Q: Which of the following is the correct formula for calculating the average atomic mass of an element from its isotopes?

$$\sum (\text{fractional abundance of isotope}_n) \times (\text{mass of isotope}_n)$$

Question 1

Which law is best illustrated by the fact that a 100.0 g sample of sodium chloride contains 39.3 g of sodium and 60.7 g of chlorine, while a 200.0 g sample contains 78.6 g of sodium and 121.4 g of chlorine?

Accepted Answer

Law of Definite Proportions

Question 2

Which of Dalton’s original atomic theory postulates has been disproven by modern science?

Accepted Answer

Atoms of a given element are identical in all respects.

Question 3

Which experiment led to the discovery of the electron and the determination of its charge-to-mass ratio?

Accepted Answer

Thomson’s cathode ray tube experiment

Question 4

A sample of carbon monoxide (CO) contains 1.33 g of oxygen for every 1.00 g of carbon, while carbon dioxide (CO$$_2) $$contains 2.67 g of oxygen for every 1.00 g of carbon. Which law does this data illustrate?

Accepted Answer

Law of Multiple Proportions

Question 5

Which atomic model is depicted as a sphere of positive charge with electrons embedded throughout, similar to a 'chocolate chip cookie'?

Accepted Answer

Plum pudding model

Question 6

Which subatomic particle was discovered by James Chadwick in 1932?

Accepted Answer

Neutron

Question 7

Which of the following best describes a metalloid?

Accepted Answer

A substance that has properties intermediate between metals and nonmetals, often acting as a semiconductor

Question 8

Which of the following is an example of an intensive physical property?

Accepted Answer

Density

Question 9

A neutral atom of phosphorus has 15 protons and 15 electrons. What is the number of electrons in a P$$^{3-}$$ ion?

Accepted Answer

18

Question 10

Which scientist reorganized the periodic table by atomic number rather than atomic mass, leading to the modern periodic law?

Accepted Answer

Henry Moseley

Question 11

Which of the following is the correct formula for calculating the average atomic mass of an element from its isotopes?

Accepted Answer

$$\sum (	ext{fractional abundance of isotope}_n) 	imes (	ext{mass of isotope}_n)$$

Question 12

A sample contains 2.94 $$	imes 10$^{22}$$ atoms of copper. What is the mass of this sample? (Molar mass of Cu = 63.55 g/mol, $$N_A = 6.022 	imes 10$$^{23}$$ mol$$^{-1}$$)

Accepted Answer

3.10 g

Question 13

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 14

A sphere of aluminum contains 8.55 $$	imes 10$^{22}$$ atoms. If the density of aluminum is 2.70 g/cm$$^3$$, what is the radius of the sphere in centimeters? (Molar mass of Al = 26.98 g/mol, $$N_A = 6.022 	imes 10$$^{23}$$ mol$$^{-1}$$)

Accepted Answer

0.697 cm

Question 15

Which of the following best describes the result of Rutherford’s gold foil experiment?

Accepted Answer

Most alpha particles passed through the foil, but a few were deflected at large angles, indicating a small, dense, positively charged nucleus.

Question 16

Which of the following is a chemical property?

Accepted Answer

Rusting of iron

Question 17

How many atoms are in 2.45 mol of copper? ($$N_A = 6.022 	imes 10$$^{23}$$ mol$$^{-1}$$)

Accepted Answer

1.48 $$	imes 10$^{24}$$ atoms

Question 18

Which of the following is a correct classification of matter?

Accepted Answer

An element is a pure substance that cannot be broken down by chemical means.

Question 19

Which group on the periodic table contains the noble gases?

Accepted Answer

Group 18

Atoms, Elements, and Moles: Foundations of General Chemistry

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