Question 1

Which of the following best describes the difference between a physical change and a chemical change?

Accepted Answer

A chemical change involves a change in the composition of a substance, while a physical change does not.

Question 2

A sample of gold has a mass of $$19.3\ \mathrm{g}$$ and a volume of $$1.00\ \mathrm{cm}^3. $$What is the density of gold, and how many significant figures should your answer have?

Accepted Answer

Density $$= 19.3\ \mathrm{g/cm}^3$$; answer should have 3 significant figures.

Question 3

Which of the following statements about the scientific method is correct?

Accepted Answer

A law describes a consistent relationship observed in nature, while a theory explains why that relationship exists.

Question 4

Which of the following is a heterogeneous mixture?

Accepted Answer

Salad with lettuce, tomatoes, and cucumbers

Question 5

A student measures the temperature of a solution as $$25.0\ ^\circ\mathrm{C}. $$What is this temperature in Kelvin?

Accepted Answer

$$298.15\ \mathrm{K}$$

Question 6

Which of the following best describes the difference between an element and a compound?

Accepted Answer

A compound consists of two or more elements chemically combined in a fixed ratio, while an element consists of only one type of atom.

Question 7

Which of the following is the correct electron configuration for a neutral atom of magnesium ($$Z=12$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$

Question 8

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 9

A $$10.0\ \mathrm{g}$$ sample of a metal at $$100.0\ ^\circ\mathrm{C} is $$placed in $$50.0\ \mathrm{g} of $$water at $$25.0\ ^\circ\mathrm{C}. $$The final temperature is $$27.0\ ^\circ\mathrm{C}. If $$the specific heat capacity of water is $$4.18\ \mathrm{J/g\cdot K}$$, what is the specific heat capacity of the metal? (Assume no heat loss to surroundings.)

Accepted Answer

$$0.42\ \mathrm{J/g\cdot K}$$

Question 10

Which of the following best explains why metals tend to form cations?

Accepted Answer

Metals have low ionization energies and tend to lose electrons to achieve a stable electron configuration.

Question 11

Which of the following is the correct scientific notation for the number $$0.000456$$?

Accepted Answer

$$4.56 	imes 10$$^{-4}$$

Question 12

Which of the following best describes the trend in atomic size across a period (left to right) in the periodic table?

Accepted Answer

Atomic size decreases from left to right.

Question 13

Which of the following molecules is polar due to its molecular geometry and difference in electronegativity?

Accepted Answer

$$\mathrm{H}_2\mathrm{O}$$

Question 14

A $$5.00\ \mathrm{g}$$ sample of a substance occupies $$2.00\ \mathrm{cm}^3. $$What is its density, and how many significant figures should your answer have?

Accepted Answer

$$2.5\ \mathrm{g/cm}^3$$; 2 significant figures

Question 15

Which of the following best describes Hund’s rule as it applies to electron configurations?

Accepted Answer

Electrons occupy orbitals singly before pairing up in the same subshell.

Question 16

Which of the following is the correct order of increasing ionization energy for the elements sodium ($$\mathrm{Na}$$), magnesium ($$\mathrm{Mg}$$), and aluminum ($$\mathrm{Al}$$)?

Accepted Answer

$$\mathrm{Na} \u003c \mathrm{Mg} \u003c \mathrm{Al}$$

Question 17

Which of the following best describes the difference between an ionic and a covalent bond?

Accepted Answer

An ionic bond involves the transfer of electrons from one atom to another, while a covalent bond involves the sharing of electrons between atoms.

Question 18

Which of the following is the correct Lewis structure for a chloride ion ($$\mathrm{Cl}^-$$)?

Accepted Answer

A Cl atom with 8 dots and a $$-$$ charge outside the brackets

Question 19

Which of the following statements about exothermic and endothermic processes is correct?

Accepted Answer

An exothermic process releases heat to the surroundings.

Question 20

Which of the following best explains why water has a higher boiling point than methane ($$\mathrm{CH}_4$$)?

Accepted Answer

Water forms hydrogen bonds due to its polarity, requiring more energy to separate the molecules.

Introduction to Chemistry: Key Concepts and Problem-Solving Guidance (Modules 1–3)

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