number of moles

The number 6.02 x 10²³ is called...

• Obama's number
• Bohr's number
• Trump's number
• Avogadro's number

Molar mass is in units of ________.

• grams

• grams/mole

• mole

• moles/gram

Answer explanation

Molar mass is defined as the mass of one mole of a substance, which is expressed in grams per mole (g/mol). Therefore, the correct answer is grams/mole.

What is the mass of 2.50 mole of oxygen gas O₂?
M(O)= 16g/mol

• 40 g

• 80 g

• 16 g

• 32 g

Answer explanation

The molar mass of O2 is 32 g/mol. For 2.50 moles, the mass is 2.50 moles × 32 g/mol = 80 g. Therefore, the correct answer is 80 g.

How many moles are present in 32.3 grams of carbon dioxide (CO₂)?

M(C)=12 g/mol ; M(O)=16 g/mol

• 44.01 moles

• 1421.52 moles

• 32.3 moles

• 0.73 moles

How many potatoes are in one dozen potatoes?

• 10

• 12

• 2

• 6.02 x 10²³

Answer explanation

A dozen refers to a quantity of 12. Therefore, in one dozen potatoes, there are 12 potatoes. The correct answer is 12.

What is the molar mass of C₂H₄O₂?

M(C)= 12 g/mol ; M(H)=1g/mol ; M(O)=16g/mol

• 40g

• 50g

• 60g

• 68g

Answer explanation

To find the molar mass of C2H4O2, calculate: (2x12) + (4x1) + (2x16) = 24 + 4 + 32 = 60g. Thus, the correct answer is 60g.

If I need 20.4 moles of sodium chloride, how much should I weigh out?

M(Na)= 23g/mol ; M(Cl)= 35.5 g/mol

• 0.549 g

• 112 g

• 1193 g

• 5077 g

Answer explanation

To find the mass of sodium chloride needed, use the formula: mass = moles × molar mass. The molar mass of NaCl is approximately 58.44 g/mol. Thus, 20.4 moles × 58.44 g/mol = 1192 g, making 1192 g the correct answer.

How many moles are 98.3 grams of aluminum hydroxide, Al(OH)₃?

M(Al) = 27g/mol ; M(O)=16g/mol ; M(H) = 1g/mol

• 1.26 moles

• 0.8 moles

• 7,673.4 moles

• 150 moles

Answer explanation

To find moles, use the formula: moles = mass (g) / molar mass (g/mol). The molar mass of Al(OH)3 is 78.00 g/mol. Thus, 98.3 g / 78.00 g/mol = 1.26 moles. Therefore, the correct answer is 1.26 moles.

Find the number of atoms in 0.5 mole of aluminium.

[Avogadro constant, N_A: 6.02x10²³mol^-1]

• 3.01x10²³

• 3.01x10²²

• 6.02x10²³

• 6.02x10²²

Answer explanation

To find the number of atoms in 0.5 mole of aluminium, multiply the number of moles by Avogadro's constant: 0.5 mol x 6.02x10^23 mol^-1 = 3.01x10^23 atoms. Thus, the correct answer is 3.01x10^23.

Find the number of molecules in 1.2 moles of hydrogen gas.

[Avogadro constant, N_A: 6.02x10²³mol^-1]

• 7.224x10²³

• 7.224x10²⁴

• 3.612x10²³

• 5.02x10²³

Answer explanation

To find the number of molecules in 1.2 moles of hydrogen gas, multiply the number of moles by Avogadro's constant: 1.2 moles x 6.02x10^23 mol^-1 = 7.224x10^23 molecules. Thus, the correct answer is 7.224x10^23.