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engineering
chemical engineering

Questions and Answers of Chemical Engineering

A 30.00-mL solution of I- was treated with 50.00 mL of 0.365 0 M AgNO3. AgI(s) was filtered off, and the filtrate (plus Fe3+) was titrated with 0.287 0 M KSCN. When 37.60 mL had been added, the
Why would a reprecipitation be employed in a gravimetric analysis?
Explain how the quartz crystal microbalance at the opening of Chapter 2 measures small masses.
Explain what is meant by the statement, "Unless the complete history of any sample is known with certainty, the analyst is well advised not to spend his or her time in analyzing it."
87Sr/86Sr isotope ratios were measured in polar ice cores of varying sample size. The 95% confidence interval, expressed as a percentage of the mean 87Sr/86Sr isotope ratio decreased with increasing
Consider a random mixture containing 4.00 g of Na2CO3 (density 2.532 g/mL) and 96.00 gof K2CO3 (density 2.428 g/mL) with a uniform spherical particle radius of 0.075 mm.(a) Calculate the mass of a
The following wet-ashing procedure was used to measure arsenic in organic soil samples byatomic absorption spectroscopy: A 0.1- to 0.5-g sample was heated in a 150-mL Teflon bomb in a microwave oven
Barbital can be isolated from urine by solid-phase extraction with C18-silica. The barbital is then eluted with 1:1 vol/vol acetone:chloroform. Explain how this procedure works.
To preconcentrate cocaine and benzoylecgonine from river water at the opening of this chapter, solid-phase extraction was carried out at pH 2 using the mixed-mode cation exchange resin in Figure
Referring to Table 27-7, explain how an anion-exchange resin can be used for absorption and analysis of SO2 released by combustion.
Why is it advantageous to use large particles (50 μm) for solidphase extraction, but small particles (5 μm) for chromatography?
In 2002, workers at the Swedish National Food Administration discovered that heated, carbohydrate-rich foods, such as french fries, potato chips, and bread, contain alarming levels (0.1 to 4 Î¼g/g)
Many metals in seawater can be preconcentrated for analysis by coprecipitation with Ga(OH)3. A 200 -Î¼L HCl
Explain what is meant by "analytical quality" and "data quality" in the following quotation: "We need to update the environmental data quality model to explicitly distinguish analytical quality from
Acid-base equilibria of Cr(III) were summarized in Problem 9-37. Cr(VI) in aqueous solution above pH 6 exists as the yellow tetrahedral chromate ion, CrO42. Between pH 2 and 6, Cr(VI) exists as an
The county landfill in the diagram was monitored to verify that toxic compounds were not leaching into the local water supply. Wells drilled at 21 locations were monitored over a year and pollutants
(a) In the analysis of a barrel of powder, the standard deviation of the sampling operation is ± 4% and the standard deviation of the analytical procedure is ± 3%. What is the overall standard
Explain how to prepare a powder with an average particle diameter near 100 μm by using sieves from Table 27-2. How would such a particle mesh size be designated?
An example of a mixture of 1-mm-diameter particles of KCl and KNO3 in a number ratio 1:99 follows Equation 27-4. A sample containing 104 particles weighs 11.0 g. What is the expected number and
When you flip a coin, the probability of its landing on each side is p = q = 1/2 in Equations 27-2 and 27 3. If you flip it n times, the expected number of heads equals the expected number of tails =
In analyzing a lot with random sample variation, you find a sampling standard deviation of ± 5%. Assuming negligible error in the analytical procedure, how many samples must be analyzed to give 95%
In an experiment analogous to that in Figure 27-3, the sampling constant is found to be Ks = 20 g. (a) What mass of sample is required for a ± 2% sampling standard deviation? (b) How many samples of
Describe the use of the following Excel functions after reading about them in the Excel help facility. (a) SQRT (b) AVERAGE (c) PI (d) FACT (e) EXP (f) LOG
Find the number of millimoles of solute in (a) 2.00 L of 0.0555 M KMnO4 (b) 750 mL of 3.25 x 10-3 M KSCN
What is the mass in milligrams of>? (a) 0.367 mol of HNO3? (b) 245 mmol of MgO? (c) 12.5 mol of NH4NO3? (d) 4.95 mol of (NH4)2Ce (NO3)6 (548.23 g/mol)
What is the mass in milligrams of solute in? (a) 16.0 mL of 0.350 M sucrose (342 g / mol) (b) 1.92 L of 3.76 x 10-3 M H2O2
What is the mass in grams of solute in? (a) 250 mL of 0.264 M H2O2 (b) 37.0 mL of 5.75 x 10-4 M benzoic acid (122 g / mol)
Calculate the p-value for each of the indicated ions in the following:
Calculate the molar H3O+ ion concentration of a solution that has a pH of (a) 4. 31. (b) 0.59. (c) 7.62. (d) 20.76.
Calculate the p-functions for each ion in a solution that is (a) 0.0300 M in NaBr. (b) 5.5 3 10-3 M in Ba(OH)2. (c) 8.7 3 10-3 M in CaCl2 and 6.6 x 10-3 M in BaCl2
Convert the following p-functions to molar concentrations: (a) pH = 1.020. (b) pBr = 7.77. (c) pLi = 12.35. (d) pMn = 0.135.
Sea water contains an average of 1.08 x 103 ppm of Na+ and 270 ppm of SO42-. Calculate (a) The molar concentrations of Na+ and SO42- given that the average density of sea water is 1.02 g / mL. (b)
A solution was prepared by dissolving 5.76 g of KCl ∙ MgCl2 ∙ 6H2O (277.85 g/mol) in sufficient water to give 2.000 L. Calculate (a) The molar analytical concentration of KCl ∙ MgCl2 in this
A 6.42% (w/w) Fe (NO3)3 (241.86 g/mol) solution has a density of 1.059 g/mL. Calculate (a) The molar analytical concentration of Fe(NO3)3 in this solution. (b) The molar NO3- concentration in the
Describe the preparation of (a) 500 mL of 4.75% (w/v) aqueous ethanol (C2H5OH, 46.1 g/mol) (b) 500 g of 4.75% (w/w) aqueous ethanol (c) 500 mL of 4.75% (v/v) aqueous ethanol
Describe the preparation of 750 mL of 6.00 M H3PO4 from the commercial reagent that is 86% H3PO4 (w/w) and has a specific gravity of 1.71.
Give two examples of units derived from the fundamental base SI units.
Describe the preparation of (a) 500 mL of 0.0750 M AgNO3 from the solid reagent
What mass of solid La (IO3)3 (663.6 g/mol) is formed when 50.0 mL of 0.250 M La3+ are mixed with 75.0 mL of 0.302 M IO3-?
Exactly 0.2220 g of pure Na2CO3 was dissolved in 100.0 mL of 0.0731 M HCl. (a) What mass in grams of CO2 were evolved? (b) What was the molar concentration of the excess reactant (HCl or Na2CO3)?
Exactly 75.00 mL of a 0.3132 M solution of Na2SO3 were treated with 150.0 mL of 0.4025 M HClO4 and boiled to remove the SO2 formed. (a) What was the mass in grams of SO2 that was evolved? (b) What
What volume of 0.01000 M AgNO3 would be required to precipitate all of the I- in 200.0 mL of a solution that contained 24.32 ppt KI?
Simplify the following quantities using a unit with an appropriate prefix: (a) 3.2 3 108 Hz. (b) 8.43 3 107 μmol. (c) 8.96 3 106 nm.
Show that one gram is one mole of unified atomic mass units.
Find the number of Na1 ions in 2.92 g of Na3PO4?
Find the amount of the indicated element (in moles) in (a) 8.75 g of B2O3 (b) 167.2 mg of Na2B4O7 ∙ 10H2O (c) 4.96 g of Mn3O4 (d) 333 mg of CaC2O4
Explain the difference between (a) Random and systematic error. (b) Absolute and relative error.
Find the mean and median of each of the following sets of data. Determine the deviation from the mean for each data point within the sets and find the mean deviation for each set. Use a spreadsheet
Suggest two sources of systematic error and two sources of random error in measuring the width of a 3-m table with a 1-m metal rule.
Describe at least three systematic errors that might occur while weighing a solid on an analytical balance.
Describe at least three ways in which a systematic error might occur while using a pipet to transfer a known volume of liquid.
What kind of systematic errors are detected by varying the sample size?
The method described in Problem 5-8 is to be used for the analysis of ores that assay about 1.2% gold. What minimum sample mass should be taken if the relative error resulting from a 0.4-mg loss is
Define (a) Standard error of the mean. (b) Variance.
Estimate the absolute standard deviation and the coefficient of variation for the results of the following calculations. Round each result to include only significant figures the numbers in
Calculate the absolute standard deviation and the coefficient of variation for the results of the following calculations. Round each result to include only significant figures the numbers in
Calculate the absolute standard deviation and the coefficient of variation for the results of the following calculations. Round each result to include only significant figures the numbers in
The standard deviation in measuring the diameter d of a sphere is ±0.02 cm. What is the standard deviation in the calculated volume V of the sphere if d 5 2.15 cm?
In a volumetric determination of an analyte A, the data obtained and their standard deviations are as follows:From the data, find the coefficient of variation of the final result for the % A that is
In Chapter 24, we show that quantitative molecular absorption spectrometry is based on Beer's law, which can be written
Six bottles of wine of the same variety were analyzed for residual sugar content with the following results:(a) Evaluate the standard deviation s for each set of data. (b) Pool the data to obtain an
Differentiate between (a) Parameter and statistic. (b) Random and systematic error.
Calculate a pooled estimate of u from the following spectrophotometric analysis for NTA (nitrilotriacetic acid) in water from the Ohio River:
Distinguish between the sample standard deviation and the population standard deviation.
From the Gaussian (normal) error curve, what is the probability that a result from a population lies between 0 and + 1σ of the mean? What is the probability of a result occurring that is between
Consider the following sets of replicate measurements:For each set, calculate the (a) Mean; (b) Median; (c) Spread, or range; (d) Standard deviation(e) Coefficient of variation.
The accepted values for the sets of data in Problem 6-7 are: Set A, 9.0; Set B, 0.630; Set C, 20.58; For the mean of each set, calculate (a) the absolute error and (b) the relative error
Estimate the absolute deviation and the coefficient of variation for the results of the following calculations. Round each result so that it contains only significant digits the numbers in
Describe in your own words why the confidence interval for the mean of five measurements is smaller than that for a single result.
A volumetric calcium analysis on triplicate samples of the blood serum of a patient believed to be suffering from a hyperparathyroid condition produced the following data: mmol Ca/L = 3.15, 3.25,
A prosecuting attorney in a criminal case presented as principal evidence small fragments of glass found imbedded in the coat of the accused. The attorney claimed that the fragments were identical in
The week 3 measurement in the data set of Problem 7-16 is suspected of being an outlier. Use the Q test to determine if the value can be rejected at the 95% confidence level.
The level of a pollutant in a river adjacent to a chemical plant is regularly monitored. Over a period of years, the normal level of the pollutant has been established by chemical analyses. Recently,
State quantitatively the null hypothesis H0 and the alternative hypothesis Ha for the following situations and describe the type I and type II errors. If these hypotheses were to be tested
The homogeneity of the chloride level in a water sample from a lake was tested by analyzing portions drawn from the top and from near the bottom of the lake, with the following results in ppm
Sir William Ramsey, Lord Rayleigh, prepared nitrogen samples by several different methods. The density of each sample was measured as the mass of gas required to fill a particular flask at a certain
The ascorbic acid concentration of five different brandsof orange juice was measured. Six replicate samplesof each brand were analyzed. The following partialANOVA table was obtained.(a) Fill in the
Four analysts perform replicate sets of Hg determinationson the same analytical sample. The results in ppb Hg areshown in the following table:(a) State the appropriate hypotheses. (b) Do the analysts
Three different analytical methods are compared for determining Ca in a biological sample. The laboratory is interested in knowing whether the methods differ. The results shown below represent Ca
Apply the Q test to the following data sets to determine whether the outlying result should be retained or rejected at the 95% confidence level. (a) 85.10, 84.62, 84.70 (b) 85.10, 84.62, 84.65, 84.70
Consider the following sets of replicate measurements:Calculate the mean and the standard deviation for each of these six data sets. Calculate the 95% confidence interval for each set of data. What
Calculate the 95% confidence interval for each set of data in Problem 7-4 if s is a good estimate of s and has a value of Set A, 0.30; Set C, 0.070; Set E, 0.0090
An atomic absorption method for the determination of the amount of iron present in used jet engine oil was found from pooling 30 triplicate analyses to have a standard deviation s = 3.6 mg Fe/mL. If
How many replicate measurements are needed to decrease the 95 and 99% confidence limits for the analysis described in Problem 7-7 to ± 2.2 mg Fe / mL?
The data in the accompanying table represent the concentration of glucose in the blood serum of an adult patient. On four consecutive days, a blood sample was drawn from the patient and analyzed in
A method for the determination of the corticosteroid methylprednisolone acetate in solutions obtained from pharmaceutical preparations yielded a mean value of 3.7 mg mL-1 with a standard deviation of
The following data were obtained in calibrating a calcium ion electrode for the determination of pCa. A linear relationship between the potential and pCa is known to exist.pCa = -log [Ca2+]E,
The data in the table below were obtained during a colorimetric determination of glucose in blood serum. Glucose concentration, mM Absorbance,
A study was made to determine the activation energy EA for a chemical reaction. The rate constant k was determined as a function of temperature T, and the data in the table below obtained.T, Kk,
The method of standard additions was used to determine nitrite in a soil sample. A 1.00-mL portion of the sample was mixed with 24.00 mL of a colorimetric reagent, and the nitrite was converted to a
The following table gives the sample means and standard deviations for six measurements each day of the purity of a polymer in a process. The purity is monitored for 24 days. Determine the overall
Describe the steps in a sampling operation
The following results were obtained for the determination of calcium in a NIST limestone sample: % CaO = 50.33, 50.22, 50.36, 50.21, and 50.44. Five gross samples were then obtained for a carload of
Changes in the method used to coat the tablets in Problem 8-6 lowered the percentage of rejects from 5.6% to 2.0%. How many tablets should be taken for inspection if the permissible relative standard
Approximately 15% of the particles in a shipment of silver-bearing ore are judged to be argentite, Ag2S (d = 7.3 g cm-3, 87% Ag); the remainder are siliceous (d = 2.6 g cm-3) and contain essentially
Briefly describe or define and give an example of(a) A weak electrolyte.(b) The conjugate acid of a Bronsted-Lowry base.(c) An amphiprotic solvent.(d) Autoprotolysis.(e) Le Châtelier's principle
Calculate the solubility-product constant for each of the following substances, given that the molar concentrations of their saturated solutions are as indicated: (a) RaSO4 (6.6 x 10-6 M). (b)
What CrO42- concentration is required to?
The solubility-product constant for Ce(IO3)3 is 3.2 x 10-10. What is the Ce3+ concentration in a solution prepared by mixing 50.00 mL of 0.0450 M Ce3+ with 50.00 mL of? (a) Water? (b) 0.0450 M
The solubility products for a series of iodides are CuI K = 1 x 10-12 AgI Ksp = 8.3 x 10-17 PbI2 Ksp = 7.1 x 10-9 BiI3 Ksp = 8.1 x 10-19 List these four compounds in order of decreasing molar

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