Q: What is Avogadro's number, and what does it represent?

$$6.022 \times 10$$^{23}$$, the number of atoms in 1 mole of any substance.

Q: How many atoms are in 3.62 g of aluminum? (Atomic mass of Al = 26.98 g/mol)

$$\frac{3.62}{26.98} \times 6.022 \times 10$$^{23}$$ = 8.08 \times 10$$^{22}$$ atoms

Q: If the recommended daily intake of sodium is 2.3 g, what mass of sodium chloride ($$NaCl) $$can you consume and still stay below this recommendation? (Atomic masses: Na = 22.99 g/mol, Cl = 35.45 g/mol)

$$2.3 \times \frac{58.44}{22.99} = 5.85 g$$

Q: Which statement about the mole is correct?

One mole of any element contains $$6.022 \times 10$$^{23}$$ atoms, but the mass of one mole differs for each element.

Q: How many moles are in $$1.204 \times 10$$^{24}$$ atoms of silver (Ag)?

$$\frac{1.204 \times 10$$^{24}$$}{6.022 \times 10$$^{23}$$} = 2.00$$ mol

Q: Which conversion would you use to find the number of atoms in a given mass of an element?

$$\text{grams} \to \text{moles} \to \text{atoms}$$

Q: If you have 2.60 lb of medium-sized nails and each dozen nails weighs 0.150 lb, how many nails did you buy?

$$2.60 \div 0.150 \times 12 = 208$$ nails

Question 1

Which of the following best describes why chemists use the mass of atoms to count them instead of counting individual atoms?

Accepted Answer

Atoms are too small and numerous to count individually, so mass provides a practical way to quantify them.

Question 2

What is Avogadro's number, and what does it represent?

Accepted Answer

$$6.022 	imes 10$$^{23}$$, the number of atoms in 1 mole of any substance.

Question 3

If you have 0.58 g of pure diamond (carbon), how many moles of carbon do you have? (Atomic mass of carbon = 12.01 g/mol)

Accepted Answer

$$0.58 \div 12.01 = 0.048$$ mol

Question 4

How many atoms are in 3.62 g of aluminum? (Atomic mass of Al = 26.98 g/mol)

Accepted Answer

$$\frac{3.62}{26.98} 	imes 6.022 	imes 10$$^{23}$$ = 8.08 	imes 10$$^{22}$$ atoms

Question 5

A mole is similar to which of the following everyday counting units?

Accepted Answer

A dozen

Question 6

What is the molar mass of sodium chloride ($$NaCl$$)? (Atomic masses: Na = 22.99 g/mol, Cl = 35.45 g/mol)

Accepted Answer

$$22.99 + 35.45 = 58.44 g/$$mol

Question 7

If the recommended daily intake of sodium is 2.3 g, what mass of sodium chloride ($$NaCl) $$can you consume and still stay below this recommendation? (Atomic masses: Na = 22.99 g/mol, Cl = 35.45 g/mol)

Accepted Answer

$$2.3 	imes \frac{58.44}{22.99} = 5.85 g$$

Question 8

Which statement about the mole is correct?

Accepted Answer

One mole of any element contains $$6.022 	imes 10$$^{23}$$ atoms, but the mass of one mole differs for each element.

Question 9

How many moles are in $$1.204 	imes 10$$^{24}$$ atoms of silver (Ag)?

Accepted Answer

$$\frac{1.204 	imes 10$$^{24}$$}{6.022 	imes 10$$^{23}$$} = 2.00$$ mol

Question 10

A copper penny contains 1 mole of copper atoms. What is the mass of copper in the penny? (Atomic mass of Cu = 63.55 g/mol)

Accepted Answer

63.55 g

Question 11

Which conversion would you use to find the number of atoms in a given mass of an element?

Accepted Answer

$$	ext{grams} 	o 	ext{moles} 	o 	ext{atoms}$$

Question 12

If you have 2.60 lb of medium-sized nails and each dozen nails weighs 0.150 lb, how many nails did you buy?

Accepted Answer

$$2.60 \div 0.150 	imes 12 = 208$$ nails

Question 13

Which of the following is the correct molar mass for sulfur (S)?

Accepted Answer

32.07 g/mol

Question 14

How many moles are in 24.0 g of carbon? (Atomic mass of C = 12.01 g/mol)

Accepted Answer

$$24.0 \div 12.01 = 2.00$$ mol

Question 15

Which statement is true about the relationship between atomic mass and molar mass?

Accepted Answer

The atomic mass in amu is numerically equal to the molar mass in g/mol for an element.

Question 16

A sample contains $$3.01 	imes 10$$^{23}$$ atoms of helium. How many moles of helium does this represent?

Accepted Answer

$$\frac{3.01 	imes 10$$^{23}$$}{6.022 	imes 10$$^{23}$$} = 0.5$$ mol

Question 17

Which of the following is NOT a correct step in converting grams of an element to number of atoms?

Accepted Answer

Multiply grams by Avogadro's number directly.

Question 18

If you have 0.75 mol of lithium (Li), how many atoms do you have? (Avogadro's number = $$6.022 	imes 10$$^{23}$$)

Accepted Answer

$$0.75 	imes 6.022 	imes 10$$^{23}$$ = 4.52 	imes 10$$^{23}$$ atoms

Question 19

Which real-world scenario best illustrates the concept of using mass to count large numbers of small objects?

Accepted Answer

Buying nails by the pound and calculating the number of nails using their average mass.

Chemical Composition: Moles, Mass, and Counting Atoms (Ch. 6.1–6.3)

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