ACT science practice test 77

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


A science class studied the pH strength of acids and bases. The terms strong and weak indicate the ability of acid and base solutions to conduct electricity. Figure 1 displays the pH scale used to rank solutions as acidic or basic, and Table 1 provides an overview of what pH levels are considered strong and weak solutions.

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Figure 1

Table 1

SolutionpH
Strong acid0–3
Weak acid4–6
Neutral7
Weak base8–10
Strong base11–14

Experiment 1

Students conducted an experiment to determine the conductivity of acid and base solutions, using a light bulb apparatus (see Figure 2). The light bulb circuit was incomplete. If the circuit is completed by a solution containing a large number of ions, the light bulb will glow brightly, indicating a strong ability to conduct electricity. If the circuit is completed by a solution containing a large number of molecules and either no ions or few ions, the solution does not conduct electricity or conducts it very weakly. Students tested the conductivity of several solutions; the results are reported in Table 2.

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Figure 2

Table 2

SolutionAcid or BaseLight Bulb
H2ONeutralNo light
HClAcidBright
HC2H3O2AcidDim
H2SO4AcidBright
H2CO3AcidDim
NaOHBaseBright
KOHBaseBright
NH4OHBaseDim

Experiment 2

Students mixed 50 mL of each chemical with 1 liter of water and then tested the pH of the solution. Table 3 displays the pH found for each chemical.

Table 3

ChemicalpH
HCL0.86
HC2H3O22.92
H2SO41.29
H2CO33.73
NaOH13.1
KOH11.2
NH4OH9.2

1. Based on the information presented in Figure 1 and Table 1, a solution with which pH would be the strongest base?

A. 12.5
B. 9.7
C. 7
D. 0.2

2. According to the results of Experiments 1 and 2, which of the following is true?

F. The weaker the acid or base, the brighter the light bulb glowed.
G. The lower the pH of the solution, the brighter the light bulb glowed.
H. The stronger the acid or base, the brighter the light bulb glowed.
J. The higher the pH of the solution, the brighter the light bulb glowed.

3. Based on the results of Experiment 2, KOH would be classified as:

A. a strong acid.
B. neutral.
C. a strong base.
D. a weak base.

4. According to the information presented in Figure 1 and Table 3, it can be concluded that which of the following acids contains the most hydrogen?

F. H2CO3
G. H2SO4
H. HC2H3O2
J. HCL

5. Suppose the students decided to test the conductivity of an additional solution according to the procedures outlined in Experiment 1. They tested a solution of NaOCl, and they found that the solution caused the light bulb to glow brightly. The students would be correct in classifying the NaOCl solution as which of the following?

A. A strong base
B. A weak base
C. A weak acid
D. Cannot be determined from the given information

6. Based on Table 3, which of the following figures best represents the pH values for the 3 bases tested?

F. image
G. image
H. image
J. image

Solid-phase microextraction (SPME) is a new technique for extracting volatile organic residue from sediment and water. The technique has several advantages (fast, simple, precise, sensitive), and requires no solvent. For this technique, a thin fused silica fiber coated with a stationary phase is exposed to a sample, either by immersion in a water or air sample or to headspace above an aqueous or solid sample (see Figure 1).

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Figure 1: SPME device

Scientists conducted a series of experiments to determine the effectiveness of using SPME to extract white phosphorus (P4) residues from water. All of the experiments were done using headspace immersion.

Experiment 1

To see how consistent SPME was, scientists conducted five trials using four different types of water (reagent grade, well, pond, salt marsh) at an aqueous concentration of 0.14 μg/L. Table 1 displays the results.

Table 1

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Experiment 2

Scientists varied the aqueous concentration and tested four different types of water using SPME, to see the effect on the mass of P4 that could be extracted (see Figure 2).

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Figure 2

Experiment 3

To see if sonication had any effect on the results of SPME, scientists ran four trials, using four identical aqueous samples, at a concentration of 0.14 μg/L. The samples were analyzed using SPME by three methods: five minutes of sonication, ten minutes of sonication, and five minutes static. Table 2 displays the results.

Table 2

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7. According to Figure 2, as the aqueous concentration increased in the test done using salt marsh water, the white phosphorus mass:

A. decreased, and then increased.
B. increased and then decreased.
C. increased.
D. decreased.

8. Based on the results from Experiment 3, which trial resulted in the smallest amount of white phosphorus being extracted?

F. Trial 2 after 5-minutes sonication
G. Trial 3 after 5-minutes static
H. Trial 1 after 5-minutes static
J. Trial 4 after 10-minutes sonication

9. In order for the scientists to conduct these experiments, it was crucial for them to expose which part of the SPME device to the headspace above the water samples?

A. The plugger
B. The needle
C. The barrel
D. The silica fiber

10. A scientist theorized that more white phosphorus would be extracted from a sample if it were exposed to a longer period of sonication. Do the results from Experiment 3 support this theory?

F. Yes, because in every trial more white phosphorus was extracted after 10-minutes sonication than after 5-minutes sonication.
G. Yes, because in every trial more white phosphorus was extracted after 5-minutes sonication than after 5-minutes static.
H. No, because in Trials 2 and 3 more white phosphorus was extracted after 5-minutes sonication than after 10-minutes sonication.
J. No, because in all trials more white phosphorus was extracted after 5-minutes static than after 5-minutes sonication.

11. According to Table 1 the mean results demonstrate that the greatest amount of white phosphorus can be extracted from which type of water?

A. Reagent
B. Well
C. Pond
D. Salt marsh

12. Based on the results of Experiment 2, if SPME extraction was used on pond water with an aqueous concentration of 0.2 μg/L, it can be inferred that the amount of white phosphorus extracted would be closest to:

F. 45 pg.
G. 100 pg.
H. 30 pg.
J. 5 pg.