Q: Given the empirical formula $$\text{CH}_2\text{O}$$ and a molar mass of $$180.2 \text{ g/mol}$$ for fructose, what is its molecular formula?

$$\text{C}_6\text{H}_{12}\text{O}_6$$

Q: A $$0.589 \text{ g}$$ diamond contains only carbon. How many carbon atoms are present? (Molar mass C = $$12.01 \text{ g/mol})$$

$$2.95 \times 10$$^{22}$$ atoms

Question 1

Which statement best describes the mole concept in chemistry?

Accepted Answer

A mole is a specific number of particles, defined as $$6.022 	imes 10$$^{23}$$ units.

Question 2

How many moles of aluminum are present in a 16.2 g aluminum can? (Molar mass of Al = $$26.98 	ext{ g/mol})$$

Accepted Answer

$$0.601 	ext{ mol}$$

Question 3

A sample contains $$3.5 	ext{ mol} of $$helium. How many helium atoms are present?

Accepted Answer

$$2.1 	imes 10$$^{24}$$ atoms

Question 4

What is the mass percent of sodium in sodium chloride ($$	ext{NaCl}$$)? (Molar mass Na = $$22.99 	ext{ g/mol}$$, Molar mass Cl = $$35.45 	ext{ g/mol})$$

Accepted Answer

$$39\%$$

Question 5

If the FDA recommends less than $$2.4 	ext{ g} of $$sodium per day, what is the maximum mass of sodium chloride ($$	ext{NaCl}) $$you can consume and stay below this limit? (NaCl is $$39\%$$ sodium by mass)

Accepted Answer

$$6.15 	ext{ g}$$

Question 6

How many oxygen atoms are present in $$1.7 	ext{ mol} of$$ $$	ext{CaCO}_3$$?

Accepted Answer

$$5.1 	ext{ mol}$$

Question 7

A $$0.358 	ext{ g}$$ sample of chromium reacts with oxygen to form $$0.523 	ext{ g} of $$metal oxide. What is the mass percent of chromium in the oxide?

Accepted Answer

$$68.4\%$$

Question 8

What is the empirical formula for a compound formed from $$3.0 	ext{ g} of $$hydrogen and $$24.0 	ext{ g} of $$oxygen?

Accepted Answer

$$	ext{HO}$$

Question 9

A $$3.249 	ext{ g}$$ sample of titanium reacts with oxygen to form $$5.40 	ext{ g} of $$metal oxide. What is the empirical formula of the oxide? (Molar mass Ti = $$47.87 	ext{ g/mol}$$, O = $$16.00 	ext{ g/mol})$$

Accepted Answer

$$	ext{TiO}$$

Question 10

Given the empirical formula $$	ext{CH}_2	ext{O}$$ and a molar mass of $$180.2 	ext{ g/mol}$$ for fructose, what is its molecular formula?

Accepted Answer

$$	ext{C}_6	ext{H}_{12}	ext{O}_6$$

Question 11

What is the mass of $$4.78 	imes 10$$^{22}$$ molecules of $$	ext{NO}_2$$? (Molar mass = 46.01$$ 	ext{ g/mol}$$)

Accepted Answer

$$3.65 	ext{ g}$$

Question 12

Which of the following is true about empirical and molecular formulas?

Accepted Answer

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

Question 13

How many moles of oxygen atoms are present in $$2.5 	ext{ mol} of$$ $$	ext{CO}_2$$?

Accepted Answer

$$5.0 	ext{ mol}$$

Question 14

What is the mass percent of chlorine in $$	ext{CCl}_4$$? (Molar mass Cl = $$35.45 	ext{ g/mol}$$, C = $$12.01 	ext{ g/mol})$$

Accepted Answer

$$90.0\%$$

Question 15

A $$0.589 	ext{ g}$$ diamond contains only carbon. How many carbon atoms are present? (Molar mass C = $$12.01 	ext{ g/mol})$$

Accepted Answer

$$2.95 	imes 10$$^{22}$$ atoms

Question 16

Which of the following best explains why chemists use the mole instead of a dozen to count atoms?

Accepted Answer

Atoms are so small and numerous that a dozen is not a practical counting unit.

Question 17

What is the mass percent of fluorine in sodium fluoride ($$	ext{NaF}$$)? (Molar mass Na = $$22.99 	ext{ g/mol}$$, F = $$19.00 	ext{ g/mol})$$

Accepted Answer

$$45.2\%$$

Question 18

How many grams of NaF should be added to $$100 	ext{ L} of $$water to fluoridate it at a level of $$1.0 	ext{ mg F/L}$$? (Molar mass NaF = $$41.99 	ext{ g/mol}$$, F = $$19.00 	ext{ g/mol})$$

Accepted Answer

$$0.221 	ext{ g}$$

Chapter 6: Chemical Composition – The Mole, Molar Mass, and Chemical Formulas

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