Moles

• What is the definition of a mole?

  A mole is a specific number of particles, equal to $6.022 \times 10^{23}$.
• How does Avogadro's constant relate to the mass of an element or compound?

  It indicates that a mole of atoms or molecules weighs the same number of grams as the relative atomic or formula mass.
• What is the relative atomic mass of carbon?

  The relative atomic mass of carbon is 12.
• What is the relative formula mass of nitrogen gas (N₂)?

  The relative formula mass of nitrogen gas is 28.
• What is the relative formula mass of hexane (C₆H₁₄)?

  The relative formula mass of hexane is 86.
• How many atoms are in 5 moles of oxygen gas?

  There are $6.022 \times 10^{23} \times 5 \times 2 =$$6.022 \times 10^{24}$ atoms.
• How do you find the mass of an atom of a certain element?

  You divide its relative atomic mass by Avogadro's constant.
• What is the mean mass of one atom of iron if its relative atomic mass is 55.8?

  The mean mass of one atom of iron is $9.27 \times 10^{-23} \text{ g}$.
• How do you calculate the number of moles in a given mass of an element or compound?

  • Use the formula: Number of Moles = Mass in g / M_r
  • For elements, replace M_r with A_r.
• How many moles are there in 66 g of carbon dioxide (CO₂)?

  There are 1.5 moles of carbon dioxide.
• What mass of carbon is there in 4.0 moles of carbon dioxide?

  The mass of carbon is 48 g.
• What is the relative formula mass of potassium bromide (KBr)?

  The relative formula mass of potassium bromide is 119.0.
• How do you calculate the mass of 0.200 moles of potassium bromide?

  The mass is $0.200 \times 119.0 =$$23.8 \text{ g}$.
• What is the relative formula mass of substance X if 0.500 moles has a mass of 87.0 g?

  The relative formula mass of X is $174.0 \text{ g/mol}$.
• What is the molar mass of water?

  • M_r of water = 18.0
• What is the molar mass of carbon dioxide?

  • M_r of carbon dioxide = 44.0
• What is the molar mass of potassium bromide?

  • M_r of potassium bromide = 119.0
• What is the molar mass of hexane?

  • M_r of hexane = 86.0
• What is the molar mass of nitrogen gas?

  • M_r of nitrogen gas = 28.0
• What is the molar mass of iron?

  • A_r of iron = 55.8
• What is Avogadro's constant?

  • Avogadro's constant = $6.022 \times 10^{23}$
• What is the formula to find the mass of an atom?

  • Mass of one atom = A_r ÷ Avogadro's constant
• What is the formula to find the number of moles?

  • Number of Moles = Mass in g / M_r