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

$\text{Atomic mass} = (\text{fraction of isotope 1} \times \text{mass of isotope 1}) + (\text{fraction of isotope 2} \times \text{mass of isotope 2})$

Question 1

Which statement best describes the law of conservation of mass in a chemical reaction?

Accepted Answer

Matter is neither created nor destroyed; the total mass remains constant.

Question 2

A sample of ammonia (NH$_3$) contains 10.0 grams of hydrogen. Given the mass ratio of nitrogen to hydrogen in ammonia is 4.7:1, how many grams of nitrogen are present?

Accepted Answer

$47$ grams

Question 3

Which of the following is NOT an element?

Accepted Answer

Salt (NaCl)

Question 4

According to Dalton's atomic theory, which statement is FALSE?

Accepted Answer

Atoms of one element can change into atoms of another element during a chemical reaction.

Question 5

An argon isotope has a mass number of 40 ($A = 40$). How many neutrons does it contain?

Accepted Answer

$22$

Question 6

Which element contains 50 protons in its nucleus?

Accepted Answer

Tin

Question 7

Which of the following best describes a cation?

Accepted Answer

An atom that has lost electrons and has a positive charge.

Question 8

Which region of the periodic table contains elements that are typically shiny, malleable, and good conductors of electricity?

Accepted Answer

Metals

Question 9

What is the correct chemical symbol for an element with the name 'gold'?

Accepted Answer

Au

Question 10

Which group in the periodic table contains the noble gases?

Accepted Answer

Group 8A

Question 11

A neutral atom of sodium ($Z = 11$) has how many electrons?

Accepted Answer

$11$

Question 12

Which of the following statements about isotopes is TRUE?

Accepted Answer

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

Question 13

Calculate the average atomic mass of chlorine given the following data: 75.77% chlorine-35 (mass = 34.97 amu) and 24.23% chlorine-37 (mass = 36.97 amu).

Accepted Answer

$35.45$ amu

Question 14

Which law states that all samples of a given compound have the same proportions of their constituent elements?

Accepted Answer

Law of definite proportions

Question 15

Which of the following elements is a metalloid?

Accepted Answer

Silicon

Question 16

A main-group element in group 2A will typically form which type of ion?

Accepted Answer

$+2$ cation

Question 17

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{fraction of isotope 1} 	imes 	ext{mass of isotope 1}) + (	ext{fraction of isotope 2} 	imes 	ext{mass of isotope 2})$

Question 18

Which of the following elements is a halogen?

Accepted Answer

Chlorine

Question 19

If an atom has 15 protons, 16 neutrons, and 15 electrons, what is its mass number?

Accepted Answer

$31$

Question 20

Which of the following statements about electrons is correct?

Accepted Answer

Electrons have a mass of almost zero and are responsible for chemical reactions.

Atoms and Elements: Structure, Laws, and the Periodic Table

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