OCR AS Chemistry (F321.1) - Atoms and Reactions Revision Notes

These revision notes are for Atoms and Reactions - the first module of F321 (Atoms, bonds and groups) from OCR AS Chemistry A.

These notes are compatible with Microsoft Word 2007 onwards.

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OCR AS Chemistry Notes


ATOMIC MASSES
RELATIVE ATOMIC MASS

Weighted average mass of an atom of an element (compared to 1/12 of the mass of an atom of carbon-12, which
is given the mass of 12)
o (This takes into account the presence of isotopes and their amounts)
n= relative…

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N = Mass
Mr OR N = Mass
Ar

EMPIRICAL + MOLECULAR FORMULA
MOLECULAR FORMULA = shows the types of atoms present and their number
o C 2H 6
EMPIRICAL FORMULA = the simplest whole number ratio of atoms
o C 2H 6 CH 2

To find empirical formula:

1.…

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o BaCl22H 2O


REACTING VOLUMES OF GASES
AVOGADRO'S LAW

Equal volumes of gases measured at same temperature and pressure contain the same number of molecules

50cm3 of O2 All have the same number of molecules

50cm3 of CO2

50cm3 of C3H8

MOLAR VOLUME

= Volume taken by 1 mole of…

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Add acid to water

ACIDS, BASES AND SALTS
ACID: a proton donor:
o H +(aq) + Cl-(aq)


o Strong acid: fully ionised / dissociated
H Cl H + + Cl-
o Weak acid: partially ionised / dissociated
C H 3COOH CH 3OO- + H +


BASE: substance which is able…

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STANDARD SOLUTION: solution of known concentration
EQUIVALENCE POINT: reached when both of them react completely and neither is in excess
STOICHIOMETRIC AMOUNT (titre): volume of one solution required to completely react with another solution
(measured using a burette)

Recording results:
o Rough titration is not used in calculation
o Must…

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