$$\text{Atomic Mass} = (\text{fractional abundance}_1 \times \text{mass}_1) + (\text{fractional abundance}_2 \times \text{mass}_2)$$

$$1.88 \times 10$$^{24}$$ atoms

$$1.51 \times 10$$^{24}$$ molecules

$$\text{grams} \rightarrow \text{moles} \rightarrow \text{molecules}$$

Question 1

Which of the following best describes a homogeneous mixture?

Accepted Answer

A mixture in which the composition is uniform throughout, such as tea with sugar.

Question 2

Which statement about the structure of the atom is correct?

Accepted Answer

Protons and neutrons are located in the nucleus, while electrons occupy the empty space around the nucleus.

Question 3

An atom of lead (Pb) has 82 protons, 125 neutrons, and 82 electrons. What is its mass number $$A$$?

Accepted Answer

$$A = 207$$

Question 4

Which of the following is the correct formula to calculate the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Atomic Mass} = (	ext{fractional abundance}_1 	imes 	ext{mass}_1) + (	ext{fractional abundance}_2 	imes 	ext{mass}_2)$$

Question 5

How many atoms are present in 3.12 moles of molybdenum (Mo)?

Accepted Answer

$$1.88 	imes 10$$^{24}$$ atoms

Question 6

Which statement about isotopes is correct?

Accepted Answer

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

Question 7

A copper rod has a length of 9.85 cm and a radius of 1.05 cm. If the density of copper is $$8.96 	ext{ g/cm}^3$$, what is the mass of the rod?

Accepted Answer

$$34.1 g$$

Question 8

Which of the following best describes a compound?

Accepted Answer

A pure substance composed of two or more elements chemically bonded together.

Question 9

What is the molar mass of water ($$H_2O$$)?

Accepted Answer

$$18.02 g/$$mol

Question 10

If you have 47.2 g of pure aluminum ($$Al$$), how many moles of aluminum do you have? (Atomic mass of Al = 26.98 g/mol)

Accepted Answer

$$1.75$$ moles

Question 11

Which of the following is the correct relationship between the mass of one mole of $$C$$ atoms and the number of atoms?

Accepted Answer

1 mole of $$C$$ atoms has a mass of $$12.01 g $$and contains $$6.022 	imes 10$$^{23}$$ atoms.

Question 12

Which subatomic particle has the smallest mass?

Accepted Answer

Electron

Question 13

A sample contains $$2.50$$ moles of $$H_2O. $$How many molecules of water are present?

Accepted Answer

$$1.51 	imes 10$$^{24}$$ molecules

Question 14

Which of the following is NOT a physical state of matter?

Accepted Answer

Plasma

Question 15

What is the formula mass of $$CO_2$$? (Atomic masses: C = 12.01 amu, O = 16.00 amu)

Accepted Answer

$$44.01$$ amu

Question 16

Which of the following statements is true regarding the neutrality of atoms?

Accepted Answer

An atom is neutral when it has equal numbers of protons and electrons.

Question 17

Which of the following is the correct conceptual plan for converting grams of a compound to number of molecules?

Accepted Answer

$$	ext{grams} ightarrow 	ext{moles} ightarrow 	ext{molecules}$$

Question 18

A sample of lead(IV) oxide ($$PbO_2) $$has a mass of $$50.0 g. $$How many molecules are present? (Molar mass of $$PbO_2 = 239.2$ g/mol)

Accepted Answer

$$1.26 	imes 10$$^{23}$$ molecules

Question 19

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

Accepted Answer

Avogadro's number is $$6.022 	imes 10$$^{23}$$ and represents the number of particles in one mole.

Atoms and the Classification of Matter

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