Q: Which of the following statements best describes the mole in chemistry?

A mole is Avogadro’s number of particles, which is $$6.022 \times 10$$^{23}$$ particles.

Q: How many sodium atoms are present in 0.50 mol of sodium?

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

Q: A 16.2 g aluminum can is made entirely of aluminum. How many aluminum atoms does it contain? (Molar mass of Al = 26.98 g/mol)

$$3.61 \times 10$$^{24}$$ atoms

Q: Which of the following is the correct formula to calculate mass percent composition of an element in a compound?

$$\text{mass percent} = \frac{\text{mass of element in 1 mol of compound}}{\text{mass of 1 mol of compound}} \times 100\%$$

Q: Which of the following is a correct conversion factor for the relationship between moles of $$CO_2$$ and moles of O atoms?

$$\frac{2 \text{ mol O}}{1 \text{ mol } CO_2$}$$

Question 1

Which of the following statements best describes the mole in chemistry?

Accepted Answer

A mole is Avogadro’s number of particles, which is $$6.022 	imes 10$$^{23}$$ particles.

Question 2

How many sodium atoms are present in 0.50 mol of sodium?

Accepted Answer

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

Question 3

A 16.2 g aluminum can is made entirely of aluminum. How many aluminum atoms does it contain? (Molar mass of Al = 26.98 g/mol)

Accepted Answer

$$3.61 	imes 10$$^{24}$$ atoms

Question 4

What is the mass percent of sodium in sodium chloride ($$NaCl$$)? (Atomic masses: Na = 22.99, Cl = 35.45)

Accepted Answer

39%

Question 5

If the FDA recommends less than 2.3 g of sodium per day, what is the maximum mass of sodium chloride ($$NaCl) $$you can consume and still stay within the recommendation? ($$NaCl is 39$$% sodium by mass.)

Accepted Answer

$$5.9 g$$

Question 6

Calculate the number of moles of carbon in a 0.58 g diamond. (Molar mass of C = 12.01 g/mol)

Accepted Answer

$$0.048$$ mol

Question 7

A sample of water is decomposed to produce 3.0 g of hydrogen and 24.0 g of oxygen. What is the empirical formula of water based on these data?

Accepted Answer

$$H_2O$$

Question 8

What is the molar mass of $$C_2Cl_4F_2 ($$Freon-114)? (Atomic masses: C = 12.01, Cl = 35.45, F = 19.00)

Accepted Answer

$$203.8 g/$$mol

Question 9

A 3.24 g sample of titanium reacts with oxygen to form 5.40 g of the metal oxide. What is the empirical formula of the oxide? (Molar mass: Ti = 47.87 g/mol, O = 16.00 g/mol)

Accepted Answer

$$TiO$$

Question 10

Which of the following best describes the relationship between empirical and molecular formulas?

Accepted Answer

The molecular formula is always a whole-number multiple of the empirical formula.

Question 11

How many moles of oxygen atoms are present in 1.7 mol of $$CaCO_3$$?

Accepted Answer

5.1 mol

Question 12

What is the mass of 1.75 mol of water ($$H_2O$$)? (Molar mass of $$H_2O = 18.02 g/$$mol)

Accepted Answer

$$31.0 g$$

Question 13

A laboratory analysis of aspirin determines the following mass percent composition: 60.00% C, 4.48% H, and 35.53% O. What is the empirical formula?

Accepted Answer

$$C_7H_6O_3$$

Question 14

Which of the following is the correct formula to calculate mass percent composition of an element in a compound?

Accepted Answer

$$	ext{mass percent} = \frac{	ext{mass of element in 1 mol of compound}}{	ext{mass of 1 mol of compound}} 	imes 100\%$$

Question 15

If you have 15 g of $$NaCl$$, how many grams of sodium does it contain? ($$NaCl is 39$$% sodium by mass.)

Accepted Answer

$$5.85 g$$

Question 16

Which of the following best explains why chemists use the mole instead of counting individual atoms?

Accepted Answer

Atoms are too small and numerous to count individually, so the mole allows chemists to count by weighing.

Question 17

A compound has an empirical formula of $$CH_2O$$ and a molar mass of 180 g/mol. What is its molecular formula?

Accepted Answer

$$C_6H_{12}O_6$

Question 18

Which of the following is a correct conversion factor for the relationship between moles of $$CO_2$$ and moles of O atoms?

Accepted Answer

$$\frac{2 	ext{ mol O}}{1 	ext{ mol } CO_2$}$$

Question 19

What is the first step in determining an empirical formula from mass percent composition data?

Accepted Answer

Assume a 100-g sample and calculate the masses of each element from the given percentages.

Chapter 6: Chemical Composition – Study Notes for Introductory Chemistry

Study Guide - Practice Questions

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