ACT science practice test 4

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.


Convection is a heat transfer process caused by moving liquid or gas currents from a hot region to a cold region. As a liquid or gas cools, it gets more dense. An example of a convection process is a cup of hot coffee: the liquid toward the top is cooled by the air, so it becomes more dense and sinks to the bottom of the cup; the hotter liquid toward the bottom of the cup is less dense, so it rises toward the top. See Figure 1, below.

Figure 1

The temperature of the liquid at the hot end of the insulated system is higher than the temperature at the cool end of the system. The difference (ΔT) between the hot liquid at the bottom and the cold liquid at the top changes depending on the starting temperature of the system. Table 1 gives ΔT for 500 mL of water in an insulated container with a height of 6.0 cm and a cross-sectional area of 4.0 cm2 when the container is heated to different temperatures.

Table 1
Heated temperature (°C)ΔT (°C)
801
1004
12010
14019

Figure 2 shows how ΔT changes with cross-sectional area for 500 mL of 100°C water in a container with a height of 6.0 cm. Figure 3 shows how ΔT changes with height for 500 mL 100°C water in a container with a cross-sectional area of 4.0 cm2.

Figure 2

Figure 3

1. System 1 and System 2 are two convection systems. Based on

Figure 2, if System 1 were the same height as System 2, but had two times the cross-sectional area and the systems were heated to the same temperature, the ratio of ΔT for System 1 to ΔT for System 2 would be:

F. 1:01
G. 1:02
H. 2:01
J. 3:01

2. For the systems described in the passage, if the containers were metal containers rather than insulated containers, heat would be transferred from the water to the container by which of the following heat transfer processes?

I. Convection

II. Conduction

III. Radiation

A. I only
B. II only
C. I and III only
D. I and II only

3. Which of the following systems, if all were heated to the same temperature, would have the greatest ΔT?

F.
G.
H.
J.

4. Based on the information in

Table 1, if an insulated container of 500 mL of water with a height of 6.0 cm and a cross-sectional area of 4.0 cm2 were heated to 120°C, which of the following pairs could represent the temperatures of the liquid at the top and bottom ends of the container?

Bottom end Top/Exposed to air end

A. 140°C 120°C
B. 140°C 110°C
C. 115°C 115°C
D. 120°C 110°C

5. The data in the passage supports the hypothesis that ΔT increases as which of the following increases?

F. Amount of insulation
G. Volume of liquid
H. Radius of the container
J. Air temperature

Metallic alloys, solid mixtures of metal, are useful for coin production when they contain a high percentage of zinc. When electric current is applied to zinc in the presence of precious metal solutions of silver nitrate, copper sulfate or potassium gold cyanide, the precious metals plate (form a coating) on the zinc surface.

- Silver nitrate, formed when silver dissolves in nitric acid, reacts with zinc to form solid silver and zinc nitrate.

- Copper sulfate, formed when copper dissolves in sulfuric acid, reacts with zinc to form solid copper and zinc sulfate.

- Potassium gold cyanide contains reactive gold ions.

A chemist performed experiments on precious metal plating.

Experiment 1

The chemist obtained 4 coin-like samples of a high percentage zinc alloy. All samples were circular, had a radius of 1 cm, and had the same thickness. The mass of each coin was recorded. Each coin was wired via a battery to a strip of either pure silver or copper metal. Coins wired to silver were placed in dilute nitric acid and coins wired to copper were placed in dilute sulfuric acid. Electric current of either 1,000 milliamperes (mA) or 2,000 mA was applied for 30 minutes to each sample. The coins were removed and the increase in mass from precious metal plating was recorded in milligrams. Results of the experiment are shown in Table 1.

Experiment 2

The chemist completely dissolved equal amounts of pure silver in 4 beakers of nitric acid. He then placed equivalent coin-like samples of zinc into the beakers for different lengths of time measured in minutes (min). The coin surfaces developed a silver metal coating without any electric current applied. The concentrations of silver coating on the coin and zinc nitrate in the surrounding solution were determined in parts per billion (ppb) and recorded in Table 2.

6. A comparison of the results for coin samples II and IV supports the hypothesis that zinc is plated more extensively when exposed to:

A. silver nitrate and a current of 1,000 mA than silver nitrate and a current of 2,000 mA.
B. copper sulfate and a current of 1,000 mA than copper sulfate and a current of 2,000 mA.
C. silver nitrate than when exposed to copper sulfate.
D. copper sulfate than when exposed to silver nitrate.

7. If the chemist were to repeat Experiment 1, but compress each coin sample to a radius of 0.5 cm to decrease the surface area exposed to the surrounding solution, how would the mass of precious metal plated most likely be affected?

F. The mass of precious metal plated would decrease for all coin samples.
G. The mass of precious metal plated would decrease for coin samples I and III and increase for coin samples II and IV.
H. The mass of precious metal plated would remain constant for all coin samples.
J. The mass of precious metal plated would increase for all coin samples.

8. According to the information in the passage, a zinc alloy coin sample exposed to which of the following conditions would result in the greatest concentration of zinc nitrate?

A. 10 minutes in a solution with a high initial concentration of silver nitrate
B. 10 minutes in a solution with a low initial concentration of silver nitrate
C. 6 minutes in a solution with a high initial concentration of silver nitrate
D. 6 minutes in a solution with a low initial concentration of silver nitrate

9. In Experiment 1, if the chemist had applied 1,580 mA to a 1 cm radius zinc alloy coin sample in a copper sulfate solution, approximately how much copper would have plated after 30 minutes?

F. 0.6 mg
G. 1.1 mg
H. 1.9 mg
J. 4.6 mg

10. In Experiment 1, which of the following variables was the same for all 4 zinc alloy coin sample trials?

A. Change in mass from plating
B. Electric current applied
C. Type of precious metal solution used
D. Initial radius of the sample

11. According to the passage, if a chemist wants to study the effect of plating zinc alloys with silver, the chemist should monitor the concentration of which of the following substances in the surrounding solution?

F. Potassium gold cyanide
G. Zinc nitrate
H. Copper sulfate
J. Sulfuric acid