Q: How many atoms of uranium are in a $$5.00 g $$sample? (Atomic mass of U $$= 238.0 g/$$mol, $$1$$ mol $$= 6.022 \times 10$$^{23}$$ atoms)

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

Q: If you have $$20.04 g of $$calcium (Ca), how many atoms of Ca are present? (Atomic mass of Ca $$= 40.08 g/$$mol, $$1$$ mol $$= 6.022 \times 10$$^{23}$$ atoms)

$$3.01 \times 10$$^{23}$$ 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}$$

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

How many iron atoms are present in a $$55.85 g $$sample of iron? (Average atomic mass of Fe $$= 55.85$$ amu, $$1$$ amu $$= 1.66 	imes 10$$^{-24}$$ g)

Accepted Answer

$$6.02 	imes 10$$^{23}$$

Question 6

Which of the following is the correct definition of Avogadro's number?

Accepted Answer

The number of atoms in exactly $$12$$ grams of $$^{12}C.$$

Question 7

A sample contains $$127.6 g of $$tellurium (Te). If the atomic mass of Te is $$127.6$$ amu, how many atoms are present in the sample? ($$1$$ amu $$= 1.66 	imes 10$$^{-24}$$ g, 1$ mol = 6.022$$ 	imes $$10^{23}$$ atoms)

Accepted Answer

$$6.022 	imes 10$$^{23}$$

Question 8

If the mass of one atom of an element is $$9.3 	imes 10$$^{-23}$$ g, which element is it most likely to be? (1$ amu = 1.66$$ 	imes $$10^{-24} g)$$

Accepted Answer

Iron (Fe)

Question 9

Which of the following represents the greatest number of atoms?

Accepted Answer

$$20$$ mol F

Question 10

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 11

How many atoms of uranium are in a $$5.00 g $$sample? (Atomic mass of U $$= 238.0 g/$$mol, $$1$$ mol $$= 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$1.27 	imes 10$$^{22}$$ atoms

Question 12

Which of the following statements about ions is correct?

Accepted Answer

Ions are atoms with variable numbers of electrons.

Question 13

Which isotope of iron is the most abundant in nature?

Accepted Answer

Iron-56

Question 14

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

Accepted Answer

$$^{24}Mg$$

Question 15

Which of the following best describes the atomic mass unit (amu)?

Accepted Answer

1 amu is defined as $$\frac{1}{12}$$ the mass of a single $$^{12}C$$ atom.

Question 16

A coin has a thickness of $$1.35 mm. If $$you stack Avogadro's number ($$6.022 	imes 10$$^{23}$$) of these coins, what would be the total height in meters?

Accepted Answer

$$8.13 	imes 10$$^{20}$$ m

Question 17

Which of the following particles has a relative charge of $$+1$$?

Accepted Answer

Proton

Question 18

If you have $$20.04 g of $$calcium (Ca), how many atoms of Ca are present? (Atomic mass of Ca $$= 40.08 g/$$mol, $$1$$ mol $$= 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$3.01 	imes 10$$^{23}$$ atoms

Question 19

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

Accepted Answer

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

Masses of Atoms and Atomic Structure

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