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engineering
chemical engineering

Quantitative Chemical Analysis 8th edition Daniel C. Harris - Solutions

For chemical disposal, why is dichromate converted to Cr(OH)3(s)?
Explain what each of the three numbered hazard ratings means for 37 wt% HCl in Figure 2-2.
State three essential attributes of a lab notebook.
Explain the principles of operation of electronic and mechanical balances. Discuss.
Explain the difference between systematic and random error.
Suppose that in a gravimetric analysis, you forget to dry the filter crucibles before collecting precipitate. After filtering the product, you dry the product and crucible thoroughly before weighing them. Is the apparent mass of product always high or always low? Is the error in mass systematic or
State whether the errors in (a) - (d) are random or systematic:(a) A 25-mL transfer pipet consistently delivers 25.031 ± 0.009 mL.(b) A 10 - mL buret consistently delivers 1.98 ± 0.01 mL when drained from exactly 0 to exactly 2 mL and consistently delivers 2.03 mL ± 0.02 mL when drained from 2
Cheryl, Cynthia, Carmen, and Chastity shot the targets below at Girl Scout camp. Match each target with the proper description. (a) Accurate and precise (b) Accurate but not precise (c) Precise but not accurate (d) Neither precise nor accurate
Rewrite the number 3.123 56 (± 0.167 89%) in the forms (a) number (± absolute uncertainty) and (b) number (± percent relative uncertainty) with an appropriate number of digits.
Find the absolute and percent relative uncertainty and express each answer with a reasonable number of significant figures.(a) 6.2 (± 0.2) - 4.1 (± 0.1) = ?(b) 9.43 (± 0.05) × 0.016 (± 0.001) = ?(c) [6.2 (± 0.2) - 4.1 (± 0.1)] ÷ 9.43 (± 0.05) = ?(d) 9.43 (± 0.05) ×{[6.2 (± 0.2) × 10-3]
Find the absolute and percent relative uncertainty and express each answer with a reasonable number of significant figures.(a) 9.23 (± 0.03) + 4.21 (± 0.02) - 3.26 (± 0.06) = ?(b) 91.3 (± 1.0) × 40.3 (± 0.2)/21.1 (± 0.2) = ?(c) [4.97 (± 0.05) - 1.86 (± 0.01)]/21.1 (± 0.2) = ?(d) 2.016 4
Verify the following calculations:(a) ˆš3.1415(± 0.0011) = 1.77243(± 0.00031)(b) log[3.1415 (± 0.0011)] = 0.49714 (± 0.00015)(c) antilog[3.141.5 (± 0.0011)] = 1.3852(± 0.0035) Ã— 103(d) ln[3.1415 (± 0.0011)] = 1.14470 ( ± 0.00035)(e)
(a) Show that the formula mass of NaCl is 58.443 ( ± 0.0012) g/mol.
What is the true mass of water weighed at 24°C in the air if the apparent mass is 1.0346 ± 0.0002 g? The density of air is 0.0012 ± 0.0001g/mL and the density of balance weights is 8.0 ± 0.5 g/mL. The uncertainty in the density of water in Table 2-7 is negligible in comparison to the
Round each number as indicated: (a) 1.236 7 to 4 significant figures (b) 1.238 4 to 4 significant figures (c) 0.135 2 to 3 significant figures (d) 2.051 to 2 significant figures (e) 2.005 0 to 3 significant figures
Twelve dietary iron tablets were analyzed by the gravimetric procedure in Section 1-4 and the final mass of Fe2O3 (FM 159.688) was 0.2774 0.0018 g. Find the average mass of Fe per tablet.(Relative uncertainties in atomic masses are small compared with relative uncertainty in the mass of Fe2O3.
We can measure the concentration of HCl solution by reaction with pure sodium carbonate: 2H+ + Na2CO3 → 2Na+ + H2O + CO2. Complete reaction with 0.9674 ± 0.0009g of Na2CO3 (FM 105.9884 ± 0.0007) required 27.35 ± 0.04 mL of HCl. Find the molarity of the HCl and its absolute uncertainty.
Avogadro's number can be computed from the following measured properties of pure crystalline silicon:4(1) atomic mass (obtained from the mass and abundance of each isotope), (2) density of the crystal, (3) size of the unit cell (the smallest repeating unit in the crystal), and (4) number of atoms
Express the molecular mass (± uncertainty) of C9H9O6N3 with the correct number of significant figures.
Write each answer with the correct number of digits. (a) 1.021 + 2.69 = 3.711 (b) 12.3 - 1.63 = 10.67 (c) 4.34 - 9.2 = 39.928 (d) 0.060 2 (2.113 104) 2.849 03 106 (e) log(4.218 1012) ? (f) antilog (3.22) ? (g) 102.384 ?
Write the formula mass of (a) BaF2 and (b) C6H4O4 with a reasonable number of digits. Use the periodic table inside the cover of this book to find atomic masses.
Write each answer with the correct number of significant figures. (a) 1.0 + 2.1 + 3.4 + 5.8 = 12.3000 (b) 106.9 - 31.4 = 75.5000 (c) 107.868 - (2.113 × 102) (5.623 × 103) = 5 519.568 (d) (26.14/37.62) × 4.38 = 3.043 413 (e) (26.14/(37.62 × 108) × (4.38 × 10-2) = 3.043413 × 10-10 (f)
What is the relation between the standard deviation and the precision of a procedure? What is the relation between standard deviation and accuracy?
List the three different cases that we studied for comparison of means, and write the equations used in each case.
The percentage of an additive in gasoline was measured six times with the following results: 0.13, 0.12, 0.16, 0.17, 0.20, 0.11%. Find the 90% and 99% confidence intervals for the percentage of the additive.
Sample 8 of Problem 4 - 3 was analyzed seven times, with x- 1.52793 and s = 0.00007. Find the 99% confidence interval for sample 8.
A trainee in a medical lab will be released to work on her own when her results agree with those of an experienced worker at the 95% confidence level. Results for a blood urea nitrogen analysis are shown below.Trainee:x- = 14.57 mg/dls = 0.53mg/dL n = 6 samplesExperiencedWorker:x- = 13.95 mg/dL s =
The CdSe content (g/L) of nanocrystals was measured by two methods for six different samples. Do the two methods differ significantly at the 95% confidence level?
Now we use a built-in routine in Excel for the paired t test to see if the two methods in Problem 4-14 produce significantly different results. Enter the data for Methods 1 and 2 into two columns of a spreadsheet. For Excel 2007, find Data Analysis in the Data ribbon. In earlier versions of Excel,
Two methods were used to measure fluorescence lifetime of a dye. Are the standard deviations significantly different? Are the means significantly different?
Do the following two sets of measurements of 6Li/7Li in a Standard Reference Material give statistically equivalent results?
If you measure a quantity four times and the standard deviation is 1.0% of the average, can you be 90% confident that the true value is within 1.2% of the measured average?
Students measured the concentration of HCl in a solution by titrating with different indicators to find the end point. Is the difference between indicators 1 and 2 significant at the 95% confidence level? Answer the same question for indicators 2 and 3.
Use Table 4-1 to state what fraction of a Gaussian population lies within the following intervals:a. μ ± σb. μ ± 2σc. μ to ± σd. μ to ± 0.5σe. - σ to 0.5 σ
Hydrocarbons in the cab of an automobile were measured during trips on the New Jersey Turnpike and trips through the Lincoln Tunnel connecting New York and New Jersey.10 The concentrations standard deviations) of m- and p-xylene were Turnpike: 31.4 ± 30.0 μg/m3 (32 measurements) Tunnel:
A Standard Reference Material is certified to contain 94.6 ppm of an organic contaminant in soil. Your analysis gives values of 98.6, 98.4, 97.2, 94.6, and 96.2 ppm. Do your results differ from the expected result at the 95% confidence level? If you made one more measurement and found 94.5, would
Nitrite (NO2) was measured by two methods in rainwater and unchlorinated drinking water. The results standard deviation (number of samples) are Sample source Gas chromatography Spectrophotometry Rain water 0.69 ± 0.005 mg/L(n = 7) 0.063 ± 0.008 mg/L (n = 5) Drinking water 0.078 ± 0.007 mg/L
Should the value 216 be rejected from the set of results 192, 216, 202, 195, and 204?
A straight line is drawn through the points (3.0, - 3.87 × 104), (10.0, - 12.99 × 104), (20.0, - 25.93 × 104), (30.0, - 38.89 × 104), and (40.0, - 51.96 × 104) to give m = - 1.298 72 × 104, b = 256.695, sm = 13.190, sb = 323.57, and sy = 392.9. Express the slope and intercept and their
Here is a least-squares problem that you can do by hand with a calculator. Find the slope and intercept and their standard deviations for the straight line drawn through the points (x,y) = (0,1),(2,2), and (3,3). Make a graph showing the three points and the line. Place error bars (± sy) on the
Explain the following statement: "The validity of a chemical analysis ultimately depends on measuring the response of the analytical procedure to known standards."
Suppose that you carry out an analytical procedure to generate a linear calibration curve like that shown in Figure 4-13. Then you analyze an unknown and find an absorbance that gives a negative concentration for the analyte. What does this mean?
The ratio of the number of atoms of the isotopes 69Ga and 71Ga in eight samples from different sources was measured in an effort to understand differences in reported values of the atomic mass of gallium:Find the (a) mean, (b) standard deviation, and (c) variance. (d) Write the mean and
Using the linear calibration curve, find the quantity of unknown protein that gives a measured absorbance of 0.264 when a blank has an absorbance of 0.095.
Consider the least-squares problem. (a) Suppose that a single new measurement produces a y value of 2.58. Find the corresponding x value and its uncertainty. (b) Suppose you measure y four times and the average is 2.58. Calculate the uncertainty based on four measurements, not one.
Consider the linear calibration curve, which is derived from the 14 corrected absorbances in the shaded region at the right side of. Create a least-squares spreadsheet like Figure 4 - 15 to compute the equation of the line and the standard deviations of the parameters. Suppose that you find
Here are mass spectrometric signals for methane in H2:a) Subtract the blank value (9.1) from all other values. Then use the method of least squares to find the slope and intercept and their uncertainties. Construct a calibration curve. (b) Replicate measurements of an unknown gave 152.1, 154.9,
Nonlinear calibration curve. Following the procedure in Box 4 - 2, find how many micrograms (μg) of protein are contained in a sample with a corrected absorbance of 0.350.
Logarithmic calibration curve. Calibration data spanning five orders of magnitude for an electrochemical determination of p-nitrophenol are given in the table. (The blank has already been subtracted from the measured current.) If you try to plot these data on a linear graph extending from 0 to 310
Confidence interval for calibration curve. To use a calibration curve based on n points, we measure a new value of y and calculate the corresponding value of x. The one-standard deviation uncertainty in x, sx, is given by Equation 4-27. We express a confidence interval for x, using Student's
(a)Calculate the fraction of bulbs in Figure 4-1 expected to have a lifetime greater than 1 005.3 h. (b) What fraction of bulbs is expected to have a lifetime between 798.1 and 901.7 h?(c) Use the Excel NORMDIST function to find the fraction of bulbs expected to have a lifetime between 800 and 900
Blood plasma proteins of patients with malignant breast tumors differ from proteins of healthy people in their solubility in the presence of various polymers. When the polymers dextran and poly(ethylene glycol) are mixed with water, a two-phase mixture is formed. When plasma proteins of tumor
Repeat Problem 4 - 6 but use the values 50, 100, and 150 for the standard deviation. Superimpose all three curves on a single graph.
What is the meaning of a confidence interval?
What fraction of vertical bars in Figure 4-5a is expected to include the population mean (10 000) if many experiments are carried out? Why are the 90% confidence interval bars longer than the 50% bars in Figure 4 - 5? $What fraction of vertical bars in Figure 4-5a is expected$
Explain the meaning of the quotation at the beginning of this chapter: "Get the right data. Get the data right. Keep the data right."
How is a control chart used? State six indications that a process is going out of control.
Here is a use objective for a chemical analysis to be performed at a drinking water purification plant: "Data and results collected quarterly shall be used to determine whether the concentrations of haloacetates in the treated water demonstrate compliance with the levels set by the Stage 1
What is the difference between an instrument detection limit and a method detection limit? What is the difference between robustness and intermediate precision?
Define the following terms: instrument precision, injection precision, intra-assay precision, intermediate precision, and interlaboratory precision.
Control chart. A laboratory monitoring perchlorate in urine measured quality control samples made from synthetic urine spiked with. The graph shows consecutive quality control measurements. Are any troubleshooting conditions from Box 5-1 observed in these data?Control chart for ClO-4 in urine.
Correlation coefficient and Excel graphing. Synthetic data are given below for a calibration curve in which random Gaussian noise with a magnitude of 80 was superimposed on y values that follow the equation y = 26.4x + 1.37. This exercise shows that a high value of R2 does not guarantee that data
In a murder trial in the 1990s, the defendant's blood was found at the crime scene. The prosecutor argued that blood was left by the defendant during the crime. The defense argued that police "planted" the defendant's blood from a sample collected later. Blood is normally collected in a vial
(a) From Box 5-2, estimate the minimum expected coefficient of variation, CV(%), for interlaboratory results when the analyte concentration is (i) 1 wt% or (ii) 1 part per trillion.(b) The coefficient of variation within a laboratory is typically ~ 0.5 - 0.7 of the between laboratory variation. If
Spike recovery and detection limit. Species of arsenic found in drinking water include AsO3 3 - (arsenite), AsO43- (arsenate), (CH3)2AsO23- (dimethylarsinate), and (CH3)AsO32- (methylarsonate) Pure water containing no arsenic was spiked with 0.40 μg arsenate/L. Seven replicate determinations gave
Detection limit. Low concentrations of Ni2+ -EDTA near the detection limit gave the following counts in a mass spectral measurement: 175, 104, 164, 193, 131, 189, 155, 133, 151, 176. Ten measurements of a blank had a mean of 45 counts. A sample containing 1.00 μM Ni2+ -EDTA gave 1 797 counts.
What are the three parts of quality assurance? What questions are asked in each part and what actions are taken in each part?
Detection limit. A sensitive chromatographic method was developed to measure sub-part per-billion levels of the disinfectant by-products iodate (IO 3 ), chlorite (ClO 2 ), and bromate (BrO 3 ) in drinking water. As the oxyhalides emerge from the column, theyreact with Br to make Br 3, which is
Olympic athletes are tested to see if they are using illegal performance-enhancing drugs. Suppose that urine samples are taken and analyzed and the rate of false positive results is 1%. Suppose also that it is too expensive to refine the method to reduce the rate of false positive results. We do
The U.S. Department of Agriculture provided homogenized baby food samples to three labs for analysis.3 Results agreed well for protein, fat, zinc, riboflavin, and palmitic acid. Results for iron were questionable: Lab A, 1.59 ± 0.14 (13); Lab B, 1.65 ± 0.56 (8); Lab C, 2.68 ± 0.78 (3) mg/100 g.
Why is it desirable in the method of standard addition to add a small volume of concentrated standard rather than a large volume of dilute standard?
An unknown sample of Cu2+ gave an absorbance of 0.262 in an atomic absorption analysis. Then 1.00 mL of solution containing 100.0 ppm (= μg/mL)Cu2+ was mixed with 95.0 mL of unknown, and the mixture was diluted to 100.0 mL in a volumetric flask. The absorbance of the new solution was 0.500. (a)
Standard addition graph. Tooth enamel consists mainly of the mineral calcium hydroxyapatite, Ca10(PO4)6(OH)2. Trace elements in teeth of archeological specimens provide anthropologists with clues about diet and diseases of ancient people. Students at Hamline University measured strontium in enamel
Europium is a lanthanide element found in parts per billion levels in natural waters. It can be measured from the intensity of orange light emitted when a solution is illuminated with ultraviolet radiation. Certain organic compounds that bind Eu(III) are required to enhance the emission. The figure
Standard addition graph. Students performed an experiment like that in Figure 5-7 in which each flask contained 25.00 mL of serum, varying additions of 2.640 M NaCl standard, and a total volume of 50.00 mL.(a) Prepare a standard addition graph and find [Na+] in the serum.(b) Find the standard
State when standard additions and internal standards, instead of a calibration curve, are desirable, and why.
How can you validate precision and accuracy?
A solution containing 3.47 mM X (analyte) and 1.72 mM S (standard) gave peak areas of 3 473 and 10 222, respectively, in a chromatographic analysis. Then 1.00 mL of 8.47 mM S was added to 5.00 mL of unknown X, and the mixture was diluted to 10.0 mL. This solution gave peak areas of 5 428 and 4 431
Chloroform is an internal standard in the determination of the pesticide DDT in a polarographic analysis in which each compound is reduced at an electrode surface. A mixture containing 0.500 mM chloroform and 0.800 mM DDT gave signals of 15.3 µA for chloroform and 10.1 µA for DDT. An unknown
Verifying constant response for an internal standard. When we develop a method using an internal standard, it is important to verify that the response factor is constant over the calibration range. Data are shown below for a chromatographic analysis of naphthalene (C10H8), using deuterated
Correcting for matrix effects with an internal standard. The appearance of pharmaceuticals in municipal wastewater (sewage) is an increasing problem that is likely to have adverse effects on our drinking water supply. Sewage is a complex matrix. When the drug carbamazepine was spiked into sewage at
Acid-base titrations similar to those in Section 5-5 had volumes and results shown in the table.14 Use Excel LINEST to find the concentrations of acids A, B, and C and estimate their uncertainty.
Distinguish raw data, treated data, and results.
What is the difference between a calibration check and a performance test sample?
What is the purpose of a blank? Distinguish method blank, reagent blank, and field blank.
Distinguish linear range, dynamic range, and range.
What is the difference between a false positive and a false negative?
Consider a sample that contains analyte at the detection limit defined in Figure 5-2. Explain the following statements: There is approximately a 1% chance of falsely concluding that a sample containing no analyte contains analyte above the detection limit. There is a 50% chance of concluding that a
To evaluate the equilibrium constant in Equation 6-2, we must express concentrations of solutes in mol/L, gases in bars, and omit solids, liquids, and solvents. Explain why.
BaCl2 ∙ H2O(s) loses water when it is heated in an oven: BaCI2 ∙ H2O (s) ⇌ BaCl2(s) + H2O(g) ∆H° = 63.11 kJ/mol at 25°C ∆S° = + 148J(K ∙ mol) at 25°C (a) Write the equilibrium constant for this reaction. Calculate the vapor pressure of gaseous H2O (PH2O)above BaCl2 ∙ H2O at 298
The equilibrium constant for the reaction of NH3 (aq) + H2O ⇌ NH+4 + OH- is Kb = 1.479 × 10-5 at 5°C 1.570 × 10 -5 at 10oC(a) Assuming ∆H° and ∆S° are constant in the interval 5° - 10°C (probably a good assumption for small ∆T ), use Equation 6-8 to find ∆H° for the reaction in
For H2(g) + Br2(g) ⇌ 2HBr(g) K = 72 × 10-4 at 1362K and ∆H° is positive. A vessel is charged with 48.0 PA HBr,1370 PaH2, and 3310 Pa Br2 at 1362 K. (a) Will the reaction proceed to the left or the right to reach equilibrium?(b) Calculate the pressure (in pascals) of each species in the
Henry's law states that the concentration of a gas dissolved in a liquid is proportional to the pressure of the gas. This law is a consequence of the equilibrium
What concentration of Fe(CN)64- (ferrocyanide) is in equilibrium with 1.0 μM Ag+ and Ag4Fe(CN)6(s). Express your answer with a prefix from Table 1-3.
Find [Cu2+] in a solution saturated with Cu4(OH)6(SO4) if [OH-1] is fixed at 1.0 × 10-6M. Note that Cu4(OH)6(SO4) gives 1 mo of SO42- for 4 mol of Cu2+. Ksp = 2.3 × 10-69
(a) From the solubility product of zinc ferrocyanide, Zn2Fe(CN)6, calculate the concentration of Fe(CN)64- in 0.10 mM ZnSO4 saturated with Zn2Fe(CN)6. Assume that Zn2Fe(CN)6 is a negligible source of Zn2+.(b) What concentration of K4Fe(CN)6 should be in a suspension of solid Zn2Fe(CN)6 in water to
A solution contains 0.0500 M Ca2+ and 0.030 0 M Ag+. Can 99% of Ca2+ be precipitated by sulfate without precipitating Ag+? What will be the concentration of Ca2+ when Ag2SO4 begins to precipitate?
A solution contains 0.010 M Ba2+ and 0.010 M Ag+. Can 99.90% of either ion be precipitated by chromate (CrO42-) without precipitating the other metal ion?
If a solution containing 0.10 M Cl-, Br-, I-, and CrO42- is treated with Ag+, in what order will the anions precipitate?
Explain why the total solubility of lead in Figure 6-3 first decreases and then increases as [ I-] increases. Give an example of the chemistry in each of the two domains.

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