Calculations 3.1

• What is the formula to calculate moles?

  Moles = Mass/RFM
• How many moles are in 400g of MgO?

  10 mol
• What is the RFM of MgO?

  40
• How do you calculate the mass of 3 moles of MgSO₄?

  Mass = 360g
• What is the RFM of MgSO₄?

  120
• How do you calculate the RFM if 10 moles of a substance has a mass of 585kg?

  RFM = 58.5
• What is the formula for percentage yield?

  Percentage Yield = (Actual Yield/Theoretical Yield) x 100
• If a chemist expects to produce 9.5 grams of ammonium sulfate but only obtains 6.7 grams, what is the percentage yield?

  Percentage yield = 70.53%

  
• What is the formula to calculate concentration?

  Moles = Concentration x Volume
• How many cm³ are in 1 dm³?

  1000 cm³
• What is the concentration of a solution of sodium hydroxide when 80 g is dissolved in 500 cm³ of water?

  4 mol dm³
• What is the RFM of NaOH?

  40
• How do you convert 500 cm³ into dm³?

  0.5 dm³
• What is the first step in deducing a chemical formula from a compound?

  Break compound apart into elements/ions present
• What is the chemical formula for Copper Sulfate?

  CuSO4

  
• What should you save for last when balancing equations?

  Hydrogen and oxygen
• What is the molar ratio of O₂ to CO₂ in the combustion of propane?

  1. 3
• If you start with 4 moles of N₂, how many moles of H₂ are needed to react completely?

  12 moles of H₂
• What are the steps to balance a chemical equation?

  1. Write down the given equation.
  2. Count the number of atoms per element on both sides.
  3. Start with single elements.
  4. Use coefficients to balance each element.
  5. Save hydrogen and oxygen for last.

  
• How do you calculate the concentration of a solution?

  1. Find moles of solute.
  2. Convert volume to dm³.
  3. Use the formula: Concentration = Moles/Volume.
• What is the process for deducing a chemical formula from a compound?

  1. Break compound into elements/ions.
  2. Deduce valencies and simplify.
  3. Cross valencies to find the formula.
• What is the significance of molar ratios in chemical reactions?

  • They indicate the proportions of reactants and products.
  • Essential for stoichiometric calculations.
  • Help predict the amounts needed for reactions.