C4-Chemical Changes

low pH

acidic

universal indicator

An indicator with a different colour for each pH value.

universal indicator for acid

red

universal indicator for alkali

blue purple

Universal indicator fo neutral

green

High pH

alkali / base

neutral

pH 7

what is an alkali?

A base that dissolves in water

acid ion

H+

alkali ion

OH-

Neutralisation reaction

acid + base -> salt + water

neutralisation symbol equation

H+ + OH- -> H2O

strong acids in water

Ionise completely- all acid particles dissociate to release H+ ions

weak acids in water

partially ionise - only a few particles dissociate to release H+ ions

weak acid reactions are..

reversible

creates an equilibrium between undissociated and dissociated acids

position of equilibrium lies to the left thanks to only a few acid particles releasing H+ ions

are strong acids more reactive and why

yes because the concentration of H+ ions speeds up the rate of reaction

what does pH mean

measure of the concentration of H+ ions in a solution

If the pH increases by 1, what happens to the concentration of hydrogen ions?

It increases by a factor of 10 (x10^?)

H+ ion concentration

10^x

acid strength

Proportion of acid molecules that ionise in water

what are metal oxides and metal hydroxides

bases

neutralisation reaction with carbon dioxide as a product too

acid + metal carbonate -> salt + water + carbon dioxide

RP: making soluble salts

1) Pick acid and insoluble base

2) Gently warm dilute acid with bunsen burner then stop

3) Add inspluble base to acid a bit at a time until it stops reacting (base is in excess). It has been neutralised.

4) Filter excess solid to get salt solution and heat the solution with electric heater to evaporate the water then leave it to cool.

5) Crystals of salt will form. Filter and dry.

Reactivity series

how reactive a metal is with acid or water

/

how easily they form positive ions

oxidation

gain of oxygen

loss of electrons

reduction

loss of oxygen

gain of electrons

2 ways of extracting metals from ores

reduction using carbon and displacement

electrolysis if its more reactive than carbon

OILRIG

oxidation is loss, reduction is gain

redox reaction

A chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction.

displacement reaction type

oxidation

Gain of oxygen, loss of electrons

reduction

loss of oxygen, gain of electrons

2 ways of extracting a metal from its ore

reduction using carbon displacement

electrolysis, if its more reactive than carbon

what is an ore

A rock which contains a metal that's worth extracting - there's enough of the metal in it to make it economic to extract

OILRIG

oxidation is loss, reduction is gain

redox reaction

the movement of electrons from one molecule to another (reduction and oxidation happening at the same time)

what type of reaction is displacement?

A displacement reaction is a redox reaction because a more reactive element transfers electrons to a less reactive element, causing one to be oxidized (lose electrons) and the other to be reduced (gain electrons), fulfilling the definition of a redox (reduction-oxidation) process

ionic equation

an equation that shows only those ions or atoms that change in a chemical reaction (reactants and products that change)

electrolysis

A process by which an electric current breaks chemical bonds.

electrolyte

An ionic compound whose aqueous solution conducts an electric current

the ore that is molten or dissolved in a solvent

electrode

metal solid that conducts electricity and is submerged in the electrolyte

RP- Electrolysis - Molten

electric current passed through electrolyte which will be an ionic compound

positive ions move to cathode (negative) and are reduced (gain electrons), becoming uncharged

negative ions move to anode (positive) and are oxidised (lose electrons), becoming uncharged

creates a flow of charge

uncharged elements are released

cathode

Negative electrode

anode

Positive electrode

why does the ore have to be molten/dissolved for electrolysis?

ionic solids cant be electrolysed as ions are in fixed positions and can't move

whereas in molten, ions move freely so can conduct electricity

When is electrolysis used?

When the metal is more reactive than carbon

why should the electrode be inert?

so it doesnt react with electrolyte

inert atom

Outermost electron shell is full, won't react with other atoms

how is electrolysis different with aqueous solutions?

there'll be H+ and OH- ions in the solution from the water, which will be drawn to the electrodes

the electrodes can only discharge one ion/element

how to determine what ion the cathode will discharge?

it releases the ion of the LEAST REACTIVE element.

this is usually hydrogen as its low on the reactivity series

how to determine what ion the anode will discharge?

if a Halide (from Group 7) is present, that is discharged

if no Halide, Hydroxide will always be released

what is a half equation?