consists of a single element or compound which contains no other substances
A mixture consists of two or more elements or compounds that are physically mixed together, they are not chemically combined
what is air?
a mixture
Pure substances melt and boil at specific and sharp temperatures e.g. pure water has a boiling point of 100°C and a melting point of 0°C
Mixtures have a range of melting and boiling points as they consist of different substance that tend to lower the melting point and broaden the melting point range
how can you use melting/boiling points to distinguish pure substances from mixtures?
if the substance has a range of melting/boiling points = impure
does this cooling graph show a pure or impure substance?
pure because the horizontal part of the graph shows that the compound has a sharp melting point
does this cooling graph show a pure or impure substance?
impure because there is a gradual decrease in temperature due to the range of melting points.
percentage range = (final value - original value) / original value x 100
symbol for relative atomic mass?
Ar.
what is the relative atomic mass?
the average mass of the atoms of an element measured relative to the mass of carbon-12
what is the relative molecular mass?
the average mass of the atoms of one molecule or compound measured relative to the mass of one atom of carbon-12
symbol for relative formula mass?
Mr and it refers to the total mass of the molecule
Empirical formula is the simplest whole number ratio of atoms of each element in a molecule
The molecular formula tells you the actual number of atoms of each element in a molecule
how to find percentage composition?
% mass of an element = (Ar x no. of atoms of the element) / Mr of the compound x 100
An alloy is a mixture of metals
Alloys are also an example of a formulation
A formulation is a mixture that has been designed as a useful product
Most metals are too soft to use on their own and are mixed with other elements to make them stronger and harder
Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms
This makes it more difficult for the layers to slide over each other, so they are usually much harder than the pure metal
filtration
Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g. sand from a mixture of sand and water)
fill in the gaps!
A) filter funnel
B) filter paper
C) liquid only (filtrate)
D) insoluble solid and liquid
Crystallisation
Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold
fill in the blanks
A) crystallised solute
B) the solute will slowly crystallise
Simple Distillation
This is used to separate a liquid and soluble solid from a solution (e.g., water from a solution of salt water) or a pure liquid from a mixture of liquids
fill in the blanks!
A) pure water vapour
B) salty water
C) pure water
D) vapur condenses in condenser
E) 100 degrees
Fractional Distillation
This is used to separate two or more liquids that are miscible with one another (e.g., ethanol and water from a mixture of the two)
chromatography is used to separate substances and provide information to help identify them.
the components of chromatography have different what?
solubilities in a given solvent
why is a pencil used in chromatography?
the ink from a pen would run into the chromatogram along with the sample
if a substance has a higher solubility what will it do?
travel further than others
what are the 2 phases in all types of chromatography?
mobile and stationary
what is the mobile phase in paper chromatography?
the solvent in which the sample molecules move - the liquid
what is the stationary phase in paper chromatography?
chromatography paper
what is the stationary phase in thin-layer chromatography?
a thin layer of an intert substance (like silica) supported on a flat unreactive surface
what is the mobile phase in thin layer chromatography?
the solvent, the liquid
how to calculate the retention factor?
distance moved by compound / distance moved by solvent
when is gas chromatography used?
to seperate a mixture of gases
what is the mobile phase in gas chromatography?
unreactive carrier gas (such as nitrogen)
what is the stationary phase in gas chromatography?