ACT Science Practice Test 46

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

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

Average global temperature is influenced by multiple different factors and has gone through significant changes throughout the history of the earth.

Global temperature affects Earth's oceans. In general, as the average global temperature increases, glacial and continental ice coverage decreases from melting. This combined with the thermal expansion of the oceans results in rising sea levels. The sea level present at any given time over the past 150,000 years can be estimated from sedimentary rock layer analysis. Figure 1 shows for the years listed the difference in average global sea level compared to what has been the average temperature value from 1961 through 1990.

Figure 2

Figure 1 adapted from "Intergovernmental Panel on Climate Change Fourth Assessment Report 2007."

Figure 2 shows the change in both the average global temperature and average global sea level from the present. The change in average global sea level is determined by:

Figure 2

Figure 2 adapted from Petit et al. "Climate and atmospheric history of the past 420,000 years from the Vostok ice core," Antarctica. Nature 399: 429–436.

Two scientists discuss why the average global sea level has risen over the past 100 years.

Scientist 1

Rising sea levels are a direct result of widespread industrial burning of fossil fuels that started in the mid-19th century. This activity caused the release of greenhouse gases like carbon dioxide, which raised the average global temperature. This increase in temperature led to depleted ice coverage and rapid thermal expansion of oceans. Figure 1 shows that global sea level was essentially constant until approximately 1900 and has since risen to a level higher than at any time in the past 150,000 years. Between 1950 and 2000, global average sea level rose by 0.1 m as global temperature rose approximately 0.5°C. Since 2000 the change in global average sea level has increased at a rate of 2% per year.

Scientist 2

Rises and falls in the global average sea level occurred many times in the past 150,000 years and well before the industrial revolution of the mid-1800s. In general, global average sea level rises and falls with global average temperature, as shown in Figure 2. Industrial activity did not begin until the 1800s and could not have been responsible for the changes in average global temperature and sea level before that time. The recent rise in sea level in response to global temperature is not significantly different from those before 1800, so human activity does not by itself have a measurable effect on average global sea level.

The force per unit area resulting from the separation of solutions of different concentrations by a selectively permeable membrane is called osmotic pressure. Molecules, including water, have a tendency to move from regions of high concentration to regions of low concentration. Selectively permeable membranes act as filters, only allowing molecules below a certain threshold size to pass through. Osmotic pressure is the pressure required to stop water from moving across such a membrane from a region of high to low water concentration.

Cupric ions (Cu₂+) and glucose were dissolved separately in equal volumes of water to make two solutions. The glucose solution was more dilute, meaning that it had a higher percentage of water molecules than the cupric ion solution. Of the three molecules used for the solutions, water is the smallest and glucose is the largest. Water and glucose solutions are colorless while cupric ion solutions are blue. However, mixing glucose and cupric ions results in a red solution.

Experiment 1

A U-shaped tube contains a selectively permeable membrane, dividing it into equal halves. Glucose solution is poured in the left and an equal volume of cupric ion solution is poured in the right. Over 2 hours, the water level fell on the left and rose on the right. At this time, the left-sided solution was red and the right-sided was blue.

Experiment 2

Cupric ion solution is poured in the left and an equal volume of pure water is poured in the right. Over 2 hours, the water level fell on the right and rose on the left. At this time, both sides of the tube contained blue-colored solutions.

Experiment 3

Glucose solution is poured in the left and an equal volume of pure water is poured in the right. Over 2 hours, the water level fell on the right and rose on the left. At this time, both sides of the tube contained colorless solutions.