Question 1

Which of the following statements correctly describes the identity of an element?

Accepted Answer

The identity of an element is defined by the number of protons in its nucleus.

Question 2

A silver coin has a mass of $31.1034768$ g. If the mass of one silver atom is $1.79 	imes 10^{-22}$ g, how many silver atoms are in the coin?

Accepted Answer

$1.74 	imes 10^{23}$ atoms

Question 3

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 4

The relative mass of a proton is $1$ amu, and the relative mass of an electron is $0.0005$ amu. What is the approximate ratio of the mass of a proton to that of an electron?

Accepted Answer

$2000:1$

Question 5

If the mass of one atom of an element is $9.3 	imes 10^{-23}$ g, which element is it most likely to be?

Accepted Answer

Iron (Fe)

Question 6

How many atoms are in $20.04$ g of calcium (Ca)? (Atomic mass of Ca = $40.08$ g/mol, Avogadro's number $= 6.022 	imes 10^{23}$ atoms/mol)

Accepted Answer

$3.011 	imes 10^{23}$ atoms

Question 7

Which of the following represents the greatest number of atoms?

Accepted Answer

$20$ mol F$

Question 8

A $5.00$ g sample of uranium (U) contains how many moles of U? (Atomic mass of U = $238.0$ g/mol)

Accepted Answer

$0.0210$ mol

Question 9

How many atoms of uranium (U) are in a $5.00$ g sample? (Atomic mass of U = $238.0$ g/mol, Avogadro's number $= 6.022 	imes 10^{23}$ atoms/mol)

Accepted Answer

$1.27 	imes 10^{22}$ atoms

Question 10

Which isotope of iron is the most abundant in nature?

Accepted Answer

Iron-56

Question 11

The atomic mass unit (amu) is defined as:

Accepted Answer

1/12 the mass of a single $^{12}C$ atom

Question 12

A sample contains $127.6$ g of tellurium (Te). How many atoms are present? (Atomic mass of Te = $127.6$ g/mol, Avogadro's number $= 6.022 	imes 10^{23}$ atoms/mol)

Accepted Answer

$6.022 	imes 10^{23}$ atoms

Question 13

Which of the following best describes an ion?

Accepted Answer

An atom with a variable number of electrons

Question 14

If you have $55.85$ g of iron (Fe), how many atoms do you have? (Atomic mass of Fe = $55.85$ g/mol, Avogadro's number $= 6.022 	imes 10^{23}$ atoms/mol)

Accepted Answer

$6.022 	imes 10^{23}$ atoms

Question 15

Which of the following particles has the smallest relative mass?

Accepted Answer

Electron

Question 16

A sample contains $2.00$ moles of magnesium (Mg). How many atoms does it contain? (Avogadro's number $= 6.022 	imes 10^{23}$ atoms/mol)

Accepted Answer

$1.20 	imes 10^{24}$ atoms

Question 17

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

Accepted Answer

$\displaystyle \frac{35}{17}Cl$

Question 18

A real-world application: The thickness of a dime is $1.35$ mm. If you stacked Avogadro's number ($6.022 	imes 10^{23}$) of dimes, what would be the total height in meters?

Accepted Answer

$8.13 	imes 10^{20}$ m

Question 19

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

Accepted Answer

It is the number of atoms in exactly 12 grams of $^{12}C$.

Question 20

A naturally occurring sample of magnesium contains three isotopes: $^{24}Mg$ (78.99%), $^{25}Mg$ (10.00%), and $^{26}Mg$ (11.01%). Which isotope is most abundant?

Accepted Answer

$^{24}Mg$

Masses of Atoms and Atomic Structure: Study Notes

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