States of Matter, Mixtures and Separation Flashcards
Pure substance in chemistry
Single element or compound, not mixed with any other substances - melts + boils at specific temperature
Pure substance in everyday language
Substance that has had nothing added to it, so it’s in its natural state e.g pure milk
Mixture
Two or more elements or compounds physically combined together, chemical properties of each substance in mixture are unchanged
Physical processes
E.g filtration, crystallisation, simple distillation, fractional distillation + chromatography can separate mixtures, don’t involve chemical reactions + no new substances made
Formulation
Mixture that has been designed as useful product, made by mixing components in carefully measured quantities to ensure that product has required properties e.g fuels, paints + foods
Chromatography
Can be used to separate mixtures + give information to help identify substances, involves stationary + mobile phase, separation depends on distribution of substances between phases
Particle model theory
Amount of energy needed to change state from solid to liquid + from liquid to gas depends on strength of forces between particles of substance, nature of particles involved depends on type of bonding + structure of substance, stronger forces between particles higher melting point + boiling point of substance
Limitations of particle model theory
No forces, all particles represented as spheres + spheres are solid
Potable water
Water that is safe to drink, should have low levels of dissolved salts + microbes, not pure water in chemical sense as it contains dissolved substances, methods used to produce potable water depend on available supplies of water + local conditions
Making water potable
Most potable water is produced by: choosing appropriate source of fresh water, passing water through filter beds, sterilising - sterilising agents used for potable water are chlorine, ozone or UV (ultraviolet) light
If supplies of fresh water are limited, desalination of salty water or sea water may be required, can be done by distillation or by processes that use membranes e.g reverse osmosis, these processes require large amounts of energy
Waste water treatment
Sewage + agricultural waste water requires removal of organic matter + harmful microbes, Industrial waste water may require removal of organic matter + harmful chemicals
Sewage treatment: screening + grit removal, sedimentation to produce sewage sludge + effluent, anaerobic digestion of sewage sludge, aerobic biological treatment of effluent
Rf value
Ratio of distance moved by compound (centre of spot from origin) to distance moved by solvent
Rf = distance moved by substance over distance moved by solvent
Different Rf values
Different compounds have different Rf values in different solvents, can be used to help identify compounds, compounds in mixture may separate into different spots depending on solvent, pure compound will produce single spot in all solvents
