c3 - elements compounds and mixtures

what is relative atomic mass

the mass of an atom compared to the mass of 1/12 of a carbon-12 atom

what is an empirical formula

the simplest whole-number ratio the atoms of each element in a compound

what is a pure substance

a substance that consists of only one element or compound

what is an alloy

a mixture of a metal with one or more other elements

how do the melting points of a pure and impure substance differ

the melting point of a pure substance is a single temperature

if the substance is impure the melting point is less than that of the pure substance AND it often melts over a range of temperatures

the greater the range of melting points, the less pure a substance is likely to be

how do you determine a melting point without losing accuracy

heat a substance and measure the temperature when it melts

heat the substance slowly so the whole sample’s temperature increases at the same time

stir the substance as it melts to ensure the entire sample is at the same temperature

what is a:

solution

solute

solvent

solution - the product formed when a substance dissolves in another

solute - the substance that dissolves

solvent - the liquid the substance dissolves in

what does dissolve mean

when the solute particles separate and are completely mixed with the particles of the solvent

what is filtration

a method used to separate an insoluble solid from a liquid

what is the residue and the filtrate

residue - the insoluble solid that is filtered out

filtrate - the liquid that passes through the filter

draw a diagram of filtration

how does crystallisation work

if you heat a solution slowly the solvent evaporates and the solute forms crystals

what is a saturated solution

a solution where no more solute can be dissolved at that temperature

describe a crystallisation practical (4)

1. evaporate the solvent till its a saturated solution

2. slowly heat it till crystals form

3. pat the crystals dry and put them in a warm oven to evaporate any remaining solvent

draw a diagram of a fractional distillation experiment

why is a fractionating column used

as it has a larger surface area so the vapours can continually condense easier

how do you calculate rf value

rf = distance travelled by substance / distance travelled by solvent

what are the two phases in gas, paper, and thin layer chromatography

stationary - silica / alumina powder in the metal column, silica / alumina powder spread on a glass / plastic plate, absorbent paper

mobile - unreactive carrier gas, solvent in liquid state

what does gas chromatography do

separates the components of a mixture and measures their amounts

how do gas chromatography (4)

1. the sampel turn into the gas state when it’s injected into the column

2. the carrier gas pushes the sample through the column

3.different components take different times to travel through the column depending on how strongly the bond to the stationary phase

4.a detector sends a signal to a computer that makes a chromatogram as each component leaves the column

what are 3 advantages to thin-layer chromatography

it is quicker

it is more sensitive so a smaller sample can be used

there is a larger range of stationary phases and solvents to choose from

how do you separate insoluble and soluble substances

dissolve then filter

how do you separate a solute dissolved in a solvent

crystallise to get the solute then simple distillation to get the solvent

how do you separate two or more substances in the liquid state

fractional distillation

how do you seperate coloured soluble substances

paper or thin-layer chromatography

how do metal and non-metal physical properties compare (6)

metal non-metal

shiny dull

malleable brittle

high melting point low melting point

solid at room temp solid / gas at room temp

ductile non-ductile

conductors insulators

what is the difference between metal and non-metal oxides

metal oxides dissolve in water to form alkaline solutions while non-metal oxides form acidic solutions

what are the chemical properties of metals and non-metals

metals lose electrons to form positive ions while non-metals gain electrons to form negative ions

metals don’t react with each other but non-metals react and produce compounds

how is the periodic table arranged

in order of increasing atomic number

rows are called periods and columns are called groups

what are ions

a charged particle formed when an atom loses or gains electrons

how do ionic compounds form

when a metal and non-metal bond and electrons are transferred from the metal to the non-metal

what is a giant ionic lattice

a structure where oppositely charged ions are held in place with ionic bonds in the solid state

what is a covalent bond

a bond formed when two non-metals share electrons to achieve a full outer shell

what are simple molecules

a molecule that only contains a few atoms