Q: How many molecules are present in $0.45$ mol of barium sulfate ($BaSO_4$)?

$2.71 \times 10^{23}$ molecules

Q: A public water supply contains $0.8$ ppb ($1 \mu g/kg$) of chloroform ($CHCl_3$) by mass. How many $CHCl_3$ molecules are present in $350$ mL of this water?

$1.68 \times 10^{15}$ molecules

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

$\frac{\text{number of atoms} \times \text{atomic weight}}{\text{formula weight of substance}} \times 100\%$

Question 1

What is the molar mass of acetaminophen (C8H9NO2), a common pain medication ingredient?

Accepted Answer

$180.159 \ g/mol$

Question 2

How many molecules are present in $0.45$ mol of barium sulfate ($BaSO_4$)?

Accepted Answer

$2.71 	imes 10^{23}$ molecules

Question 3

A sample contains $1.10$ mol of aluminum sulfide ($Al_2S_3$). How many sulfur atoms are present?

Accepted Answer

$1.99 	imes 10^{24}$ atoms

Question 4

How many oxygen atoms are present in $1.00$ g of magnesium nitrate ($Mg(NO_3)_2$)?

Accepted Answer

$2.45 	imes 10^{22}$ atoms

Question 5

What is the mass percent of oxygen in adenosine triphosphate (ATP), $C_{10}H_{16}N_5O_{13}P_3$?

Accepted Answer

$41.004\%$

Question 6

A sample of hematite contains $34.97$ g of iron and $15.03$ g of oxygen. What is the empirical formula of hematite?

Accepted Answer

$Fe_2O_3$

Question 7

A compound contains $0.130$ g of nitrogen and $0.370$ g of oxygen. What is its empirical formula?

Accepted Answer

$N_2O_5$

Question 8

Sorbitol has a molar mass of $182$ g/mol and a mass percent composition of $39.56\%$ C, $7.74\%$ H, and the remainder O. What is the empirical formula of sorbitol?

Accepted Answer

$C_3H_7O_3$

Question 9

If $15.0$ mL of acetic acid ($CH_3COOH$, $d = 1.048$ g/mL) is dissolved to produce $500.0$ mL of solution, what is the molarity of acetic acid?

Accepted Answer

$0.524 \ M$

Question 10

What mass of $Na_2SO_4 \cdot 10H_2O$ is needed to prepare $355$ mL of $0.445$ M $Na_2SO_4$?

Accepted Answer

$78.2 \ g$

Question 11

A $275$ mL solution of $0.105$ M $NaCl$ evaporates to $237$ mL. What is the new concentration?

Accepted Answer

$0.122 \ M$

Question 12

A public water supply contains $0.8$ ppb ($1 \mu g/kg$) of chloroform ($CHCl_3$) by mass. How many $CHCl_3$ molecules are present in $350$ mL of this water?

Accepted Answer

$1.68 	imes 10^{15}$ molecules

Question 13

If you have a sample of aquamarine that contains $3.0 	imes 10^{20}$ atoms of Si, what does the sample weigh in milligrams?

Accepted Answer

$14.0 \ mg$

Question 14

Which equation correctly relates mass, moles, and molar mass?

Accepted Answer

$n = \frac{m}{M}$

Question 15

What is Avogadro's number?

Accepted Answer

$6.022 	imes 10^{23}$

Question 16

Which formula is used to calculate the percent composition of an element in a compound?

Accepted Answer

$\frac{	ext{number of atoms} 	imes 	ext{atomic weight}}{	ext{formula weight of substance}} 	imes 100\%$

Question 17

Which statement about empirical and molecular formulas is correct?

Accepted Answer

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

Question 18

Which equation is used to calculate the molarity of a solution?

Accepted Answer

$M = \frac{n}{V}$

Question 19

When diluting a solution, which quantity remains constant?

Accepted Answer

The amount of solute

Chapter 3: Mole Concept, Molar Mass, Percent Composition, and Solution Concentration in General Chemistry

Study Guide - Practice Questions

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