C8 Chemical analysis Flashcards
define pure scientifically
consists of only 1 element or compound
define alloy
a mixture of 2 or more elements (usually metals)
how many carats gold is 100% gold?
24
calculate the percentage of gold if the gild is 9 carat
37.5% gold
9/24 x 100
what makes a substance impure?
one different atom of molecule
give 3 examples of an alloy
steel, bronze, brass
what is steel made out of?
iron + carbon
what is steel bronze out of?
copper + iron
what is brass made out of?
copper + zinc
what is the main property of an impure substance?
the melting point is less then that of a pure substance
if a substance is impure, why is the melting point less than that of a pure substance?
because it often melts over a range of temperatures of the substances that its made up
how do you know the purity of a substance?
the greater the difference between tis known pure melting point, the lower the purity
what is a formulation?
a useful mixture with each substance having a precise purpose
how are formulations made?
by mixing the components in carefully measured quantities
what are 2 important stages of chromatography?
-the stationary phase
-the mobile phase
what are the 2 factors that the travel of a substance in chromatography depend upon?
-how soluble the substance is in the mobile
-the affinity to the stationary phase
if there is higher affinity in chromatography how does it affect the travel time?
the slower the substance moves in a set time
if there is more solubility in the substance for chromatography how does it affect the travel time?
it moves quicker in a set time
in the apparatus setup for chromatography why is there a lid on top?
prevents evaporation of solvent
in the apparatus setup for chromatography why is the line a pencil?
the pencil doesn’t dissolve in the solvent
in the apparatus setup for chromatography why is water used?
it dissolves colours and is absorbed through the paper
describe a method to work out a mixture of colours in the unknown sample is made up of
-use a ruler to draw a pencil line 2cm away from the edge of the paper
-put a small spot of known colourings and the unknown on the line equal distance apart
-label each spot in pencil
-pour water into the beaker but make sure the surface isnt toughing the colourings
-keep the paper vertical and ensure it doesn’t touch the beaker walls
-wait for the water to travel 3/4 up the paper
-remove the paper and wait for it to dry
-calculate the Rf values pf all the coloured spots
why do the ink spots in chromatography travel at different distances?
they have different solubilities/ affinities
how do you calculate Rf values?
distance moved by the substance / distance moved by the solvent