Quantitative Chemistry

• Percentage mass of an element in a compound

  Ar x number of atoms of that element / Mr of the compound x 100
• Avogadro's number


  6.02 x 10^23
• What is a mole?


  amount of substance that contains an avogadro number of particles
• Number of moles (equation)

  Mass in g of an element or compound/Mr of the element or compound
• Mass conservation in chemical reactions

  During a chemical reaction, no atoms are made or destroyed, so the mass of the products is the same as the mass of the reactants
• What do the big numbers in front of the chemical formulas of the reactants and products tell you?

  How many moles of each substance takes part or is formed during the reaction
• Balancing equations using reacting masses

  1) Divide the mass of each substance by its RFM to find the number of moles

  2) Divide the number of moles of each substance by the smallest number of moles

  3) If a number isn't whole multiply all of them by the same amount so it is a whole number

  4) Write the balances symbol equations by placing these numbers in front of it
• limiting reactant


  the substance that controls the quantity of product that can form in a chemical reaction
• Amount of product formed is..

  directly proportional to the amount of limiting reactant
• Calculating mass of product

  1) Write our balanced equation

  2) Work out RFM of the reactant and product you want

  3) Divide The mass by RFM to find the moles

  4) Use the balances equation to work our how many moles there'll be of the other substance.

  5) Use the number of moles to calculate the mass (moles x rfm)
• One mole of gas

  Occupies a volume of 24dm3 at room temperature and pressure
• Rule of gas occupation

  At the same temp and pressure, equal numbers of moles of any gas will occupy the same volume
• Volume of gas (equation)

  Volume of gas(dm^3) = mass of gas(g)/Mr of gas x 24
• Concentration


  Amount of a substance in a certain volume of solution
• Concentration equation involving mass and volume

  concentration(g/dm^3) = mass of solute(g)/volume(dm^3)
• Concentration equation involving number of moles and volume


  Concentration(mol/dm^3)=number of moles of solute(mol)/volume of solvent(dm^3)
• What are titrations.


  Experiments that let you find the volumes needed for two solutions to react together completely.
• converting mol/dm3 to g/dm3


  Mass = moles x Mr
• Atoms economy


  Tells you how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as useful products
• Atom economy equation


  relative formula mass of desired products / relative formula mass of all reactants x 100
• The higher the atom economy...

  the greener the process
• Why is atom economy better for profits and the environment?

  As they only produce one product so no waste products are made making it cheaper also lots of waste products are unsustainable making low atom economy bad for the environment
• Percentage yield equation


  (mass of product actually made / maximum theoretical mass of product) x 100
• 100 percent yield means...

  That you have obtained all the product you expected
• Why is yield never 100%?

  1) not all reactants react to make a product

  2) there might be side reactions

  3) lose some product when you spectate it from the reaction mixture