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Unit Chemistry 2
RAM, RFM, Moles, % of an Element in a Compound, Atom Economy.
Candidates should use their skills, knowledge and
understanding of how science works:
Atoms can be represented as shown:
Mass number
23
Na
Atomic Number 11
The relative masses of protons, neutrons and electrons
particle Mass
Charge
Position
Proton
1
+
nucleus
Neutron
1
0
nucleus
Electron Very small
shells
The total number of protons and neutrons in an atom is
called its mass number.
Atoms of the same element can have different
numbers of neutrons; these atoms are called isotopes
of that element.
HT The relative atomic mass of an element RAM (Ar)
compares the mass of atoms of the element with the
12
C isotope. It is an average value for the isotopes of
the element.
The relative formula mass RFM (Mr) of a compound is
the sum of the relative atomic masses of the atoms in
the numbers shown in the formula.
The relative formula mass of a substance, in grams, is
known as one mole of that substance.
The percentage of an element in a compound can be
calculated from the relative mass of the element in the
formula and the relative formula mass of the
compound.
HT The masses of reactants and products can be
calculated from balanced symbol equations.
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 because:
a)the reaction may not go to completion because it is
reversible
b)some of the product may be lost when it is separated
from the reaction mixture
c)some of the reactants may react in ways different to
the expected reaction.
HT The amount of a product obtained is known as the
yield. When compared with the maximum theoretical
amount as a percentage, it is called the percentage
yield.
The atom economy (atom utilisation) is a measure of
the amount of starting materials that end up as useful
products. It is important for sustainable development
and for economical reasons to use reactions with high
atom economy.
Strengths:
Weaknesses:
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GCSE
Text Book
Revision
Guide
p.116-117
p.42
p.118-119
p.43
p.44
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p.120-121
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p.122-123
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p.45
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p.124-125
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p.45-46
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