Question 1

Which of the following statements explains why elements of the alkali metal family are highly reactive?

Accepted Answer

Alkali metals are highly reactive because they have a single electron in their outermost shell, making them easily ionized as they readily lose this electron to achieve a stable electronic configuration.

Question 2

Which of the following statements describes the role of a buffer?

Accepted Answer

Buffers are designed to maintain the pH of a solution within a narrow range by neutralizing small amounts of added acid or base. This is crucial in many biological and chemical processes where the pH needs to be stabilized to prevent harmful effects on the system.

Question 3

How many grams of KCl are dissolved in 2.00 L of a 0.200 M solution of KCl?

Accepted Answer

To find the grams of KCl, use the formula: grams = molarity (M) × volume (L) × molar mass (g/mol). The molar mass of KCl is approximately 74.55 g/mol. So, 0.200 M × 2.00 L × 74.55 g/mol = 29.82 g, which rounds to 29.8 g.

Question 4

A leaf gently floats on a pond. Which of the following statements best explains why the leaf stays on top of the water?

Accepted Answer

The leaf stays on top of the water primarily due to the surface tension of the water, which is a result of the hydrogen bonds between water molecules. These bonds create a "skin" on the water's surface that can support lightweight objects like a leaf.

Question 5

Silver (Ag) has 47 protons in each atom. Based on this information, which of the following also describes an atom of silver

Accepted Answer

An atom of silver (Ag) with 47 protons is electrically neutral, meaning it must also have 47 electrons to balance the positive charge of the protons.

Question 6

In a hydrogen fluoride (HF) molecule, a hydrogen atom and a fluorine atom are held together by a polar covalent bond. Which of the following best explains why this bond is polar?

Accepted Answer

The bond is polar because of the large difference in electronegativities between hydrogen and fluorine atoms, which causes an unequal sharing of electrons.

Question 7

Which of the following lists three states of water in order of increasing entropy?

Accepted Answer

Entropy measures the disorder or randomness in a system. The order of increasing entropy for water is solid (ice), liquid, and gas (vapor), as the molecular movement and disorder increase from solid to gas.

Question 8

Which of the following activities could cause liquid molecules to overcome intermolecular attractive forces and become gas molecules?

Accepted Answer

Increasing the temperature of the liquid provides the molecules with enough energy to overcome intermolecular forces, allowing them to escape into the gas phase.

Question 9

Which of the following are most directly involved in chemical bonding?

Accepted Answer

Valence electrons are the outermost electrons of an atom and are primarily responsible for the chemical properties of the element, including its ability to form bonds with other atoms.

Question 10

Which of the following statements explains why oxygen is classified asa pure substance and air is classifiedas a mixture?

Accepted Answer

Oxygen is classified as a pure substance because it consists of only one type of molecule, O2, whereas air is a mixture because it contains a variety of gases such as nitrogen, oxygen, carbon dioxide, and others in varying proportions.

Question 11

A hospital buys a compound that contains an isotope of barium. Several months later, most of the barium has changed to the element lanthanum. Which of the following is responsible for this change?

Accepted Answer

The transformation of barium into lanthanum over time is due to radioactive decay, a process where an unstable atomic nucleus loses energy by emitting radiation, leading to the change of one element into another.

Question 12

A student made a homogeneous mixture of water and salt. Which of the following statements applies to this homogeneous mixture?

Accepted Answer

A homogeneous mixture where one substance (salt) is completely dissolved in another (water) is called a solution. Salt does not chemically combine with water but dissolves in it, maintaining its chemical identity.

Question 13

Which of the following statements best explains why elements in the same family of the periodic table have similar bonding properties?

Accepted Answer

Elements in the same family (or group) of the periodic table have similar valence electron configurations, which determines their bonding properties. The number of valence electrons influences how elements interact with other elements, leading to similarities in chemical behavior within a group.

Question 14

Which of the following statements best explains why potassium (K) reacts easily with bromine (Br)?

Accepted Answer

Potassium (K) has one electron in its outermost shell (making it eager to lose that electron to achieve a stable electronic configuration), while bromine (Br) has seven electrons in its outermost shell and needs one more to complete its octet (making it eager to gain an electron). This complementary need for electrons facilitates the reaction between them.

Question 15

Which of the following statements best explains why atoms bond?

Accepted Answer

Atoms bond to become more chemically stable. This is because by sharing or transferring electrons through bonds, atoms achieve a full outer electron shell, resembling the electron configuration of noble gases, which is the most stable arrangement.

Question 16

When a sample of potassium chloride dissolves in water, it separates into potassium ions and chloride ions. Which of the following best accounts for the positive charge of the potassium ions?

Accepted Answer

Potassium ions have a positive charge because they have one fewer electron than protons. When potassium loses an electron, it has more protons than electrons, resulting in a net positive charge.

Question 17

Which of the following statements applies to a nuclear fission reaction?

Accepted Answer

Nuclear fission reactions release significant amounts of energy as the nuclei of certain heavy elements, such as uranium or plutonium, split into smaller parts. This process is the basis for nuclear power generation and atomic bombs, highlighting its capability to release large energy quantities.

Question 18

Gold-198 has a half-life of approximately 3 days. If a 100 g sample of gold-198 decays for 9 days, approximately how much gold-198 remains in the sample?

Accepted Answer

After 9 days, which is 3 half-lives (9 days / 3 days per half-life), the amount of gold-198 would have halved 3 times. Starting with 100 g, after one half-life (3 days), it would be 50 g; after two half-lives (6 days), it would be 25 g; and after three half-lives (9 days), it would be approximately 12.5 g, which rounds to 13 g.

Question 19

Formaldehyde in solution is used as a preservative. It has a melting point of -92°C. When the temperature of a sample of formaldehyde rises from -93°C to -91°C, which of the following occurs?

Accepted Answer

As the temperature of formaldehyde rises from -93°C to -91°C, the molecules gain kinetic energy, which allows them to move more freely. This is a general characteristic of substances as they absorb heat; their particles tend to move more vigorously. The other options (B, C, and D) do not accurately describe what happens to formaldehyde (or most substances) as they warm up in this temperature range.

Question 20

A hiker carries drinking water in a cloth-covered, metal container called a canteen. During the summer, the hiker wets the cloth covering so that the water in the canteen stays cool. Which of the following statements explains why a wet covering keeps the water cool?

Accepted Answer

Evaporation of water from the covering absorbs heat from the surroundings (in this case, the canteen and its contents), which results in a cooling effect. This process is known as evaporative cooling.

Quiz 2: Chemistry