S1 - Particles and Mixtures Flashcards
what are the three states of matter?
-solid: strong forces of attraction between particles, keep a definite shape and volume, vibrate about their positions
-liquids: weak forces of attraction between particles, free to move, random arrangement, definite volume but don’t keep a definite shape
-gases: very weak forces of attraction between particles, free to move + are far apart, don’t keep a definite shape or volume, constantly moving in random motion but not direction (travel in straight lines)
inter conversions between the states of matter:
Gas -> Liquid: condensation
Liquid -> Solid: freezing (gas to solid = deposition)
Solid -> Liquid: melting
Liquid -> Gas: evaporation (solid to gas = sublimation)
-deposition: particles lose kinetic energy, move less and become more regularly arranged and close together
-sublimation: particles gain more energy, move around more and randomly arranged and further apart
experiments involving the dilution of coloured solutions and diffusion in gases:
diffusion:
-movement of particles from an area of high concentration to an area of low concentration
-for this to work, particles must be able to move, therefore, diffusion does not occur in solids, since the particles cannot move from place to place (only vibrate)
-therefore, coloured solutions are diluted by adding water, because the particles of the colour diffuse to the air of low concentration, mixing with the water molecules, causing dilution to occur
solvent, solute, solution and saturated solutions:
-solvent: liquid in which a solute dissolves
-solute: substance that dissolves in a liquid to form a solution
-solution: mixture formed when a solute has dissolved in a solvent
-saturated solution: solution in which no more solvent can be dissolved
element, compound and mixture:
-element: substance made from only one type of atom
-compound: substance made of two or more elements that have reacted chemically with each other
-a mixture: consists of 2 or more elements or compounds not chemically combined together
pure substances:
pure substance: a single element or compound, not mixed with any other substance
-melt and boil at specific temperatures: this melting and boiling points data can be used to distinguish pure substances from mixture (which melt over a range of temperature due to them consisting of 2 or more elements or compounds)
experimental techniques: simple distillation
-used to separate a pure liquid from a mixture of liquids
-works when the liquids have different boiling points
-commonly used to separate ethanol from water
-(as an eg: ethanol) ethanol has a lower b.p than water so it evaporates first, the ethanol vapour is then cooled and condensed inside the condenser to form a pure liquid
-sequence of events in distillation is as follows: heating -> evaporating -> cooling -> condensing
experimental techniques: fractional distillation
-the oil is heated in the fractionating column and the oil evaporates and condenses at a number of different temperatures
-the many hydrocarbons in crude oil can be separated into fractions each of which contains molecules with a similar number of carbon atoms
-the fractionating column works continuously, heated crude oil is piped in at the bottom. The vaporised oil rises up the column and the various fractions are constantly tapped off at the different levels where they condense
-the fractions can be processed to produce fuels and feedstock for the petrochemical industry
experimental techniques: filtration
-if you have produced e.g. a precipitate (which is an insoluble salt), you would want to separate the salt/precipitate from the salt solution
-you would do this by filtering the solution, leaving behind the precipitate
experimental techniques: cristallisation
-if you were to have produced a soluble salt and you wanted to separate this salt from the solution that it was dissolved in
-you would first warm the solution in an open container, allowing the solvent to evaporate, leaving a saturated solution
-allow this solution to cool
-the sold will come out of the solution and crystal will start to grow, these can be collected and allowed to dry
experimental techniques: paper chromatography
paper chromatography:
-analytical technique separating compounds by their relative speeds in a solvent as it spreads through paper
-the more soluble a substance is, the further up the paper it travels
how does a chromatogram provide information for the composition of a mixture?
-paper chromatography separates mixtures into individual components, so reveals the number of components in mixture and these components can be identified using Rf values
-compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents
how to calculate Rf values to identify components of a mixture:
-Rf value: distance moves by substance/distance moved by solvent
practical: paper chromatography
1) draw line (with a pencil- pencil marks are insoluble) near the bottom of a sheet of filter paper
2) add spots of different inks to the line at regular intervals
3) losely roll the sheet up and put is in a beaker of a solvent e.g: water
4) the solvent used depends on what is being tested
5) make sure the level of solvent is below the baseline- you don’t want the inks to dissolve into the solvent
6) place a lid on top of the container to stop the solvent from evaporating
7) the solvent seeps up the paper, carrying the inks with it
8) each die will move up the paper at a different rate hence spots in different places
9) when the solvent has nearly reached the top of the paper, take it out of the beaker and leave it to dry
10) the end results of the pattern of spots is the chromatogram
atom and molecule:
-all substances are made of atoms
-a substance with only one sort of atom = element -> an atom is the smallest piece of an element that can exist
-a molecule = formed when atoms join together by chemical bonds
