Q: A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 500.0 mL of solution. What is the molarity ($$M) of $$the solution? ($$M_{\text{NaCl}} = 58.44\ \text{g/mol})$$

$$M = \frac{10.0\ \text{g}}{58.44\ \text{g/mol} \times 0.500\ \text{L}} = 0.342\ \text{mol/L}$$

Q: A radioactive isotope decays with a half-life of 5 years. If you start with 80 g, how much remains after 15 years?

$$80\ \text{g} \rightarrow 40\ \text{g} \rightarrow 20\ \text{g} \rightarrow 10\ \text{g}$$

Question 1

Which of the following best explains why sodium (Na) reacts vigorously with water, while magnesium (Mg) reacts much less vigorously under the same conditions?

Accepted Answer

Sodium has a lower ionization energy, making it easier to lose its outer electron.

Question 2

A sample of gas occupies 2.0 L at 1.0 atm and 300 K. If the pressure is increased to 2.0 atm and the temperature is raised to 600 K, what will be the new volume of the gas? (Assume ideal gas behavior.)

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$ $$T_2$$}{$$T_1$$ $$P_2$$} = \frac{1.0 	imes 2.0 	imes 600}{300 	imes 2.0} = 2.0\ 	ext{L}$$

Question 3

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have the same number of valence electrons.

Question 4

A 10.0 g sample of a metal at 100.0°C is placed in 50.0 g of water at 20.0°C. The final temperature of the system is 22.0°C. What is the specific heat capacity ($$c) of $$the metal? (Assume $$c_{	ext{water}} = 4.18\ 	ext{J/g} \cdot 	ext{°C})$$

Accepted Answer

$$c = \frac{(50.0)(4.18)(22.0-20.0)}{10.0(100.0-22.0)} = 0.134\ 	ext{J/g} \cdot 	ext{°C}$$

Question 5

Which of the following best describes the VSEPR theory prediction for the shape of a molecule of methane ($$CH_4$$)?

Accepted Answer

Tetrahedral

Question 6

A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 500.0 mL of solution. What is the molarity ($$M) of $$the solution? ($$M_{	ext{NaCl}} = 58.44\ 	ext{g/mol})$$

Accepted Answer

$$M = \frac{10.0\ 	ext{g}}{58.44\ 	ext{g/mol} 	imes 0.500\ 	ext{L}} = 0.342\ 	ext{mol/L}$$

Question 7

Which of the following is a correct balanced equation for the combustion of propane ($$C_3H_8$$)?

Accepted Answer

$$C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$$

Question 8

Which of the following statements about acids and bases is correct according to the Brønsted-Lowry definition?

Accepted Answer

An acid is a substance that donates a proton ($$H^+).$$

Question 9

A radioactive isotope decays with a half-life of 5 years. If you start with 80 g, how much remains after 15 years?

Accepted Answer

$$80\ 	ext{g} ightarrow 40\ 	ext{g} ightarrow 20\ 	ext{g} ightarrow 10\ 	ext{g}$$

Question 10

Which of the following best explains why water ($$H_2O) $$has a higher boiling point than methane ($$CH_4$$)?

Accepted Answer

Water molecules form hydrogen bonds, which are stronger than the London dispersion forces in methane.

Question 11

Which of the following is the correct electron configuration for a neutral atom of sulfur ($$S$$, atomic number 16)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^4$$

Question 12

A patient receives an intravenous solution containing 0.9% NaCl (normal saline). What is the main reason this solution is used in medicine?

Accepted Answer

It is isotonic with human blood cells, preventing cell lysis or crenation.

Question 13

Which of the following best describes the process of titration in acid-base chemistry?

Accepted Answer

A solution of known concentration is gradually added to a solution of unknown concentration until the reaction reaches equivalence.

Question 14

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

Accepted Answer

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

Question 15

Which of the following best describes the difference between ionic and covalent bonding?

Accepted Answer

Ionic bonds involve the transfer of electrons, while covalent bonds involve the sharing of electrons.

Question 16

A sample contains 0.25 mol of $$CO_2. $$How many molecules of $$CO_2$$ are present in the sample? ($$N_A = 6.022 	imes 10$$^{23}$$\ 	ext{mol}^{-1})$$

Accepted Answer

$$0.25 	imes 6.022 	imes 10$$^{23}$$ = 1.51 	imes 10$$^{23}$$ molecules

Question 17

Which of the following is a correct statement about the effect of temperature on reaction rate?

Accepted Answer

Increasing temperature increases the reaction rate by increasing the kinetic energy of the molecules.

Question 18

Which of the following is the correct net ionic equation for the reaction between aqueous solutions of $$NaCl$$ and $$AgNO_3$$?

Accepted Answer

$$Ag^+ (aq) + Cl^- (aq) \rightarrow AgCl (s)$$

Question 19

Which of the following best explains why carbon forms four covalent bonds in organic molecules?

Accepted Answer

Carbon has four valence electrons and needs four more to complete its octet.

CHEM 280 General Chemistry Syllabus and Study Guide

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