1.
The atoms and molecules that make up a rock.
Correct Answer
A. Are in constant motion
Explanation
The correct answer is "are in constant motion" because atoms and molecules are always vibrating and moving, even in solid objects like rocks. This constant motion is due to thermal energy and is what gives materials their physical properties.
2.
A substance that contains only one type of atom is a(n)
Correct Answer
B. Element
Explanation
An element is a substance that contains only one type of atom. It cannot be broken down into simpler substances by chemical means. Elements are represented by symbols on the periodic table and have specific properties that distinguish them from other substances. Compounds, on the other hand, are substances made up of two or more different types of atoms bonded together. Heterogeneous and homogeneous mixtures both contain multiple types of substances mixed together, but they are not pure substances like elements.
3.
A sealed metal container holds a gas. What happens when the container is heated?
Correct Answer
A. The gas exerts more pressure
Explanation
When the sealed metal container is heated, the gas molecules inside gain more energy and move faster, resulting in an increase in their average kinetic energy. As a result, the gas molecules collide more frequently with the walls of the container, exerting a greater force per unit area. This increase in force per unit area is what we perceive as an increase in pressure. Therefore, when the container is heated, the gas exerts more pressure.
4.
Which of these is an example of matter?
Correct Answer
D. Smoke from a fire
Explanation
Smoke from a fire is an example of matter because it consists of tiny particles that can be seen and felt. Matter is anything that has mass and occupies space, and smoke fits this definition as it has mass and takes up physical space. The other options - sound of thunder, sunlight, and heat from an oven - are forms of energy rather than matter, as they do not have mass or occupy space in the same way that smoke does.
5.
How are atoms and elements related?
Correct Answer
B. Every element contains only one kind of atom
Explanation
Every element contains only one kind of atom. This means that all atoms of a particular element have the same number of protons in their nucleus. For example, all carbon atoms have 6 protons, all oxygen atoms have 8 protons, and so on. This relationship between atoms and elements is fundamental to the periodic table, where elements are organized based on their atomic number (number of protons). Therefore, the statement that every element contains only one kind of atom accurately describes the relationship between atoms and elements.
6.
Suppose you examine an unknown liquid. You determine that it contains a single type of molecule. What is the liquid?
Correct Answer
A. A pure substance
Explanation
The correct answer is a pure substance. This is because if the unknown liquid contains a single type of molecule, it means that it is not a mixture of different substances. A pure substance consists of only one type of element or compound, and since the liquid contains only one type of molecule, it can be classified as a pure substance.
7.
When substances combine to make compounds, the proportions of each substance in the compound.
Correct Answer
D. Are the same throughout the compound
Explanation
When substances combine to make compounds, the proportions of each substance in the compound are the same throughout the compound. This means that the ratio of the elements in the compound remains constant regardless of the amount of each substance used. This is a fundamental principle in chemistry known as the law of definite proportions, which states that a compound is always composed of the same elements in the same ratio by mass.
8.
A Cork and a pebble are placed in 100 ml of water, and each displaces 10 ml of water. The cork floats but the pebble sinks.
Correct Answer
B. The cork's volume is greater
Explanation
The cork floats because it has a greater volume than the pebble. When an object is placed in water, it displaces an amount of water equal to its own volume. Since both the cork and the pebble displace 10 ml of water, it means that they have the same volume. However, the cork floats because it is less dense than water, while the pebble sinks because it is denser than water. This indicates that the cork's volume is greater than the pebble's volume.
9.
In which of the following states can molecules and atoms move?
Correct Answer
A. Solid, liquid, or gas
Explanation
Molecules and atoms can move in all three states of matter, which are solid, liquid, and gas. In a solid, the particles are closely packed together but they still vibrate and can move within their fixed positions. In a liquid, the particles are not as closely packed as in a solid, allowing them to move more freely and flow. In a gas, the particles are widely spaced and move rapidly in all directions. Therefore, molecules and atoms have the ability to move in all three states of matter.
10.
Mass can be measured in units of?
Correct Answer
A. Grams
Explanation
Mass is a measure of the amount of matter in an object. It is commonly measured in grams, which is a unit of mass in the metric system. Grams are used to measure the mass of small objects or substances. Newtons, on the other hand, are a unit of force, not mass. Cubic centimeters and milliliters are units of volume, not mass. Therefore, grams is the correct unit for measuring mass.
11.
The amount of matter in a desk is the desk's:
Correct Answer
C. Mass
Explanation
Mass refers to the amount of matter present in an object. In the context of a desk, mass would indicate how much material is used to construct the desk. Volume refers to the amount of space occupied by the desk, size is a general term that can refer to various dimensions of the desk, and state refers to the physical state of matter (solid, liquid, gas), which is not relevant in this case. Therefore, the correct answer is mass.
12.
Which of these is a physical change, not a chemical change?
Correct Answer
D. An aluminum can melts
Explanation
Melting of an aluminum can is a physical change because it involves a change in the state of matter from solid to liquid without any alteration in the chemical composition of the substance. The molecules in the can rearrange themselves to form a liquid state, but the aluminum itself remains the same.
13.
The process of a solid changing directly to a gas is called?
Correct Answer
C. Sublimation
Explanation
Sublimation is the process in which a solid directly changes into a gas without going through the liquid state. This occurs when the substance's vapor pressure exceeds the atmospheric pressure, causing the solid particles to escape and form a gas. Examples of sublimation include dry ice (solid carbon dioxide) turning into carbon dioxide gas and mothballs (solid naphthalene) evaporating into the air. Evaporation, on the other hand, is the process in which a liquid changes into a gas, while freezing is the process in which a liquid changes into a solid, and condensation is the process in which a gas changes into a liquid.
14.
Which of these is a chemical change, not a physical change?
Correct Answer
B. A loaf of bread baked in the oven
Explanation
A loaf of bread being baked in the oven is a chemical change because it involves a chemical reaction called the Maillard reaction. During baking, the heat causes the proteins and sugars in the bread to undergo a complex series of reactions, resulting in the browning and formation of new compounds that give the bread its characteristic taste and aroma. This change is irreversible and involves the formation of new substances, making it a chemical change rather than a physical change.
15.
When a gas changes into a liquid, the process is called?
Correct Answer
D. Condensation
Explanation
When a gas changes into a liquid, the process is called condensation. This occurs when the gas molecules lose energy and slow down, causing them to come closer together and form a liquid. Condensation is the opposite of evaporation, where a liquid changes into a gas. Sublimation refers to the process of a solid directly changing into a gas without going through the liquid phase. Chemical change refers to a process where the substance undergoes a chemical reaction and forms new substances with different properties.
16.
To identify a substance by its density, you must determine its:
Correct Answer
A. Mass and volume
Explanation
To identify a substance by its density, you must determine its mass and volume. Density is defined as the mass of an object divided by its volume. By measuring the mass of the substance and calculating its volume, you can then divide the mass by the volume to determine the density. This allows you to compare the density of the substance to known densities and identify the substance based on its unique density value.
17.
There are two kinds of electric charge. They are:
Correct Answer
C. Positive and negative
Explanation
The two kinds of electric charge are positive and negative. This is based on the concept of electric charge, which is a fundamental property of matter. Positive charge is associated with protons, while negative charge is associated with electrons. These charges interact with each other, with opposite charges attracting and like charges repelling. This understanding of electric charge is fundamental to the study of electricity and electromagnetism.
18.
Which is an example of a chemical change to matter?
Correct Answer
B. Iron rusting
Explanation
Iron rusting is an example of a chemical change to matter because it involves a reaction between iron and oxygen in the presence of moisture, which results in the formation of a new substance, iron oxide (rust). This process is irreversible and involves a change in the chemical composition of the iron, making it a chemical change rather than a physical change.
19.
When water boils it changes from a:
Correct Answer
D. Liquid to a gas
Explanation
When water boils, it undergoes a phase change from a liquid to a gas. This occurs when the water is heated to its boiling point, which is 100 degrees Celsius (212 degrees Fahrenheit) at sea level. As the temperature increases, the water molecules gain enough energy to break free from their liquid state and become water vapor, resulting in the process of boiling.
20.
The most common element in the universe is:
Correct Answer
B. Hydrogen
Explanation
Hydrogen is the most common element in the universe because it is the lightest and simplest element, consisting of only one proton and one electron. It is estimated that about 90% of the atoms in the universe are hydrogen. It is found in abundance in stars, where nuclear fusion reactions convert hydrogen into helium, releasing vast amounts of energy. Additionally, hydrogen is also present in interstellar clouds and gas giants like Jupiter and Saturn. Its abundance and widespread distribution make hydrogen the most common element in the universe.
21.
Electrons
Correct Answer
D. Move around outside the nucleus
Explanation
Electrons are negatively charged particles that orbit around the nucleus of an atom. They are found in energy levels or shells and move rapidly in these orbits. The movement of electrons outside the nucleus determines the chemical and physical properties of an element, as well as its reactivity and bonding behavior. Therefore, the statement that electrons move around outside the nucleus is correct.
22.
Mg (+2 charge) is a magnesium ion that has:
Correct Answer
A. Two fewer electrons than a neutral magnesium atom
Explanation
A magnesium ion with a +2 charge means that it has lost two electrons. Therefore, it has two fewer electrons than a neutral magnesium atom.
23.
Most elements on the periodic table are:
Correct Answer
B. Metals
Explanation
Metals are the correct answer because they make up the majority of elements on the periodic table. Metals are typically shiny, solid at room temperature, good conductors of heat and electricity, and malleable. They are found on the left side and middle of the periodic table. Metalloids are elements that have properties of both metals and nonmetals, noble gases are a group of elements that are generally inert and nonreactive, and nonmetals are elements that are typically poor conductors of heat and electricity.
24.
The least active elements are:
Correct Answer
D. Noble gases
Explanation
Noble gases are the least active elements because they have a full outer electron shell, making them stable and less likely to react with other elements. They have a low tendency to gain, lose, or share electrons, which is why they are generally unreactive. This characteristic makes them useful in various applications, such as in lighting and as inert gases in industrial processes.
25.
Most nonmetals are:
Correct Answer
B. Poor conductors of heat
Explanation
Nonmetals are poor conductors of heat because they lack free electrons that can easily move and transfer thermal energy. In nonmetals, the electrons are tightly bound to the atoms, making it difficult for heat to be conducted through them. This is in contrast to metals, which have delocalized electrons that can easily transfer heat. Therefore, nonmetals do not efficiently conduct heat and are considered poor conductors.
26.
The positively charged particles in an atom are:
Correct Answer
D. Protons
Explanation
Protons are positively charged particles found in the nucleus of an atom. They have a mass of approximately 1 atomic mass unit and carry a positive charge of +1. Electrons, on the other hand, are negatively charged particles that orbit around the nucleus. Neutrons are neutral particles found in the nucleus. Therefore, the correct answer is protons, as they are the positively charged particles in an atom.
27.
Nitrogen-14 and Nitrogen-15 are examples of:
Correct Answer
A. Isotopes
Explanation
Nitrogen-14 and Nitrogen-15 are examples of isotopes. Isotopes are atoms of the same element that have different numbers of neutrons in their nucleus. In this case, both Nitrogen-14 and Nitrogen-15 have the same number of protons (7), but Nitrogen-14 has 7 neutrons while Nitrogen-15 has 8 neutrons. Therefore, they are isotopes of nitrogen.
28.
A sodium atom has a charge of 1+. It must have one:
Correct Answer
D. Fewer electron than usual
Explanation
A sodium atom typically has 11 protons and 11 electrons, giving it a neutral charge. However, in this case, the sodium atom has a charge of 1+, indicating that it has lost one electron. Therefore, it has fewer electrons than usual, resulting in a positive charge.
29.
Two atoms have the same number of protons. They must be:
Correct Answer
B. Atoms of the same element
Explanation
Two atoms having the same number of protons indicates that they have the same atomic number, which defines the element. Therefore, they must be atoms of the same element. Isotopes can have different numbers of neutrons, so it cannot be concluded that they are isotopes of each other. The atomic mass number is the sum of protons and neutrons, which may vary between isotopes of the same element. The charge of an atom depends on the number of electrons, not protons, so it cannot be determined that they are neutrally charged.
30.
A group of atoms held together by covalent bonds is a(n)
Correct Answer
C. Molecule
Explanation
A group of atoms held together by covalent bonds is called a molecule. In a covalent bond, atoms share electrons, resulting in the formation of a stable molecule. This is different from an ionic bond where electrons are transferred from one atom to another. Compounds can also be formed by a combination of different elements, but not all compounds are made up of covalent bonds. Therefore, the correct answer in this case is molecule.
31.
The nucleus of an atom contains:
Correct Answer
C. Neutrons and protons
Explanation
The nucleus of an atom contains neutrons and protons. Neutrons have no charge and are responsible for adding mass to the nucleus. Protons, on the other hand, have a positive charge and determine the atomic number of the atom, thus defining its identity. Electrons, which have a negative charge, are found outside the nucleus in the electron cloud. Therefore, the correct answer is neutrons and protons.
32.
Atoms are made up of?
Correct Answer
C. Electrons, neutrons, and protons
Explanation
Atoms are made up of electrons, neutrons, and protons. Electrons are negatively charged particles that orbit around the nucleus of an atom. Neutrons are neutral particles found in the nucleus, while protons are positively charged particles also located in the nucleus. These three subatomic particles together make up the structure of an atom.