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Unformatted text preview: CHEM 209
10/2/06 NAME: ' 1'. (30 POINTS) A Chemistry major obtains a high-paying summer job in an analytical
laboratory and is given the task of determining the ethanol content (in vol %) of a '
commercial mouthwash sample. He/she decides to do this by- gas chromatography
because the experiment was so enjoyable in Chem 209. Accordingly, he/she makes up several standard ethanol solutionsranging from 0 to 12% ethanol (vol %), injects 2.0 pL - of each into the GC, and uses the areas of the ethanol peak to create a calibration curve
whose linear regression equation is: y= 43.2 x The student then takes exactly 8.0 mL of the mouthwash sample and dilutes this to 25 mL
with deionized water. He/she then injects 2.0 uL of the diluted sample into the GC and
obtains an area of 132.5 for the ethanol peak. ' - ' (a) Calculate the ethanol concentration (vol %) of the mouthwash sample. SHOW ALL
WORK. (b) Suppose that chromatogram obtained for the mouthwash sample contained seven
What is the minimumnumber of different species in the sample? What is the maximum number of different species in the sample? Brieﬂy indicate two reasons why these two numbers might not be the same. (c) Suppose that you need to “speed up” a chromatogram (i.e., decrease the retention
times of all the peaks). Suggest three Speciﬁc GC conditions that you could change in
order to accomplish this. (1)
(3) 2. (10 POINTS) Write the equilibrium constant expression for the following chemical
reaction: H803" + 13' + 31-120 '—-""’ HSO4' +3'I' + 2H30+ K: 3. (30 POINTS) (3) Write the balanced chemical reaction that occurs during the complete titration of Na2003 with HCl. (b) 0n the graph below, sketch the shape of the titration curve expected for this
titration. mL HCl (c) If the Na2C03 weight talcen for the titration 0.3333 gram and concentration of the
HCl solution was 0.096M, calculate the equivalence point volume expected. SHOW ALL
WORK CLEARLY. (Formula weights: Na2C03 = 105.99 g/mole; RC] = 36.46 g/mole) 4. (20 POINTS) Draw block diagrams of each of the following analytical instruments, .
labeling all the important Components. ' (a) a gas chromatograph (GC) (b) a visible spectrophotometer (e.g., the Spectronic 20) 5. (10 POINTS) Calculate the following and snow YOUR WORK: (a) the pH of a 0.005M NaOH solution. (b) the %T of a solution whose absorbance is 0.20. ...
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