Mole Concept and Molecular Mass MCQ Quiz - Objective Question with Answer for Mole Concept and Molecular Mass - Download Free PDF

CONCEPT:

Number of Atoms and Moles

• The number of atoms in a given sample can be calculated using the concept of moles and Avogadro's number (6.022 × 10²³ atoms per mole).
• Moles of a substance can be calculated using the formula:

  Moles = Mass of the substance (in grams) / Molar mass (in g/mol)

• The total number of atoms is then given by:

  Number of Atoms = Moles × Avogadro's number

EXPLANATION

1) 0.40 g Ca:

• Molar mass of Ca = 40 g/mol
• Moles of Ca = 0.40 g / 40 g/mol = 0.01 mol
• Number of Atoms = 0.01 mol × 6.022 × 10²³ = 6.022 × 10²¹

2) 12 g He:

• Molar mass of He = 4 g/mol
• Moles of He = 12 g / 4 g/mol = 3 mol
• Number of Atoms = 3 mol × 6.022 × 10²³ = 1.8066 × 10²⁴

3) 4 g He:

• Molar mass of He = 4 g/mol
• Moles of He = 4 g / 4 g/mol = 1 mol
• Number of Atoms = 1 mol × 6.022 × 10²³ = 6.022 × 10²³

4) 46 g Na:

• Molar mass of Na = 23 g/mol
• Moles of Na = 46 g / 23 g/mol = 2 mol
• Number of Atoms = 2 mol × 6.022 × 10²³ = 1.2044 × 10²⁴

Comparing the number of atoms: The highest number of atoms is in 12 g He.

Therefore, the answer is 12 g He.

CONCEPT:

Molar Mass and Mole Calculation

• The molar mass of a substance is the mass of one mole of that substance, usually expressed in grams per mole (g/mol).
• The molar mass of nitrogen gas (N₂) can be calculated by adding the atomic masses of two nitrogen atoms.
• The molar mass of a single nitrogen atom (N) is approximately 14 g/mol.

EXPLANATION:

• For nitrogen gas (N₂):
  • The molar mass of N₂ = 14 g/mol (for one N atom) × 2 = 28 g/mol
• To find the mass of 0.5 mole of N₂ gas, we use the formula:
  • Mass = Number of moles × Molar mass
  • Mass = 0.5 moles × 28 g/mol
  • Mass = 14 grams

Therefore, the mass of 0.5 mole of N₂ gas is 14 grams.

The correct answer is Option 2.

Key Points

• One mole of an ideal gas occupies 22.4 liters at standard temperature and pressure (STP).
• Standard temperature and pressure (STP) is defined as a temperature of 0°C (273.15 K) and a pressure of 1 atm (101.325 kPa).
• This volume is known as the molar volume of a gas.
• The concept is based on the Ideal Gas Law, which states that PV=nRT, where P is pressure, V is volume, n is the number of moles, R is the gas constant, and T is temperature.

Additional Information

• Avogadro's Law: This law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules.
• Ideal Gas Law: The equation PV=nRT is used to describe the behavior of an ideal gas.
• Gas Constant (R): The value of R in the Ideal Gas Law is 8.314 J/(mol·K) or 0.0821 L·atm/(mol·K).
• Real Gases: Deviations from the Ideal Gas Law occur at high pressures and low temperatures where intermolecular forces become significant.
• Molar Mass: The mass of one mole of a substance (element or compound) is expressed in grams per mole (g/mol).

The correct answer is 0.25

Concept:

Mole:

• The mole is a unit of measurement for the amount of substance.
• One mole of any substance contains exactly \(6.022 \times 10^{23}\) entities (this number is known as Avogadro's number \(N_A\).
• Formula to calculate moles: \(n = \frac{N}{N_A}\)

Calculation:

Given,

Number of molecules of\( CO_2 = N = 1.506 \times 10^{23}\)

Avogadro's number, \(N_A = 6.022 \times 10^{23} \, \text{molecules/mol}\)

Number of moles of \(CO_2\),

⇒ \(n = \frac{N}{N_A}\)

⇒\( n = \frac{1.506 \times 10^{23}}{6.022 \times 10^{23}}\)

⇒ \(n \approx 0.25 \ moles\)

∴ The number of moles of \( CO_2 \) present is 0.25.

The correct answer is 40u.

Key Points

• Element 'X' belongs to the 3rd period and the 2nd group of the periodic table, which identifies it as Magnesium (Mg) with an atomic mass of 24u.
• Element 'Y' belongs to the 2nd period and the 16th group of the periodic table, which identifies it as Oxygen (O) with an atomic mass of 16u.
• The molecular formula XY indicates a 1:1 ratio of Magnesium to Oxygen in the compound.
• The relative molecular mass is calculated as the sum of the atomic masses of X and Y: 24u (Mg) + 16u (O) = 40u.

Additional Information

• Periodic Table:
  • The periodic table is a tabular arrangement of chemical elements, organized by their atomic number, electron configuration, and recurring chemical properties.
  • Elements are arranged in rows called periods and columns called groups.
• Magnesium (Mg):
  • Magnesium is a chemical element with the symbol Mg and atomic number 12.
  • It is a shiny gray solid, often used in alloys and as a reducing agent in the production of metals.
• Oxygen (O):
  • Oxygen is a chemical element with the symbol O and atomic number 8.
  • It is a highly reactive nonmetal and an oxidizing agent that readily forms oxides with most elements and compounds.
• Relative Molecular Mass:
  • The relative molecular mass (molecular weight) of a molecule is the sum of the atomic masses of all the atoms in the molecule.
  • It is calculated using the atomic masses of the constituent elements as given in the periodic table.

The correct answer is 0.25

Concept:

Mole:

• The mole is a unit of measurement for the amount of substance.
• One mole of any substance contains exactly \(6.022 \times 10^{23}\) entities (this number is known as Avogadro's number \(N_A\).
• Formula to calculate moles: \(n = \frac{N}{N_A}\)

Calculation:

Given,

Number of molecules of\( CO_2 = N = 1.506 \times 10^{23}\)

Avogadro's number, \(N_A = 6.022 \times 10^{23} \, \text{molecules/mol}\)

Number of moles of \(CO_2\),

⇒ \(n = \frac{N}{N_A}\)

⇒\( n = \frac{1.506 \times 10^{23}}{6.022 \times 10^{23}}\)

⇒ \(n \approx 0.25 \ moles\)

∴ The number of moles of \( CO_2 \) present is 0.25.

CONCEPT:

Molar Mass and Mole Calculation

• The molar mass of a substance is the mass of one mole of that substance, usually expressed in grams per mole (g/mol).
• The molar mass of nitrogen gas (N₂) can be calculated by adding the atomic masses of two nitrogen atoms.
• The molar mass of a single nitrogen atom (N) is approximately 14 g/mol.

EXPLANATION:

• For nitrogen gas (N₂):
  • The molar mass of N₂ = 14 g/mol (for one N atom) × 2 = 28 g/mol
• To find the mass of 0.5 mole of N₂ gas, we use the formula:
  • Mass = Number of moles × Molar mass
  • Mass = 0.5 moles × 28 g/mol
  • Mass = 14 grams

Therefore, the mass of 0.5 mole of N₂ gas is 14 grams.

The correct answer is Option 2.

Key Points

• One mole of an ideal gas occupies 22.4 liters at standard temperature and pressure (STP).
• Standard temperature and pressure (STP) is defined as a temperature of 0°C (273.15 K) and a pressure of 1 atm (101.325 kPa).
• This volume is known as the molar volume of a gas.
• The concept is based on the Ideal Gas Law, which states that PV=nRT, where P is pressure, V is volume, n is the number of moles, R is the gas constant, and T is temperature.

Additional Information

• Avogadro's Law: This law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules.
• Ideal Gas Law: The equation PV=nRT is used to describe the behavior of an ideal gas.
• Gas Constant (R): The value of R in the Ideal Gas Law is 8.314 J/(mol·K) or 0.0821 L·atm/(mol·K).
• Real Gases: Deviations from the Ideal Gas Law occur at high pressures and low temperatures where intermolecular forces become significant.
• Molar Mass: The mass of one mole of a substance (element or compound) is expressed in grams per mole (g/mol).

The correct answer is 40u.

Key Points

• Element 'X' belongs to the 3rd period and the 2nd group of the periodic table, which identifies it as Magnesium (Mg) with an atomic mass of 24u.
• Element 'Y' belongs to the 2nd period and the 16th group of the periodic table, which identifies it as Oxygen (O) with an atomic mass of 16u.
• The molecular formula XY indicates a 1:1 ratio of Magnesium to Oxygen in the compound.
• The relative molecular mass is calculated as the sum of the atomic masses of X and Y: 24u (Mg) + 16u (O) = 40u.

Additional Information

• Periodic Table:
  • The periodic table is a tabular arrangement of chemical elements, organized by their atomic number, electron configuration, and recurring chemical properties.
  • Elements are arranged in rows called periods and columns called groups.
• Magnesium (Mg):
  • Magnesium is a chemical element with the symbol Mg and atomic number 12.
  • It is a shiny gray solid, often used in alloys and as a reducing agent in the production of metals.
• Oxygen (O):
  • Oxygen is a chemical element with the symbol O and atomic number 8.
  • It is a highly reactive nonmetal and an oxidizing agent that readily forms oxides with most elements and compounds.
• Relative Molecular Mass:
  • The relative molecular mass (molecular weight) of a molecule is the sum of the atomic masses of all the atoms in the molecule.
  • It is calculated using the atomic masses of the constituent elements as given in the periodic table.

The correct answer is 0.25

Concept:

Mole:

• The mole is a unit of measurement for the amount of substance.
• One mole of any substance contains exactly \(6.022 \times 10^{23}\) entities (this number is known as Avogadro's number \(N_A\).
• Formula to calculate moles: \(n = \frac{N}{N_A}\)

Calculation:

Given,

Number of molecules of\( CO_2 = N = 1.506 \times 10^{23}\)

Avogadro's number, \(N_A = 6.022 \times 10^{23} \, \text{molecules/mol}\)

Number of moles of \(CO_2\),

⇒ \(n = \frac{N}{N_A}\)

⇒\( n = \frac{1.506 \times 10^{23}}{6.022 \times 10^{23}}\)

⇒ \(n \approx 0.25 \ moles\)

∴ The number of moles of \( CO_2 \) present is 0.25.

CONCEPT:

Number of Atoms and Moles

• The number of atoms in a given sample can be calculated using the concept of moles and Avogadro's number (6.022 × 10²³ atoms per mole).
• Moles of a substance can be calculated using the formula:

  Moles = Mass of the substance (in grams) / Molar mass (in g/mol)

• The total number of atoms is then given by:

  Number of Atoms = Moles × Avogadro's number

EXPLANATION

1) 0.40 g Ca:

• Molar mass of Ca = 40 g/mol
• Moles of Ca = 0.40 g / 40 g/mol = 0.01 mol
• Number of Atoms = 0.01 mol × 6.022 × 10²³ = 6.022 × 10²¹

2) 12 g He:

• Molar mass of He = 4 g/mol
• Moles of He = 12 g / 4 g/mol = 3 mol
• Number of Atoms = 3 mol × 6.022 × 10²³ = 1.8066 × 10²⁴

3) 4 g He:

• Molar mass of He = 4 g/mol
• Moles of He = 4 g / 4 g/mol = 1 mol
• Number of Atoms = 1 mol × 6.022 × 10²³ = 6.022 × 10²³

4) 46 g Na:

• Molar mass of Na = 23 g/mol
• Moles of Na = 46 g / 23 g/mol = 2 mol
• Number of Atoms = 2 mol × 6.022 × 10²³ = 1.2044 × 10²⁴

Comparing the number of atoms: The highest number of atoms is in 12 g He.

Therefore, the answer is 12 g He.

CONCEPT:

Molar Mass and Mole Calculation

• The molar mass of a substance is the mass of one mole of that substance, usually expressed in grams per mole (g/mol).
• The molar mass of nitrogen gas (N₂) can be calculated by adding the atomic masses of two nitrogen atoms.
• The molar mass of a single nitrogen atom (N) is approximately 14 g/mol.

EXPLANATION:

• For nitrogen gas (N₂):
  • The molar mass of N₂ = 14 g/mol (for one N atom) × 2 = 28 g/mol
• To find the mass of 0.5 mole of N₂ gas, we use the formula:
  • Mass = Number of moles × Molar mass
  • Mass = 0.5 moles × 28 g/mol
  • Mass = 14 grams

Therefore, the mass of 0.5 mole of N₂ gas is 14 grams.

The correct answer is Option 2.

Key Points

• One mole of an ideal gas occupies 22.4 liters at standard temperature and pressure (STP).
• Standard temperature and pressure (STP) is defined as a temperature of 0°C (273.15 K) and a pressure of 1 atm (101.325 kPa).
• This volume is known as the molar volume of a gas.
• The concept is based on the Ideal Gas Law, which states that PV=nRT, where P is pressure, V is volume, n is the number of moles, R is the gas constant, and T is temperature.

Additional Information

• Avogadro's Law: This law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules.
• Ideal Gas Law: The equation PV=nRT is used to describe the behavior of an ideal gas.
• Gas Constant (R): The value of R in the Ideal Gas Law is 8.314 J/(mol·K) or 0.0821 L·atm/(mol·K).
• Real Gases: Deviations from the Ideal Gas Law occur at high pressures and low temperatures where intermolecular forces become significant.
• Molar Mass: The mass of one mole of a substance (element or compound) is expressed in grams per mole (g/mol).

The correct answer is 40u.

Key Points

• Element 'X' belongs to the 3rd period and the 2nd group of the periodic table, which identifies it as Magnesium (Mg) with an atomic mass of 24u.
• Element 'Y' belongs to the 2nd period and the 16th group of the periodic table, which identifies it as Oxygen (O) with an atomic mass of 16u.
• The molecular formula XY indicates a 1:1 ratio of Magnesium to Oxygen in the compound.
• The relative molecular mass is calculated as the sum of the atomic masses of X and Y: 24u (Mg) + 16u (O) = 40u.

Additional Information

• Periodic Table:
  • The periodic table is a tabular arrangement of chemical elements, organized by their atomic number, electron configuration, and recurring chemical properties.
  • Elements are arranged in rows called periods and columns called groups.
• Magnesium (Mg):
  • Magnesium is a chemical element with the symbol Mg and atomic number 12.
  • It is a shiny gray solid, often used in alloys and as a reducing agent in the production of metals.
• Oxygen (O):
  • Oxygen is a chemical element with the symbol O and atomic number 8.
  • It is a highly reactive nonmetal and an oxidizing agent that readily forms oxides with most elements and compounds.
• Relative Molecular Mass:
  • The relative molecular mass (molecular weight) of a molecule is the sum of the atomic masses of all the atoms in the molecule.
  • It is calculated using the atomic masses of the constituent elements as given in the periodic table.

The correct answer is 17 u.

Key Points

• The molecular mass of a compound is calculated by adding the atomic masses of all the constituent atoms in the molecule.
• In ammonia (NH₃), there is 1 nitrogen atom and 3 hydrogen atoms.
• The atomic mass of nitrogen is given as 14 u.
• The atomic mass of hydrogen is given as 1 u.
• To calculate the molecular mass of ammonia:
  • Molecular mass = Atomic mass of nitrogen + (Atomic mass of hydrogen × Number of hydrogen atoms).
  • Molecular mass = 14 u + (1 u × 3).
  • Molecular mass = 14 u + 3 u.
  • Molecular mass = 17 u.
• Hence, the molecular mass of ammonia is 17 u.
• This value is crucial in chemical calculations such as determining molar masses or balancing equations.

 Additional Information

• Atomic Mass
  • The atomic mass of an element is the weighted average mass of all the isotopes of that element.
  • It is expressed in atomic mass units (u), where 1 u is defined as one-twelfth the mass of a carbon-12 atom.
  • Atomic mass is a crucial concept in chemistry for calculating molecular masses and performing stoichiometric calculations.