Q: A sample of nitrogen gas occupies 2.50 L at 1.00 atm and 25°C. What will be its volume at 0.500 atm and 25°C, assuming ideal gas behavior?

$$V_2$$ = $$V_1$$ \times \frac{$$P_1$$}{$$P_2$$} = 2.50\ \mathrm{L} \times \frac{1.00\ \mathrm{atm}}{0.500\ \mathrm{atm}} = 5.00\ \mathrm{L}$$

Question 1

Which of the following statements best describes the scientific method as applied in chemistry?

Accepted Answer

It is a cyclical process involving observation, hypothesis formation, experimentation, and revision, used to investigate chemical phenomena.

Question 2

A sample of nitrogen gas occupies 2.50 L at 1.00 atm and 25°C. What will be its volume at 0.500 atm and 25°C, assuming ideal gas behavior?

Accepted Answer

$$V_2$$ = $$V_1$$ 	imes \frac{$$P_1$$}{$$P_2$$} = 2.50\ \mathrm{L} 	imes \frac{1.00\ \mathrm{atm}}{0.500\ \mathrm{atm}} = 5.00\ \mathrm{L}$$

Question 3

Which of the following is the correct electron configuration for a neutral atom of sulfur ($$Z=16$$)?

Accepted Answer

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

Question 4

Which of the following compounds is named correctly according to IUPAC nomenclature rules?

Accepted Answer

NaCl: sodium chloride

Question 5

Which statement best explains why ionic compounds tend to have high melting points?

Accepted Answer

Ionic compounds have strong electrostatic forces between oppositely charged ions, requiring more energy to break.

Question 6

A chemical reaction is endothermic if:

Accepted Answer

The system absorbs heat from the surroundings, resulting in a positive $$\Delta H.$$

Question 7

Which of the following best describes the difference between atomic number and mass number?

Accepted Answer

Atomic number is the number of protons; mass number is the sum of protons and neutrons.

Question 8

Which of the following Lewis structures correctly represents the bonding in carbon dioxide ($$\mathrm{CO}_2$$)?

Accepted Answer

O=C=O, with each oxygen having two lone pairs

Question 9

Which of the following best describes the VSEPR theory prediction for the shape of ammonia ($$\mathrm{NH}_3$$)?

Accepted Answer

Trigonal pyramidal, due to three bonding pairs and one lone pair on nitrogen

Question 10

A solution is prepared by dissolving 5.00 g of NaCl in enough water to make 250.0 mL of solution. What is the molarity of the solution? ($$\mathrm{NaCl}$$ molar mass = 58.44 g/mol)

Accepted Answer

$$M = \frac{5.00\ \mathrm{g}}{58.44\ \mathrm{g/mol}} \div 0.250\ \mathrm{L} = 0.342\ \mathrm{mol/L}$$

Question 11

Which of the following is a correct balanced chemical equation for the combustion of methane ($$\mathrm{CH}_4$$)?

Accepted Answer

$$\mathrm{CH}_4 + 2\ \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + 2\ \mathrm{H}_2\mathrm{O}$$

Question 12

Which of the following best explains why water is a polar molecule?

Accepted Answer

Water has a bent molecular shape and a significant difference in electronegativity between hydrogen and oxygen.

Question 13

Which of the following is the correct formula for calculating the pressure of a gas using the ideal gas law?

Accepted Answer

$$P = \frac{nRT}{V}$$

Question 14

Which of the following statements about oxidation and reduction is correct?

Accepted Answer

Oxidation is the loss of electrons, while reduction is the gain of electrons.

Question 15

Which of the following best describes the difference between a covalent and an ionic bond?

Accepted Answer

A covalent bond involves the sharing of electrons between atoms, while an ionic bond involves the transfer of electrons from one atom to another.

Question 16

A student mixes solutions of silver nitrate ($$\mathrm{AgNO}_3) $$and sodium chloride ($$\mathrm{NaCl}). $$What type of reaction occurs, and what is the precipitate formed?

Accepted Answer

A double displacement reaction occurs, forming silver chloride ($$\mathrm{AgCl}) as $$the precipitate.

Question 17

Which of the following best describes the periodic trend for atomic radius across a period?

Accepted Answer

Atomic radius decreases from left to right across a period due to increasing nuclear charge.

Question 18

Which of the following is the correct formula for calculating the percent yield of a chemical reaction?

Accepted Answer

$$	ext{Percent Yield} = \frac{	ext{Actual Yield}}{	ext{Theoretical Yield}} 	imes 100\%$$

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