C2: How Much?

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• Created by: foxes
• Created on: 14-03-16 18:36
• 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.