ACT Science Practice Test 91

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.


Carboxylic acids are organic compounds containing a carboxyl (-COOH) group. These molecules are acidic since they are able to donate protons in solution. The acidity and other physical properties of carboxylic acids are affected by the composition of the atoms bound to the carboxyl group. Table 1 lists the freezing points and boiling points for several carboxylic acids.

Figure 1 shows how the vapor pressure (in mm Hg) of 3 carboxylic acids changes as a function of temperature.


Figure 1

Figure 2 shows how the vapor pressure of the same 3 carboxylic acids changes as a function of concentration when mixed with water at 20°C.


Figure 2

1. Which of the carboxylic acids listed in Table 1 has the highest melting point?

A. Propionic acid
B. Valeric acid
C. Acetic acid
D. Formic acid

2. According to Figure 2, the vapor pressure of a 0.5 mole fraction solution of water in formic acid is closest to the vapor pressure of which of the following water in formic acid solutions?

F. 0.9 mole fraction
G. 0.8 mole fraction
H. 0.6 mole fraction
J. 0.4 mole fraction

3. According to Figure 2, as the mole fraction of water in an acetic acid and water solution increases from 0 to 1, the vapor pressure:

A. decreases, then increases.
B. increases, then decreases.
C. decreases only.
D. increases only.

4. CH3 (CH2)4 COOH is the chemical formula for the carboxylic acid named hexanoic acid. Based on Table 1, this compound most likely boils at a temperature:

F. lower than 160°C.
G. between 200°C and 220°C.
H. between 220°C and 240°C.
J. higher than 240°C.

5. According to Figure 1, does acetic acid or formic acid resist vaporization more at 60°C ?

A. Formic acid, because formic acid has the lower vapor pressure.
B. Formic acid, because formic acid has the higher vapor pressure.
C. Acetic acid, because acetic acid has the lower vapor pressure.
D. Acetic acid, because acetic acid has the higher vapor pressure.

A solenoid is a device that creates a magnetic field from electric current and can be used to exert a force on a nearby bar magnet to activate a mechanical device.

Scientists performed experiments on the solenoid apparatus shown in Figure 1.


Figure 1

A wire carrying current from a voltage source was coiled into a hollow cylinder to form a solenoid with a length of XY. A solid cylinder bar magnet was suspended near the top of the solenoid as shown in Figure 2.


Figure 2

When the voltage source was turned on, the solenoid exerted a measurable force on the suspended bar magnet.

The bar magnet was attached to a digital suspension scale that measured weight in newtons (N). With the voltage source off, the scale read 4.7 N. Prior to the start of each experimental trial, the scale was adjusted to read 5.0000 N.

Experiment 1

The scientists applied various levels of voltage in volts (V) to the circuit and recorded the weight indicated by the suspension scale for each trial. Results were recorded in Table 1.

Table 1

Voltage (V) Weight (N)

7.25 5.0078

8.00 5.0095

8.75 5.0113

Experiment 2

The scientists removed the bar magnet, inverted it, and reattached it to the suspension scale so that the opposite end was now facing the solenoid. The procedures of Experiment 1 were repeated and results were recorded in Table 2.

Table 2

Voltage (V) Weight (N)

7.25 4.9922

8.00 4.9905

8.75 4.9887

Experiment 3

The bar magnet was returned to the original alignment it was in during Experiment 1. The length XY of the solenoid coil was varied while a voltage of 8.00 V was applied to the circuit. Weights were recorded in Table 3.

Table 3

Solenoid length XY (cm) Weight (N)

9.50 5.0105

8.50 5.0131

7.50 5.0169

6. Based on the results of Experiments 1 and 3, the length XY of the solenoid coil in Experiment 1 was most likely:

F. shorter than 7.50 cm.
G. between 7.50 cm and 8.50 cm.
H. between 8.50 cm and 9.50 cm.
J. longer than 9.50 cm.

7. In Experiments 1 and 2, the orientation of the bar magnet relative to the solenoid opening determined which of the following?

A. Solenoid length XY
B. Direction of the force exerted by the solenoid on the bar magnet
C. Density of the bar magnet
D. Magnetic field strength of the solenoid

8. Which of the following provides the best explanation for the results of Experiment 3 ? The force exerted on the bar magnet by the solenoid magnetic field:

F. decreased as the voltage applied to the circuit decreased.
G. increased as the voltage applied to the circuit decreased.
H. decreased as the length XY of the solenoid decreased.
J. increased as the length XY of the solenoid decreased.

9. Suppose the scientists maintained the same bar magnet orientation in Experiment 3 as in Experiment 2. Based on the results of Experiments 1 and 2, with the solenoid length XY equal to 9.50 cm, the weight on the scale would most likely have been:

A. 5.0169
B. 5.0105
C. 4.9895
D. 4.9831

10. Prior to all experiments, the suspension scale was calibrated to read exactly 0 N when nothing was attached. Once the bar magnet was attached, the scientists made which of the following adjustments to the scale reading for each of the experimental trials?

F. The displayed weight was adjusted downward by approximately 1.3 N.
G. The displayed weight was adjusted upward by approximately 1.3 N.
H. The displayed weight was adjusted downward by approximately 0.3 N.
J. The displayed weight was adjusted upward by approximately 0.3 N.

11. Which of the following graphs best depicts the results of Experiment 3 ?

A.
B.
C.
D.