Q: Which of the following is the correct formula for calculating average atomic mass?

$$\text{Average atomic mass} = \sum (\text{fractional abundance} \times \text{isotope mass})$$

Question 1

Which of the following best describes a compound?

Accepted Answer

A substance composed of two or more elements chemically combined in fixed proportions.

Question 2

Which of the following is an example of a homogeneous mixture?

Accepted Answer

Salt dissolved in water.

Question 3

Which statement about isotopes is correct?

Accepted Answer

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

Question 4

A sample contains 75% $$^{35}\mathrm{Cl} ($$atomic mass = 34.97 u) and 25% $$^{37}\mathrm{Cl} ($$atomic mass = 36.97 u). What is the average atomic mass of chlorine in this sample?

Accepted Answer

$$35.47\ \mathrm{u}$$

Question 5

Which of the following diagrams best represents a pure element?

Accepted Answer

A box containing only one type of atom, all identical.

Question 6

Which of the following is NOT a physical property?

Accepted Answer

Ability to react with acid

Question 7

Which of the following statements about ions is correct?

Accepted Answer

Cations are positively charged because they lose electrons.

Question 8

A neutral atom of sodium ($$^{23}\mathrm{Na}) $$has how many protons, neutrons, and electrons?

Accepted Answer

11 protons, 12 neutrons, 11 electrons

Question 9

Which of the following best describes a heterogeneous mixture?

Accepted Answer

A mixture in which the different components can be seen as individual substances.

Question 10

Which of the following is a chemical change?

Accepted Answer

Rusting of iron

Question 11

Which of the following is true about the periodic table?

Accepted Answer

Elements in the same group have similar chemical properties.

Question 12

Which of the following is the correct formula for calculating average atomic mass?

Accepted Answer

$$	ext{Average atomic mass} = \sum (	ext{fractional abundance} 	imes 	ext{isotope mass})$$

Question 13

Which of the following best explains why atoms are electrically neutral?

Accepted Answer

They have equal numbers of protons and electrons.

Question 14

Which of the following is a property of metals?

Accepted Answer

Malleable and ductile

Question 15

Which of the following is the correct symbol for an ion with 17 protons, 18 electrons, and 18 neutrons?

Accepted Answer

$$^{35}\mathrm{Cl}^-$$

Question 16

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

Accepted Answer

A mixture can be separated by physical means, while a compound can only be separated by chemical means.

Question 17

Which of the following is the correct notation for an isotope of carbon with 6 protons and 8 neutrons?

Accepted Answer

$$^{14}\mathrm{C}$$

Question 18

Which of the following is a real-world example of a heterogeneous mixture?

Accepted Answer

Blood

Question 19

Which of the following best describes the process of ion formation?

Accepted Answer

Atoms gain or lose electrons to form ions.

Question 20

A sample contains two isotopes of boron: 20% $$^{10}\mathrm{B} ($$atomic mass = 10.01 u) and 80% $$^{11}\mathrm{B} ($$atomic mass = 11.01 u). What is the average atomic mass of boron in this sample?

Accepted Answer

$$10.81\ \mathrm{u}$$

Introduction to Chemistry: Classification of Matter, Atoms, and Isotopes

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