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CHEM 210 Final Exam
Questions and Answers
- if the p-value is greater than 0.1, we generally conclude the data are consis- tent with the null hypothesis: true
- what is the best way to characterize the random error present in a mea- surement?: take replicate measurements of your analytes and using the standard deviation and a t-table specify an error bar with a confidence limit
- statistical interference assesses whether an observed phenomenon in the data can reasonably be attributed to chance or not: true
- suppose we collected a sample size n = 100 from some population and used the data to calculate a 95% confidence interval for the population mean. now suppose we are going to increase the sample size to n = 300. keeping all else constant, which of the following would we expect to occur as a result of increasing the sample size?: (1) the standard error would decrease, (2) the margin of error would decrease
- in designing a clinical trial where each subject receives both a placebo and a proposed treatment, what statistical test would be most appropriate?: paired t-test
- an atomic absorption analysis is to be done on the calcium in a sample of powdered milk. a 12.55 gram sample of the powder is wet ashed in nitric acid and diluted to 50.00 mL with distilled water. a 1.00 mL aliquot of this is transferred to a 50.00 mL solution using EDTA. using a wavelength of 422.6 nm in an atomic absorption experiment, this diluted
dilution of the previous tube. if the concentration of the antibiotic tube 1 is 3200 ug/mL, what is the concentration of the antibiotic in tube 6?: 100 ug/mL solution: (1/2)^5 x 3200 = 100
10.to measure the Ca in breakfast cereal, 0.561 g of crushed Cheerios was digested at 600*C in air for 2 hours. the residue was dissolved in 6 M HCl, quantitatively transferred to a volumetric flask and dilution to 100.0 mL. then 5.00-mL aliquots were transferred to 50.0-mL volumetric flasks. each was treated with standard Ca2+ ion solution (20.0 ppm), diluted to volume with H2O, and analyzed by flame atomic absorption. a graph was constructed from the readings. use this graph to determine the wt% Ca in Cheerios.: 0.4% 11.the pH of the titration solution at the equivalence point is 9.45. this is consistent with titration of a weak acid with strong base.: true 12.how many liters of a 2 M Ba(OH)2 are needed to titrate a 4 L solution of 6 M H3PO4?: 18 L solution: (4 x X) = (4 x 18)
the activity coefficient increases 18.glutamic acid is an amino acid consisting of 2 carboxylic acid functional groups and an amine functional group. pkas are listed as 2.19, 4.25, and 9.67. the approximate pH of 0.025 M HL- is?: 6. solution: (1/2) x (4.25 + 9.67) 19.what is the pH of a solution with an ammonium concentration of 70 mM and an ammonia concentration of 712 mM? (pKb of ammonia is 3.45): 11. 20.the amino acid valine has pKa1 = 2.29 and pKa2 = 9.72. what is the principal species at 6.00?: HA- 21.the titration solution consists of essentially pure weak acid...: at the equiv- alence point of a weak acid/strong base titration
- find the pH of a solution prepared by dissolving 0.800 g of potassium hydrogen malonate (C3H3KO4, FM = 142.152 g/mol) and 1.50 g of dipotassium
NaOH is added to 30.00 mL of 0.150 M weak acid, HA. Ka = 4.75 x 10^-6: 5. 28.the temperature program for a separation starts at a temperature of 50C and ramps the temperature up to 270C at a rate of 10*C/min. which statement is NOT true for this separation?: strongly retained analytes will give broad peaks 29.as the temperature of a GC column increases, the of the analyte increases, the retention time , and the peak shapes .: vapor pressure; decreases; sharpen 30.a 3.7 x 10^-4 M solution of a compound X has an absorbance of 0.542 when measured at 740 nm. assuming a pathlength of 1 cm, calculate compound X's molar absorptivity.: 1443 M-1cm- 31.an electrode with a fixed potential is the...: reference electrode
32.a 10.00 mL sample is titrated with 0.50 mL of titrant. the observed ab- sorbance is 0.3219. calculate the corrected absorbance.: 0. solution: (0.3219) x (10.5/10) 33.which comparison of open tubular columns to packed columns is INCOR- RECT?: packed columns have a lower sample capacity
- when a molecule absorbs a photon, the molecule is promoted to an excited state, M. the rate at which M is created is proportional to the concentration of M. there are 3 pathways that M* may take to return to the ground state. which statement below is INCORRECT for these 3 pathways?: the rate at which the excited state returns to the ground state is independent of the pathway to the ground state and the concentration of excited state molecules
- the energy difference between the ground and excited state
excited-state population. as the temperature of the flame increases, the excited-state population.: increases; increases 36.which of the following are TRUE for Beer's Law?: (1) absorbance increases as concentration increases; (2) the molar absorptivity value is chromophore and wavelength specific, (3) the absorption spectrum is a graph showing absorbance changes with wavelength 37.fluorimeters and UV-vis spectrophotometers have several, but not all, de- sign aspects in common. which, if any, of the following is NOT true.: both have their detectors positions at 90* away from the incoming light source 38.hollow-cathode lamps emit light with very sharp linewidths. which mecha- nisms are responsible for broadening atomic emission line widths?: (1) pres- sure broadening; (2) doppler effect 39.under what conditions are split and splitless injection used?: (1) split injection is preferred for samples where the analyte of interest constitute >0.1% of the sample; (2) splitless injection is preferred for trace analysis of analytes that are <0.01% of the sample
- a galvanic cell with a large equilibrium constant has a cell potential: - positive 41.which of the following statements are true regarding the effect of flame temperature on atomic absorbance and atomic emission spectroscopy?: (1) varying the flame temperature by 10 K hardly affects the ground-state population of the analyte and would not noticeably affect the analyte signal in atomic absorption; (2) varying the flame temperature by 10 K affects the excited-state population of the analyte and will noticeably affect the analyte signal in atomic emission 42.which is true for the relationship between quencher concentration and fluorescent intensity?: as quencher concentration increases, fluorescent intensity decreases 43.for quantitative analysis with gas chromatography...: the area of a peak reported by the instrument for a compound is proportional to the quantity of that compound 44.which of the following is not true about the liquid junctional
47.over time, the voltage of the cell S.C.E. || Ag+ (1 M) | Ag(s) decreases and the activity of Ag+ decreases. which of the following statements is true?: the activity of the Cl- in the S.C.E. will remain essentially constant 48.when a half-reaction is multiplied by a coefficient, the standard electrode potential, E, must be multiplied as well.: false 49.a dead battery is a galvanic cell...: at equilibrium 50.when F2(g) is 0.50 bar and aF- is 0.10 M, the half-cell potential for the half reaction (E = 2.890 V) is...: 0. solution: (0.5 x 0.1) + 2. 51.in an electrolytic cell...: cathode is negative 52.if the surface area of an electrochemical cell electrode is tripled, what else is necessarily tripled?: current 53.the pH of a S.H.E. is?: 0 54.for liquid junction potential to be nearly zero...: the external solution concen- tration must be equal to the internal solution concentration
55.which of the following is least likely to be found in the salt bridge of a galvanic cell?: SO 56.a potential difference at an interface between a metal and electrolyte solution is due to...: charge transfer 57.if the standard cell potential is provided, what other data is needed to calculate G?: half-reactions of the cell 58.if the Ecell = 0.023 V versus S.C.E., what is the cell potential versus Ag|AgCl?: 0.068 V 59.the junction 0.10 M HCl / 3.5 M KCl develops a LJP of +3. mV at 25C because...: the mobility of H+ is much higher than the mobility of K+ 60.in the cell Cd(s) | Cd2+ (1 M) || H+ (1 M) | Pt: cations from the salt bridge diffuse into the right half-cell, and anions from the salt bridge diffuse into the left half-cell 61.which of the following choices is indicative of a spontaneous reaction, assuming standard conditions?: Keq > 1 62.in a working galvanic cell, the overall cell reaction is...: spontaneous
