analytical chem midterm

What volume of 12.1 M HCl must be diluted to prepare a 0.2500 M HCl solution with a volume of 2.000 L? A) 41.3 mL B) 96.8 mL C) 10.3 mL D) 24.2 mL E) 6.05 mL

A) 41.3 mL

A buffer is prepared by mixing 200.0 mL of 0.1500 M NaOH with 200.0 mL of 0.200 M CH3CO2H in a 1-L volumetric flask and then diluted to volume with distilled deionized water. Calculate the pH of the buffer. Ka = 1.75 × 10−5 A) 5.23 B) 9.72 C) 7.00 D) 8.77 E) 4.28

A) 5.23

Calculate the pH of a 0.340 M NaO2CCO2H solution. pK1 = 1.250 and pK2 = 4.266. A) 2.37 B) 4.89 C) 2.79 D) 3.38 E) −0.029

C) 2.79

Doubling the number of calibration curve data points decreases the standard uncertainty in the slope and y-intercept by a factor of: A) 2. B) ½. C) 4. D) sqrt(2) E) 1/sqrt(2)

E) 1/sqrt(2)

Calculate pPb when 25.00 mL of 0.100 M CO32− is titrated with 21.00 mL of 0.100 M Pb2+. Ksp = 7.4 x 10−14 for PbCO3. A) 11.07 B) 2.06 C) 11.41 D) 1.72 E) 11.99

A) 11.07

Calculate pPb when 25.00 mL of 0.100 M CO32− is titrated with 28.00 mL of 0.100 M Pb2+. Ksp = 7.4 x 10−14 for PbCO3. A) 11.21 B) 10.88 C) 6.57 D) 2.25 E) 1.92

A) 11.21

How many millimoles of NaOH or HCl must be added to 500.0 mL of 0.250 M NaO2CCO2H to prepare a pH 3.90 buffer? Assume no change in volume. pK1 = 1.250 and pK2 = 4.266. A) 37.65 mmol NaOH B) 87.35 mmol HCl C) 124.7 mmol HCl D) 0.30 mmol NaOH E) The answer cannot be calculated from given information.

A) 37.65 mmol NaOH

For significant digits and calculations, the following statements are true, EXCEPT for which one(s)? I Addition and subtraction―round off the answer according to the number of decimal places in the number with the most decimal places. II Multiplication and division―the answer is limited to number of digits in the number with the fewest significant digits. III Logarithms and antilogarithms ―the number of significant figures in the antilogarithm should equal the number of digits in the mantissa. A) I B) II C) III D) I and II E) I and III

A) I

In which solution is solubility of silver chloride the largest? A) Pure water B) 0.05 M CaCl2 C) 0.10 M NaCl D) 0.10 M FeCl3 E) 0.15 M AgNO3

A) Pure water

For a fixed absolute uncertainty, as the magnitude of the measurement------- , the percent relative uncertainty------- . A) increases; decreases B) increases; increases C) decreases; decreases D) decreases; increases E) increases; remains constant

A) increases; decreases

A student attempts to separate Cl− and I− from a solution that is 0.05 M Cl− and 0.10 M I− with Pb(NO3)2. As Pb(NO3)2is added, which anion will precipitate first and what will the concentration of the anion be when the second anion begins to precipitate? Ksp = 1.7 x 10−5 for PbCl2 and Ksp = 9.8 x 10−9 for PbI2. A) iodide precipitates first; 0.0068 M iodide B) iodide precipitates first; 0.0012 M iodide C) iodide precipitates first; 0.05 M iodide D) chloride precipitates first; 0.0012 chloride E) chloride precipitates first; 0.10 M chloride

A) iodide precipitates first; 0.0068 M iodide B) iodide precipitates first; 0.0012 M iodide

A student prepares a solution using a 1 L volumetric flask. When he finishes, the meniscus is above the calibration mark on the flask neck. The concentration of the solution is: A) less than calculated. B) greater than calculated. C) unchanged. D) irrelevant. E) impossible to predict.

A) less than calculated.

Calculate the mean and standard deviation for the results below for the concentration of lead in a soil sample. 23.2 ppm, 20.1 ppm, 24.7 ppm, 19.9 ppm, 21.8 ppm A) 21.9 ± 3.4 (n = 5) ppm B) 21.9 ± 2.0 (n =5) ppm C) 27.4 ± 2.0 (n = 5) ppm D) 22.0 ± 1.8 (n = 5) ppm E) 27.4 ± 4.2 (n = 5) ppm

B) 21.9 ± 2.0 (n =5) ppm

What volume of a 36% HCl solution must be diluted to prepare 1.000 L of a 0.1000 M HCl solution? The density of 36% HCl is 1.18 g/mL. A) 11.7 mL B) 8.6 mL C) 1.2 mL D) 10.1 mL E) 64.6 mL

B) 8.6 mL

There are two types of metal hydroxides, soluble metal hydroxides and insoluble hydroxides, both of which are strong bases. Which of the following statements is NOT true for strong bases? A) Dilute solutions are completely dissociated. B) Fe(OH)2 is a strong soluble base. C) For strong base solutions with a concentration between 10−6 and 10−8 M, the pOH is determined using systematic equilibrium. D) For strong base solutions with concentrations ³ 10−6 M, the pOH is calculated from the concentration of the strong base. E) For strong base solutions with concentrations £ 10−8 M, the pOH is always 7.

B) Fe(OH)2 is a strong soluble base.

There are seven common strong acids. Which of the following statements is NOT true for strong acids? A) Dilute solutions are completely ionized. B) HNO2 is a strong acid. C) For strong acid solutions with a concentration between 10−6 and 10−8 M, the pH is determined using systematic equilibrium. D) For strong acid solutions with concentrations ³ 10−6 M, the pH is calculated from the concentration of the strong acid. E) For strong acid solutions with concentrations £ 10−8 M, the pH is always 7.

B) HNO2 is a strong acid.

A technician determines the concentration of calcium in milk using two instrumental methods. If Fcalculated > Ftable for the two sets of calcium data, what conclusion(s) can the technician make? I The difference in standard deviations for the two instrumental methods is significant. II The difference in standard deviations for the two instrumental methods is not significant. III The data comes from populations with the same standard deviation. IV The data does not come from populations with the same standard deviation. A) I and III B) I and IV C) II and III D) II and IV E) Only II

B) I and IV

For a 0.0005 M HBr solution, the dissociation of water produces -------- H3O+ and --------- OH−. A) 1.00E-07 M; 2.00E-11 M B) 5.00E-04 M; 5.00E-04 M C) 2.00E-11 M; 2.00E-11 M D) 1.00E-07 M; 1.00E-07 M E) 5.00E-04 M; 2.00E-11 M

C) 2.00E-11 M; 2.00E-11 M

is the upward force exerted on an object in a gaseous or liquid fluid. The mass measured by an analytical balance in air is its actual mass. A) buoyancy; heavier than B) buoyancy; lighter than C) electromagnetic force; heavier than D) electromagnetic force; lighter than E) tare; equal to

B) buoyancy; lighter than

Calculate the error for the molar mass of acetic acid, CH3CO2H. The atomic masses for each element are C = 12.0106 ± 0.0010, H = 1.00798 ± 0.00014, and O = 15.9990 ± 0.0008. A) ± 0.010 g/mol B) ± 0.0026 g/mol C) ± 0.0013 g/mol D) ± 0.0042 g/mol E) ± 0.021 g/mol

B) ± 0.0026 g/mol

For which measurement has the number of significant digits been incorrectly determined? A) 12.9830 g six significant digits B) 1920.3 m five significant digits C) 0.0043 g four significant digits D) 1.003 L four significant digits E) 59.0 km three significant digits

C) 0.0043 g four significant digits

Calculate the percentage dissociation for a 0.010 M hypochlorous acid solution. The Ka for hypochlorous acid is 3.0 x 10−8. A) 0.35% B) 0.30% C) 0.17% D) 0.99% E) 0.65%

C) 0.17%

Calculate the mass of Na2CO3 needed to prepare a 15.00 mM solution with a volume of 500.0 mL. (Na2CO3 = 105.9888 g/mol) A) 1.258 g B) 3.180 g C) 0.7949 g D) 7.076 g E) 0.0141 g

C) 0.7949 g

Calculate pPb at the equivalence point when 25.00 mL of 0.100 M CO32- is titrated with 0.100 M Pb2+. Ksp = 7.4 x 10−14for PbCO3. A) 5.17 B) 7.96 C) 6.57 D) 4.87 E) 8.26

C) 6.57

A student must prepare 500.0 mL of solution containing 0.999 grams of solid copper(II) sulfate. Which of the following statements are FALSE regarding the proper procedure to prepare this solution? I The 0.999 grams of solid copper(II) sulfate is dissolved in a 500.0-mL volumetric flask containing 500.0 mL of water. II The 0.999 grams of solid copper(II) sulfate is dissolved in a 500.0-mL volumetric flask containing 400 mL of distilled water before dilution to 500.0-mL. III The 0.999 grams of solid copper(II) sulfate is placed in an empty 500.0-mL volumetric flask, diluted to 500.0 mL and allowed to dissolve. A) I and II B) II and III C) I and III D) I, II, and III E) None are false.

C) I and III

Organic solvents, concentrated acids, and concentrated ammonia should be handled in a fume hood. II A respirator should be worn when handling organic solvents. III All containers should be labeled to indicate what they contain. IV Contact lenses are adequate to protect eyes from liquids and gases in the lab. A) I and II B) II and IV C) I and III D) III and IV E) II and III

C) I and III

Which of the statements below are TRUE for expressing the concentration of a 54.9-ppm Fe solution in terms of molarity? I Iron's molar mass must be known to calculate the moles iron in solution. II Iron's density must be known to calculate the mass iron in solution. III The solution density must be known to calculate the solution volume. IV The type of glassware used to prepare the solution must be known. A) I, III, and IV B) I and II C) I and III D) II and III E) None of these is true.

C) I and III

A technician determines the concentration of calcium in milk using two instrumental methods. If Fcalculated < Ftable for the two sets of calcium data, what conclusion(s) can the technician make? I The difference in standard deviations for the two instrumental methods is significant. II The difference in standard deviations for the two instrumental methods is not significant. III The data comes from populations with the same standard deviation. IV The data does not come from populations with the same standard deviation. A) I and III B) I and IV C) II and III D) II and IV E) Only II

C) II and III

Which of the answers below is INCORRECT for diprotic acids and bases? A) Solutions of H2A are treated as monoprotic to calculate [H+], [HA−] and [H2A]. B) The pH for HA− solutions is appro×imated with pH = ½(pK1 + pK2). C) Ka1Kb1 = Kw and Ka2Kb2 = Kw D) Solutions of A2− is treated as monobasic to calculate [OH−], [HA−], and [A2−]. E) A zwitterion is a neutral molecule with both positive and negative charges.

C) Ka1Kb1 = Kw and Ka2Kb2 = Kw

is a consistent error that can be detected and corrected. A) User error B) Internal error C) Systematic error D) Random error E) Indeterminate error

C) Systematic error

Which is NOT a property of buffers? A) Buffers resist changes in pH when acids or bases are added or when dilution occurs. B) Buffers are a mixture of weak acid and conjugate base. C) The pH of a buffer is independent of ionic strength. D) The pH of a buffer is dependent on temperature. E) Buffers are a mixture of weak bases and conjugate acid.

C) The pH of a buffer is independent of ionic strength.

Which of the following terms is INCORRECTLY defined? A) titration error: the difference between the end point and the equivalent point B) direct titration: titrant is added to analyte until reaction is complete C) equivalent point: volume of titrant added in excess of the end point to change a physical property of the analyte solution D) blank titration: titration performed without analyte to calculate titration error E) standardization: titration of a known amount of analyte to determine the concentration of the titrant

C) equivalent point: volume of titrant added in excess of the end point to change a physical property of the analyte solution

A Na2CO3 standard solution is prepared by transferring 2.4817 grams of primary standard-grade sodium carbonate to a 250.0-mL volumetric flask, dissolving the sample in ~100 mL of distilled deionized water and diluted to the mark. A 25.00-mL aliquot is taken and titrated with 42.65 mL of HCl solution. Calculate the concentration of the HCl solution. A) 0.05490 M B) 0.1598 M C) 0.3196 M D) 0.1098 M E) 0.1997 M

D) 0.1098 M

the density of a solution is determined using a class A 25-mL volumetric flask and an analytical balance. If the mass of the empty volumetric flask is 26.9872 ± 0.0003 g, the mass of the flask filled with solution is 53.9820 ± 0.0003 g, and the tolerance for the flask is ± 0.03 mL, what is the density of the solution? A) 1.07979 ± 0.00001 g/mL B) 1.0798 ± 0.0004 g/mL C) 1.0798 ± 0.0003 g/mL D) 1.080 ± 0.001 g/mL E) 1.0798 ± 0.0005 g/mL

D) 1.080 ± 0.001 g/mL

Calculate the molarity of a 30.0% hydrogen peroxide solution. The reported density of 30% hydrogen peroxide is 1.135 g/cm3. (H2O2 = 34.0147 g/mol) A) 7.77 M B) 0.0100 M C) 0.100 M D) 10.0 M E) 8.82 M

D) 10.0 M

The sulfur content of an ore is determined gravimetrically by reacting the ore with concentrated nitric acid and potassium chlorate, converting all sulfur to sulfate. The excess nitrate and chlorate is removed by reaction with concentrated hydrochloric acid and the sulfate is precipitated using barium cation. Ba2+ (aq) + SO42- (aq) ® BaSO4 (s) Analysis of 10.1830 grams of a sulfur containing ore yielded 13.0221 grams of BaSO4. What is the percent by mass sulfur in the ore? (BaSO4 = 233.43 g/mol) A) 32.18% B) 52.63% C) 10.74% D) 17.57% E) The answer cannot be calculated with available data.

D) 17.57%

A 0.01 M solution of a weak base has a percent association of 18.32%. Calculate the Kb for the weak base. A) 1.83 × 10−3 B) 2.43 × 10 −11 C) 5.46 × 10−12 D) 4.11 × 10−4 E) 1.22 × 10−12

D) 4.11 × 10−4

Calculate the mass NaCH3CO2 contained in 500.0 mL of a 0.1500 M NaCH3CO2 solution. (NaCH3CO2 = 82.0343 g/mol) A) 914.3 µg B) 283.4 g C) 24.61 µg D) 6.378 g E) 24.61 g

D) 6.378 g

ulfurous acid is a diprotic acid with Ka1 = 1.40 × 10−2 and Ka2 = 6.73 × 10−8. Which of the statements below are FALSE? I Kb2 = 7.14 × 10−13 II Kb1 = 1.49 × 10−7 III For 0.1 M H2SO3, [H+] = 7.61 × 10−2 for Ka1. IV For 0.1 M NaHSO3, pH » 4.515. A) I, II, and IV B) I, II, and III C) I and II D) I, II, III, and IV E) II, III, and IV

D) I, II, III, and IV

For the reaction aA (aq) + bB (s) « cC (l) + dD (g), all of the statements below are TRUE, except: A) B) concentrations of solutes are expressed in moles per liter. C) concentrations of gases are expressed in bars. D) concentrations of pure solids, pure liquids and solvents are omitted because they are negligible. E) quantities in the equilibrium expression are the ratio of the concentration of the species to the concentration in its standard state.

D) concentrations of pure solids, pure liquids and solvents are omitted because they are negligible.

The end point for the Volhard titration is indicated by: A) adsorption of a colored indicator on the precipitate at the end point. B) reduction of a colored indicator at the end point. C) deprotonation of a colored acid-base indicator at the end point. D) formation of a soluble, colored complex at the end point. E) protonation of a soluble, colored complex at the end point.

D) formation of a soluble, colored complex at the end point.

A 1.9450 g sample containing only Na2CO3 and NaHCO3 is titrated with 35.31 mL of 0.8724 M HCl. Calculate the percentage sodium carbonate and sodium bicarbonate. A) 43.53% Na2CO3; 56.47% NaHCO3 B) 44.45% Na2CO3; 55.55% NaHCO3 C) 55.55% Na2CO3; 44.45% NaHCO3 D) 71.62% Na2CO3; 28.38% NaHCO3 E) 56.47% Na2CO3; 43.53% NaHCO3

E) 56.47% Na2CO3; 43.53% NaHCO3

expresses the margin of uncertainty associated with a measurement. A) Nominal uncertainty B) Maximum uncertainty C) Relative uncertainty D) Minimum uncertainty E) Absolute uncertainty

E) Absolute uncertainty

Which of the following is INCORRECT for Brønsted-Lowry acids and bases? A) Acids are proton donors. B) NH4+ is the conjugate acid of the weak base NH3. C) When an acid and a base react, the acid and base neutralize each other and form a salt. D) Water reacts with itself to form hydronium and hydroxide, a process called autoprotolysis. E) CH3CN is a protic solvent.

E) CH3CN is a protic solvent.

Which scenario below has the lowest relative uncertainty? A) Delivering 35.50 mL of titrant with a 50 +/− 0.05 mL class A buret. B) Delivering 15.40 mL of titrant with a 50 +/− 0.05 mL class A buret. C) Delivering 18.50 mL of titrant with a 25 +/−0.03 mL class A buret. D) Delivering 5.40 mL of titrant with a 25 +/−0.03 mL class A buret. E) Delivering 97.30 mL of titrant with a 100 +/−0.10 mL class A buret.

E) Delivering 97.30 mL of titrant with a 100 +/−0.10 mL class A buret.

The molar solubility of a saturated iron(II) carbonate solution derived from the Ksp value is 5.6 x 10−6 M. The molar solubility is greater than 5.6 x 10−6 M when accounting for additional reactions. Which of the reactions below will not increase the solubility of iron(II) carbonate? A) Fe2+ (aq) + OH− (aq) « FeOH+ (aq) B) CO32− (aq) + H+ (aq) « HCO3− (aq) C) HCO3− (aq) + H+ (aq) « H2 CO3 (aq) D) H2CO3 (aq) « CO2 (g) + H2O (l) E) FeOH+ (aq) + OH− « Fe(OH)2 (s)

E) FeOH+ (aq) + OH− « Fe(OH)2 (s)

For the graphical equivalence point determination for a precipitation reaction, which of the following is(are) TRUE? I The steepest slope of the titration curve is the equivalence point. II The equivalence point occurs where the first derivative of the titration curve reaches its largest value. III The equivalence point occurs where the second derivative of the titration curve equals zero. A) I only B) II and III C) II only D) III only E) I, II, and III

E) I, II, and III

Which of the statements below are TRUE regarding the mean and standard deviation? I As the number of measurements increases, approaches m if there is no random error. II The square of the standard deviation is the average deviation. III The mean is the center of the Gaussian distribution. IV The standard deviation measures the width of the Gaussian distribution. A) II, III, and IV B) I, III, and IV C) I and II D) I, II, and IV E) III and IV

E) III and IV

For the statements below, which is(are) TRUE for confidence intervals? I As the percentage confidence increases, the confidence interval range decreases. II Confidence intervals are calculated using the calculated mean and standard deviation of a set of n measurements; and the results of the F test. III The 95% confidence interval will include the true population mean for 95% of the sets of n measurements. A) I only B) II only C) I and III D) I and II E) III only

E) III only

Which of the classes of acids and bases and strength have been incorrectly matched? A) RCO2H: weak acid B) R3N: weak base C) RCO2−: weak base D) R3NH+: weak acid E) R4NOH: weak base

E) R4NOH: weak base

A student titrated extracted chloride from a soil sample with 0.1 M silver nitrate. During the titration he performed the following actions while operating the buret. · Washed the buret with silver nitrate solution · Drained titrant slowly · Delivered a fraction of a drop near end point · Read bottom of concave meniscus · Avoided parallax · Accounted for graduation thickness in readings His instructor notes on the student's lab report that the student forgot to when operating his buret. A) eliminate air bubbles B) estimate reading the buret to 1/10 of a division C) fill the buret to exactly 0.00 mL D) eliminate air bubbles and fill the buret to exactly 0.00 mL. E) eliminate air bubbles and estimate reading the buret to 1/10 of a division.

E) eliminate air bubbles and estimate reading the buret to 1/10 of a division.