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?

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

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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