CHEM 101L- EXP. 7 QUESTIONS AND ANSWERS
Define Beer's Law verbally and be able to describe the usefulness of this concept
in making measurements of chemical species and properties.
- tells us how much there is of something
- relates absorbency to concentration
- defines how strongly the solution being studied absorbs light at a particular
wavelength.
- This is unique for each different chemical at each different wavelength.
- The quantity of light absorbed by a substance dissolved in a nonabsorbing solvent is
directly proportional to the concentration of the substance and the path length of the
light through the solution
Define Beer's law mathematically
What are the key features of a Beer's Law plot? Identify key regions of the plot.
What is the value of plotting these data individually rather than averaging values
for the standard curve?
- The curve helped us identify the unknown concentration by giving a set plot
- Slope equates to the product of the molar extinction coefficient x path length.
- Intercept represents background signal not associated with analyte.
- Correlation coefficient is equal to R2 value.
- Better not to average because it give us an idea of where the unknown concentration
will fall
Interpret the quality of the standard curve based on experimental data, and
anticipate the effect of errors in the standard curve on the results of the
experiment. What is the purpose of making multiple measurements of each
standard solution?
- linear regression represents calibration curve
- Making multiple measurements improved the accuracy (helps incase one side of the
cuvette is scratched or blocked)
Define absorbance, transmittance
- Absorbance - how much light does not get through
- Transmittance- how much light gets through the cuvette
molar extinction coefficient
- How strongly the analyte absorbs light at a particular wavelength
- Different for each and every wavelength and analyte
Blank
Does not contain analyte
molarity
Concentration in mol/L of solution
path length
The path length of the light through the solution (cm)
colorimetry
- instrumental method based on the measurement of light absorption by colored solution
and is used to perform chemical analysis
stock solution
Define Beer's Law verbally and be able to describe the usefulness of this concept
in making measurements of chemical species and properties.
- tells us how much there is of something
- relates absorbency to concentration
- defines how strongly the solution being studied absorbs light at a particular
wavelength.
- This is unique for each different chemical at each different wavelength.
- The quantity of light absorbed by a substance dissolved in a nonabsorbing solvent is
directly proportional to the concentration of the substance and the path length of the
light through the solution
Define Beer's law mathematically
What are the key features of a Beer's Law plot? Identify key regions of the plot.
What is the value of plotting these data individually rather than averaging values
for the standard curve?
- The curve helped us identify the unknown concentration by giving a set plot
- Slope equates to the product of the molar extinction coefficient x path length.
- Intercept represents background signal not associated with analyte.
- Correlation coefficient is equal to R2 value.
- Better not to average because it give us an idea of where the unknown concentration
will fall
Interpret the quality of the standard curve based on experimental data, and
anticipate the effect of errors in the standard curve on the results of the
experiment. What is the purpose of making multiple measurements of each
standard solution?
- linear regression represents calibration curve
- Making multiple measurements improved the accuracy (helps incase one side of the
cuvette is scratched or blocked)
Define absorbance, transmittance
- Absorbance - how much light does not get through
- Transmittance- how much light gets through the cuvette
molar extinction coefficient
- How strongly the analyte absorbs light at a particular wavelength
- Different for each and every wavelength and analyte
Blank
Does not contain analyte
molarity
Concentration in mol/L of solution
path length
The path length of the light through the solution (cm)
colorimetry
- instrumental method based on the measurement of light absorption by colored solution
and is used to perform chemical analysis
stock solution
