GEOL 463
Env Geochem
Name ____________________
Lab: Dilutions and Spectral Properties of Solutions
Overview:
The purpose of this week’s lab is to
 prepare calibration standards
 use a UV-Vis spectrometer to determine the spectral peaks for several dye solutions, and
create a calibration curve
 calculate how much of each single-element standard solution is needed to make a multielement stock solution, and
 calculate the elemental concentrations in a stock solution and serial dilutions of that stock
solution.
Need:
15 ml centrifuge tubes
Cuvets
Pipet, Pipet tips
Pre-made bottles of dye solutions (red, green, blue, and yellow)
Distilled water
Instructions
Start the UV-Visible spectrophotometer using the instructions in the file “UV-VisSpec_
scanning-for-peaks.docx”.
Maximum Absorbance
1. Prepare five cuvets, one with each of the following solutions: distilled water, red, green,
blue, and yellow. With a clean cloth, wipe the clear (non-ridged) sides of the cuvets and
place in the UV-Visible Spectrophotometer so that the clear sides are perpendicular the
path of the light.
2. Find the maximum absorbance (peak) for each solution, and record the wavelength and
absorbance at that point.
(24pts)
Maximum absorbance
Sample Name
Distilled water
Red solution
Green solution
Blue solution
Yellow solution
Units:
Wavelength at maximum
absorbance
Units:
Calibration Curve
3. Choose one of the dye colors. Record that color here: ____________.
a. Using the table below, calculate the volumes needed to make each solution, and
the dye concentration of each solution.
(30pts)
To Make Solution in Column 1
*Solution
to
Prepare
Solution
to Dilute
Volume of
Solution in Column
(mL)
distilled
water
(mL)
Total
solution
(mL)
Assuming the concentration of
the stock dye solution is 100 dye
units, give the concentration of
the solution in Column 1.
1:2
stock
5
1:20
1:2
5
1:200
1:20
5
1:5
stock
5
1:50
1:5
5
* The ratio indicates the fraction of the stock dye solution. For example, the 1:2 solution
has ½ the concentration of the stock solution.
a. Next, using the above calculations, prepare the serial dilutions of the stock
solution.
(5 pts)
b. Place the solutions in order from most concentrated to least concentrated. How
does the dye concentration compare to color intensity?
(5 pts)
4. Use the file “Quantifying a Sample on UV-Vis spec.docx” to create a calibration curve
from the dilutions of the stock solution.
a. Roughly sketch the calibration curve below. Is the calibration curve curved or a
straight line? What equation describes this line? What is the r2 value?
(10pts)
b.
Analyze the three unknowns provided by your instructor and record the data
below.
(8 pts)
Sample Name
Concentration
(units =
)
Preparing a multi-element stock solution
5. A multi-element stock solution was created by adding small volumes of single-element
standards to distilled water (see the table on the next page). Use the data in the table to
make the following calculations.
a. Calculate the volume of each single-element standard solution that was added to
create the stock solution. (Hint: use the mass and density.)
(3 pts)
b. Calculate the total volume of the stock solution; record on the table.
(2 pts)
c. Calculate the concentration of each element in the stock solution.
(4 pts)
d. Calculate the concentrations of the solutions made from dilutions of the stock
standard. For example, elemental concentrations in a 1:10 dilution of the stock
solution are 1/10th the concentration of the stock solution.
(9 pts)
Element
Density
of
original
standard
soln
Conc of
original
standard
soln
Mass of
standard
soln
used to
make
stock
soln
g/ml
mg/l
g
Al
1.0600
10,000
5.000
Ca
1.0373
10,000
4.000
Fe
1.0546
10,000
2.500
K
1.0206
10,000
4.000
Mg
1.0051
1,000
5.000
Na
1.0207
10,000
2.200
P
1.0030
1,000
5.000
Si
1.0372
10,000
2.500
Sr
1.0222
1,000
0.600
Distilled
water
Total
Stock
Soln
1.0000
69.00
100.00
Elemental concentrations in the dilutions of the stock
solution
Volume of
standard
soln used
to make
stock
soln
Conc in
stock
soln
mL
mg/L
1/100
1/50
(mg/L)
1/10
1/5