Week 1 Flipped Lecture: Dilutes and Calibration Curves + 9/11 Friday Problem Set

What is a Blank and what is it used for?

a sample solution that has no analyte and is used to measure just the effect of the cuvette and analytical reagents

The blank is used to zero (calibrate) the spectrometer.

What is a Standard Solution?

a solution that has a known concentration of analyte

What is a Calibration Curve used for? How is it prepared?

can be used to determine the concentration of an unknown solution

Prepared by measuring the absorbance of standard solutions at a constant wavelength and plotting the absorbance versus concentration. The calibration curve is bracketed by the standard solutions (If the greatest absorbance of a standard is 0.33, then the absorbance of any unknown with an absorbance value about 0.33 cannot be determined.)

Describe two ways to prepare standard solutions. Which is better?

Serial Dilutions: use stock to create a solution, dilute a small amount of that solution to create another solution, and repeat to create a set of solutions concentrations that cover a range of magnitude

Series Dilutions (Simple/Linear dilutions): use different amounts stock to separately create multiple solutions with different concentrations

A series is more accurate and precise than serial dilutions.

How many standard solutions are needed to create a good calibration curve?

At least 5 standard solutions are needed (this doesn’t include the blank)

How do you sketch an absorbance spectrum for a given color(s)?

Discuss axes, units, and the height and location of peaks/troughs.

Label the y-axis as absorbance (with units going from 0 to 0.1 to at least 1.0). The exact absorbance of the curve doesn’t matter if you don’t have that information. If there are multiple colors, draw the absorbance of the peaks relative to each other.

• If the concentration and molar extinction coefficient are the same for both colors in the solution, then the absorbance should be the same.

• If one of the colors is more efficient at absorbing light or has a higher concentration, then the absorbance for that color should be higher.

Label the x-axis as wavelength (in nm). The units don’t have to start at 0. The peak of the curve should be located at the range of the absorbed color. The trough (close to the x-axis) should be located at the range of the observed color.

What is ppm and ppb in grams and liters?

ppm = 1 mg/kg

For pure water only: ppm = 1 mg/L

ppb = 1 μg/kg

For pure water only: ppb = 1 μg/L