$\frac{\text{mass of element}}{\text{total mass of compound}} \times 100$

$1 \text{ mol} = 1 \text{ gram}$

Question 1

Which of the following best defines Avogadro’s number?

Accepted Answer

The number of atoms in 12 grams of carbon-12

Question 2

A sample contains $3.4$ grams of lead ($Pb$). How many atoms of lead are present in the sample? (Molar mass of $Pb = 207.2$ g/mol)

Accepted Answer

$9.88 	imes 10^{22}$ atoms

Question 3

Which statement about the mole is correct?

Accepted Answer

A mole is Avogadro’s number of atoms, molecules, or ions

Question 4

What is the molar mass of $AlCl_3$?

Accepted Answer

$133.33$ g/mol

Question 5

How many moles of $Cl$ are present in $0.243$ g of $AlCl_3$? (Molar mass of $AlCl_3 = 133.33$ g/mol)

Accepted Answer

$0.00546$ mol

Question 6

A compound contains $15.55\%$ tin and $54.45\%$ chlorine by mass. What is its empirical formula?

Accepted Answer

$SnCl_2$

Question 7

If a compound has the empirical formula $CH_2O$ and a molar mass of $180$ g/mol, what is its molecular formula?

Accepted Answer

$C_6H_{12}O_6$

Question 8

Calculate the percent composition of sulfur in $PbSO_4$ (Molar mass: $Pb = 207.2$ g/mol, $S = 32.07$ g/mol, $O = 4 	imes 16.00$ g/mol).

Accepted Answer

$10.57\%$

Question 9

A $5$ gram sample of sulfuric acid ($H_2SO_4$) is analyzed. How many moles of hydrogen are present? (Molar mass of $H_2SO_4 = 98.09$ g/mol)

Accepted Answer

$0.102$ mol$

Question 10

Which of the following is the correct sequence for converting grams of a substance to number of atoms?

Accepted Answer

Grams $\rightarrow$ Moles $\rightarrow$ Atoms

Question 11

A compound is found to have $40.0\%$ C, $6.67\%$ H, and $53.33\%$ O by mass. What is its empirical formula?

Accepted Answer

$CH_2O$

Question 12

How many moles of $Na$ are present in $10$ g of sodium? (Molar mass of $Na = 22.99$ g/mol)

Accepted Answer

$0.435$ mol$

Question 13

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

Accepted Answer

Empirical formula shows the simplest whole-number ratio of elements

Question 14

What is the percent by mass of chlorine in $AlCl_3$? (Molar mass: $Al = 26.98$ g/mol, $Cl = 35.45$ g/mol)

Accepted Answer

$79.8\%$

Question 15

A compound has the empirical formula $CHCl_3$ and a molar mass of $545$ g/mol. What is its molecular formula?

Accepted Answer

$C_9H_9Cl_{27}$

Question 16

How many moles of $Pb$ are present in $3.4$ grams of lead? (Molar mass of $Pb = 207.2$ g/mol)

Accepted Answer

$0.0164$ mol$

Question 17

Which of the following is the correct formula for calculating percent composition by mass?

Accepted Answer

$\frac{	ext{mass of element}}{	ext{total mass of compound}} 	imes 100$

Question 18

If you have $0.100$ moles of $H_3PO_4$, how many moles of $H^+$ ions can be produced?

Accepted Answer

$0.300$ mol$

Question 19

Which of the following is NOT a correct conversion factor for mole calculations?

Accepted Answer

$1 	ext{ mol} = 1 	ext{ gram}$

Question 20

Which of the following statements about Avogadro’s number is correct?

Accepted Answer

It is a very large number used to count atoms, molecules, or ions in a mole

Chapter 6: Chemical Composition – Study Notes

Study Guide - Practice Questions