Quantative Chemistry

  • Created by: KHand21
  • Created on: 27-02-17 17:15
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  • Chemistry Calculations
    • Formulae
      • Balancing a formulae: count the amount of each element on both sides and change the numbers in front, until there are the same amounts.
      • Word equations: which chemicals react together (reactants) and which chemicals are produced (products.)
      • The formulae of a compound shows how many of each type of atom join together to make the compound.
      • Empirical formulae: the formulae in it's simplest form.
        • To convert to a molecular formulae, you do the Mr divided by the total mass in the empirical formulae.
      • Symbol equation: shows the masses that will react or have been reacted.
      • State symbols:      (s) solid           (l) liquid          (g) gas         (aq) aqueous
      • Limiting reactants
        • The chemical that will run out first
          • The reactant in excess is still there at the end of the equation
            • Balance the equation and the one will the lowest number of moles is the limiting reactant.
    • Reacting masses
      • 1. Balance the equation. 2. Write the given mass. 3. Write the Mr.
        • Unknown mass = mass / Mr of known compound x Mr of unknown compound
        • If you are given the mass of the reactant and product you can use ratios to answer the question.
      • Mass is never lost or gained, it is conserved
        • However some reactants may react in an unexpected way, some products may be lost and not all reversible reactions may be completed.
    • Concentration
      • The strength of a solution or how much solute is dissolved in the solvent.
        • 1 L = 1 dm3 1ml = 1 cm3  1dm3 = 1000 cm3 or ml
      • Molar concentration = moles of solute / dm3 of solvent
      • % concentration = mass of solute / 100ml of solvent
      • g/l concentration = mass of solute / dm3 of solvent
    • Mole calculations
      • m = n / Mr      n = m x Mr      Mr = n / m
      • 1. Balance the equation. 2. Mr calculations. 3. Find out the m or n.   4. Use the co-eff to work out the n or m of the product.
    • Atom economy & percentage yield
      • % yield = (actual mass / theoretical mass) x 100
        • % is how much mass is lost.
      • Atom economy = (Mr of desired product / sum of Mr of all reactants) x 100
        • % of the product you want
      • Percentage yields can be affected by: not scraping all of the product from equipment, having impureatives in the reaction and having side reactions.


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