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

$$2.71 \times 10$$^{23}$$ molecules

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

$$1.99 \times 10$$^{24}$$ atoms

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

$$2.45 \times 10$$^{22}$$ atoms

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

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