ACT Science Practice Test 39

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.

Figure 1

Table 1

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.

Figure 2

Table 2

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

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).

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

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).

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

The melting point of a substance is the temperature at which the solid phase transitions to the liquid phase. When a substance melts, the attractive forces holding the molecules together are reduced sufficiently to allow the molecules to flow. The stronger the intermolecular forces in solid form, the higher the melting point will be.

The boiling point of a substance is the temperature at which the vapor pressure in the liquid phase equals the atmospheric temperature of its surroundings. When a substance boils, the substance transitions from a liquid phase to a gaseous phase and the intermolecular forces are completely severed. The stronger the attractive forces between the molecules in the liquid phase, the higher the boiling point will be.

Table 1 and Figure 1 show details of some of the elements from the third row of the periodic table.

Table 1

Figure 1

From 1971 to 2006, there was a dramatic reduction in the number of feral honeybees in the United States, and a significant, though somewhat gradual, decline in the number of colonies maintained by beekeepers. In early 2007 the rate of attrition reached new proportions, and the term Colony Collapse Disorder (CCD) was coined to describe this sudden decline. CCD is said to have occurred when a bee colony abruptly disappears, with little or no build-up of dead bees in or around the colonies. The cause or causes of the syndrome are not yet well understood. Proposed causes include environmental change-related stress, malnutrition, disease, and pests.

Study 1

In an attempt to quantify the degree and extent of losses experienced in the United States, scientists tracked beekeeping operations with various numbers of colonies between September 2006 and March 2007. For the sake of this study, a colony has encountered CCD when it loses at least 90% of its population in a period of 30 days. This loss must be accompanied by little or no trace of dead bees in or around the hive. Figure 1 displays the total losses experienced by all beekeeping operations.

Figure 1

Study 2

Scientists studying CCD surveyed beekeepers whose hives have been affected by the disorder. The beekeepers were asked what they believe caused the CCD in their colonies. Table 1 displays the five most commonly suspected causes of CCD losses and the average percentage of loss experienced by operations of varying sizes due to each suspected cause. The scientists then surveyed beekeepers whose hives had collapsed for reasons unrelated to CCD, asking them the same question. Figure 2 compares the results from the scientists’ two surveys, displaying the total loss experienced due to suspected causes of CCD and non-CCD losses, averaged for operations of all sizes.

Table 1

Figure 2