WA AP Chemistry HW 2-9

WA AP Chemistry
HW 2-9 ( 20 points)
Name:
Date:
There will be an exam question based on these problems and on the part of the complex ion lab
dealing with this topic.
Show all work for full credit. Only
computer generated or graphs on graph
Concentration (M) %Transmittance
paper will be accepted. No graphs = no
0.000
100.0
credit!
1. The following data were
collected from a colorimeter with
solutions of manganese (II)
chloride.
0.010
0.030
0.050
0.070
0.090
96.6
90.2
83.9
78.0
72.4
a.) Determine the
absorbance of each of these standard solutions, using A = -log(%T/100).
b.) Graph A vs. C.
c.) By interpolating the graph, determine the concentration of an unknown
manganese (II) chloride solution that transmits 85% of the light through this
colorimeter.
2. A team is trying to calibrate a new colorimeter for a type of green dye. They find that a 2.00
ppt solution transmits 85.7% of the light, a 6.00 ppt solution transmits 63.0%, and a 10.00
ppt solution transmits 46.3%. (ppt = parts per trillion)
a.) Determine the absorbance of each of these standard solutions, using
A = -log(%T/100).
b.) Graph A vs. c.
c.) If a solution of green dye transmits 50.0% of the light through this colorimeter, what
is its concentration?
3. A scientist suspects that there is too much iron(III) ion in their drinking water. To test this,
they precipitate this ion with excess potassium thiocyanate solution and determines the
absorbance of the resulting solution in a spectrophotometer.
The following data was collected
Concentration (M)
Absorbance
0.010
0.20
0.020
0.40
0.029
0.60
0.042
0.82
?
0.11
a. Write the balanced, net ionic reaction for this reaction.
b. Graph the absorbance vs. concentration and determine the equation for the best-fit line.
c. If all the solutions made were 100.0 mL, how many grams of iron(III) ion were in the
unknown?
d. The average person drinks 8, 10 ounce cups of water each day. How much iron(III) ion
is the scientist getting from the water alone?

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