Definitions and Formulae (amount of substance 1) Flashcards
definition of an atom
the smallest part of an element that can exist
definition of an element
a substance made of only one type of atom
definition of an ion
an an atom which has lost or gained electrons
definition of a molecule
a substance which contains atoms joined by covalent bonds
definition of a compound
a substance containing more than one type of atom chemically combined
define Relative Atomic Mass (Ar)
the average mass of one atom compared with 1/12 of the mass of an atom of carbon-12
define Relative Molecular Mass (Mr)
the average mass of one molecule compared with 1/12 of the mass of an atom of carbon-12
what is the formula to calculate % composition
% composition = rfm of element/rfm of compound x 100
what is an anhydrous salt
without water/dry solid
what is a hydrated salt
lattice of ions with water molecules trapped within (water of crystallisation - number of water molecules)
how can you determine the moles of water in a hydrated salt
- measure the mass of the hydrated salt
- measure the mass of empty crucible
- measure mass of crucible and hydrated salt
- do the mass of (hydrated salt and crucible) - mass of crucible
- heat the crucible until it reaches a constant mass
- mass of (anhydrous salt + crucible) - mass of empty crucible
how do you calculate the mass of an individual particle
- 1 mole of any substance weighs the same as the Mr of that substance in grams
mass of one ion = Mr/avagadros constant
what is the limiting reactant
it is the reactant which is completely used up by the end of the reaction and it determines how much product is formed
how do you calculate percentage yield
% yield = actual mass of product / theoretical mass of product x 100
why is the percentage yield never 100%
- reaction is incomplete
- loss of products e.g. when transferring
- reaction is reversible
