Chem 108 Exam 1

1.

Which of the following is a property of both gases and liquids?

A.

Definite shape
B.

Indefinite shape
C.

Definite volume
D.

Indefinite volume

Correct Answer
B. Indefinite shape

Explanation
Both gases and liquids have indefinite shape, meaning that they do not have a fixed or specific shape. Unlike solids, which have a definite shape, gases and liquids can take the shape of their container. They are able to flow and move freely, allowing them to fill the space available to them. This property is a characteristic of both gases and liquids, distinguishing them from solids.

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2.

The description "two substances present, two phases present" is correct for

A.

Heterogeneous mixtures
B.

Homogeneous mixtures
C.

Elements
D.

Compounds

Correct Answer
A. Heterogeneous mixtures

Explanation
The description "two substances present, two phases present" is correct for heterogeneous mixtures. In heterogeneous mixtures, different substances are physically combined but not chemically bonded. These mixtures can be easily distinguished as they have visible boundaries between their components and can exist in two or more phases. Examples of heterogeneous mixtures include a mixture of oil and water or a salad dressing with separate layers.

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3.

In which of the following pairs of properties are both properties physical properties?

A.

Melts at 73 degrees, decomposes upon heating
B.

Good reflector of light, blue in color
C.

Has a high density, is very hard
D.

More than one correct response

Correct Answer
D. More than one correct response

Explanation
The given question asks for a pair of properties that are both physical properties. A physical property refers to a characteristic of a substance that can be observed or measured without changing its chemical composition. From the options provided, "melts at 73 degrees, decomposes upon heating" and "has a high density, is very hard" are both pairs of properties that are physical in nature. Melting point and density are physical properties that can be measured without altering the substance's chemical composition. Decomposing upon heating and being very hard are also physical properties that can be observed without changing the substance's chemical composition. Therefore, there is more than one correct response in this question.

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4.

A substance has a freezing point of -20 degrees C. This is an example of a

A.

Physical property
B.

Chemical property
C.

Physical change
D.

Chemical change

Correct Answer
A. pHysical property

Explanation
The freezing point of a substance refers to the temperature at which it changes from a liquid state to a solid state. In this case, the substance has a freezing point of -20 degrees C, indicating that it will solidify at this temperature. This characteristic of the substance, its ability to freeze at a specific temperature, is a physical property.

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5.

The nucleus of an atom

A.

Contains neutrons and electrons
B.

Has no charge because of the presence of neutrons
C.

Repels the negatively charged electrons in an atom
D.

Does not account for a large amount of the total volume of an atom

Correct Answer
D. Does not account for a large amount of the total volume of an atom

Explanation
The correct answer is "does not account for a large amount of the total volume of an atom". The nucleus of an atom is a small, dense region located at the center of the atom. It contains protons and neutrons, which are responsible for the majority of the atom's mass. However, the nucleus occupies only a tiny fraction of the total volume of the atom. The majority of the atom's volume is occupied by the electron cloud, where the negatively charged electrons are found.

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6.

An atom contains 33 protons, 35 neutrons, and 33 electrons. The atomic number and mass number for this atom are

A.

35 and 33
B.

33 and 35
C.

33 and 68
D.

35 and 68

Correct Answer
C. 33 and 68

Explanation
The atomic number of an atom is determined by the number of protons, which in this case is 33. The mass number is determined by the sum of protons and neutrons, which is 33 protons + 35 neutrons = 68. Therefore, the correct answer is 33 and 68.

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7.

The nuclear charge for an atom of ^18 (down)9 F is

A.

Zero
B.

+9
C.

+18
D.

+28

Correct Answer
B. +9

Explanation
The nuclear charge for an atom is determined by the number of protons in its nucleus. In this case, the atom is fluorine (F) with an atomic number of 9, which means it has 9 protons. The nuclear charge is equal to the number of protons, so the correct answer is +9.

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8.

Chlorine, which exists in nature in two isotopic forms, has an atomic mass of 35.5 amu. This means that

A.

All chlorine atoms have masses of 35.5 amu
B.

More than half of all chlorine atoms have masses of 35.5
C.

35.5 amu is the upper limit for the mass of a chlorine atom
D.

The mass of one isotope must be lighter than 35.5 amu while the mass of the other isotope is heavier than 35.5 amu

Correct Answer
D. The mass of one isotope must be lighter than 35.5 amu while the mass of the other isotope is heavier than 35.5 amu

Explanation
The atomic mass of an element is the weighted average of the masses of all its isotopes, taking into account their abundance. Since chlorine exists in nature in two isotopic forms, with atomic masses of 35 amu and 37 amu, the average atomic mass is 35.5 amu. This means that there must be one isotope of chlorine with a mass lighter than 35.5 amu (35 amu) and another isotope with a mass heavier than 35.5 amu (37 amu). Therefore, the statement "The mass of one isotope must be lighter than 35.5 amu while the mass of the other isotope is heavier than 35.5 amu" is correct.

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9.

Isotopes of a given element

A.

Have the same mass number but different numbers of protons
B.

Have different mass numbers but identical numbers of protons
C.

Have the same atomic number but different chemical properties
D.

Have the same mass number but different chemical properties

Correct Answer
B. Have different mass numbers but identical numbers of protons

Explanation
Isotopes of a given element have different mass numbers but identical numbers of protons. Isotopes are atoms of the same element that have different numbers of neutrons, resulting in different mass numbers. However, they have the same number of protons, which determines the element's atomic number. This means that isotopes have identical numbers of protons, giving them the same chemical properties. The difference in mass numbers between isotopes affects their physical properties, such as their atomic mass and stability.

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10.

The modern periodic table arranges the elements in order of

A.

Year of discovery
B.

Decreasing size of nucleus
C.

Increasing reactivity with oxygen
D.

Increasing number of protons

Correct Answer
D. Increasing number of protons

Explanation
The modern periodic table arranges the elements in order of increasing number of protons. This is because the number of protons in an atom determines its atomic number, which is a unique identifier for each element. As the atomic number increases, the elements are arranged in a sequential order, allowing for easy classification and organization. This arrangement also helps to identify trends and patterns in the properties of elements as you move across the periodic table.

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