the student t value for at least 6 degrees of freedom times the standard deviation of at least 7 measurements of a sample whose concentration is 1 to 5 times the detection limit. 13 of 19 The term robustness refers to (a) the ability of an analytical method to be unaffected by small, deliberate changes in operating parameters. (b) the changes in the instrument detection limit as the operating parameters of the 29  Overall 38 instrument are adjusted to optimize the sensitivity of the measurements. (c) linearity of the data obtained from a series of measurements taken by an instrument when multiple samples are analyzed. 14 of 19 A chemist is involved in checking the results that were obtained in a routine analysis of magnesium. The chemist decided to purchase a certified standard. This standard would be purchased from the (a) EPA, the Environmental Protection Agency. (b) NIST, the National Institute of Standards and Technology. (c) NBS, the National Bureau of Standards. 15 of 19 Which of the following is true regarding a blank used in an analytical analysis? (a) A method blank is a sample containing all components except the analyte and is taken through all steps of the analytical procedure. (b) A field blank is a sample containing all components except the analyte and is taken through all steps of the analytical procedure. (c) A reagent blank is the same as a method blank; that is, it has been taken through all of the steps of the analytical procedure. 16 of 19 You have taken several sediment samples from the bottom of the Great Lakes and wish to analyze the material for the presence of polycyclic aromatic hydrocarbons, a class of compounds with many Environmental Protection Agency (EPA) priority pollutants. Which calibration method is most appropriate for the analysis? (a) method of standard addition (b) method of calibration curve (c) method of internal standard 17 of 19 30  Overall 39 A solution containing 0.0837 M of X and 0.0660 M of S (standard) gave peak areas of 423 and 347, respectively. To analyze the unknown, 10.00 mL of 0.146 M S were added to 10.00 mL X, and the mixture was diluted to 25.00 mL. This mixture gave a chromatogram with peak areas of AX = 553 and AS = 582. What is the concentration of X in the unknown? (a) 0.144 molar (b) 0.0578 molar (c) 0.0584 molar 18 of 19 Which statement is correct? (a) An internal standard is the same substance as the analyte. (b) An internal standard is the same substance as the analyte matrix. (c) An internal standard is a different substance from the analyte. 19 of 19 Performance test samples (also called quality control samples or blind samples) are (a) samples of known composition that are provided to the analyst as unknowns. Results are then compared with the known values, usually by a quality assurance manager. (b) samples of unknown composition that are provided to the analyst as knowns. Results are then compared with the known values, usually by a quality assurance manager. (c) samples of known composition that are provided to the analyst as unknowns. Results are then compared with the known values, usually by the analyst. 31  Overall 40 Department of Chemistry and Biochemistry CHE 311/311L Analytical Chemistry Class Practice –Chapters 8 Key: Question # Key 1 c Q4: A = kC, 0.185 =kC; 0.248=k[(5.00x95.5+50.0C)/100] 2 c C= 5.68 ppm. 3 c Q5: 1.15 = k1(5.00x/50); 0.93 = k2(5.009.50/50); 4 a 0.86 = k1/k21.34; x = 18.3 ppm 5 a 6 a Q6: peak area = k[C] 7 a Q12: y dl = y blank + 3s, s calculated from n>=7 8 a 9 b 10 c 11 a 12 b 13 a 14 b 15 c 16 a 17 a 18 a 19 a  Overall 41 Department of Chemistry and Biochemistry University of Southern Mississippi CHE 311 Class Practice Answer Sheet: Chapter_____06__________ Name__________________________ USM ID________________________ Date___________________________ Q 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A 1  Overall 42 Chapter 06-Chemical Equilibrium 1 of 18 The mathematical equation which represents the solubility product when the insoluble compound Mn2S3 is dissolved in water is (a) [Mn3+][S2-] = Ksp. (b) [Mn3+]3[S2-]2 = Ksp. (c) [Mn3+]2[S2-]3 = Ksp. 2 of 18 Given that the solubility product for La(IO3)3 is 1.0 x 10-11, what is the concentration of La3+ in a saturated solution of lanthanum iodate? (a) 7.8 x 10-4 molar (b) 0.44 x 10-3 molar (c) 7.2 x 10-5 molar 3 of 18 If a 0.100 M solution of NaOH is added to a solution containing 0.200 M Ni 2+, 0.200 M Ce3+, and 0.200 M Cu2+, which metal hydroxide will precipitate first? Ksp for Ni(OH)2 = 6.0 X 10-16, Ksp for Ce(OH)3 = 6.0 X 10-22, and Ksp for Cu(OH)2 = 4.8 x 10-20. (a) Ni(OH)2 (b) Ce(OH)3 (c) Cu(OH)2 4 of 18 What is the lead concentration of a saturated solution of lead(II) sulfate containing 0.020 molar Na2SO4? Ksp for PbSO4 = 6.3 x 10-7. (a) 7.9 x 10-4 molar (b) 5.6 x 10-3 molar (c) 3.2 x 10-5 molar 32  Overall 43 5 of 18 A beaker contains 250.0 mL of 0.150 molar silver ion (Ag+). To this beaker is added 250.0 mL of 0.300 M bromide ion (Br-). What is the concentration of Ag+ in the final solution? Ksp for AgBr = 5.0 x 10-13. (a) 7.1 x 10-7 molar (b) 6.7 x 10-12 molar (c) 3.3 x 10-12 molar 6 of 18 In the following reaction, identify the conjugate acid-base pair:NO2- + H2O HNO2 + OH-. (a) NO2-, OH- (b) NO2-, H2O (c) NO2-, HNO2 7 of 18 A solution was found to contain 8.26 x 10-4 M NaOH. Calculate the pH of the solution. (a) 3.08 (b) 10.9 (c) 1.00 8 of 18 Calculate the hydrogen ion concentration of a 0.100 molar solution of chloroacetic acid (ClCH2CO2H). Ka for chloroacetic acid = 1.36 x 10-3. (a) 0.0117 molar (b) 0.0369 molar (c) 7.39 x 10-12 molar 33  Overall 44 9 of 18 Calculate the hydrogen ion concentration of a 0.100 M solution of methyl amine (CH 3NH2). Ka for methyl amine hydrochloride = 2.3 x 10-11. (a) 1.5 x 10-6 molar (b) 6.6 x 10-3 molar (c) 1.5 x 10-12 molar 10 of 18 Calculate the pH of a 0.100 molar solution of sodium chloroacetate. Ka for chloroacetic acid (ClCH2CO2H) = 1.4 x 10-3. (a) 1.17 x 10-8 (b) 7.93 (c) 1.93 11 of 18 Calculate the pH of a 0.050 M solution of iodic acid. Ka for iodic acid = 0.17. (a) 1.39 (b) 1.03 (c) 1.30 12 of 18 A 0.100 M solution of nitrous acid (HNO2) had a pH of 2.07. What is the Ka value for nitrous acid? (a) 7.2 x 10-4 (b) 7.2 x 10-5 (c) 8.5 x 10-2 13 of 18 34  Overall 45 Find the concentration of phenol and phenolate ion in a 0.0100 M solution of phenol. Ka for phenol = 1.05 x 10-10. (a) 1.02 x 10-6 molar phenol and 1.02 x 10-6 molar phenolate ion (b) 1.02 x 10-6 molar phenol and 1.00 x 10-2 molar phenolate ion (c) 1.00 x 10-2 molar phenol and 1.02 x 10-6 M phenolate ion 14 of 18 Which is the strongest base? (a) HCl (b) CH3NH2 (c) RbOH 15 of 18 Which of these statements concerning the solubility is correct? (a) A salt is less soluble if one of its ions is already present in solution. (b) A salt is no more soluble if one of its ions is already present in solution. (c) A salt is more soluble if one of its ions is already present in solution. 16 of 18 What is the solubility of the mineral hydroxyapatite found in tooth enamel, if the ionic composition is Ca5(PO4)3OH (Ksp = 2.34 x 10-59)? (a) 3.06 x 10-7 molar (b) 8.67 x 10-8 molar (c) 4.34 x 10-7 molar 17 of 18 What is the calcium concentration in the mineral hydroxyapatite found in tooth enamel if the ionic composition is Ca5(PO4)3OH (Ksp = 2.34 x 10-59)? (a) 1.53 x 10-6 molar (b) 8.67 x 10-8 molar 35  Overall 46 (c) 4.34 x 10-7 molar 18 of 18 What concentration of carbonate must be added to 0.10 M Ag + to precipitate 99.99% of the Ag+ (Ksp Ag2CO3 = 8.1 x 10-12)? (a) 8.1 x 10-2 M (b) 8.1 x 10-7 M (c) 8.1 x 10-10M 36  Overall 47 Department of Chemistry and Biochemistry University of Southern Mississippi CHE 311 Class Practice Answer Sheet: Chapter_______07________ Name__________________________ USM ID________________________ Date___________________________ Q 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A Q 21 22 23 24 25 26 27 28 29 30 A 1  Overall 48 Chapter 07-Activity and the Systematic Treatment Of Equilibrium 1 of 23 Chloride concentration in aqueous samples can be determined by adding silver nitrate to the solution to precipitate AgCl as a colloid. Nitric acid is added to the solution to encourage coagulation of the colloid for filtration. If too much nitric acid is added to the solution, the solubility of the AgCl begins to increase. How can this be explained? (a) Hydrogen and nitrate ions enter the counter ion layer surrounding the colloid causing the counter ion layer to shrink, and the colloidal particles to coagulate. As the colloid coagulates, more AgCl dissolves. (b) The greater the ionic strength of a solution, the higher the charge in the ionic atmosphere. Each ion-plus-atmosphere contains less net charge, so there is more attraction between any particular cation and anion. (c) An ionic atmosphere surrounds ions in solution. The charge of the atmosphere is less than the charge of the central ion. The greater the ionic strength of the solution the greater the charge in the ionic atmospheres and the less attraction the ions have for one another. 2 of 23 An activity coefficient (a) measures the deviation of behavior of ions from ideality. (b) is obtained by multiplying the concentration of a solution times the ionic strength. (c) replaces the concentration term in chemical calculations. It corrects for the ionic strength of the solution. 3 of 23 The Debye-Hückel equation is log γ = (-0.51z2√μ)/[1 + (α√μ/305)]. Which of the following statements is true? (a) As the ionic strength increases, the activity coefficient increases. (b) As the charge of the ion increases, the departure of its activity coefficient from unity decreases. (c) The smaller the hydrated radius of the ion, the more important activity effects become. 4 of 23 37  Overall 49 A solution contains 0.100 M sodium nitrate (NaNO3) and 0.200 M MgCl2. Find the ionic strength of the solution. (a) μ = 0.700 molar (b) μ = 0.600 molar (c) μ = 0.500 molar 5 of 23 Using Equation 7-7 and Table 7-1 in your text, calculate the activity coefficient for Ca in a 0.01 M solution of Ca(ClO4)2. (a) 0.580 (b) 0.675 (c) 0.485 6 of 23 Calculate the solubility of silver bromate (AgBrO3), using activities, in a saturated solution of silver bromate. Ksp for Ag(BrO3) = 5.5 x 10-5. (a) 7.4 x 10-3 molar (b) 8.1 x 10-3 molar (c) 7.8 x 10-3 molar 7 of 23 What is the pH of water containing 0.0333 M Ca(NO3)2. (a) 7.00 (b) 6.98 (c) 7.02 8 of 23 At very low concentrations the activity coefficients approach 1. Ignoring activity coefficients, calculate the solubility of Co(OH) 3 in a saturated solution of Co(OH)3. Ksp for cobalt(III) hydroxide = 3 x 10-45. (a) 3 x 10-12 molar 38  Overall 50 (b) 3 x 10-38molar (c) 3 x 10-24 molar 9 of 23 Magnesium carbonate is slightly soluble in water. The Ksp for MgCO3 is 3.5 X 10-8. The carbonate ion being a conjugate base may form the bicarbonate ion (HCO 3-) and carbonic acid (H2CO3) in solution. Which of the following represents the correct mass balance equation at a pH of 7.5 for this system? (a) 2[Mg2+] = 2[CO32-] + [HCO3-] + [H2CO3] (b) [Mg2+] = [CO32-] + [HCO3-] + [H2CO3] (c) [Mg2+] = [CO32-] + [HCO3-] 10 of 23 If one were to calculate the solubility of AgCN in an aqueous solution, one would take into account the solubility product equation for AgCN (Ksp = 2.2 x 10-16 = [Ag+][CN-]) and the acid dissociation constant for hydrocyanic acid (Ka = [H+][CN-]/[HCN] = 6.2 x 10-10), as well as the mass balance equation ([Ag+] = [CN-] + [HCN]). If the solution were held at a pH of 5.0 the solubility of AgCN would be (a) 3.55 x 10-12 molar. (b) 1.48 x 10-8 molar. (c) 1.88 x 10-6 molar. 11 of 23 Given the chemical equilibrium HC2H3O2 + H2O C2H3O2- + H3O+, which of the following best represents the mathematical expression of this equilibrium. (a) [H3O+][C2H3O2-]/HC2H3O2 = Ka (b) [H3O+] γH3O+ [C2H3O2-] γC2H3O2-/HC2H3O2 γHC2H3O2 = Ka (c) [H3O+][C2H3O2-]/HC2H3O2 = Ka γa 12 of 23 39  Overall 51 Silver arsenate (Ag3AsO4) is only slightly soluble in water. The compound arsenic acid (H3AsO4) behaves in much the same manner as phosphoric acid. Which of the following represent a mass balance equation for the solution at pH 8.0? (a) [Ag+]/3 = [AsO43-] + [HAsO42-] + [H2AsO4-] + [H3AsO4] (b) [Ag+] = [AsO43-] + [HAsO42-] + [H2AsO4-] + [H3AsO4] (c) [Ag+] + [H+] = 3[AsO43-] + 2[HAsO42-] + [H2AsO4-] + [H3AsO4] + [OH-] 13 of 23 A solution contains a 0.100 M Al(NO3)3 and 0.100 M MgCl2. Which of the following represents the correct charge balance equation for this system? (a) 3[Al3+] + 2[Mg2+] = [NO3-] + [Cl-] (b) [Al3+] + [Mg2+] + [H+] = 3[NO3-] + 2[Cl-] + [OH-] (c) 3[Al3+] + 2[Mg2+] + [H+] = [NO3-] + [Cl-] + [OH-] 14 of 23 Which of the following equations represents a charge balance equation for a saturated solution of Ag3AsO4? (a) [Ag+] + [H+] = 3[AsO43-] + 2[HAsO42-] + [H2AsO4-] + [OH-] (b) [Ag+] + [H+] = 3[AsO43-] + 2[HAsO42-] + [H2AsO4-] + [H3AsO4] + [OH-] (c) [Ag+]/3 = [AsO43-] + [HAsO42-] + [H2AsO4-] + [H3AsO4] 15 of 23 One of the most popular questions ever created for chemistry exams involved calculating the pH of a 1.0 x 10-8 M solution of hydrochloric acid. So here it is for you. What is the correct answer? (a) 8.00 (b) 6.00 (c) 6.99 16 of 23 40  Overall 52 Magnesium carbonate is slightly soluble in water. The Ksp for MgCO3 is 3.5 x 10-8. The carbonate ion being a conjugate base may form the bicarbonate ion (HCO 3-) and carbonic acid (H2CO3) in solution. Ka1 and Ka2 for carbonic acid are 4.46 x 10-7 and 4.69 x 10-11, respectively. What is the solubility of MgCO3 in a solution that has at least a pH of 7.5? (a) 2.53 x 10-5 molar (b) 5.03 x 10-3 molar (c) 1.87 x 10-4 molar 17 of 23 Hydrosulfuric acid H2S(aq) was used for years in chemistry laboratories to precipitate metal sulfides from solution. The H2S dissociates in two steps to form the S2- ion that then reacts with the metal ion in solution. By controlling the hydrogen ion concentration, the amount of sulfide in the solution can be controlled, and thus, very insoluble metal sulfides may be precipitated while other metals remain in solution. Given that for H2Saq Ka1 = 9.5 x 10-8, Ka2 = 1.3 x 10-14, Ksp for MnS = 3.0 x 10-11, and that a saturated solution of H2S is approximately 0.100 M, calculate the hydrogen ion concentration required to prevent the precipitation of MnS. (a) 4.75 x 10-9 molar (b) 2.36 x 10-9 molar (c) 2.11 x 10-6 molar 18 of 23 Aqueous H2S dissociates in two steps to form hydrogen ion (H+) and sulfide ion (S2-). Given that a saturated solution of H2S is approximately 0.100 M and Ka1 and Ka2 for H2S are 9.5 x 10-8 and 1.3 x 10-14, respectively, calculate the hydrogen ion concentration of a saturated solution of H2S. (a) 3.14 x 10-8 molar hydrogen ion (b) 9.75 x 10-5 molar hydrogen ion (c) 4.99 x 10-8 molar hydrogen ion 19 of 23 Using equation 7-6 and Table 7-1 in your text, calculate the activity coefficient for Ca in a 0.01 M solution of Ca(ClO4)2. (a) 0.545 (b) 0.675 41  Overall 53 (c) 0.485 20 of 23 Neglecting activity coefficients and assuming complete dissociation, calculate the pH of a 4.0 x 10-8 M Ca(OH)2 solution. (a) 6.60 (b) 7.40 (c) 7.17 21 of 23 Using the equilibria below, what is the [H3AsO4] equal to in terms of [AsO43-]? Ag3AsO4 (s) 3Ag+ + AsO4 3- Ksp = 1.03 x 10-22 H3AsO4 H+ + H2AsO4- Ka1 = 5.8 x 10-3 H2AsO4- H+ + HAsO42- Ka2 = 1.10 x 10-7 HAsO42- ; H+ + AsO43- Ka3 = 3.2 x 10-12 (a) [H3AsO4] = ([H2AsO4-][H+])/Ka1 (b) [H3AsO4] = ([AsO43-][H+]3)/Ka3 Ka2 Ka1 (c) [H3AsO4] = Ka3 Ka2 Ka1/([AsO43-][H+]3) 22 of 23 Assuming compete dissociation of the salts, what is the ionic strength of 2 x 10 -4 M MgCl2 and 3 x 10-4 M AlCl3? (a) 1.3 x 10-3 (b) 4.0 X 10-3 (c) 2.4 x 10-3 42  Overall 54 23 of 23 Using the equilibria below, calculate the solubility of PbS in a solution with a pH = 3.00? PbS (s) Pb2+ + S2- Ksp = 3.0 x 10-28 H2S H+ + HS- Ka1 = 9.5 x 10-8 HS- H+ + S2- Ka2 = 1.3 X 10-14 (a) 4.9 x 10-7 molar (b) 1.7 x 10-14 molar (c) 5.7 x 10-10 molar 43  Overall 55 Department of Chemistry and Biochemistry University of Southern Mississippi CHE 311 Class Practice Answer Sheet: Chapter_____08__________ Name__________________________ USM ID________________________ Date___________________________ Q 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A Q 21 22 23 24 25 26 27 28 29 30 A 1  Overall 56 Chapter 08-Monoprotic Acid-Base Equalibria 1 of 16 Which of the following pairs of compounds and ions could be used to form a buffer solution? (a) 0.10 M HCl and 0.10 M NaCl (b) 0.10 M NH4Cl and 0.10 M NH3 (c) 0.10 M HNO2 and 1.0 x 10-4 M NaNO2 2 of 16 Which of the combination of ions and molecules may produce a buffer solution in an aqueous environment? (a) 50.00 mL of 0.100 M NaOH and 50.00 mL of 0.100 M CH 3COOH (b) 50.00 mL of 0.100 M HNO3 and 50.00 mL of 0.100 M CH3COOH (c) 50.0 mL of 0.050 M HNO3 and 50.0 mL of 0.100 M CH3COONa 3 of 16 Calculate the ratio of ethyl amine (CH3CH2NH2) to the ethyl ammonium ion (CH3CH2NH3+) in a solution with a pH of 11.0. pKa for CH3CH2NH3+ = 10.636. (a) 2.31 (b) 10.81 (c) 0.432 4 of 16 A buffer solution was prepared by mixing 50.0 mL of a 0.100 M solution of CH3COOH with 0.500 grams of NaCH3COO. The resulting mixture is diluted to 100.0 mL. What is the pH of the solution? Ka for acetic acid is 1.8 x 10-5. (a) 4.53 (b) 7.6 (c) 5.83 44  Overall 57 5 of 16 How many grams of NaCH3COO must be added to 150.0 mL of a 0.150 M solution of CH3COOH to produce a buffer of pH 4.75? Assume that the volume will remain constant, pKa for CH3COOH = 4.757 (a) 0.147 molar (b) 12.1 grams (c) 1.81 grams 6 of 16 A buffer solution was prepared by dissolving 5.00 grams of sodium propanate (NaCH3CH2CO2) in a solution containing 0.100 moles of propanoic acid (CH3CH2CO2H) and diluting the mixture to 500.0 mL. To this solution was added 5.00 mL of 1.00 M HCl. Calculate the pH of the resulting solution. pKa for propanoic acid is 4.874. (a) 4.65 (b) 4.62 (c) 4.52 7 of 16 A beaker containing 500.0 mL was determined to contain 0.150 M ammonia (NH3) and 0.150 M ammonium chloride NH4Cl. To this solution was added 50.0 mL of 0.150 M HCl. What was the change in pH of the ammonia-ammonium ion solution? pKa for NH4+ = 9.244. (a) The pH of the solution will go down 0.087 pH units. (b) The pH of the solution will go up 0.13 pH units. (c) The pH of the solution will go up 0.087 pH units. 8 of 16 How many mL of 0.100 M HCl should be added to 500.0 mL of 0.150 M sodium acetate (NaCH3CO2) to produce a buffer pH 5.000? pKa acetic acid = 4.757. (a) 273 mL (b) 1000 mL (c) 476 mL 45  Overall 58 9 of 16 Using the acid dissociation constant table in your textbook, which buffer system will give the greatest buffer capacity at pH 5.0? (a) chlorous acid/chlorite ion (b) hydrogen cyanide/cyanide ion (c) propanoic acid/propanate ion 10 of 16 An indicator may be selected for an acid-base application based on the pH range where the indicator changes color. A chemist wanted an indicator to change color between pH 5.8 and 6.1. The following compounds were available for selection: In a Ka = 1.5 X 10-3, Inb Ka = 1.3 X 10-6, and Inc Ka = 1.8 X 10-8. Which would be the proper indicator to select? (a) Ina (b) Inb (c) Inc 11 of 16 How many grams of NaOH must be added to 1.50 L of a 0.400 M solution of oxoacetic acid (HCOCO2H) to produce a buffer pH 4.00? pKa for oxoacetic acid = 3.46. (a) 18.7 grams (b) 0.470 grams (c) 5.33 grams 12 of 16 What is the Ka of 0.0450 M HA, if the measured pH is 5.78? (a) 6.1 x 10-11molar (b) 1.7 x 10-6 molar (c) 3.7 x 10-5 molar 13 of 16 46  Overall 59 If one measures the equilibrium constant for each of the following solutions, which relationship is correct? A - mix CH2CH2CH2CH2COOH with CH2CH2CH2NH2 B - mix HNO3 with CsOH C - mix KOH with HCOOH (a) K for A > K for B > K for C (b) K for C > K for A > K for B (c) K for B > K for C > K for A 14 of 16 Calculate the pH of a solution prepared by dissolving 0.0775 mol acetic acid (HCOOH) and 0.0460 mol sodium acetate (HCOONa) in 1 L of water. The Ka of acetic acid is 1.77 x 10-4. (a) 3.107 (b) 3.525 (c) 3.752 15 of 16 A solution prepared by dissolving 0.0775 mol acetic acid (HCOOH) and 0.0460 mol sodium acetate (HCOONa) in 1 L of water. What is the pH if 0.0100 mol of KOH is added to the solution. The Ka of acetic acid is 1.77 x 10-4. (a) 3.107 (b) 3.525 (c) 3.671 16 of 16 What weight of sodium lactate (CH3CHOHCOONa; MW = 112.05) must be added to 500 mL of 0.200 M lactic acid (CH3CHOHCOOH, MW= 90.07; Ka = 1.4 X 10-4) in order to produce a buffered solution with a pH = 4.50? (a) 4.03 grams (b) 50.09 grams (c) 0.893 grams 47  Overall 60 Department of Chemistry and Biochemistry University of Southern Mississippi CHE 311 Class Practice Answer Sheet: Chapter_______09________ Name__________________________ USM ID________________________ Date___________________________ Q 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A Q 21 22 23 24 25 26 27 28 29 30 A 1  Overall 61 Chapter 09-Polyprotic Acid-Base Equalibria 1 of 15 Using the symbol H2M to represent maleic acid, what is the pH and M2- concentration of a solution containing 0.100 M H2M? For maleic acid pK1 = 1.91 and pK2 = 6.33. (a) pH = 1.54 and [M2-] = 3.51 x 10-2 molar (b) pH = 1.54 and [M2-] = 4.68 x 10-7 molar (c) pH = 3.89 and [M2-] = 1.29 x 10-4 molar 2 of 15 The amino acid glycine (H2NCH2COOH) has two equilibrium constants, one for the –COOH group, and one for the –NH3 group. pKa for –COOH = 2.350 and pKa for –NH3 = 9.778. At pH 6.06, which compounds or ions predominate in solution? (a) A mixture of H3NCH2COOH and H3NCH2COO- (b) A mixture of H3NCH2COO- and H2NCH2COO2- (c) H3NCH2COO- only 3 of 15 A 0.200 M solution of HCl is added to a solution containing 0.150 moles of sodium phosphate (Na3PO4). The resulting solution is then diluted to exactly 1.00 L, at which time the pH was found to be pH 8.00. What is the concentration of H 2PO4- in the solution? For phosphoric acid, Ka1 = 7.11 x 10-3, Ka2 = 6.32 x 10-8, and Ka3 = 7.1 X 10-13. (a) 0.0205 molar (b) 0.150 molar (c) 0.0750 molar 4 of 15 Sulfurous acid (H2SO3) has pKa1 = 1.91 and pKa2 = 7.18. At what pH does [HSO 3-] = [SO32-]? (a) 1.91 (b) 4.54 (c) 7.18 48  Overall 62 5 of 15 Find the fraction of association of a 0.100 molar solution of hydrazoic acid. Ka for hydrazoic acid = 2.20 x 10-5. (a) 98.6% (b) 1.45% (c) 0.40% 6 of 15 Which of the following statements is true regarding the isoionic point and the isoelectric point? (a) The isoionic point and the isoelectric point are the same thing. (b) At the isoelectric point only the ions H2A+, A-, H+, and OH- are present and the concentrations of H2A+ and A- are not equal to each other. (c) At the isoelectric point, the average charge of the polyprotic acid is 0, and the concentration of H2A+ is equal to the concentration of A-. 7 of 15 How many grams of NaH2PO4 would be added to 5.60 grams of Na3PO4 to produce 500.0 mL of a buffer at pH = 7.3? For H3PO4 pKa1 = 2.148, pKa2 = 7.199, and pKa3 = 12.15. (a) 7.36 g NaH2PO4. (b) 1.63 g NaH2PO4. (c) 5.73 g NaH2PO4. 8 of 15 How many mL of 12.0 M HCl would be added to 500.0 mL of 0.100 M Na2SO3 to produce a buffer with a pH of 7.50? Assume no volume change. For H2SO3 Ka1 = 1.23 x 10-2 and Ka2 = 6.6 x 10-8. (a) 1.36 mL HCl (b) 2.81 mL HCl (c) 4.17 mL HCl 49  Overall 63 9 of 15 What is the pH of a 0.100 M solution of potassium hydrogen phthalate, KHC 8H4O2? For phthalic acid, pKa1 = 2.950 and pKa2 = 5.408. (a) 1.98 (b) 3.20 (c) 4.18 10 of 15 Given a 0.100 M solution of the hypothetical diprotic acid H2M, calculate the fraction of species in the form H2M (αH2M). For H2M, Ka1 = 1.0 x 10-4 and Ka2 = 1.0 x 10-7. (a) 3.12% (b) 96.88% (c) 0.00% 11 of 15 How many mL of 12.0 M HCl should be added to 500.0 mL of 0.100 M Na2SO3 (Kb2 = 8.13 x 10-13 and Kb1 =1.5 x 10-7) to produce a buffer at pH of 7.00? Assume no volume change. (a) 2.51 mL (b) 3.39 X 10-5 mL (c) 8.11 mL 12 of 15 Given the hypothetical acid H4A2+, what species determines the isoionic pH? (a) H4A2+ (b) A2- (c) H2A 13 of 15 50  Overall 64 Given the hypothetical acid H4A2+ (pKa1 = 1.4, pKa2 = 3.44, pKa3 = 6.01, and pKa4 = 8.45), what is the principle species in solution at pH = 9.00? (a) H3A+ (b) A2- (c) H2A 14 of 15 Given the hypothetical acid H4A2+, the concentration of which species are equal at the isoelectric pH? (a) [H4A2+] = [H3A+] (b) [H3A+] = [HA-] (c) [H2A] = [HA-] 15 of 15 Calculate the pH for 0.200 M KHA (Ka1 = 1.00 x 10-5 and Ka2 = 1.00 x 10-9). (a) 2.849 (b) 11.151 (c) 7.000 51  Overall 65 Department of Chemistry and Biochemistry University of Southern Mississippi CHE 311 Class Practice Answer Sheet: Chapter______10_________ Name__________________________ USM ID________________________ Date___________________________ Q 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A Q 21 22 23 24 25 26 27 28 29 30 A 1  Overall 66 Chapter 10-Acid-Base Titrations 1 of 21 A solution containing 75.0 mL of 0.150 M HCl is titrated with 75.0 mL of 0.300 M NaOH. What is the pH of the resulting solution? (a) 7.00 (b) 13.20 (c) 12.90 2 of 21 Consider the titration of 25.0 mL of 0.150 M HBr with 0.0750 M NaOH. What is the volume of NaOH required to reach the equivalence point? (a) 25.0 mL (b) 50.0 mL (c) 12.5 mL 3 of 21 A solution containing 50.0 mL of 0.1500 M C2H3COOH is titrated with 0.1500 M NaOH. What is the pH of the solution after the addition of 25.0 mL of NaOH? pKa for C2H3COOH is 4.76. (a) 4.76 (b) 9.24 (c) 1.30 4 of 21 When an ant bites you, the reason it stings is because of an injection of formic acid. What is the pH when 50.0 mL of 0.1480 M formic acid (HCOOH) is titrated with 40.2 mL of 0.1841 M NaOH? pKa formic acid = 3.745. (a) 10.040 (b) 4.201 (c) 3.96 52  Overall 67 5 of 21 In a titration, 48.6 mL of 0.1280 M KOH is added to 45.0 mL of 0.1200 M hydroxyacetic (HOCH2CO2H) acid. Calculate the pH of the solution. pKa for HOCH2CO2H = 3.831. (a) 2.06 (b) 2.38 (c) 11.94 6 of 21 In a titration, 25.0 mL of 0.154 M HNO3 was added to 45.0 mL of 0.213 M ammonia (NH3). What is the pH at this point? pKa NH4+ = 9.245. (a) 9.42 (b) 4.58 (c) 9.07 7 of 21 The weak base trimethyl amine, (CH3)3N, was titrated with HCl. If 25.30 mL of 0.150 M HCl was added to 35.15 mL of 0.108 M trimethyl amine, what is the pH of the solution? pKa for (CH3)3NH+ = 9.80. (a) 6.30 (b) 2.70 (c) 8.50 8 of 21 A titration was performed by adding 35.85 mL of 0.1350 M HNO3 to 55.80 mL of 0.08673 M KOH. What is the pH of the solution? (a) 1.28 (b) 7.00 (c) 3.28 53  Overall 68 9 of 21 25.0 mL of 0.100 M triethyl amine, (CH3CH2)3N, is titrated with 0.0500 M HCl. The following data was obtained: mL HCl added pH 0.0 11.86 25.0 10.71 50.0 6.79 What is the pKa for the triethylammonium ion? (a) 11.86 (b) 10.71 (c) 6.79 10 of 21 A flask containing 36.8 mL of 0.138 M sodium acetate (NaC 2H3O2) is titrated with 24.9 mL of 0.128 M HNO3. Calculate the pH of the solution. pKa for acetic acid = 4.76. (a) 4.53 (b) 9.47 (c) 4.98 11 of 21 In the titration of 30.0 mL of a 0.200 M solution of a hypothetical compound NaH 2M, what is the pH of the solution after the addition of 0.00 mL of 0.100 M NaOH? For H 3M, pKa1 = 3.00, pKa2 = 6.00, and pKa3 = 9.00. (a) 1.85 (b) 4.50 (c) 3.35 12 of 21 54  Overall 69 In the titration of 30.0 mL of a 0.200 M solution of a hypothetical compound NaH 2M, what is the pH of the solution after the addition of 30.0 mL of 0.100 M NaOH? For H 3M, pKa1 = 3.00, pKa2 = 6.00, and pKa3 = 9.00. (a) 6.00 (b) 3.00 (c) 7.50 13 of 21 In the titration of 30.0 mL of a 0.200 M solution of a hypothetical compound NaH 2M, what is the pH of the solution after the addition of 60.0 mL of 0.100 M NaOH? For H 3M, pKa1 = 3.00, pKa2 = 6.00, and pKa3 = 9.00. (a) 6.00 (b) 9.00 (c) 7.50 14 of 21 In the titration of 30.0 mL of a 0.200 M solution of a hypothetical compound NaH 2M, what is the pH of the solution after the addition of 70.0 mL of 0.100 M NaOH? For H 3M, pKa1 = 3.00, pKa2 = 6.00, and pKa3 = 9.00. (a) 8.30 (b) 5.30 (c) 12.00 15 of 21 In the titration of 30.0 mL of a 0.200 M solution of a hypothetical compound NaH 2M, what is the pH of the solution after the addition of 120 mL of 0.100 M NaOH? For H3M, pKa1 = 3.00, pKa2 = 6.00, and pKa3 = 9.00. (a) 7.50 (b) 9.15 (c) 10.80 16 of 21 55  Overall 70 In the titration of 30.0 mL of a 0.200 M solution of a hypothetical compound NaH 2M, what is the pH of the solution after the addition of 180 mL of 0.100 M NaOH? For H3M, pKa1 = 3.00, pKa2 = 6.00, and pKa3 = 9.00. (a) 9.15 (b) 8.73 (c) 12.40 17 of 21 For the titration of 10.00 mL of a 0.100 M nicotine (pKb1 = 6.15 and pKb2 = 10.85) with 0.100 M HCl, calculate the initial pH. (a) 10.42 (b) 13.00 (c) 3.58 18 of 21 For the titration of 10.00 mL of a 0.100 M nicotine (pKb1 = 6.15 and pKb2 = 10.85) with 0.100 M HCl, calculate the pH at ½Ve1. (a) 10.85 (b) 7.85 (c) 5.50 19 of 21 For the titration of 10.00 mL of a 0.100 M nicotine (pKb1 = 6.15 and pKb2 = 10.85) with 0.100 M HCl, calculate the pH at Ve1. (a) 8.50 (b) 7.85 (c) 5.50 20 of 21 What two assumptions must be true for the pH of an intermediate of a diprotic acid to equal (pKa1 + pKa2)/2? 56  Overall 71 (a) Ka2F >> Kw and Ka1F