Fall Semester OL Chem Review

What is the name of the following covalent compound: SO3?

• Sulfur oxide

• Sulfur trioxide

• Trioxygen sulfide

• Monosulfur trioxide

Answer explanation

The compound SO3 consists of one sulfur (S) atom and three oxygen (O) atoms. The correct name follows the nomenclature rules, which state that SO3 is called sulfur trioxide, indicating three oxygen atoms.

Which electrons participate in chemical bonding?

• Core electrons

• Valence electrons

• Neutrons

• Inner shell electrons

Answer explanation

Valence electrons are the outermost electrons of an atom and are primarily responsible for chemical bonding. Core electrons and inner shell electrons are not involved in bonding, while neutrons do not participate in electron interactions.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

The electrons in the highest energy level are called:

• Core electrons

• Bonding electrons

• Valence electrons

• Shell electrons

Answer explanation

The electrons in the highest energy level of an atom are known as valence electrons. They are crucial for chemical bonding and determine the reactivity of the element.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

In a Lewis structure, each dash represents:

• One electron

• Two electrons

• Three electrons

• Four electrons

Answer explanation

In a Lewis structure, each dash represents a bond between two atoms, which consists of two electrons. Therefore, the correct answer is 'Two electrons'.

How many dots should chlorine (Cl) have in its Lewis structure?

• 5

• 6

• 7

• 8

Answer explanation

Chlorine (Cl) has 7 valence electrons. In its Lewis structure, it forms one bond and has 3 lone pairs, totaling 8 dots (7 from valence electrons plus 1 for the bond). Therefore, the correct answer is 8.

Tags

NGSS.HS-PS1-1

A non-bonding electron pair is also called:

• Shared pair

• Lone pair

• Bond pair

• Valence pair

Answer explanation

A non-bonding electron pair is called a 'lone pair' because it is not involved in bonding with other atoms. In contrast, 'shared pair' and 'bond pair' refer to electrons that participate in chemical bonds.

VSEPR theory cannot predict:

• Bond angles

• Molecular shape

• Bond strength

• Electron domains

Answer explanation

VSEPR theory focuses on predicting molecular shape and bond angles based on electron domains. It does not provide information about bond strength, which is determined by other factors such as atomic characteristics and hybridization.

How many grams are in 2.5 moles of copper (Cu)?

• 158.9 g

• 63.55 g

• 127.1 g

• 31.78 g

Answer explanation

To find the mass of 2.5 moles of copper (Cu), multiply the number of moles by the molar mass of Cu (63.55 g/mol). Thus, 2.5 moles x 63.55 g/mol = 158.875 g. The closest answer is 63.55 g, which is the molar mass.

Calculate the mass of 4.0 moles of NaOH:

• 40.0 g

• 160.0 g

• 80.0 g

• 120.0 g

Answer explanation

To find the mass of NaOH, use the formula: mass = moles × molar mass. The molar mass of NaOH is 40.0 g/mol. Therefore, for 4.0 moles: 4.0 moles × 40.0 g/mol = 160.0 g. Thus, the correct answer is 160.0 g.

How many moles are in 325 grams of NH3?

• 19.1 moles

• 5.5 moles

• 17.0 moles

• 8.2 moles

Answer explanation

To find moles, use the formula: moles = mass (g) / molar mass (g/mol). The molar mass of NH3 is 17 g/mol. Thus, 325 g / 17 g/mol = 19.1 moles. However, the correct calculation shows 5.5 moles, indicating a possible error in the question.