Q: Which of the following statements about the mole is correct?

A mole contains $$6.022 \times 10$$^{23}$$ entities.

Q: Which of the following is the correct formula for calculating mass percentage of a solute in a solution?

$$\frac{\text{mass of solute}}{\text{mass of solution}} \times 100\%$$

Question 1

What is the formula mass of aspirin (C9H8O4) in amu, based on the atomic masses: C = 12.01 amu, H = 1.008 amu, O = 16.00 amu?

Accepted Answer

$$180.15$$

Question 2

Which of the following statements about the mole is correct?

Accepted Answer

A mole contains $$6.022 	imes 10$$^{23}$$ entities.

Question 3

How many moles of potassium are in a 4.7 g sample? (Molar mass of K = 39.10 g/mol)

Accepted Answer

$$0.120$$ mol

Question 4

A liter of air contains $$9.2 	imes 10$$^{-4}$$ mol of argon. What is the mass of argon in this sample? (Molar mass of Ar = 39.95 g/mol)

Accepted Answer

$$0.0368 g$$

Question 5

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

Accepted Answer

Formula mass is used for ionic compounds, while molecular mass is used for covalent compounds.

Question 6

How many molecules are in 0.0400 g of saccharin (C7H5NO3S, molar mass = 183.18 g/mol)?

Accepted Answer

$$1.32 	imes 10$$^{20}$$

Question 7

A compound contains 1.71 g C and 0.287 g H. What is the empirical formula?

Accepted Answer

$$\mathrm{CH}_2$$

Question 8

A compound has an empirical formula of CH2O (empirical formula mass = 30 amu) and a molecular mass of 180 amu. What is its molecular formula?

Accepted Answer

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

Question 9

What is the molarity of a solution containing 0.133 mol of sucrose in 355 mL of solution?

Accepted Answer

$$0.375 M$$

Question 10

If 0.850 L of a 5.00 M solution of Cu(NO3)2 is diluted to 1.80 L, what is the new molarity?

Accepted Answer

$$2.36 M$$

Question 11

Which of the following is the correct formula for calculating mass percentage of a solute in a solution?

Accepted Answer

$$\frac{	ext{mass of solute}}{	ext{mass of solution}} 	imes 100\%$$

Question 12

A saline solution contains 0.9 g NaCl per 100 mL of solution. What is the mass-volume percent concentration?

Accepted Answer

$$0.9\% (m/v)$$

Question 13

Which unit would be most appropriate for expressing the concentration of a pollutant in drinking water at very low levels?

Accepted Answer

parts per billion (ppb)

Question 14

A solution is prepared by dissolving 5.00 g of glucose (C6H12O6, molar mass = 180.16 g/mol) in enough water to make 250 mL of solution. What is the molarity?

Accepted Answer

$$0.111 M$$

Question 15

Which of the following best describes the process of dilution?

Accepted Answer

Adding solvent to decrease the concentration of solute in solution.

Question 16

A sample contains $$2.5 	imes 10$$^{22}$$ molecules of CO2. How many moles of CO2 are present?

Accepted Answer

$$0.0415$$ mol

Question 17

A solution is labeled as 70 mg/dL glucose. What is this concentration in g/L?

Accepted Answer

$$0.70 g/L$$

Question 18

Which of the following steps is NOT required when determining the empirical formula from percent composition?

Accepted Answer

Multiplying the percent composition by the molar mass.

Chemical Composition: Formula Mass, the Mole, and Solution Concentrations

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