대교 ACT

DIRECTIONS: The passage in this test is followed by several questions. After reading the passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passage as often as necessary. You are NOT permitted to use a calculator on this test.

Several methods were investigated to reduce pollution emissions from a steel mill smokestack. Steel is mostly iron (Fe), but it also contains carbon (C). Impurities containing sulfur (S), nitrogen (N), or phosphorus (P) form gaseous compounds with oxygen that become pollutants. The smoke contains these pollutants and also tiny dust particles that pollute the air, are blown around by the wind, and eventually fall to the ground.

Method 1

Steel mill smoke was passed across a set of electrified plates in the smokestack. The electrified plates attracted the dust particles in the smoke and removed them from the emissions. The efficiency of dust particle removal, which is dependent on the size of the particles, is shown in Table 1.

Table 1
Voltage on plates (V)	Particles removed (%)
100	20
200	50
500	90
1,000	80
3,000	70

Method 2
    The smoke was passed through filters of different pore size in the smokestack that trapped dust particles and also decreased the amount of smoke leaving the stack. The data are shown in Table 2.
Table 2

Filter pore size
(microns) Particles trapped
(%) Amount of time for filters
to drop to 50% efficiency
(hours)

1,000      5       2,000

500      20       1,000

200      50       200

100      80       25

50      90       1

Method 3
    To reduce pollution by chemical means, the smokestack emissions were bubbled through solutions of concentrated alkali (solutions of OH^– ions). Table 3 shows the percent of the 3 pollutants removed versus the alkali concentration.
Table 3

Alkali
concentration
(%) S
removed
(%) N
removed
(%) P
removed
(%)

1      80    60    10

3      90    65    40

5      91    60    35

10      92    50    30

15      93    20    25

1. If the plant's smoke contained equal amounts of S, N, and P, which of the following alkali concentrations would remove the most total pollution?
A.  1%
B.  3%
C.  5%
D. 10%

2. Which of the following statements about the alkali concentration is consistent with the results of Method 3 ?
F. A higher alkali concentration results in more P removed.
G. A higher alkali concentration results in more S removed.
H. A lower alkali concentration requires more filters to remove dust particles.
J. A lower alkali concentration results in an increased time required to remove all of the chemical pollutants.

3. Based on the characteristics of the filters used in Method 2, which of the following best describes the practical problem involved in choosing the best type of smokestack filter? The filter that traps the highest percentage of particles:
A. requires the highest voltage across the electrified plates.
B. reacts with alkali solutions.
C. needs to be replaced least often.
D. needs to be replaced most often.

4. If the smokestack of the steel mill was doubled in height, what effect, if any, would this be expected to have on the removal of pollutants?
F. Filter efficiency would decrease because dust particles could more easily fall back down the stack.
G. Electrostatic plate efficiency would increase because voltage increases with height.
H. Dust particles would accumulate into larger pieces and would be more easily removed from the smoke.
J. It cannot be determined from the given information.

5. Which of the following assumptions about reducing pollution emissions is common to both Methods 1 and 2 ?
A. Emissions can only be removed by filters.
B. Emissions can only be removed by electrified plates.
C. Emissions must be captured in the smokestack to be removed.
D. Emissions must be captured after they leave the smokestack.

6. To further investigate the effects of voltage on the removal of dust particles from steel mill smoke, the scientists could use which of the following procedures?
F. Determining where the particulate matter falls to the ground after leaving the smokestack
G. Determining what sizes of particles are removed from the smoke at different voltages
H. Determining how the filters react when an alkali solution is passed through them
J. Determining how the filters react when an acid solution is passed through them

Set 4: Science

1. The best answer is B. Method 3 results show S, N, and P removal rates for various alkali concentrations.

A. 1%
Incorrect.At 1%, the removal of P (10%) was well below its maximum and the S and N removal percentages were below their maximums also.

B. 3%
Correct.At 3% alkali concentration, N and P removal percentages were at maximums (65% N, 40% P) while the S removal percentage (90%) was near its maximum (93%). Compared to the other choices of alkali concentrations, this concentration would remove the highest overall percentage of pollution.

C. 5%
Incorrect.S, N, and P removal percentages were all below their maximums at this alkali concentration.

D. 10%
Incorrect.S, N, and P removal percentages were all below their maximums at this alkali concentration.

2. The best answer is G. In Method 3, smokestack emissions were bubbled through solutions of varying concentrations of alkali.

F. A higher alkali concentration results in more P removed.
Incorrect.Method 3 results show that higher alkali concentrations first result in higher P removal percentages, but as alkali concentrations continue to increase, P removal percentages decrease.

G. A higher alkali concentration results in more S removed.
Correct.Method 3 results consistently show that as alkali concentrations increase, S removal percentages increase.

H. A lower alkali concentration requires more filters to remove dust particles.
Incorrect.The study of filter efficiency in pollutant removal was not studied in Method 3.

J. A lower alkali concentration results in an increased time required to remove all of the chemical pollutants.
Incorrect.The time required for pollutant removal was not studied in Method 3.

3. The best answer is D. Method 2 shows that filters with smaller pore sizes trap a larger percentage of particles, but drop to 50% efficiency after only 1 hour, requiring that they be replaced quite frequently.

A. requires the highest voltage across the electrified plates.
Incorrect.Method 2 does not study the effect of voltage on particle removal.

B. reacts with alkali solutions.
Incorrect.Method 2 does not study the effect of alkali solutions on particle removal.

C. needs to be replaced least often.
Incorrect.The filter that trapped 90% of the particles dropped to 50% efficiency in only 1 hour. Therefore, it would have to be replaced most often, not least often.

D. needs to be replaced most often.
Correct.The filter that trapped 90% of the particles dropped to 50% efficiency in only 1 hour. It would have to be replaced most often.

4. The best answer is J. None of the three methods examined the effect of smokestack height on pollutant removal.

F. Filter efficiency would decrease because dust particles could more easily fall back down the stack.
Incorrect.None of the three methods examined the effect of smokestack height on filter efficiency.

G. Electrostatic plate efficiency would increase because voltage increases with height.
Incorrect.None of the three methods examined the effect of smokestack height on voltage or electrostatic plate efficiency.

H. Dust particles would accumulate into larger pieces and would be more easily removed from the smoke.
Incorrect.None of the three methods examined the effects of smokestack height on particle flocculation and removal.

J. It cannot be determined from the given information.
Correct.None of the three methods examined the effect of smokestack height on pollutant removal, so no effect can be predicted from the given information.

5. The best answer is C. Both Methods 1 and 2 examine ways to remove particles inside the smokestack.

A. Emissions can only be removed by filters.
Incorrect.Only Method 2 examined how filters reduce smokestack emissions.

B. Emissions can only be removed by electrified plates.
Incorrect.Only Method 1 examined how electrified plates reduce smokestack emissions.

C. Emissions must be captured in the smokestack to be removed.
Correct.Both electrified plates (Method 1) and filters (Method 2) were installed and studied inside a smokestack to see how well they removed particles and reduced pollution.

D. Emissions must be captured after they leave the smokestack.
Incorrect.Neither method studied ways to remove pollutant emissions after the particles left the smokestack.

6. The best answer is G. The effects of voltage on particle removal was examined in Method 1. Further investigations about voltage should test something not already studied in Method 1.

F. Determining where the particulate matter falls to the ground after leaving the smokestack
Incorrect.This procedure would not give any additional information about how voltage affects the removal of dust particles because voltage is not part of the experimental design.

G. Determining what sizes of particles are removed from the smoke at different voltages
Correct.Method 1 only looked at particle removal in general. Determining what sizes of particles are removed by different voltages would give the scientists more information on how voltage removes dust particles.

H. Determining how the filters react when an alkali solution is passed through them
Incorrect.This method would give no new information about the effects of voltage on removal of dust particles because voltage is not part of the experimental design.

J. Determining how the filters react when an acid solution is passed through them
Incorrect.This method would give no new information about the effects of voltage on removal of dust particles because voltage is not part of the experimental design.