topic 2 Flashcards
solids
there are strong forces of attraction between particles which hold them in fixed positions in a regular lattice fragment
- don’t move, fixed positions
- don’t have much energy
- vibrate on a spot
liquids
- some force of attraction between the particles
- free to move past each other but still touching
- not a definite shape and volume
- more energy
- constantly moving in a random shape
- hotter the liquid gets the faster it moves
gases
- no force of attraction
- travel in a straight line and only interact when they collide
- don’t keep a definite shape or volume
- always will a container, exert pressure of the walls
- more energy
- hotter the gas the faster they move
liquid to solid
freezing
solid to liquid
melting
liquid to gas
evaporating
gas to liquid
condensing
solid to gas
subliming
gas to solid
deposition
when a solid is heated…
particles gain more energy
they vibrate more
weakens forces making the solid expand
at a certain temperature the particles have enough energy to break free from their positions (melting) and the solid turns into a liquid
when a liquid is heated
- the particles get even more energy
- this energy makes the particles move faster which weakens and breaks the bond holding holding the liquid together
- at a certain temp the particles have enough energy to break their bonds. This is called evaporation and the liquid turns into a gas
chemical changes for atoms
atoms are rearranged during chemical reaction
- chemical changes are different to physical changes
- chemical changes happen during chemical reactions when bonds between atoms break and the atoms change places.
- the atoms from the substances you start off with (the reactants) are rearranged to form different substances (the products)
- chemical changes are often hard to reverse
pure substances
- a substance is pure if it’s completely made up of a single element or
compound
mixtures
if you’ve got more than one compound present or different elements that aren;t all part of a single compunds
testing for purity
you can test for purity using melting points
- every pure substances has a specific, sharp melting and boiling point
- MIXTURES will melt gradually over a range of temperatures
- PURE substances have sharp melting points
what is distillation
used to separate mixtures that contain liquids. Two types: simple and fractional
what is simple distillation
used for separating out a liquid from a solution
For example, water can be separated from salt solution by simple distillation. This method works because water has a much lower boiling point than salt. When the solution is heated, the water evaporates. It is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.
what is fractional distillation
Fractional distillation is a method for separating a liquid from a mixture of two or more liquids. For example, liquid ethanol can be separated from a mixture of ethanol and water by fractional distillation. This method works because the liquids in the mixture have different boiling points. When the mixture is heated, one liquid evaporates before the other.
what is filtration
if the product of a reaction is an insoluble solid, you can use filtration to separate it out from the liquid reaction mixture
- put some filter paper into a funnel and pour in your mixture. The liquid part of the mixture runs through the paper leaving behind a solid residue
crystallisation
separates a soluble solid from a solution
To obtain large, regularly shaped crystals:
put the solution in an evaporating basin
warm the solution by placing the evaporating basin over a boiling water bath
stop heating before all the solvent has evaporated
After the remaining solution has cooled down, pour the excess liquid away (or filter it). Dry the crystals using a warm oven or in air.
chromatography
a method used to separate a mixture of soluble substances and identify them
there are two phrases: mobile phase and
stationary phase
chromatography mobile phase
where the molecules CAN move. This is always a liquid or a gas
chromatography stationary phase
where the molecules CAN’T move. This can be a solid or a really thick liquid
mixtures in mobile and stationary phase
the components in the mixture separate out as the mobile phase moves over the stationary phase - they all end up in different places in the stationary phase
- this happens because the chemicals spend different amounts of time dissolved in the mobile phase and stick to the stationary phase.
paper chromatography
in paper chromatography the stationary phase is a piece of filter paper and the mobile phase is a solvent (e.g water or ethanol)
a pure substance produces one spot on the chromatogram
an impure substance produces two or more spots
stages in paper chromatography
the stationary phase, which in paper chromatography is very uniform, absorbent paper
the mobile phase is the solvent that moves through the paper, carrying different substances with it
molecules with higher solubility (less attracted to the paper) will spend more time in the mobile phase
method for paper chromatography
- line at the bottom of the paper
- draw spots of the line
- dip paper in breaker with solvent
- the solvent will start to move up the paper
- see spots forming at different points on the paper
calcualting Rf
distance travelled by solute/ distance travelled by solvent
ratio between the distance travelled by the dissolved substances (solute) and the distance travelled by the solvent
3 water purifying treatments
filtration
sedimentation
chlorination
filtration (water)
a wire mesh screens out large twigs and then gravel and sand beds filter out any other solid bits
sedimentation (water)
iron sulfate or aluminium sulfate is added to the water, which makes fine particles clump together and settle at the bottom
chlorination (water)
chlorine gas is bubbled through to kill harmful bacteria and other microbes
why can normal water give a false result
it has small amounts of ions (such as calcium, iron and copper) that can interfere with reactions
deionised water is used instead - ions have been removed
purifying sea water
simple distillation
- sea water is heated so that water vapour leaves it quickly
- the water is then cooled and condensed forming water without the dissolved salts
water for drinking
water from water source - sedimentation tank (small particles settle out) - filtration 9using tanks containing beds of sand and gravel) - choline is added in a process called chlorination (kills microorganisms in the treated water)
