Chemistry Practice Questions
1. What is the name for the horizontal rows of the periodic table?
2. Which of the following substances allows for the fastest diffusion?
3. What is the name for the number of protons in an atom?
A. atomic identity
B. atomic mass
C. atomic weight
D. atomic number
4. Which of the following could be an empirical formula?
Questions 5 and 6 are based on the following text:
The nucleus of an atom contains both protons and neutrons. Protons have a single positive electric charge, while neutrons have a charge of zero. The number of protons that a nucleus contains, called the atomic number and abbreviated as Z, determines the identity of an atom of matter. For example, hydrogen contains a single proton (Z = 1), whereas helium contains two (Z = 2).
Atoms of a single element may differ in terms of the number of neutrons in their atomic nuclei, however. The total number of protons and neutrons in an atom is referred to as the atomic mass, or M. Helium typically has an atomic mass equal to 4, but there is another helium isotope for which M = 3. This form of helium has the same number of protons, but only one neutron.
In an atomic fusion reaction, nuclei collide with one another with enough force to break them apart. The resulting nuclei may have a lower atomic mass than the reactants, with the difference released as energy. Electric charge, however, is always conserved.
5. Two atoms of helium-3 (atomic mass = 3) collide in a fusion reaction to produce a single atom of helium-4 (atomic mass = 4). What might be another product of this reaction?
A. a neutron
B. a proton
C. two electrons
D. a proton and a neutron
E. two protons
6. Hydrogen atoms usually contain a single neutron. Deuterium and tritium are isotopes of hydrogen containing two and three neutrons, respectively. How many electrons orbit the tritium nucleus if the atom is electrically neutral?
Questions 7 and 8 are based on the following text:
An electrochemical battery is a device powered by oxidation and reduction reactions that are physically separated so that the electrons must travel through a wire from the reducing agent to the oxidizing agent. The reducing agent loses electrons and is oxidized in a reaction that takes place at an electrode called the anode. The electrons flow through a wire to a second electrode, the cathode, where an oxidizing agent gains electrons and is thus reduced. To maintain a net zero charge in each compartment, there is a limited flow of ions through a salt bridge.
In a car battery, for example, the reducing agent is oxidized by the following reaction, which involves a lead (Pb) anode and sulfuric acid (H2SO4). Lead sulfate (PbSO4), protons (H+), and electrons (e-) are produced.
Pb + H2SO4 = PbSO4 +2 H+ + 2 e-
At the cathode, which is made of lead oxide (PbO2), the below reaction occurs. During this reaction, the electrons produced at the anode are used:
PbO2 + H2SO4 + 2 e- + 2 H+= PbSO4 + 2 H2O
7. Electrons are produced by a chemical reaction that takes place at the:
C. lead oxide electrode.
E. salt bridge.
8. In an oxidation reaction:
A. an oxidizing agent gains electrons.
B. an oxidizing agent loses electrons.
C. a reducing agent gains electrons.
D. a reducing agent loses electrons.
E. an oxidizing agent reduces an electrode.
9. What does aerobic mean?
A. in the presence of oxygen
10. What is the name for substances that cannot be broken down into simpler types of matter?
11. When atoms of one element are combined with atoms of another element, the result is a(n) _________ of a compound.
1. B: The horizontal rows of the periodic table are called periods. The vertical columns of the periodic table are known as groups or families. Developed by Dmitri Mendeleev to organize the known elements according to their similarities, all of the periodic table elements in a group have similar properties, and the relationships between the elements in each period moving from left to right are similar. New elements can be added to the periodic table without necessitating a redesign.
2. A: Diffusion is fastest through gases, followed by liquid, then plasma, and lastly, solids. In chemistry, diffusion is defined as the movement of matter by the random motions of molecules. In a gas or a liquid, the molecules are in perpetual motion; for instance, in a quantity of seemingly immobile air, molecules of nitrogen and oxygen are constantly bouncing off each other. In solids, there is a miniscule degree of diffusion, which rises in proportion to the temperature of the substance.
3. D: The number of protons in an atom is the atomic number. Protons are the fundamental positive unit of an atom and are located in the nucleus. In a neutral atom (an atom with neither positive nor negative charge), the number of protons in the nucleus is equal to the number of electrons orbiting the nucleus. In written form, the atomic number is the subscript in front of the element’s symbol, for example: 13Al. Atomic mass is the average mass of the various isotopes of a given element; atomic identity and atomic weight are not chemistry concepts.
4. C: CH could be an empirical formula. An empirical formula is the smallest expression of a chemical formula. To be empirical, a formula must be incapable of being reduced. For this reason, answer choices A, B, and D are incorrect, as they could all be reduced to a simpler form. Note that empirical formulas are not the same as compounds, which do not have to be irreducible. Two compounds can have the same empirical formula but different molecular formulas. The molecular formula represents the actual number of atoms in the molecule.
5. E: The charge must be conserved in the reaction. Since the reactants, the two helium atoms, each have two protons, they will have a total electric charge of +4. The reaction product, helium-4, also has two protons, and therefore has a total charge of +2. Two positive charges are lacking to balance the reaction. Of the choices given, only E, with two protons, has a charge of +2.
6. B: Since tritium is an isotope of hydrogen, the nucleus contains a single proton, giving it a charge of +1. The extra neutrons do not contribute to the charge. Electrons have a charge of -1. In order to neutralize the single positive charge of the nuclear proton, a single orbiting electron is required.
7. A: As described in the text, negatively charged electrons are produced by a reaction that reduces the positively charged lead anode. The reducing agent, in turn, is oxidized by this reaction. These electrons travel through the wire to the negatively charged cathode, where they react with the sulfuric acid oxidizer and reduce it, forming lead sulfate. In a car battery, the anode is normally indicated by a red mark.
8. A: In an oxidation reaction, an oxidizing agent gains electrons from a reducing agent. By contributing electrons, the reducing agent reduces, or makes more negative, the charge on the oxidizer. In the car battery, reduction of the positively charged anode provides electrons, which then flow to the cathode, where an oxidation takes place. In an oxidation, an oxidizing agent increases (makes more positive) the charge on a reducer. In this way, the extra electrons in the negatively charged cathode are neutralized by the surrounding oxidizing agent.
9. A: Aerobic means in the presence of oxygen.
10. D: An element is a substance that cannot be broken into simpler types of matter.
11. C: When atoms from two elements combine, the result is a molecule of a compound.