C2: How Much?

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  • Created on: 14-03-16 18:36
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  • C2: How Much?
    • The relative mass of protons and neutrons is 1.
    • We use relative atomic masses (A'r') in calculations to compare the masses of atoms.
      • Often shown in periodic tables.
    • The yield of a chemical reaction describes how much product is made.
    • Reversible reaction: the products of the reaction can react to make the original reactants.
      • A reversible reaction can be shown using the (reversible reaction) sign 'arrow right' 'arrow left'.
        • For example: heating (thermal decomposition) ammonium chloride (reversible reaction).
          • Reversible reaction: the products of the reaction can react to make the original reactants.
            • A reversible reaction can be shown using the (reversible reaction) sign 'arrow right' 'arrow left'.
              • For example: heating (thermal decomposition) ammonium chloride (reversible reaction).
      • Chemical analysis is used to identify food additives (to ensure they are safe).
        • Paper chromatography can be used to detect and identify artificial colours.
      • Modern instrumental techniques - provide fast, accurate and sensitive ways of analysing chemical substances.
    • Atomic number of an atom - its number of protons (equals its number of electrons).
      • Na (Sodium) - 23 (mass number, top number) and 11 (atomic number, bottom number).
        • Mass number of an atom - is the total number of protons and neutrons in its nucleus.
    • Isotopes = atoms of the same element with different numbers of neutrons.
      • Some isotopes are unstable and radioactive.
    • The relative formula mass (M'r') is found by adding up the relative atomic masses of the atoms is its formula.
      • One mole of any substance is its relative formula mass in grams.
    • The percentage yield of a chemical reaction tells us how much product is made compared with the maximum amount that could be made.
      • It is important to maximise yield and minimise energy wasted to conserve the Earth's limited resources and reduce pollution.
      • Percentage yield = (amount of product collected / maximum amount of product possible) x100%
    • It is not usually  possible to get 100% yield from a chemical reaction because reactions may not go to completion, other reactions may happen or some product may be lost when separated or collected.
    • One way of separating mixtures so that the compounds can be identified is to use gas chromatography linked to a mass spectrometer.
      • The mass spectrometer can be used to find the relative molecular mass of a compound from its molecular ion peak.

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