Separating Mixtures Flashcards
how do you identify a pure substance
by measuring its melting/boiling point because a pure substance has a specific, sharp melting/boiling point
what happens to the melting point of a solid if an impurity is present
the melting point is lowered
what happens to the boiling point of a liquid if a dissolved impurity is present
it increases the boiling point
what are the differences between a pure substance and a mixture
a pure substance is made up of a single element or compound but a mixture has two or more substances
a pure substances’ compound cannot be changed, but a mixtures can
a pure substance has a specific, sharp melting/boiling point but a mixture melts/boils over a range of temperatures
a compound cannot be separated into its elements using physical processes
why are flat sections seen on a cooling curve when a gas is condensing to liquid or a liquid is freezing to a solid
energy is given out when bonds are formed between the particles which prevents the continuation of cooling
what is a solution
a mixture of a solid substance dissolved in a liquid
what is a solvent
a liquid in which a substance dissolves in to form a solutin
what is a solute
a solid that dissolves in the solvent
what solvents are used to dissolves substances that are insoluble in water
white spirit, ethanol and propanone
what does magnetism do
separates magnetic materials from non-magnetic materials
what does crystallisation do
it separates a soluble solid from its solution
what does filtration do
it separates an insoluble solid from a liquid
what does simple distillation do
separates the solvent from its solution
what does fractional distillation do
separates liquids with different boiling points
what does chromatography do
it separates a mixture of different colours
explain the process of filtration
a filter funnel is lined with filter paper
the mixture is poured through the filter paper
the filter paper only allows liquids to pass through
the insoluble solid is left in the filter paper and the liquid is collected in the beaker below
what is the solid which remains in the filter paper
residue
what is the liquid that passes through the filter paper
filtrate
what are the hazards in filtration
you could slip and fall if some water was spilt on the floor
how do you avoid slipping on water split on the floor during filtration
mop up spillages immediately to reduce the risk of slipping
explain the process of crystallisation
heat the solution slowly using a gentle blue flame until most of the water evaporates
leave the solution in a warm place to cool and crystallise
the remaining solvent will evaporate slowly and crystals will form
dry the crystals between filter papers
how do you get large crystals in crystallisation
heat the solution slowly using a gentle blue flame
do not evaporate all of the water
leave the solution to cool at room temperature so crystals form
what are the hazards in crystallisation
if the solution is heated until too dry, the hot liquid/crystals could spit out from the evaporating basin causing burns
the apparatus will get too hot and could cause a burn if touched
how to avoid hot crystals spitting out in crystallisation
use a gentle blue flame and stop heating before the solution is dry.
Wear safety glasses
how to avoid being burned by hot apparatus in crystallisation
use a pair of tongs to hold hot apparatus
wear heat resistant gloves
how do you make a solute dissolve more quickly in a solvent
grind up the solid / crush the solid with a pestle and mortar
dissolve the solid in a warm solvent
stir the mixture with a glass rod
why are anti bumping granules added to the mixture in distillation
they are added to the flask so that the liquid boils smoothly
why does the solute not evaporate
the boiling point is very high
explain the process of distillation
the salt solution is heated in a round bottom flask
water boils and evaporates to form water vapour
the hot vapour rises from the flask and enters the condenser
as it passes through the condenser, the vapour is cooled and condensed. It changes from a gas to a liquid and the liquid drips into a beaker
why should the cold water enter the condenser from the bottom and leave from the top
this keeps the condenser full of water
why is the flaks heated gently during distillation
to stop the solution boiling over into the condenser
how do you avoid hazards from using a bunsen burner flame in distillation
avoid naked flames as ethanol is flammable
use an electric heater to heat the flask
tie long hair and tuck in tie to avoid it catching fire
how to avoid hazards from the liquid boiling too rapidly in distillation
add some anti-bumping granules to the flask
using an electric heater
what is fractional distillation used for in industry
to separate the different fractions in crude oil
to separate the gases in liquid air
explain the process of fractional distillation
a fractionating column containing glass beads is put on top of the flask. The fractionating column is hottest at the bottom and coldest at the top.
the mixture is heated, so the vapour rises
the liquids will have different boiling points so will evaporate at different temperatures
ethanol will leave the column first as it has a lower boiling point and water will leave second as it has a higher boiling point
what is paper chromatography used for
to separate a mixture of different colours
distinguish between pure and impure substances
identify substances by calculating their rF values
what is the stationary phase
the chromatography paper
what is the mobile phase
the solvent e.g. water, ethanol etc….
explain the process of chromatography
Draw a pencil line near the bottom of the chromatography paper
place small spots of the ink on the pencil line and allow them to dry
label the inks with a pencil
place the paper in a beaker of water so that the water level is below the pencil line
remove the paper when the water is near the top of the paper, and use a pencil to draw a line where he water has reached
dry the paper and examine the chromatogram
how do you know if a substance is insoluble from a chromatogram
it did not move from its original position
why should the base line not be draw in ink and only pencil
because the ink will move up the paper and confuse the results whereas pencil does not dissolve in the solvent
what do you use if the substance is insoluble in water for chromatogrpahy
ethanol or propanone
Rf =
distance travelled by the substance / distance travelled from the solvent
what variables should be kept the same in chromatography
the same type of paper, the same solvent and the same temperature
what are the hazards in chromatography
there could be a fire when organic solvents like ethanol are used
you could slip and fall if some water was spilt on the floor
how to avoid fires when using organic solvents in chromatography
avoid naked flames
place a lid on the beaker/container to prevent the solvent from evaporating
how to identify colourless substances in a mixture
Draw a pencil line near the bottom of the chromatography paper
place small spots of the ink on the pencil line and allow them to dry
label the inks with a pencil
place the paper in a beaker of water so that the water level is below the pencil line
remove the paper when the water is near the top of the water, and use a pencil to draw a line where he water has reached
dry the paper
spray the paper with a locating agent such as ninhydrin and warm the paper in an oven for 10mins
the amino acids will appear as purple spots
make a pencil dot at the top of each spot
measure the distance from the base line to each amino acid
measure the distance from the base line to the solvent front
calculate the Rf value for each amino acid
identify the amino acids by comparing Rf values obtained with Rf values of known amino acids
what are the industrial uses of water
manufacture of ethanol
manufacture of sulfuric acid
manufacture of hydrogen/ammonia
in power stations
why is distillation not suitable for producing drinking water
it uses large amounts of energy so is not suitable
where do we get water in our homes from
rivers, lakes, aquifers or ground water
how do you know if water is safe for drinking
it should contain no microbes and only low levels of dissolved substances
what are the main stages in treating water to remove impurities make it safe to drink
screening
sedimentation
filtration
chlorination
what is screening
the water from the river is pumped in and a sieve traps and removes any large objects such as leaves or twigs
what is sedimentation
a coagulant is added to the water which makes small insoluble particles stick togehter
what is filtration
the water is passed through a bed of sand and gravel to filter out insoluble solids. The sand and gravel traps the insoluble solids and the water drains through
what is chlorination
small amounts of chlorine added to kill bacteria
why may water that looks colourless and clean not be safe to drink
the water may contain microbes and some dissolved substances
what water is used in chemical analysis
distilled water
why is tap water not used in chemical analysis
it contains small amounts of dissolved salts for example nitrates
what could happen if tap water was used in chemical analysis
the dissolved salts may react to form precipitates which will lead to incorrect conclusions and the salts will be detected by the machines leading to incorrect results
