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

$$1.74 \times 10$$^{23}$$ atoms

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

$$3.011 \times 10$$^{23}$$ atoms

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

$$1.27 \times 10$$^{22}$$ atoms

Q: 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 $$= 6.022 \times 10$$^{23}$$ atoms/mol)

$$6.022 \times 10$$^{23}$$ atoms

Q: 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 $$= 6.022 \times 10$$^{23}$$ atoms/mol)

$$6.022 \times 10$$^{23}$$ atoms

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

$$1.20 \times 10$$^{24}$$ atoms

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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