Quantitative Analysis

5.8C (HT only) Calculate the concentration of solutions in mol dm^-3 and convert concentration in g dm^-3 into mol dm^-3 and vice versa
  • Concentration of a solution can be measured in mol. per given volume of solution e.g. mol. per dm^3 (mol./dm^3)
  • If the volumes of two solutions that react completely are known and the concentration of one solution is known, the concentration of the other solution can be calculated
  • Mass of a solute and the volume of a solution are related to the conc. of the solution (see below)
    • Use mass to find mol.: mol. = mass / molar mass, then use conc. = mol. / vol. as seen below

  • g dm^-3 -> mol dm^-3 divide by molar mass in grams and to go the other way you just multiply by molar mass in grams
  • NB: sometimes you have to convert volumes from cm^3 to dm^3, you can do this by dividing by 1,000
5.9C Core Practical: Carry out an accurate acid-alkali titration, using burette, pipette and a suitable indicator 
5.10C Carry out simple calculations using the results of titrations to calculate an unknown concentration of a solution or an unknown volume of solution required

*see 5.8C and use that formula

5.11C Calculate the percentage yield of a reaction from the actual yield and the theoretical yield

Percentage yield =       Amount of product produced                               x 100

                                     Maximum amount of product possible

  • It is not always possible to obtain the calculated amount of a product for 3 reasons…
    • Reaction may not go to completion because it is reversible
    • Some of the product may be lost when it is separated from the reaction mixture
    • Some of the reactants may react in ways different to the expected reaction
  • Amount of product obtained is known as yield
  • (HT only) be prepared to calculate the theoretical mass of a product from a given mass of reactant and the balancing equation for the reaction
    • Calculate mol. of reactant by using mol. = mass / molar mass
    • Use balancing numbers to find mol. of product e.g. 2HCl + Mg -> MgCl2 if you have mol. of HCl, you would divide by 2 to get mol. of MgCl2.
    • Calculate theoretical mass of a product by then using mass = mol. x molar mass
5.12C Describe that the actual yield of a reaction is usually less than the theoretical yield and that the causes of this include: incomplete reactions, practical losses during the experiment, and competing, unwanted reactions (side reactions)

*see 5.11C

5.13C Recall the atom economy of a reaction forming a desired product
  • Measure of the amount of starting materials that end up as useful products
  • Important for sustainable development and for economic reasons to use reactions with high atom economy

= (Mr of desired product from reaction / sum of Mr of all reactants) x 100

  • (HT only) be prepared to give reasons why a particular reaction pathway is chosen, in reference to information given in the question regarding atom economy, yield, rate, equilibrium position and usefulness of by-products
5.14C Calculate the atom economy of a reaction forming a desired product

*see 5.13C

5.15C (HT only) Explain why a particular reaction pathway is chosen to produce a specified product, given appropriate data such as atom economy, yield, rate, equilibrium position and usefulness of by-products
  • look for a high atom economy, high yield, fast rate, equilibrium position to the right and useful by-products – be prepared to look for these within given information for the question and present them as an answer
5.16C (HT only) Describe the molar volume, of any gas at room temperature and pressure, as the volume occupied by one mole of molecules of any gas at room temperature and pressure (The molar volume will be provided as 24 dm3 or 24000 cm3 in calculations where it required)
  • Equal amounts in mol. of gases occupy the same volume under the same conditions of temperature and pressure (e.g. RTP)
  • Volume of 1 mol. of any gas at RTP (room temperature and pressure: 20 degrees C and 1 atmosphere pressure) is 24 dm^3
  • This sets up the equation:

Volume of gas at RTP = Mol. x 24

  • Use this equation to calculate the volumes of gaseous reactants and products at RTP
5.17C (HT only) Use the molar volume and balanced equations in calculations involving the masses of solids and volumes of gases

*see 5.16C

5.18C Use Avogadro’s law to calculate volumes of gases involved in a gaseous reaction, given the relevant equation

*see 5.16C