introduction to the particulate nature of matter

solubility rules

• all nitrates are soluble

• all chlorides are soluble (except for silver and lead)

• all sulphates are soluble (except for barium and lead)

• all salts of sodium, potassium and lithium are soluble

which of the following statements is correct?

solid → liquid → gas trends

inter-particle forces are strong → inter-particle forces are weaker → inter-particle forces negligible

particles closely packed → particles more spaced → particles spread out

(increasing kinetic energy and temperature →)

temperature

a measure of the average kinetic energy of particles

absolute temperature

measured in kelvin and directly proportional to the average kinetic energy of the particles

atom

the smallest particle of an element to show the characteristic properties of that element

element

a pure substance that contains only one type of atom

compound

a pure substance that contains two or more different types of atom chemically combined in a fixed ratio

• compounds have different properties from their compound elements

mixture

a mixture is composed of 2 or more substances (elements+/compounds) that are not chemically bonded together and so retain their individual properties

homogenous mixture

has the same (uniform) composition and properties and consists of only one phase e.g. sea water and alloys

heterogenous mixture

does not have one uniform composition, so it’s properties are not the same throughout. it is usually possible to see the separate components e.g. salad dressing

examples of homogenous vs heterogenous mixtures

• sand and water - heterogenous

• smoke - heterogenous

• sugar and water - homogenous

• salt and iron filings - heterogenous

• ethanol and water in wine - heterogenous

• steel - homogenous

pure substances

have sharp and specific melting points

impure substances

impurities lower the melting point/raise the boiling point and cause a substance to melt over a temperature range e.g. salt on icy roads

absolute zero

(-273.15) is the temperature at which the movement of particles will stop

0K=-273.15°C

0°C=273.15K

types of vaporisation

boiling - particles leave through the entire body of liquid during boiling. liquids boil at a specific temperature at a certain pressure

evaporation - only takes place at the surface and at temperatures below the boiling point

first two stages in a pure substance being heated graph

• as the solid is heated, the vibrational energy of its particles increases and so the temperature increases

• at its melting point, the vibrations are sufficiently energetic for the molecules to move away from their fixed positions and form a liquid. energy added during this stage is used to break some of the inter-particle forces, not to raise the kinetic energy, so the temperature remains constant

Filtration

separates an insoluble solid from a liquid based on particle size: the solid (residue) is trapped by filter paper while the liquid (filtrate) passes through.

evaporation

separates a dissolved solid from a solution based on boiling point. the solvent is driven off by heating, leaving the solute behind.

crystallisation

separates a dissolved solid from a solution. based on temperature-dependent solubility: a hot solution is cooled slowly; as solubility decreases, the solute crystallises out. recrystallisation purifies an impure solid by dissolving in minimum hot solvent, filtering while hot, then cooling to form pure crystals.

simple distillation

separates a solvent from a solution. based on boiling pint:the solution is heated; the solvent evaporate and passes through a condenser, where it cools and is collected.

separating funnel

separates immiscible liquids with different boiling pints. based on density: the denser liquid settles to the bottom and is drained through the tap, leaving the less dense liquid behind.

fractional distillation

separates miscible liquids with different boiling points. based on small differences in boiling point: a fractionating column provides multiple condensation-evaporation cycles, improving separation.

solvent extraction

separates mixtures of solids. based on different solubilities in the same solvent: one compound dissolves while the other remains undissolved and is removed by filtration

paper chromatography

separates dissolved substances in a mixture. based on different affinities for the stationary phase (paper) an the mobile phase (solvent). the solvent rises by capillary action, carrying components at different rates.

describe a method to obtain pure crystals of copper(II) sulfate from a solution of copper sulfate and water

• place the solution into an evaporating basin over heat

• heat until crystals appear when a drop of solution is placed on a cold tile

• leave to cool for crystals to form slowly

which elements can be separated from each other by physical methods?