Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.

Lesson: UV–Vis Sample Preparation

Worksheet • 6 Questions

Q1:

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 solvent with a lower UV cutoff
  • BIncreasing the acquisition time for each absorbance measurement
  • CDissolving more of the analyte in the solvent
  • DPre-concentrating the analyte solution
  • EUsing a cuvette with a shorter path length

Q2:

𝛽 -carotene is a highly absorbing chromophore. Which solvent would be the best choice for analysis?

  • AEthanol
  • BMethylene bromide
  • CHexyne
  • DBenzene

Q3:

A sample of 0.10 M triethylamine in hexane is prepared for analysis. Which material should be used as the blank reference?

  • AHexane
  • B Air
  • C 0.10 M triethylamine in water
  • DWater
  • ETriethylamine

Q4:

Which of the following would be the best solvent for a compound with a 𝜆 m a x of 281 nm? You may assume that the compound is completely soluble in each.

  • AEthanol (UV cutoff = 205 nm)
  • BToluene (UV cutoff = 285 nm)
  • CAcetone (UV cutoff = 329 nm)
  • DBenzene (UV cutoff = 278 nm)

Q5:

When preparing a calibration curve for sample analysis, which of the following is best practice?

  • APrepare a stock solution and use serial dilution for the remaining standards.
  • BPrepare each sample “from scratch” to avoid cross contamination.
  • CUse very concentrated solutions to ensure a good signal.
  • DOnly use two data points to ensure a straight line.

Q6:

Why must solutions with high concentrations be diluted prior to analysis via Beer’s Law?

  • AThe relationship between absorbance and concentration is not linear at high concentrations.
  • BThere is no need to work with dilute concentrations; any concentration will work.
  • CThe detector will reach its detection threshhold.
  • DThe molar absorptivity of a compound is dependent on its concentration.
  • EThe photon source is too weak to provide accurate results.
Preview