Q: Which of the following is the correct formula for calculating percent composition by mass of an element in a compound?

$\frac{\text{mass of element in 1 mol of compound}}{\text{molar mass of compound}} \times 100\%$

Question 1

A 10.0 g sample of NaCl is dissolved in enough water to make 500.0 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

Accepted Answer

$0.342\ \mathrm{M}$

Question 2

Which of the following best describes a supersaturated solution?

Accepted Answer

A solution that contains more solute than would normally dissolve in a given volume of solvent at a given temperature.

Question 3

A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula of this compound?

Accepted Answer

$\mathrm{CH_2O}$

Question 4

How many atoms are present in 0.250 mol of aluminum?

Accepted Answer

$1.51 	imes 10^{23}$ atoms

Question 5

A 4.99 g sample of a compound contains 1.52 g of nitrogen and 3.47 g of oxygen. What is the empirical formula of the compound? (Atomic masses: N = 14.01, O = 16.00)

Accepted Answer

$\mathrm{N_2O_3}$

Question 6

Which of the following statements about strong electrolytes is correct?

Accepted Answer

They completely ionize in water and conduct electricity very efficiently.

Question 7

You have a 10.0 M stock solution of HCl. How many milliliters of this stock solution are needed to prepare 250.0 mL of a 1.0 M HCl solution?

Accepted Answer

$25.0\ \mathrm{mL}$

Question 8

A solution is prepared by dissolving 5.00 g of potassium phosphate ($\mathrm{K_3PO_4}$, molar mass = 212.27 g/mol) in enough water to make 1.50 L of solution. What is the molarity of the solution?

Accepted Answer

$0.0157\ \mathrm{M}$

Question 9

Which of the following will increase the solubility of a gas in water?

Accepted Answer

Decreasing the temperature and increasing the pressure above the solution.

Question 10

What is the pH of a solution in which the $[\mathrm{H^+}] = 3.4 	imes 10^{-3}\ \mathrm{M}$?

Accepted Answer

$2.47$

Question 11

A sample of a hydrate of magnesium sulfate ($\mathrm{MgSO_4} \cdot x\mathrm{H_2O}$) is found to be 51.2% $\mathrm{MgSO_4}$ by mass. What is the value of $x$ in the hydrate? (Molar mass: $\mathrm{MgSO_4} = 120.4\ \mathrm{g/mol}$, $\mathrm{H_2O} = 18.0\ \mathrm{g/mol}$)

Accepted Answer

$7$

Question 12

Which of the following best describes the role of the solvent in an aqueous solution?

Accepted Answer

It is the substance present in the greatest amount and does the dissolving.

Question 13

A 100.0 mL sample of 2.00 M NaOH is diluted to a final volume of 500.0 mL. What is the new concentration?

Accepted Answer

$0.400\ \mathrm{M}$

Question 14

Which of the following is the correct formula for calculating percent composition by mass of an element in a compound?

Accepted Answer

$\frac{	ext{mass of element in 1 mol of compound}}{	ext{molar mass of compound}} 	imes 100\%$

Question 15

A solution is prepared by dissolving 10.0 g of glucose ($\mathrm{C_6H_{12}O_6}$, molar mass = 180.2 g/mol) in enough water to make 250.0 mL of solution. What is the molarity of the solution?

Accepted Answer

$0.222\ \mathrm{M}$

Question 16

Which of the following is a weak electrolyte in aqueous solution?

Accepted Answer

Acetic acid ($\mathrm{CH_3COOH}$)

Question 17

A compound has an empirical formula of $\mathrm{CH_2}$ and a molar mass of $56.1\ \mathrm{g/mol}$. What is its molecular formula?

Accepted Answer

$\mathrm{C_4H_8}$

Question 18

Which of the following best explains why ionic compounds are always written with the empirical formula?

Accepted Answer

Because they exist as repeating units in a crystal lattice, not as discrete molecules.

Question 19

Which of the following will NOT affect the solubility of a solid in water?

Accepted Answer

Increasing the pressure above the solution.

Unit 2: The Mole and Solutions – General Chemistry Study Notes

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