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Chem calculations
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Cards (9)
Calculate %
mass
of an
element
in a
compound
(Ar x number of
atoms
of that element /
Mr
of compound ) x 100
number of
moles
in a given
mass
mass in g /
Mr
Conservation of mass
No
atom
are destroyed or created. There are the same number and types of atoms on each side of a reaction equationl
if
mass
seems to change, usually a
gas
is involved
Gases and solutions
volume of gas
= ( mass of gas /
Mr of gas
) x 24
Concentration
= number of
moles of solute
/ volume of solvent
Atom economy
= (
relative formula mass
of
desired products
/ relative formula mass of all
reactants
) x 100
percentage yield
( mass of product actually made/ maximum thereorical mass of product) x 100
yield
is always less than 100%
not all
reactants
react to make a
product
there could be side reactions
Titrations
allow you to find
acid
amount needed to neutralise a quantity of
alkali
, vice versa.
use
pipette
, add set volume of alkali to a conical flask. Add 2-3 drops of
indicator
.
use funnel to fill a
burette
with some acid of known
concentration
.Record initial volume of acid in burette
use burette, add acid to alkali a bit at a time. swirl the flask
the indicator changes colour when alkali has been neutralised(
phenolphthalein
is pink = alkali and colourless acidic)
record final
vol
of acid in burette with initial reading and find vol of acid used to neutralise alkali