Quantitative Chemistry

• Ar = relative atomic mass = mass number - An average mass number of each isotope for an element, taking into account their abundances
• Mr = Relative molecular mass - When you add together the relative atomic mass values for all the atoms in a compound e.g. Ar of C = 12 and Ar of O = 16 so the Mr of CO = 12 + 16 = 28
• Conservation of mass - In a chemical reaction mass is neither created or destroyed. The total mass of products = total mass of reactants
• 1 mol = 6.02 x 10^23 - Avogadro's constant
• Mole formular

  A) Mass

  B) moles

  C) Mr

  
• Calculating mass using moles = 1) Balance the equation (2) Calculate the moles using = Mass / Mr (3) Find the molar ratio (4) Rearrange formular to find mass = Mr x moles
• Percentage yield = Mass of actual yield / mass or theoretical yield x 100
• Percentage yield is always between 0-100%. 0% means no reactants have been converted to product and 100% the product you expected to get.
• Percentage yield in industry - Companies want higher percentage yield to reduce waste + cost. Yield will not always be 100% as processes e.g. filtration, evaporation, transferring liquids, heating and impurities will affect the yield. These things can be minimised but it near impossible to get rid of them completely.
• Atom economy - A measure of the amount of mass wasted when manufacturing a chemical and how much ends up as desired product. = Relative formular mass of desired product / relative formular mass of all products x 100
• Atom economy in industry - Low atom economy reactions use up products quickly and make lots of waste making them unsustainable. This is not profitable as often raw materials needed for the reactions are expensive and waste needs to be disposed of responsibly which can also be costly. Sometimes companies can sell their waste products making them become useful 'by-products'. More products means there is likely to be a lower atom economy. Companies need to think about yield, rate of reaction, equilibrium, storage and raw material expense when choosing a reaction to make a certain product.
• Limiting reactants - The substance is totally consumed when the reaction is complete. The reactant that isn't used up is in 'excess'
• Limiting factors - e.g. Mg + Cl2 --> MgCl2. You start with 0.5 mols of Mg + 1 mol of Cl2 then you end with 0 mols of Mg (the limiting reactant) + 0.5 mols of Cl2 creating 0.5 mols of MgCl2. The number of mols you have of the limiting reactant = Moles of product you can make
• Concentration - Mass of a solute in a give volume of solution= Mass of solute (g) / Volume of solvent (dm^3) = Concentration (g/dm3)
• Concentration - Number of mols of a solute in a given volume of solution = Number of mols of solute (mol) / Volume of solvent (dm^3) = Concentration (mol/dm^3)
• Volume conversions - cm^3 --> dm^3 = ÷ 1000
• Concentration conversions - mol/dm^3 --> g/dm^3 = concentration in mol/dm^3 x relative formular mass
• Concentration example