UF PHA6936 FINAL EXAM PREP
EXAMPREP COMPREHENSIVE QUESTIONS
AND CORRECT ANSWERS ALREADY
PASSED
⩥ Beer's Law calibration curve:
Use the following data to generate a calibration curve of Absorbance vs
Concentration at λmax = 420.6 nm.
concentration 1: 6e-5 M; absorbance 1: 1.330
concentration 2: 2e-5 M; absorbance 1: 0.451
concentration 1: 1e-5 M; absorbance 1: 0.239
concentration 1: 2e-6 M; absorbance 1: 0.042
Record the equation and analyze your data:
- do all of the data points fall on the trendline? Is your R2 value greater
than 0.990?
- what does y represent?
,- what does x represent?
- why should the y-intercept of the linear trendline be very close to 0?.
Answer: equation: y=22066x + 0.008
yes, all points fall on the trendline or are very close. R2 = 0.9998
y = absorbance
x = solute concentration (mol/L)
a y-intercept of 0 indicates 0 absorbance at 0 M concentration of colored
solute
⩥ Serial Dilution:
- Perform calculations to determine the amount of 6.00x10-5 M stock
solution needed to prepare 20.00 mL of 2.00x10-5 M dye solution.
- Perform calculations to determine the amount of 2.00x10-5 M stock
solution needed to prepare 20.00 mL of 1.00x10-5 M dye solution.
,- Perform calculations to determine the amount of 1.00x10-5 M stock
solution needed to prepare 20.00 mL of 2.00x10-6 M dye solution..
Answer: x = 6.67 ml
x = 10 ml
x = 4 ml
⩥ using this Beer's Law calibration curve equation, y=22066x + 0.008,
at λmax = 420.6 nm, determine the concentrations for each of the
absorbances values below:
absorbance 1: 2.224
absorbance 2: 1.558
if absorbance 1 is from a 1e-3 M stock solution and absorbance 2 is from
a 1e-4 M stock solution, do all of these data points follow Beer's Law?
(did the concentrations you obtained using the equation match the
concentrations of the stock solutions?). If not, why? (***hint: look at the
excel graph you generated and determine the maximum absorbance at
λmax = 420.6 nm that falls on/very close to the trendline).
Answer: for absorbance 1:
x = 1e-4 M
, for absorbance 2:
x = 7.02e-5 M
No. These concentrations obtained from the absorbances, y = 2.224 and
y = 1.558, do not follow Beer's Law. The concentrations calculated do
not match the stock solution concentrations, 1e-3 M and 1e-4 M. The
maximum absorbance value that follows Beer's Law is 1.330 at λmax =
420.6 nm because 1.330 falls on the trendline. The absorbances, y =
2.224 and y = 1.558, do not follow the trendline because their
absorbances surpass the maximum absorbance at λmax = 420.6 nm.
⩥ consider that you have a 100 mM stock solution and you need to
prepare 10 ml of a 30 mM solution.
How many ml of the stock solution do you need?
How many ml of deionized water do you need?
enter each of your answers to 2 sig figs.
Answer: 3.0 ml stock
7.0 ml DI water
EXAMPREP COMPREHENSIVE QUESTIONS
AND CORRECT ANSWERS ALREADY
PASSED
⩥ Beer's Law calibration curve:
Use the following data to generate a calibration curve of Absorbance vs
Concentration at λmax = 420.6 nm.
concentration 1: 6e-5 M; absorbance 1: 1.330
concentration 2: 2e-5 M; absorbance 1: 0.451
concentration 1: 1e-5 M; absorbance 1: 0.239
concentration 1: 2e-6 M; absorbance 1: 0.042
Record the equation and analyze your data:
- do all of the data points fall on the trendline? Is your R2 value greater
than 0.990?
- what does y represent?
,- what does x represent?
- why should the y-intercept of the linear trendline be very close to 0?.
Answer: equation: y=22066x + 0.008
yes, all points fall on the trendline or are very close. R2 = 0.9998
y = absorbance
x = solute concentration (mol/L)
a y-intercept of 0 indicates 0 absorbance at 0 M concentration of colored
solute
⩥ Serial Dilution:
- Perform calculations to determine the amount of 6.00x10-5 M stock
solution needed to prepare 20.00 mL of 2.00x10-5 M dye solution.
- Perform calculations to determine the amount of 2.00x10-5 M stock
solution needed to prepare 20.00 mL of 1.00x10-5 M dye solution.
,- Perform calculations to determine the amount of 1.00x10-5 M stock
solution needed to prepare 20.00 mL of 2.00x10-6 M dye solution..
Answer: x = 6.67 ml
x = 10 ml
x = 4 ml
⩥ using this Beer's Law calibration curve equation, y=22066x + 0.008,
at λmax = 420.6 nm, determine the concentrations for each of the
absorbances values below:
absorbance 1: 2.224
absorbance 2: 1.558
if absorbance 1 is from a 1e-3 M stock solution and absorbance 2 is from
a 1e-4 M stock solution, do all of these data points follow Beer's Law?
(did the concentrations you obtained using the equation match the
concentrations of the stock solutions?). If not, why? (***hint: look at the
excel graph you generated and determine the maximum absorbance at
λmax = 420.6 nm that falls on/very close to the trendline).
Answer: for absorbance 1:
x = 1e-4 M
, for absorbance 2:
x = 7.02e-5 M
No. These concentrations obtained from the absorbances, y = 2.224 and
y = 1.558, do not follow Beer's Law. The concentrations calculated do
not match the stock solution concentrations, 1e-3 M and 1e-4 M. The
maximum absorbance value that follows Beer's Law is 1.330 at λmax =
420.6 nm because 1.330 falls on the trendline. The absorbances, y =
2.224 and y = 1.558, do not follow the trendline because their
absorbances surpass the maximum absorbance at λmax = 420.6 nm.
⩥ consider that you have a 100 mM stock solution and you need to
prepare 10 ml of a 30 mM solution.
How many ml of the stock solution do you need?
How many ml of deionized water do you need?
enter each of your answers to 2 sig figs.
Answer: 3.0 ml stock
7.0 ml DI water
