Calculations

• If in doubt, work out...

  Moles = mass/mr

  Mass = moles x mr
• What is the formula for percentage by mass?

  mr of what you are trying to find/mr of whole thing X100
• What is the formula for atom economy?

  mr of desired products/mr of all reactant x100
• What could the reasons be that a scientist may not achieve 100% yeild, and what formula would they use to calculate that?

  Reasons: Side reactions, incomplete reactions, impurities, some stuck on apparatus Formula: Actual yield/Theoretical yield x 100%.

  -to work out theoretical yield:

  -work out the mols for the Known Substance (what you have values for) , mole ratio it to find moles of unknown, use that value to work out mass (mol x Mr of what your looking for), substitute that value into the equation, this value is the theoretical yield.
• What is the process of calculating titrations?

  1. Calculate moles of known substance using (conc x vol = mols)
  2. put value into ratio to work out unknown substance
  3. work out conc. of unkown using (conc = amount(mol)/vol(dm^3))
  4. if asked for g/dm^3, multiply value in mol/dm^3 by Mr of products
• What is the process of calculating limiting reactants?

  1. work out moles of each substance (remeber units!)
  2. use the balanced equation to form ratio, look to simplify?
  3. place worked out values into equation and divide to compare
  4. always write a little sentence!
• What is the process of calculating maximum mass?

  1. work out the moles of known substance that you have values for
  2. ratio it to find out the moles of the unknown substance
  3. use mole ratio to find out Mr
  4. use moles x mr to find maximum mass
• What are the two formulas for concentration?

  Conc. = mass of substance(g) / volume of solution(dm^3)

  Conc. = no. of mols (mols) / volume of solution (dm^3)
• What is the percentage yeild formula?

  Percentage Yield = (Actual Yield / Theoretical Yield) x 100
• What are the formulas needed for titrations?

  conc x vol = mols

  conc = amount (mols) / vol (dm^3)
• What to do exactly with mole ratio equations?


  -calculate Mr of substance with KNOWN mass

  -calculate its moles

  -ratio it using big numbers from equation (double check that equation is properly balanced)

  -work out moles of unknown mass substance

  -calculate its mass!