Q: A sample of magnesium reacts completely with oxygen to form magnesium oxide. If 24.3 g of magnesium reacts with 16.0 g of oxygen, what is the mass percent of magnesium in magnesium oxide?

$$\frac{24.3}{24.3+16.0} \times 100 = 60.3\%$$

Q: A molecule of water contains two hydrogen atoms and one oxygen atom. What is the total number of protons in a water molecule?

$$2 \times 1 + 1 \times 8 = 10$$

Q: Which of the following is the correct molar mass of calcium nitrate, $$Ca(NO_3$)_2$$? (Atomic masses: Ca = 40.1, N = 14.0, O = 16.0)

$$40.1 + 2 \times (14.0 + 3 \times 16.0) = 164.1\ \text{g/mol}$$

Q: A sample contains $$3.01 \times 10$$^{23}$$ molecules of CO_2$. How many moles of CO_2$ are present?

$$\frac{3.01 \times 10$$^{23}$$}{6.022 \times 10$$^{23}$$} = 0.500\ \text{mol}$$

Question 1

Which of the following statements best describes the Law of Definite Proportions?

Accepted Answer

A compound always contains the same elements in the same proportion by mass.

Question 2

Which scientist is credited with the first modern atomic theory, which included the idea that all matter is composed of indivisible atoms?

Accepted Answer

John Dalton

Question 3

A sample of magnesium reacts completely with oxygen to form magnesium oxide. If 24.3 g of magnesium reacts with 16.0 g of oxygen, what is the mass percent of magnesium in magnesium oxide?

Accepted Answer

$$\frac{24.3}{24.3+16.0} 	imes 100 = 60.3\%$$

Question 4

Which of the following best explains why isotopes of the same element have nearly identical chemical properties?

Accepted Answer

They have the same number of electrons and the same electron configuration.

Question 5

Which of the following is the correct electron configuration for a neutral atom of sodium ($$Z=11$$)?

Accepted Answer

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

Question 6

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties because they have the same number of valence electrons.

Question 7

A molecule of water contains two hydrogen atoms and one oxygen atom. What is the total number of protons in a water molecule?

Accepted Answer

$$2 	imes 1 + 1 	imes 8 = 10$$

Question 8

Which of the following best describes a heterogeneous mixture?

Accepted Answer

A mixture in which the composition is not uniform throughout.

Question 9

Which of the following is the correct molar mass of calcium nitrate, $$Ca(NO_3$)_2$$? (Atomic masses: Ca = 40.1, N = 14.0, O = 16.0)

Accepted Answer

$$40.1 + 2 	imes (14.0 + 3 	imes 16.0) = 164.1\ 	ext{g/mol}$$

Question 10

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

Accepted Answer

A molecule is two or more atoms bonded together, while a compound is a molecule that contains at least two different elements.

Question 11

Which of the following ions is isoelectronic with neon ($$Ne$$)?

Accepted Answer

$$F^-$$

Question 12

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of CO_2$. How many moles of CO_2$ are present?

Accepted Answer

$$\frac{3.01 	imes 10$$^{23}$$}{6.022 	imes 10$$^{23}$$} = 0.500\ 	ext{mol}$$

Question 13

Which of the following best explains why sodium forms a $$+1$$ ion and chlorine forms a $$-1$$ ion in sodium chloride?

Accepted Answer

Sodium loses one electron to achieve a noble gas configuration, while chlorine gains one electron to achieve a noble gas configuration.

Question 14

Which of the following is a correct example of the Law of Multiple Proportions?

Accepted Answer

Carbon forms two oxides: $$CO$$ and $$CO_2$$, where the ratio of the masses of oxygen that combine with a fixed mass of carbon is a small whole number.

Question 15

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

Accepted Answer

A physical property can be observed without changing the substance's identity, while a chemical property describes how a substance reacts to form new substances.

Question 16

Which of the following is the correct formula for the compound formed between calcium and phosphate ions?

Accepted Answer

$$Ca_3$$($$PO_4)_2$

Question 17

Which of the following statements about Avogadro's number is correct?

Accepted Answer

One mole of any substance contains $$6.022 	imes 10$$^{23}$$ particles.

Question 18

Which of the following best describes the difference between a pure substance and a mixture?

Accepted Answer

A pure substance has a fixed composition, while a mixture contains two or more substances physically combined.

Question 19

Which of the following is the correct chemical formula for aluminum sulfate?

Accepted Answer

$$Al_2$$($$SO_4)_3$

Question 20

Which of the following best explains why noble gases are generally unreactive?

Accepted Answer

They have full valence electron shells, making them stable.

Atoms, Molecules, and the Periodic Table: Fundamental Concepts in General Chemistry

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