A Level Chemistry Eduqas

This subject is broken down into 32 topics in 3 modules:

  1. Core Ideas, Principles and Concepts 15 topics
  2. Physical and Inorganic Chemistry 9 topics
  3. Organic Chemistry and Analysis 8 topics
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This page was last modified on 28 September 2024.

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Chemistry

Core Ideas, Principles and Concepts

C1: Formulae and Equations

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C1: Formulae and Equations

C1: Formulae and Equations

Empirical and Molecular Formulae

  • An empirical formula shows the simplest whole-number ratio of atoms of each element in a compound.
  • Molecular formulae indicate the actual numbers of atoms of each type of element present in a molecule.
  • To determine the molecular formula from the empirical formula, you'll need to know the relative molecular mass of the substance.

Balancing Chemical Equations

  • A balanced chemical equation respects the Law of Conservation of Mass, indicating that matter can neither be created nor destroyed.
  • Balancing a chemical equation involves ensuring that the number of each type of atom on the left (reactants) equals the number on the right (products).
  • Coefficients (numbers placed before the elements or compounds) are used to balance the equation.

State Symbols in Chemical Equations

  • In chemical equations, the state of matter (solid, liquid, gas or aqueous) of reactants and products is often indicated.
  • The state symbols are (s) for solids, (l) for liquids, (g) for gases, and (aq) for solutions in water (aqueous).

Using Moles in Calculations

  • A mole is the amount of a chemical substance that contains exactly 6.02 x 10^23 particles (Avogadro's number).
  • The molar mass (Mr) of a substance is the mass per mole of its entities (atoms, molecules, ions etc.) and it's measured in grams per mole (g/mol).
  • The mole concept can be used to calculate amounts of reactants or products in a chemical reaction, or to analyse the composition of a sample.

Stoichiometry

  • Stoichiometry involves the calculation of quantities (typically in grams or moles) in chemical reactions.
  • It's based on the balanced chemical equation and the concept of molar ratios.
  • The limiting reagent is the reactant that is completely consumed in the reaction and determines the maximum amount of product that can be formed.

Percentage Yield and Atom Economy

  • Percentage yield compares the actual yield of a reaction to the theoretical yield that could be obtained if all reactants were converted to product.
  • Atom economy is a measure of how efficiently the atoms of the reactants are converted into useful product atoms.
  • Atom economy is particularly important in green chemistry, where the goal is to minimise waste.

Course material for Chemistry, module Core Ideas, Principles and Concepts, topic C1: Formulae and Equations

Chemistry

Physical and Inorganic Chemistry

PI1: Redox Reactions

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PI1: Redox Reactions

Oxidation States

  • An oxidation state is a measure of the number of electrons that an atom uses to bond with atoms of another element.
  • Oxidation states can be used to identify whether a substance has been oxidised or reduced in a reaction.
  • The oxidation state of an atom in a single-element form is always zero.
  • The sum of oxidation states for all atoms in a compound or ion must equal the overall charge.
  • Oxidation state rules: Hydrogen has +1, oxygen has -2, fluorine has -1, group 1 metals have +1, group 2 metals have +2 and aluminium has +3.

Balancing Redox Reactions

  • Balancing a redox reaction involves adjusting the numbers of atoms and charges on each side to make them equal.
  • Write down the unbalanced equation ('skeleton equation') for the reaction.
  • Separate the reaction into half-reactions: one for oxidation and one for reduction.
  • Balance the atoms in the half-reactions. First balance all atoms except hydrogen and oxygen. Then balance oxygen by adding H2O molecules, and then balance hydrogen by adding H+ ions.
  • Equalise the charges on each side of the half-reaction by adding electrons to the side that needs them.
  • Ensure that the number of electron transfers is the same in both half-reactions.
  • Add the reactions together and simplify to write the final, balanced equation.

Redox Titrations

  • A redox titration is used to determine the concentration of an unknown solution by measuring its capacity to oxidise or reduce a known quantity of a reagent.
  • Redox indicators such as methylene blue or potassium permanganate (KMnO4) are used.
  • The end point of a redox titration is indicated by a colour change.
  • Use the balanced redox equation to calculate the molar ratio between the substances involved.
  • Use the molar ratio, along with the volume and concentration data of the known substance, to calculate the concentration of the unknown substance.

Effect of Oxidation State on Properties of Transition Metals

  • Higher oxidation states are typically less stable and more reactive, making elements in higher oxidation states strong oxidising agents.
  • The colour of transition metal compounds is related to the presence of d-d transitions, which depend on the oxidation state of the metal.
  • The catalytic activity of transition metals often depends on the ability to change oxidation state.
  • Different oxidation states can also influence the magnetism of transition metals. Transition metals in some oxidation states may be paramagnetic (attracted to magnetic fields).

Course material for Chemistry, module Physical and Inorganic Chemistry, topic PI1: Redox Reactions

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