ACT Science Practice Test 2

Directions: The ACT Science passage below is followed by several questions. After reading the passage, choose the best answer to each question. You may refer to the passage as often as necessary. Calculators may NOT be used on this test.

Passage II

A scientist wishes to study the relationship between the pressure, volume, and temperature of a gas. He conducts three experiments, the results of which are recorded below.

Experiment 1: The scientist varies the volume and pressure of gas in a cylinder while keeping all other factors constant. The scientist records the results in table 1 below.
ACTSCIexp1

Experiment 2: The scientist varies the volume and temperature of gas in a cylinder while keeping all other factors constant. The scientist records the results in table 2 below.
ACTSCIexp2

Experiment 3: The scientist alters the temperature of gas in a cylinder by heating the cylinder and measures the pressure at each temperature. The scientist records the results in table 3 below.
ACTSCIexp3

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Question 1
Based on the results of experiment 3, if the pressure of a gas is doubled while holding the volume and amount of gas in the cylinder constant, what will be the impact on temperature?

A
The temperature will stay the same
B
The temperature will be doubled
C
The temperature will be halved
D
The temperature will be quadrupled
Question 1 Explanation: 
The correct answer is (B). From table 3, we see that as temperature increases, pressure increases. Since temperature is directly proportional to pressure (P/T = 3), we can infer that doubling the pressure of the gas will lead to a doubling of the temperature.
Question 2
Which of the following could be the graph of Pressure * Volume versus Pressure?

A
s1a
B
s1b
C
s1c
D
s1d
Question 2 Explanation: 
The correct answer is (D). From table 1, we see that Pressure * Volume is constant as pressure increases. The correct plot will be a horizontal line.
Question 3
Based on the results of experiment 2, what would be the volume of gas in the cylinder if the cylinder is heated to 350K?

A
1300 ml
B
1400 ml
C
1500 ml
D
1600 ml
Question 3 Explanation: 
The correct answer is (B). From table 2, we see that a temperature of 300K corresponds to a volume of 1200 ml. At a temperature of 500K, the volume is 2000 ml. As temperature increases, volume increases. We can conclude that volume is directly proportional to temperature since V/T = 4. Since:
s2ex
The following equation can be used for interpolation:
Final Volume = Initial Volume + slope * change in temperature.
Therefore, at 350K, Volume = 1200 + 4*(350 − 300) = 1400 ml.
Question 4
If the scientist now wishes to study the relationship between the volume of a gas (in ml) and the amount of the gas (in moles), which of the following experiments will help the scientist accomplish this goal?

A
Experiment 1: Fill a balloon with one mole of hydrogen gas and another balloon with one mole of helium gas at constant temperature and measure the volumes of the two balloons.
B
Experiment 2: Fill a cylinder of fixed volume with hydrogen gas and another cylinder of fixed volume with helium gas at standard conditions of temperature and pressure and measure the weights of the gases in the two cylinders.
C
Experiment 3: Fill a balloon with one mole of hydrogen gas and another balloon with two moles of hydrogen gas at constant temperature and pressure and measure the volumes of the two balloons.
D
Experiment 4: Fill a 1 liter cylinder with hydrogen gas and a 2 liter cylinder with propane gas at room temperature and measure the mass of gas in each cylinder.
Question 4 Explanation: 
The correct answer is (C). In order to study the relationship between the volume of gas and the amount of gas, the scientist should set up an experiment in which only those two factors are allowed to vary while all other factors are held constant. Experiment 3 is such an experiment. Experiment 1 will not work because we need to hold both temperature and pressure constant in order for experiment 1 to work, but only temperature is held constant. Experiment 1 also does not vary the amount of gas in moles. Experiment 2 will not work because the volume is held constant. We need to let the volume vary in order to study the relationship between volume and the amount of gas. Experiment 4 will not work because pressure is not held constant.
Question 5
Based on the results of experiment 2, if the scientist blows air into a balloon until the diameter of the balloon reaches 20 cm and then proceeds to hold the balloon over the cool flame of a Bunsen burner, what should we expect to happen to the balloon as it is heated?

A
The temperature of the balloon will stay the same
B
The volume of the balloon will decrease
C
The volume of the balloon will increase
D
The temperature of the balloon will decrease
Question 5 Explanation: 
The correct answer is (C). From experiment 2, we see that as temperature increases, volume increases. Therefore, we should expect that as the balloon is heated, the volume of the balloon will increase.
Question 6
Looking at the results of experiments 1, 2, and 3, what would you expect to happen to the volume of gas in a cylinder if the pressure and temperature of the gas are both doubled while holding all other factors constant?

A
The volume will be doubled
B
The volume will stay the same
C
The volume will be halved
D
The effect on the volume cannot be determined
Question 6 Explanation: 
The correct answer is (B). From experiment 1, we see that volume is inversely proportional to pressure. From experiment 2, we see that the volume is directly proportional to the temperature. Since volume is directly proportional to temperature and inversely proportional to pressure, doubling the temperature of the gas will offset the effect of doubling the pressure. The net effect is a wash (no change in volume). An experiment to illustrate this will involve heating a cylinder of gas to twice the temperature and doubling the pressure by compressing the gas with a piston to half the pressure. The heating will cause the volume to double, while the compression will cause the volume to be halved. ½ * 2 = 1.
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