SC2: states of matter & mixtures Flashcards
the kinetic particle theory
describes the arrangement, movement & energy of particles in a substance
how do solid particles vibrate?
around a fixed point
what energy do solids have?
low
how close are the particles in a solid?
very close
what pattern do solids have?
regular
energy in liquids
liquids have greater energy than solids
how do liquids move?
slide past each other
how are liquids arranged?
randomly
how close are liquid particles?
quite close
how much energy do gases have?
highest
how do gas particles move?
quickly and randomly
how close are gas particles?
far apart
what arrangement do gases have?
random
can solids be compressed?
no, they are close together and have no space to move into
can solids flow?
no as particles have nowhere to move
do solids have a definite shape and volume?
yes
do liquids have fixed volume and shape?
fixed vol not shape
can liquids be compressed?
not easily as their particles are close
can liquids take the shape of containers?
yes as they can flow
can gases be compressed?
yes as particles are far away from each other and have lots of space to move into
do gases have a definite shape or volume?
no
can gases take the shape of a container?
yes, as particles move quickly in all directions
changes of state
transformations of matter from one state to a different one (physical change only, no more substances made)
melting
solid to liquid
evaporate
liquid to gas
freezing
liquid to solid
condense
gas to liquid
sublimation
a change directly from the solid to the gas without becoming liquid
melting, evaporation & boiling
-particles in the solid have enough energy to overcome the forces between them
-they break out of fixed arrangement and move more freely
condensing & freezing
-energy is transferred from a substance to the surroundings when a substance
-the particles lose energy and bonds form between particles
what is particle theory?
scientists understanding of solids, gases & liquids
what are some limitations of particle theory?
-it doesn’t consider the forces between molecules
-it assumes that all particles are spheres even though particles have complex shapes
predicting a physical state
-state of a substance at a given temp can be predicted if it’s melting point & boiling point are known
-if given temp is less than melting point, then it’s a solid
-if given temp between melting & boiling points then it’s a liquid
-if given temp larger than boiling point then it’s a gas
pure substance
only one element or compound
mixture
two or more substances that are not chemically combined
element
only contains one type of atom
compound
2 or more elements chemically combined
what melting point does a pure substance have?
sharp
what melting point does a mixture have?
melts over a range of temperatures
when a pure substance changes state the temperature…
stays the same
when an impure substances changes state the temperature…
changes slightly
filtration
used to separate an insoluble solid from a liquid
why does filtration work?
the filter paper has tiny holes that are big enough to let small molecules and dissolved ions through
crystallisation
-used to produce solid crystals from a solution
-when the solution is warmed, some of the solvent evaporates and leaves a concentrated solution
solution
a mixture that forms when one substance dissolves another
solute
the substance that is dissolved
solvent
the substance in which the solute dissolves
how to obtain large, regularly shaped crystals in crystallisation?
-put the solution to into an evaporating basin
-warm it by placing the basin over a bunsen burner
-stop all the heating b4 the solvent evaporates
-pour excess liquid away & dry the crystals
simple distillation
-used to separate a solvent and solute in a solution
-the dissolved solute has a higher boiling point than the solvent, so when the solution is heated, solvent vapour evaporates from the solution, gas moves and cools & condense
simple distillation steps
- the water is heated
- water vapour is produced
- water vapour cools, condenses & drops into the beaker
- the water is condensed & the salt stays behind
fractional distillation
-used to separate different liquids from a mixture of liquids
-works because different liquids have different boiling points
-vapour rises through a column which is hot at the bottom and cold at the top, the vapour condenses when it reaches a part of the column that’s below its boiling point
-liquid flows out of the column
paper chromatography
separates the mixtures of soluble substances
paper chromatography steps
- water & ethanol solution is heated (the solvent)
- as the paper is lowered into the solvent, some dye spreads up the paper
- the paper has absorbed the solvents & dye had spread further up the page
stationary phase
the phase that does not move in chromatography (eg: paper)
the mobile phase
the solvent that moves through the paper & carries different substances with it
why do different substances move at different rates in chromatography?
-the different dissolved substances in a mixture are attracted to the two phases in different proportions
-this causes them to move at different rates through the paper
what does separation by chromatography produce?
-a chromotogram
-a paper chromatogram can be used to distinguish between pure and impure substances
how many dots would a pure and impure substance have?
pure = 1
impure = 2 or more
how can you tell if substances are the same in chromatography?
they have the same amount of spots, match in colour and travel the same distance up the paper
how to calculate the rf value
distance travelled by substance / distance travelled by solvent
paper chromatography steps
- draw pencil line across paper 1-2cm from bottom
- use pipette to add small spots of ink to the pencil line on paper
- place the paper into a container with a suitable solvent in the bottom
- allow the solvent to move through the paper and remove the chromatogram before it reaches the top
- allow chromatogram to dry, then measure the distance travelled by each spot and distance
treating fresh water (steps)
-large objects removed by screening using grids
-coarse filter removes larger insoluble grit particles
-aluminium sulfate is added to clump smaller insoluble particles together, these settle in the bottom of a sedimentation tank
-a fine filter bed removes very small insoluble particles
-chlorine gas is added to kill harmful microorganisms
treating seawater
-seawater contains too much dissolved salt to be suitable for drinking
simple distillation used to treat it:
-seawater is boiled & the water vapour is lead away & cooled
-it condenses to form pure water, leaving the salt behind
facts about the distillation process
-expensive as large amounts of energy are needed to heat the seawater
-water produced by distillation is useful in the laboratory for dissolving substances (does not contain any dissolved ions that might interfere with a chemical analysis)
