Calculating Reacting Masses from Chemical Equations

Moles and Mass

• One mole of iron has a mass of 55.85 grams.
• Nitrogen gas (N₂) has a relative formula mass of 28, meaning one mole weighs 28 grams.
• The equation to convert between moles and mass is Mass (g) = Moles × Relative Formula Mass (g/mol).
• For 42g of carbon, use the relative atomic mass of carbon (12 g/mol), resulting in 3.5 moles of carbon present.
• The mass of one mole of a substance represents its molecular or atomic weight in grams.

Relative Formula Mass

• If a substance has a relative formula mass of 16, it contains 16 grams in one mole.
• Relative formula mass (Mr) in a chemical equation represents the sum of the atomic masses of all atoms in a compound.

Chemical Equations and Balancing

• The notation (aq) indicates an aqueous solution, meaning the substance is dissolved in water.
• To balance a chemical equation, adjust the coefficients to ensure equal numbers of each type of atom on both sides of the equation.
• A word equation represents the substances involved in a chemical reaction using their names instead of chemical formulas.

Calculating Concentration and Gas Volume

• Calculating relative formula masses is essential for stoichiometry, determining quantities in reactions.
• The molar volume of any gas at room temperature and pressure is 24 dm³.
• If 6 moles of a gas occupy 144 dm³, the volume for 9 moles at the same conditions is 216 dm³.

Concentration and Empirical Formulas

• The formula to calculate concentration in grams per decimeter cubed (g/dm³) is Concentration = Mass (g) / Volume (dm³).
• For the formula Fe₂O₄, the empirical formula is FeO.
• The term 'empirical formula' represents the simplest whole-number ratio of atoms in a compound.

Reaction Stoichiometry

• In the equation 2NaOH + Mg → Mg(OH)₂ + 2Na, from 2 moles of Mg, 4 moles of Na would be formed.
• The formula to calculate percentage yield is Percentage Yield = (Actual Yield / Theoretical Yield) × 100%.
• In the reaction Mg + 2HCl → MgCl₂ + H₂, 2 moles of HCl are required to produce 1 mole of MgCl₂.
• For a solution with a concentration of 40 g/dm³ and a volume of 0.5 dm³, the mass of solute is 20 grams.