Untitled Quiz

Stoichiometry

• Stoichiometry is the branch of chemistry that relates the amounts of reactants and products in a chemical reaction.
• It is essential for determining the quantities of reactants needed to produce a specific amount of product.

Calculating Percentage Composition

• To determine the percentage composition of an element in a compound:
  • Calculate the relative molecular mass of the compound.
  • Divide the atomic mass of the element by the relative molecular mass of the compound.
  • Multiply the result by 100 to get the percentage.

Example (CaO)

• Relative molecular mass of CaO = 56
• Percentage of Ca = (40/56) * 100 = 71.43%
• Percentage of O = (16/56) * 100 = 28.57%

Empirical Formula Calculation

• Molecular formula: Shows the number and types of atoms in a molecule.
• Empirical formula: Shows the simplest whole number ratio of atoms in a compound.
• Molecular formula = empirical formula * n (where 'n' is a whole number)

Example (Glucose)

• Empirical formula of glucose = CH₂O
• Relative molecular mass of glucose = 180
• 180 = (12 + 2 + 16) * n
• n = 6
• Molecular formula of glucose = C₆H₁₂O₆

Calculating Empirical Formula from Masses

• In an experiment involving a reaction between an oxide of copper and hydrogen, the mass of copper oxide can be used to determine the empirical formula.

Example (Copper Oxide):

• If 5.4 g of copper oxide produces 4.8 g of copper, the mass of oxygen is 0.6 g.
• Calculate the moles of each element (copper and oxygen).
• Determine the ratio of copper to oxygen atoms to find the empirical formula (Cu₂O in this example).

Calculating Masses of Reactants/Products using Balanced Chemical Equation

• Using balanced chemical equations(example Mg + O₂ → MgO).
• To calculate the mass of magnesium oxide formed when 9 g of magnesium is burned in excess oxygen, use the molar ratio approach.
• Example: Given the mass of a reactant, use stoichiometry to find the mass of the product.

Gas Volume Calculations

• To determine the volume of CO₂ formed when 30 g of carbon are burned in excess oxygen, using the balanced chemical equation and molar volume information
• Determine Moles of carbon
• Calculate CO₂ volumes at standard temperature and pressure
• Example: 30 g of carbon produced 56 L of CO₂.