principles of chemistry

describe the structure of solids

particles arranged regularily and packed closely together

vibrate in fixed positions

strong forces between particles

small amount of kinetic energy

describe the structure of liquids

particles are mostly touching with some gaps

particles move about at random

medium forces between particles

moderate amount of kinetic energy

descrive the structure of gases

particles move at random and quickly

particles are far apart

weak forces between particles

high amount of kinetic energy

collide with eachother and sides of container

what is the proper name for the conversion of solid to liquid?

melting

what is the proper name for the conversion between liquid and gas?

boiling / evaporating

what is the proper name for the conversion between liquid and solid?

freezing

Describe what happens when water vapour cools to form liquid water

particles lose kinetic energy

particles move closer together

particles move slower and less randomly

describe what happens when liquid water boils to form water vapour

particles gain kinetic energy

particles move further apart

particles move quicker and more randomly

describe what happens when liquid water cools to form ice

particles lose kinetic energy

particles move closer together

particles move slower and less randomly

describe what happens when ice melts to form liquid water

particles gain kinetic energy and vibrate more

particles move further apart as forces of attraction are overcome

particles move quicker and more randomly

how does evaporation occur?

particles in liquid have differing amounts of energy

particles with the greatest amount of kinetic energy break away from surface of liquid

average kinetic energy of remaining particles is lowered

in a closed container both evaporation and condensation occur simultaneously

define diffusion

net movement of particles from an area of high concentration to an area of low concentration

how can diffusion be demonstrated experimentally?

use cotton wool soaked in ammonia (NH3) and hydrochloric acid (HCl)

white ring forms closer to HCl end

tells you that NH3 diffuses faster

NH3 has a lower Mr, so is lighter

diffuses more quickly than HCl

Define solvent

liquid in which a solute dissolves

Define solute

a solid which dissolves in a solvent

define solution

mixture of a solute and a solvent

define a saturated solution

a solution where no more solute can dissolve in the solvent

what is an element?

a substance which contains one type of atom only

cannot be split into anything simpler by any chemical means

what is a compound?

a substance made up of two or more elements chemically combined

what is a mixture?

a substance made up of two or more elements NOT chemically combined together

what are some examples of elements?

iron, lead, sulfur, nitrogen, oxygen

what are some examples of compounds?

calcium carbonate, ammonia, carbon dioxide, water, iron sulfide

what are some examples of mixtures?

honey, air, sea water, blood, soup

what is a pure substance?

contains one type of material only

eg. one type of element or molecule

describe the melting and boiling points of pure substances

fixed

eg. boiling point of pure water is exactly 100 degrees celcius

eg. melting point of pure water is exactly 0 degrees celcius

describe the melting and boiling points of mixtures

melts over a range of temperatures

boils over a range of temperatures

what method is used to separate an insoluble solute from a solvent?

filtration

what method is used to seperate a soluble solute from a solvent?

evaporation or distillation

what method is used to seperate liquids of different boiling points?

fractional distillation

what method is used to seperate pure water from sea water

simple distillation

what method is used to seperate petrol and water and why is this used?

seperating funnel

petrol and water are immiscible (dont mix)

what is paper chromatography used to seperate?

dyes/inks ie. liquids with different solubilities

how do you carry out paper chromatography?

use a pencil line as reference line

add spots of ink/dye to pencil line

place filter paper in solvent

• make sure solvent level is below pencil line

leave until solvent nearly reaches top of paper

allow to dry

furthest dot has the greatest solubility

why should the line be drawn in pencil?

pencil does not contain ink so does not run

explain why it is important for the solvent level to be below the spots of dye

to prevent spots dissolving in the solvent

how do you calculate the Rt value?

Rt = distance travelled by component / distance travelled by solvent