4.3 chem spec

    Cards (31)

    • The law of conservation of mass states that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants
    • Multipliers
      In normal script before a formula and in subscript within a formula
    • Relative formula mass (Mr)

      The sum of the relative atomic masses of the atoms in the numbers shown in the formula
    • In a balanced chemical equation, the sum of the relative formula masses of the reactants in the quantities shown equals the sum of the relative formula masses of the products in the quantities shown
    • Calculating percentage by mass in a compound
      Given the relative formula mass and the relative atomic masses
    • Some reactions may appear to involve a change in mass but this can usually be explained because a reactant or product is a gas and its mass has not been taken into account
    • Explaining observed changes in mass in non-enclosed systems during a chemical reaction
      Given the balanced symbol equation for the reaction and explain these changes in terms of the particle model
    • Uncertainty in measurements
      • Represent the distribution of results and make estimations of uncertainty
      • Use the range of a set of measurements about the mean as a measure of uncertainty
    • Chemical amounts
      • Measured in moles
      • Symbol for the unit mole is mol
      • The mass of one mole of a substance in grams is numerically equal to its relative formula mass
      • One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance
      • The number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant
      • The value of the Avogadro constant is 6.02 x 10^23 per mole
    • Calculating masses of reactants and products from balanced symbol equations
      1. Interpret chemical equations in terms of moles
      2. Calculate the masses of substances shown in a balanced symbol equation
      3. Calculate the masses of reactants and products from the balanced symbol equation and the mass of a given reactant or product
    • Balancing an equation given the masses of reactants and products
      Convert the masses in grams to amounts in moles and convert the numbers of moles to simple whole number ratios
    • In a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactant is used
    • Limiting reactant
      The reactant that is completely used up, which limits the amount of products
    • Explaining the effect of a limiting quantity of a reactant on the amount of products
      In terms of amounts in moles or masses in grams
    • Concentration of a solution
      Measured in mass per given volume of solution, eg grams per dm3 (g/dm3)
    • Calculating the mass of solute in a given volume of solution of known concentration
      In terms of mass per given volume of solution
    • Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product
    • Yield
      The amount of a product obtained
    • Percentage yield
      The yield compared with the maximum theoretical amount as a percentage
    • Calculating percentage yield of a product
      From the actual yield of a reaction
    • Atom economy (atom utilisation)

      A measure of the amount of starting materials that end up as useful products
    • Calculating the atom economy of a reaction
      Using the balanced equation for the reaction
    • Explaining why a particular reaction pathway is chosen to produce a specified product
      Given appropriate data such as atom economy (if not calculated), yield, rate, equilibrium position and usefulness of by-products
    • Concentration of a solution
      Measured in mol/dm3
    • Calculating the amount in moles of solute or the mass in grams of solute in a given volume of solution

      From its concentration in mol/dm3
    • Calculating the concentration of a solution

      If the volumes of two solutions that react completely are known and the concentration of one solution is known
    • Equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure
    • Volume of one mole of any gas at room temperature and pressure (20oC and 1 atmosphere pressure)
      24 dm3
    • Calculating the volume of a gas at room temperature and pressure
      From its mass and relative formula mass
    • Calculating volumes of gaseous reactants and products

      From a balanced equation and a given volume of a gaseous reactant or product
    • Change the subject of a mathematical equation
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