Reacting masses

• Calculating the masses of reactants and products in chemical reactions

  1. Calculate the number of moles of reactants using the equation: number of moles = mass / relative atomic/formula mass

  2. Use the balanced chemical equation to determine the relationship between the number of moles of reactants and products

  3. Calculate the mass of products using the equation: mass = number of moles x relative formula mass
• Mole


  Unit used to measure the amount of a substance, equal to the number of particles (atoms, molecules, or ions) in 12 grams of pure carbon-12
• Relative atomic mass


  The average mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom
• Relative formula mass


  The sum of the relative atomic masses of the atoms in a chemical formula
• Calculating the masses of reactants and products in chemical reactions

  1. Calculate the number of moles of reactants using the equation: number of moles = mass / relative atomic/formula mass

  2. Use the balanced chemical equation to determine the relationship between the number of moles of reactants and products

  3. Calculate the mass of products using the equation: mass = number of moles x relative formula mass
• Mole


  Unit used to measure the amount of a substance, equal to the number of particles (atoms, molecules, or ions) in 12 grams of pure carbon-12
• Relative atomic mass


  The average mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom
• Relative formula mass


  The sum of the relative atomic masses of the atoms in a chemical formula
• Calculating reacting masses


  1. Look at the big numbers in the equation

  2. Calculate the number of moles

  3. Divide the number of moles by the appropriate factor

  4. Multiply the number of moles by the relative formula mass
• Mole


  Unit used to measure the amount of a substance
• Equations show the mole ratios of reactants and products
• Calculating mass of magnesium chloride from 146 g of hydrochloric acid

  1. Calculate number of moles of hydrochloric acid (146 g / 36.5 g/mol = 4 mol)

  2. Divide moles of hydrochloric acid by 2 to get moles of magnesium chloride (4 mol / 2 = 2 mol)

  3. Calculate mass of magnesium chloride (2 mol x 95 g/mol = 190 g)
• Calculating mass of sodium sulfate from 240 g of sodium hydroxide

  1. Calculate number of moles of sodium hydroxide (240 g / 40 g/mol = 6 mol)

  2. Divide moles of sodium hydroxide by 2 to get moles of sodium sulfate (6 mol / 2 = 3 mol)

  3. Calculate mass of sodium sulfate (3 mol x 142 g/mol = 426 g)
• Calculating mass of hydrogen peroxide to produce 64 g of oxygen

  1. Calculate number of moles of oxygen (64 g / 32 g/mol = 2 mol)

  2. Multiply moles of oxygen by 2 to get moles of hydrogen peroxide (2 mol x 2 = 4 mol)

  3. Calculate mass of hydrogen peroxide (4 mol x 34 g/mol = 136 g)