Q: A sample contains 40.0 mg of saccharin ($$\mathrm{C_7H_5NO_3S}$$, molar mass = $$183.18\ \mathrm{g/mol}). $$How many saccharin molecules are present in the sample?

$$1.31 \times 10$$^{20}$$ molecules

Q: Which of the following best describes Avogadro's number?

The number of particles in 1 mole of a substance, $$6.022 \times 10$$^{23}$$.

Q: Which of the following is the correct formula to calculate molarity ($$M$$)?

$$M = \dfrac{\text{moles of solute}}{\text{liters of solution}}$$

Question 1

Which of the following statements best describes the difference between formula mass and molar mass?

Accepted Answer

Formula mass is the sum of the average atomic masses of all atoms in an ionic compound's formula (in amu), while molar mass is the mass of one mole of a substance (in g/mol).

Question 2

A sample contains 40.0 mg of saccharin ($$\mathrm{C_7H_5NO_3S}$$, molar mass = $$183.18\ \mathrm{g/mol}). $$How many saccharin molecules are present in the sample?

Accepted Answer

$$1.31 	imes 10$$^{20}$$ molecules

Question 3

What is the percent by mass of nitrogen in ammonia ($$\mathrm{NH_3$}$$)? (Atomic masses: N = 14.01, H = 1.008)

Accepted Answer

$$82.2\%$$

Question 4

A compound has an empirical formula of $$\mathrm{CH_2O}$$ and a molar mass of $$180\ \mathrm{g/mol}. $$What is its molecular formula?

Accepted Answer

$$\mathrm{C_6H_{12}O_6$}$$

Question 5

How many moles of $$\mathrm{NaCl}$$ are present in $$58.44\ \mathrm{g} of$$ $$\mathrm{NaCl}$$? (Molar mass $$= 58.44\ \mathrm{g/mol})$$

Accepted Answer

$$1.00$$ mol

Question 6

A 473 mL energy drink contains $$0.158$$ mol of sucrose. What is the molarity of sucrose in the drink?

Accepted Answer

$$0.334\ \mathrm{M}$$

Question 7

A 1.2 mL blood sample contains $$0.95 mg of $$ethanol ($$\mathrm{C_2H_5OH}$$, molar mass $$= 46.07\ \mathrm{g/mol}). $$What is the blood alcohol concentration (BAC) in molarity?

Accepted Answer

$$0.017\ \mathrm{M}$$

Question 8

A solution is prepared by dissolving $$7.5\ \mathrm{g} of$$ $$\mathrm{K_2SO_4} in $$enough water to make $$895\ \mathrm{mL} of $$solution. What is the concentration of $$\mathrm{K^+}$$ ions in the solution? (Molar mass $$= 174.26\ \mathrm{g/mol})$$

Accepted Answer

$$0.096\ \mathrm{M}$$

Question 9

A sample of magnetite contains $$5.80\ \mathrm{g} Fe $$and $$2.21\ \mathrm{g} O. $$What is the empirical formula of magnetite? (Atomic masses: Fe = 55.85, O = 16.00)

Accepted Answer

$$\mathrm{Fe_3O_4}$$

Question 10

How many chloride ions are present in $$1.45\ \mathrm{g} of $$barium chloride ($$\mathrm{$$BaCl_2$$}$$, molar mass $$= 208.23\ \mathrm{g/mol}$$)?

Accepted Answer

$$8.36 	imes 10$$^{21}$$ ions

Question 11

A solution is made by mixing $$18.0\ \mathrm{mL} of$$ $$0.15\ \mathrm{M}$$ $$\mathrm{$$BaCl_2$$}$$ with $$35.0\ \mathrm{mL} of$$ $$0.25\ \mathrm{M}$$ $$\mathrm{NaCl}. $$What is the final concentration of chloride ions in the resulting solution?

Accepted Answer

$$0.66\ \mathrm{M}$$

Question 12

Which of the following best describes Avogadro's number?

Accepted Answer

The number of particles in 1 mole of a substance, $$6.022 	imes 10$$^{23}$$.

Question 13

A compound contains 63.2% Mn and 36.8% S by mass. What is its empirical formula? (Atomic masses: Mn = 54.94, S = 32.07)

Accepted Answer

$$\mathrm{MnS}$$

Question 14

How many moles of $$\mathrm{HCl}$$ are dissolved in $$25\ \mathrm{mL} of$$ $$0.75\ \mathrm{M}$$ $$\mathrm{HCl}$$ solution?

Accepted Answer

$$0.019$$ mol

Question 15

A solution is prepared by dissolving $$7.25 	imes 10$$^{22}$$ molecules of $$\mathrm{$$C_{14}H$$_{11}$$O_3$$}$$ in enough water to make 27.7$$\ \mathrm{g}$$ of solution. What is the molar mass of $$\mathrm{$$C_{14}H$$_{11}$$O_3$$}$$?

Accepted Answer

$$242\ \mathrm{g/mol}$$

Question 16

Which of the following is the correct formula to calculate molarity ($$M$$)?

Accepted Answer

$$M = \dfrac{	ext{moles of solute}}{	ext{liters of solution}}$$

Question 17

A solution is made by dissolving $$8.25\ \mathrm{g} of$$ $$\mathrm{Ca(NO_3$)_2}$$ and $$7.25\ \mathrm{g} of$$ $$\mathrm{Fe(NO_3$)_3} in $$enough water to make $$525\ \mathrm{mL} of $$solution. What is the concentration of nitrate ions in the solution? (Molar masses: $$\mathrm{Ca(NO_3$)_2} = 164.10\ \mathrm{g/mol}$$, $$\mathrm{Fe(NO_3$)_3} = 241.86\ \mathrm{g/mol})$$

Accepted Answer

$$0.231\ \mathrm{M}$$

Question 18

Which of the following best describes an empirical formula?

Accepted Answer

It shows the lowest whole-number ratio of atoms of each element in a compound.

Question 19

How many grams of $$\mathrm{NH_3$}$$ are required to make $$0.145\ \mathrm{L} of a$$ $$3.0\ \mathrm{M}$$ solution? (Molar mass $$= 17.03\ \mathrm{g/mol})$$

Accepted Answer

$$7.40\ \mathrm{g}$$

Chapter 3: The Mole, Formula Mass, and Composition of Substances and Solutions

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