In this worksheet, we will practice describing UV–vis sample preparation, including filtration, dilution, cuvette selection, and reference selection.
Why must solutions with high concentrations be diluted prior to analysis via Beer’s Law?
- AThe photon source is too weak to provide accurate results.
- BThe detector will reach its detection threshhold.
- CThe molar absorptivity of a compound is dependent on its concentration.
- DThe relationship between absorbance and concentration is not linear at high concentrations.
- EThere is no need to work with dilute concentrations; any concentration will work.
Which of the following would be the best solvent for a compound with a of 281 nm? You may assume that the compound is completely soluble in each.
- ABenzene (UV cutoff = 278 nm)
- BToluene (UV cutoff = 285 nm)
- CAcetone (UV cutoff = 329 nm)
- DEthanol (UV cutoff = 205 nm)
-carotene is a highly absorbing chromophore. Which solvent would be the best choice for analysis?
- BMethylene bromide
When preparing a calibration curve for sample analysis, which of the following is best practice?
- AOnly use two data points to ensure a straight line.
- BPrepare each sample “from scratch” to avoid cross contamination.
- CUse very concentrated solutions to ensure a good signal.
- DPrepare a stock solution and use serial dilution for the remaining standards.
When a sample is analyzed by UV-Vis spectroscopy, the results may be unreliable if the signal-to-noise ratio is too low. Which of the following is not a method for avoiding this issue?
- AUsing a cuvette with a shorter path length
- BDissolving more of the analyte in the solvent
- CPre-concentrating the analyte solution
- DUsing a solvent with a lower UV cutoff
- EIncreasing the acquisition time for each absorbance measurement
A sample of 0.10 M triethylamine in hexane is prepared for analysis. Which material should be used as the blank reference?
- B 0.10 M triethylamine in water
- E Air