3.2 Use of amount of substance in relation to masses of pure substances

• A mole represents 6.022 x 10^23 particles, which is known as Avogadro's constant.


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• To find the moles in 50g of carbon, you would use the molar mass of carbon, which is 12.01 g/mol
• The formula to calculate moles is Mass / Molar Mass
• A mole is a standard unit that represents a fixed number of particles, known as Avogadro's constant
• Avogadro's number is used to calculate the number of particles in one mole of a substance.

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• What is the molar mass of a substance?

  The mass of one mole
• Avogadro's number is a fixed value of 6.022 x 10^23 particles per mole.


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• You can convert between mass and moles of a substance using its molar mass.


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• The molar mass of a substance is measured in grams per mole
• The molar mass of a substance is measured in grams per mole
• The formula to calculate moles is: Moles = Mass / Molar Mass
• Steps to find the moles in 50g of carbon (C)

  1️⃣ Mass of carbon = 50 g

  2️⃣ Molar mass of carbon = 12.01 g/mol

  3️⃣ Moles of carbon = 50 g / 12.01 g/mol = 4.16 moles
• At STP, the temperature is 0 °C.


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• What is Avogadro's number?

  $6.022 \times 10^{23}$
• Molar mass allows you to convert between mass and moles
• 100g of NaCl contains 1.71 moles


  True
• What is the molar mass of carbon (C)?

  12.01 g/mol
• How many moles are in 44.8 L of oxygen gas at STP?

  2 moles
• To calculate percentage composition, you divide the mass of the element by the total mass of the compound
• What is the relative formula mass (RFM)?

  Sum of atomic masses
• The RFM of carbon dioxide (CO₂) is 44.01 g/mol


  True
• What is the fixed value of Avogadro's number?

  6.022 x 10^23
• Match the quantity with its formula:

  Moles ↔️ Mass / Molar Mass

  Mass ↔️ Moles x Molar Mass

  Molar Mass ↔️ Mass / Moles
• Where can molar masses be found?

  Periodic table
• At STP, the temperature is 273 K and the pressure is 1 atm
• To calculate moles from mass, the formula is: Moles = Mass / Molar Mass
• The formula to calculate moles is Mass / Molar Mass


  True
• The molar mass can be found on the periodic
• The molar mass of NaCl is calculated by summing the atomic masses of Na and Cl
• At STP, the molar volume of a gas is 22.4 L/mol
• STP conditions are defined as 0 °C and 1 atm


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• The percentage composition of water is 11.2% hydrogen and 88.8% oxygen


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• To calculate the RFM of carbon dioxide (CO₂), you add the atomic mass of carbon to twice the atomic mass of oxygen
• In quantitative chemistry, the amount of substance is measured in moles
• Steps to calculate moles from mass

  1️⃣ Identify the mass of the substance in grams

  2️⃣ Determine the molar mass of the substance from the periodic table

  3️⃣ Use the formula: Moles = Mass / Molar Mass
• Where can you find the molar mass of a substance?

  Periodic table
• Relationships between mass, moles, and molar mass

  1️⃣ Moles = Mass / Molar Mass

  2️⃣ Mass = Moles x Molar Mass

  3️⃣ Molar Mass = Mass / Moles
• What is the first step to calculate the moles in 50g of carbon?

  Identify the mass
• Avogadro's number is the number of particles in 1 mole
• Molar masses can be found on the periodic table.

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