ACT science practice test 52

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.


Since ancient times, scientists, philosophers, and other thinkers considered the smallest pieces of matter to be tiny spherical structures called atoms that were stacked in various arrangements. The ancient Greek philosopher Democritus also suggested that these atoms were indivisible and indestructible. The turn of the twentieth century brought with it a renewed interest in exploring atoms. Two ground-breaking experiments challenged the idea that atoms are the smallest constituent of matter. These experiments were very different, but both pointed to the fact that atoms contained even smaller parts.

Experiment 1: The 1897 Cathode Ray Tube Experiments

Scientists in the late 1890s investigated a curious new device known as a cathode ray tube (CRT). The CRT consisted of a glass tube with a metal wire coming out of each end. When all of the air was removed from the tube and a voltage was applied across the wires, mysterious green rays appeared at one end of the tube. These rays were called cathode rays. It was not immediately known if these rays were a type of wave or a type of particle, but several experiments were conducted on them. First it was discovered that the rays would always be attracted to an area of excess positive charge and away from an area of excess negative charge. Precise measurements could not determine the exact mass of the cathode rays, but it was determined that they did have mass. After that discovery, the rays were considered a particle instead of a wave.

The mass-to-charge ratio of the cathode rays was determined to be more than 1,000 times smaller than the same ratio for any known atom or ion. After subsequent experiments, researchers determined that cathode rays were small particles that broke off of an atom when a voltage was applied.

Experiment 2: The 1911 Gold Foil Experiment

At the time, the accepted model of the atom was a relatively solid sphere, similar to a ball of chocolate chip cookie dough. An experiment in 1911 brought that model into question. A beam of alpha particles (small, high-energy, positively charged particles) was shot into a piece of gold foil approximately 8.6 × 10-8 m in thickness. The alpha particles were thought to have enough energy to pass straight through the foil and hit a detector on the other side, and most of the particles did just that. However, a small fraction of alpha particles were deflected a few degrees as they passed through the foil. Upon closer examination of the data, a more startling fact was found-some alpha particles never hit the detector.

More detectors were added around the gold foil, and it was discovered that a tiny portion of the alpha particles, 1 out of every 20,000 particles, was deflected 90 degrees or more from the beam. Some particles even bounced straight back toward the alpha particle source. The scientist was so surprised by the results that he stated, "It was as if you fired a 15-inch shell at a sheet of tissue paper and it came back to you." It was concluded that there must be some particle inside an atom causing these major deflections of alpha particles.

1. Which of the following best describes what each experiment concluded about the newly discovered small particles that make up atoms?

Experiment 1, Experiment 2

A. Dense and sturdy, Positively charged
B. Negatively charged, Dense
C. Positively charged, Negatively charged
D. Small, Low energy

2. Which of the following is the best conclusion concerning why the cathode rays in Experiment 1 had a mass-to-charge ratio 1,000 times smaller than that of any known atom?

A. Cathode ray particles are 1,000 times less massive than any known atom.
B. Cathode ray particles have 1,000 times less charge than any known atom.
C. Cathode ray particles have 1,000 times more charge than any known atom.
D. Cathode ray particles could either be less massive or have a greater charge than any known atom.

3. Modern chemistry books discuss several subatomic particles. Figure 9.4 offers a common diagram of such particles. The symbol (-) means negative, (+) means positive, and (ø) means neutral. Which particle would have an undefined mass-to-charge ratio?


Figure 9.4

A. Electron
B. Proton
C. Neutron
D. Nucleus

4. Which of the following statements do the data from both experiments support?

A. Atoms are highly charged particles.
B. Atoms are composed of a dense core known as a nucleus.
C. Atoms are not indestructible and indivisible.
D. The mass-to-charge ratio of atoms is much smaller than was originally thought.

5. Atoms, once thought to be solid spheres, have instead been proven to be mostly empty space with just a few tiny particles giving each atom its properties. Which data from either Experiment 1 or Experiment 2 best explains this fact?

A. Experiment 1: Cathode rays are attracted to areas of positive electric charge.
B. Experiment 1: Cathode rays have a small mass-to-charge ratio.
C. Experiment 2: Some alpha particles were deflected from the beam at wide angles.
D. Experiment 2: One out of every 20,000 particles got deflected to a large extent.

6. A micrometer (μm) is a common unit to measure small objects. One micrometer is equivalent to 0.000001 m. How thick was the gold foil in Experiment 2?

A. 8,600 μm
B. 86 μm
C. 0.86 μm
D. 0.086 μm

7. Which scientists would be most likely to write the following in their lab notebook: "I can see no escape from the conclusion that they are charges of negative electricity carried by particles of matter"?

A. Scientists working on Experiment 1
B. Scientists working on Experiment 2
C. Scientists working on either experiment
D. Scientists working on both experiments

8. Which headline best matches the conclusions of the experiment?

A. Gold Foil: Alpha Particles Are Found Inside Atoms
B. Cathode Rays Destroy Atoms
C. Gold Foil: Solid Particle in Atom Incredibly Small
D. Cathode Rays: Most Go Through But a Few Bounce Off