Reacting Masses

• What should you be able to do by the end of the video on moles?

  Use the idea of moles to calculate the masses of reactants and products in chemical reactions
• Why is the topic of moles considered tricky?

  Because it involves several concepts and calculations
• What is the equation to calculate the number of moles for elements?

  The number of moles is the mass divided by the relative atomic mass
• What is the equation to calculate the number of moles for compounds?

  The number of moles is the mass divided by the relative formula mass
• What should you do if you cannot calculate relative formula mass?

  You should watch the video on that topic before proceeding
• How do you calculate the mass of magnesium chloride produced from 72 g of magnesium?

  1. Write the chemical equation: Mg + Cl → MgCl₂
  2. Calculate moles of magnesium:

  • Moles = mass / relative atomic mass = \( \frac{72 \text{ g}}{24} = 3 \text{ moles} \)

  1. Use the ratio from the equation: 1 mole of Mg produces 1 mole of MgCl₂
  2. Calculate mass of MgCl₂:

  • Mass = moles × relative formula mass = \( 3 \times 95 = 285 \text{ g} \)
• What mass of magnesium chloride can be produced from 72 g of magnesium?

  285 g
• What mass of calcium sulfate can be produced from 80 g of calcium?

  272 g
• How do you calculate the mass of calcium carbonate needed to produce 224 g of calcium oxide?

  1. Write the chemical equation: CaCO₃ → CaO + CO₂
  2. Calculate moles of calcium oxide:

  • Moles = mass / relative formula mass = \( \frac{224 \text{ g}}{56} = 4 \text{ moles} \)

  1. Use the ratio from the equation: 1 mole of CaCO₃ produces 1 mole of CaO
  2. Calculate mass of CaCO₃:

  • Mass = moles × relative formula mass = \( 4 \times 100 = 400 \text{ g} \)
• What mass of calcium carbonate is needed to produce 224 g of calcium oxide?

  400 g
• What will the next video cover regarding calculating reacting masses?

  • More complicated examples
  • Further applications of moles in chemical reactions
• What concept is used to calculate the masses of reactants and products in chemical reactions?

  The idea of moles
• What does the equation "1 mole of magnesium plus 1 mole of chlorine makes 1 mole of magnesium chloride" represent?

  It represents the stoichiometry of the reaction between magnesium and chlorine
• How do you interpret the large number in front of hydrochloric acid in a chemical equation?

  It indicates the number of moles of hydrochloric acid required
• In the reaction involving hydrochloric acid, how many moles of magnesium chloride are produced from 2 moles of hydrochloric acid?

  1 mole of magnesium chloride
• What is the relative formula mass of hydrochloric acid?

  36.5
• How do you calculate the number of moles of hydrochloric acid from its mass?

  Number of moles = mass / relative formula mass
• If you have 146 g of hydrochloric acid, how many moles do you have?

  4 moles
• How do you find the mass of magnesium chloride produced from the moles calculated?

  Multiply the number of moles by the relative formula mass of magnesium chloride
• What is the relative formula mass of magnesium chloride?

  95
• What mass of magnesium chloride is produced from 2 moles of magnesium chloride?

  190 g
• What is the process to calculate the mass of sodium sulfate from sodium hydroxide?

  • Identify the stoichiometry: 2 moles of sodium hydroxide produce 1 mole of sodium sulfate.
  • Calculate moles of sodium hydroxide: Number of moles = mass / relative formula mass (240 g / 40 = 6 moles).
  • Divide by 2 for sodium sulfate: 6 moles of sodium hydroxide yield 3 moles of sodium sulfate.
  • Calculate mass of sodium sulfate: 3 moles * 142 = 426 g.
• What is the relative formula mass of sodium hydroxide?

  40
• How many moles of sodium sulfate are produced from 6 moles of sodium hydroxide?

  3 moles of sodium sulfate
• What is the process to calculate the mass of hydrogen peroxide from oxygen produced?

  • Identify the stoichiometry: 2 moles of hydrogen peroxide produce 1 mole of oxygen.
  • Calculate moles of oxygen: Number of moles = mass / relative formula mass (64 g / 32 = 2 moles).
  • Determine moles of hydrogen peroxide needed: 2 moles of oxygen require 4 moles of hydrogen peroxide.
  • Calculate mass of hydrogen peroxide: 4 moles * 34 = 136 g.
• What is the relative formula mass of hydrogen peroxide?

  34
• How many moles of hydrogen peroxide are needed to produce 2 moles of oxygen?

  4 moles of hydrogen peroxide
• What mass of hydrogen peroxide is produced from 4 moles?

  136 g
• What are the key steps in calculating reacting masses using moles?

  1. Identify the stoichiometry from the balanced equation.
  2. Calculate the number of moles from the mass and relative formula mass.
  3. Use stoichiometry to find moles of the desired product.
  4. Calculate the mass of the product using its relative formula mass.