CHEM 2001 -s15 EXAM 2
NAME:ANSWERS………………………………
Constants h=6.626 10-34 Js , c= 2.9979 108 m/s
What is TRUE or what is NOT TRUE (circle one)
1) FTIR spectra are measured in cm-1 units.
TRUE or NOT TRUE
2) Diode arrays and CCDs are positioned in front of the sample when used in VIS-UV absorption instruments
TRUE or NOT TRUE
3) The more open the monochromator’s slit is in VIS-UV the smaller is the bandwidth
TRUE or NOT TRUE
4) In the emission spectrum measurements the wavelength of the light going to the sample is kept constant.
TRUE or NOT TRUE
5) Fluorescence using laser is an excellent method for imaging and kinetics studies of biological systems (cells, molecules).
TRUE or NOT TRUE
6) Typically, molecules with a high degree of conjugation (Pi electrons) will show MORE luminescence
TRUE or NOT TRUE
7) VISIBLE LIGHT (VIS) LUMINESCENCE instrument has detector positioned at 90 degrees relative to incident light
TRUE or NOT TRUE
8) FTIR spectroscopy uses interferometer
TRUE or NOT TRUE
9) We use absorbance, A, in most analytical applications and not transmittance because it easy to plot/draw
TRUE or NOT TRUE (concentration)
10) UV-VIS sample cells (cuvetts) for measurements bellow 401nm are made of KBr
TRUE or NOT TRUE
11) Globar (Silicon carbide) is the light source used in ICP:
TRUE or NOT TRUE
12) Pyroelectric detecors are used in UV-VIS spectroscopy
TRUE or NOT TRUE
13) A molecule phosphoresces at a wavelength of 542 nm.
The time period is on the order of 10-15 s
TRUE or NOT TRUE 1.8e-15
14) A molecule phosphoresces at a wavelength of 542 nm.
The energy of 542 nm light is on the order of 10-15 J.
TRUE or NOT TRUE
15) ATR is used in FTIR spectroscopy to bend the light
TRUE or NOT TRUE
16) Multiple readings/scans averaging, and double beams are used to eliminate chemical interferents in spectroscopy
TRUE or NOT TRUE
17) You have a laser producing 350 nm monochromatic light in your lab. It can be useful for fluorescence
TRUE or NOT TRUE
18) Nebulizers are used to disperse fluid and the flame is used to atomize samples in AAS.
TRUE or NOT TRUE
19) Spectral, chemical and ionization interferents can all alter measurements in AAS
TRUE or NOT TRUE
20) PMT is used in FTIR spectroscopy
TRUE or NOT TRUE
21) Prism is used instead of grating in some molecular spectroscopy instruments
TRUE or NOT TRUE
22) AAS or AES (ICP) is a good choice for the determination of the concentration of Ca in a sample of baby food.
TRUE or NOT TRUE
………… …………………………
23) AAS or AES (ICP) is a good choice for the determination of the concentration of CO from the engine of your car
TRUE or NOT TRUE
24) Qualitative analysis of toluene, small organic molecule, can be done using FTIR spectroscopy
TRUE or NOT TRUE
25. CO molecule vibration may show a single feature close to 1700 cm-1 in IR spectrum
TRUE or NOT TRUE
.26) If the molecule does not fluoresce, UV-VIS absorption could be the best method to determine concentrations of some water soluble proteins.
TRUE or NOT TRUE
27) H2 molecules produce FTIR vibrational spectra.
TRUE or NOT TRUE
28) Sensitivity of spectroscopic methods are defined as
d A/d [c]……change of absorbance divided by the change of concentration
TRUE or NOT TRUE
29) One measures absorbance before and absorbance after spiking with analyte to eliminate interferents
TRUE or NOT TRUE
30) The corrected absorbance Acorr from a measurement where the transmittance of blank TB= 90% and the transmittance of the sample with analyite is T=20% is less than 0.7
TRUE or NOT TRUE
31) A sample of a diluted dye solution (10 mL in 50 mL) has an absorbance of 0.42 at 426nm in a quartz cuvette ( sample cell ) with path-length 5.00 cm. Molar absorptivity is e426 = 4805 M-1cm-1.
The concentration of the original dye solution is more than 10-5 M
TRUE or NOT TRUE
32)
You perform calibration for absorbance measurements at the wavelength 540nm with standard solutions: given are the following transmittances for these concentrations:
T (transmittance %) : Absorbance A(corrected) Concentration of analyte:
63.22
25.11
15.85
10.00
-Write down the values for corrected absorbances that will be used to obtain the calibration curve.
-Draw a simple figure with the calculated dots and draw a line connecting these dots ( the linear calibration curve).
- Estimate the slope and intercept values for that calibration function and FIND the molecular absorptivity at that wavelength, e560 , if the cell length is 1 cm.