ACT Practice Passage and Questions
Paper chromatography can be used to identify metal ions in wastewater. A drop of sample solution is placed on filter
paper. The bottom of the paper is set in a solvent that travels up the paper (see Figure 1).
Figure 1
The solvent carries the ions up the paper. Some ions move faster, and therefore farther than others, resulting in a
separation as they move up the paper. The paper is dried, then stained, causing the ions to appear as colored spots. Rf
values are calculated for each spot:
Table 1 shows Rf values for 5 ions. Table 2 shows Rf values from 3 samples of wastewater. The same solvent was used
for all ions and samples.
Table 1
Molar mass
(g/mole)
Distance
traveled
(cm)
Rf
Spot color
Nickel
(Ni2+)
58.7
0.8
0.08
pink
Cobalt
(Co2+)
58.9
3.5
0.35
brown-black
Copper
(Cu2+)
63.5
6.0
0.60
blue
Cadmium
(Cd2+)
112.4
7.8
0.78
yellow
Mercury
(Hg2+)
200.6
9.5
0.95
brown-black
Ion
Table 1 adapted from Thomas McCullough, CSC, and Marissa Curlee, "Qualitative Analysis of Cations Using Paper
Chromatography." ©1993 by the American Chemical Society.
Table 2
Sample
Rf
Spot color
Note: Samples contain only the metal ions listed in Table 1.
1
0.60
0.78
blue
yellow
2
0.35
0.95
brown-black
brown-black
3
0.08
0.78
0.95
pink
yellow
brown-black
1. The information in Tables 1 and 2 supports the conclusion that Sample 3 contains:
A. Cu2+ and Cd2+ only.
B. Co2+ and Hg2+ only.
C. Ni2+, Co2+, and Cd2+ only.
D. Ni2+, Cd2+, and Hg2+ only
2. Based on the information in Tables 1 and 2, one can conclude that Sample 2 contains:
F. 1 metal ion only.
G. 2 metal ions only.
H. either 1 or 2 metal ions.
J. more than 2 metal ions.
3. Based on the information in Table 1, which of the following lists the metal ions in order from the fastest to slowest
speed with which they moved up the paper?
A. Hg2+, Cd2+, Cu2+, Co2+, Ni2+
B. Cd2+, Cu2+, Co2+, Hg2+, Ni2+
C. Ni2+, Hg2+, Co2+, Cu2+, Cd2+
D. Ni2+, Co2+, Cu2+, Cd2+, Hg2+
4. Based on the information in Table 2, which of the following figures best illustrates the appearance of the filter paper
after Sample 1 was analyzed?
F.
G.
H.
J.
5. Based on the information in Table 1, to best identify a metal ion using paper chromatography, one should know the:
A. spot color for the ion only.
B. distance the solvent traveled only.
C. Rf value and spot color for the ion only.
D. distance the solvent traveled and spot color of the ion only.
1.
D is the best answer. Sample 3 had 3 colored spots: a pink spot with an Rf = 0.08, a yellow spot with an Rf = 0.78, and a
brown-black spot with an Rf = 0.95. These 3 spots correspond with 3 spots from Table 1: the pink spot with an R f = 0.08
for Ni2+, the yellow spot with an Rf = 0.78 for Cd2+, and the brown-black spot with an Rf = 0.95 for Hg2+. So Sample 3
contains Ni2+, Cd2+, and Hg2+.
A is not the best answer. If Sample 3 contained Cu2+, then the sample should have produced a blue spot with an R f =
0.60.
B is not the best answer. If Sample 3 contained Co2+, then the sample should have produced a brown-black spot with an
Rf = 0.35.
C is not the best answer. If Sample 3 contained Co2+, then the sample should have produced a brown-black spot with an
Rf = 0.35.
2.
G is the best answer. Sample 2 had 2 colored spots: a brown-black spot with an Rf = 0.35 and a brown-black spot with
an Rf = 0.95. These 2 spots correspond with 2 spots from Table 1: the brown-black spot with an Rf = 0.35 for Co2+ and the
brown-black spot with an Rf = 0.95 for Hg2+. Co2+ and Hg2+ are metal ions, so Sample 2 contains 2 metal ions.
F is not the best answer. Sample 2 had 2 colored spots: a brown-black spot with an Rf = 0.35 and a brown-black spot
with an Rf = 0.95. These 2 spots correspond with 2 spots from Table 1: the brown-black spot with an Rf = 0.35 for Co2+ and
the brown-black spot with an Rf = 0.95 for Hg2+. Co2+ and Hg2+ are metal ions, so Sample 2 contains 2 metal ions, not 1
metal ion.
H is not the best answer. Sample 2 had 2 colored spots: a brown-black spot with an Rf = 0.35 and a brown-black spot
with an Rf = 0.95. These 2 spots correspond with 2 spots from Table 1: the brown-black spot with an Rf = 0.35 for Co2+ and
the brown-black spot with an Rf = 0.95 for Hg2+. Co2+ and Hg2+ are metal ions, so Sample 2 contains 2 metal ions. The data
are not consistent with the conclusion that Sample 2 might contain only 1 metal ion.
J is not the best answer. Sample 2 had 2 colored spots: a brown-black spot with an Rf = 0.35 and a brown-black spot
with an Rf = 0.95. These 2 spots correspond with 2 spots from Table 1: the brown-black spot with an Rf = 0.35 for Co2+ and
the brown-black spot with an Rf = 0.95 for Hg2+. Co2+ and Hg2+ are metal ions, so Sample 2 contains 2 metal ions. The data
are not consistent with the conclusion that Sample 2 contains more than 2 metal ions.
3.
A is the best answer. As the Rf value increased, the speed that an ion moved up the paper also increased. Hg 2+ had
the largest Rf, so Hg2+ traveled the fastest. Cd2+ had the second largest Rf, so Cd2+ traveled the second fastest. Cu2+ was
the third fastest. Co2+ was the fourth fastest. Ni2+ was the slowest of the 5 ions.
B is not the best answer. As the Rf value increased, the speed that an ion moved up the paper also increased. Hg2+ had
a larger Rf than did Cd2+, so Hg2+ should precede Cd2+ in the list.
C is not the best answer. As the Rf value increased, the speed that an ion moved up the paper also increased. Hg 2+ had
a larger Rf than did Ni2+, so Hg2+ should precede Ni2+ in the list.
D is not the best answer. As the Rf value increased, the speed that an ion moved up the paper also increased. Hg 2+ had
a larger Rf than did Ni2+, so Hg2+ should precede Ni2+ in the list.
4.
F is the best answer. According to Table 2, Sample 1 had a blue spot and a yellow spot. Based on the formula, the
blue spot traveled a distance of (0.60) × (distance traveled by the solvent) and the yellow spot traveled a distance of
(0.78) × (distance traveled by the solvent). This figure shows the correct location of both spots.
G is not the best answer. According to Table 2, Sample 1 had a blue spot and a yellow spot. Based on the formula, the
blue spot traveled a distance of (0.60) × (distance traveled by the solvent); however, the figure indicates that the blue spot
traveled a distance of (0.10) × (distance traveled by the solvent).
H is not the best answer. According to Table 2, Sample 1 had a blue spot and a yellow spot. Based on the formula, the
blue spot traveled a distance of (0.60) × (distance traveled by the solvent); however, the figure indicates that the blue spot
traveled a distance of (0.48) × (distance traveled by the solvent). Likewise, the yellow spot traveled a distance of (0.78) ×
(distance traveled by the solvent); however, the figure indicates that the yellow spot traveled a distance of (0.50) ×
(distance traveled by the solvent).
J is not the best answer. According to Table 2, Sample 1 had a blue spot and a yellow spot. Based on the formula, the
blue spot traveled a distance of (0.60) × (distance traveled by the solvent); however, the figure indicates that the blue spot
traveled a distance of (0.10) × (distance traveled by the solvent). Likewise, the yellow spot traveled a distance of (0.78) ×
(distance traveled by the solvent); however, the figure indicates that the yellow spot traveled a distance of (0.20) ×
(distance traveled by the solvent).
5.
C is the best answer. Spot color can be used to restrict the range of options used to identify a metal ion. However,
some metals, such as cobalt and mercury, have the same spot color (brown-black). To determine the identity of a brownblack spot, one also needs to know the Rf of the spot.
A is not the best answer. Spot color can be used to restrict the range of options used to identify a metal ion. However,
some metals, such as cobalt and mercury, have the same spot color (brown-black), so additional information is required to
accurately identify some metal ions.
B is not the best answer. Knowing the distance traveled by the solvent does not help one determine the type of metal
ion that is present in a sample.
D is not the best answer. Spot color can be used to restrict the range of options used to identify a metal ion. However,
some metals, such as cobalt and mercury, have the same spot color (brown-black). To determine the identity of a brownblack spot, one also needs to know the Rf of the spot.