Chemistry ✿ chemical changes

metal + oxygen →

metal oxide

oxidation

gain of oxygen, loss of electrons

reduction

loss of oxygen, gain of electrons

how is a metals reactivity determined?

by how easily they lose their electrons

state 4 observations that would occur when potassium, sodium and lithium react with water

• fizzing as hydrogen gas is produced

• vigorously moves on water surface

• potassium produces lilac flame

• forms a strong alkali making universal indicator purple

why do highly reactive metals (e.g., potassium and sodium) lose electrons very easily?

because their outer electrons are far from the nucleus and less attached

why do less reactive metals (e.g., iron and copper) lose electrons not as easily?

because their outer electrons are closer to the nucleus and more strongly attracted

metal + water →

metal hydroxide + hydrogen

metal + acid →

salt + hydrogen

state 4 observations that would occur when magnesium, zinc and iron react with a dilute acid

magnesium

• reacts vigorously with cold dilute acids

• produces a lot of bubbles

zinc and iron

• react slowly

• react strongly as they are heated up

potassium, sodium, and lithium are ______ in dilute acids as they are _________

explosive, reactive

what are metals higher than carbon in the reactivity series extracted by?

electrolysis

what are metals below carbon in the reactivity series extracted by? and why?

reduction using carbon, usually in a blast furnace

this is because carbon only takes away oxygen

which metal is found in the earth as the metal itself?

gold

redox reaction

a chemical reaction in which both reduction and oxidation occur at the same time (displacement reaction)

displacement reaction

when a more reactive metal displaces a less reactive metal from its compound

equation for neutralisation

acid + base/ alkali → salt + water

if an alkali is reacted with hydrochloric acid it produces which salt?

chlorides

if an alkali is reacted with nitric acid it produces which salt?

nitrates

if an alkali is reacted with sulfuric acid it produces which salt?

sulfates

what happens to an ionic compound if it is molten?

the ions are free to move (delocalised) and can then conduct electricity

electrolytes

ionic compound that is molten or dissolved in water

electrolysis

decomposition of an ionic liquid by the passing of an electric current through it

cathode

the negative electrode, positive ions move here

anode

the positive electrode, negative ions move here

electrode

an electrical conductor that is places in electrolyte

why are metals mostly produced at the cathode?

metals are positive ions, cathode attracts positive ions as it is negative (opposites attract)

cations

positively charged ions

anions

negatively charged ions

oxidation

occurs at the positive electrode, where negative ions lose electrons

reduction

occurs at the negative electrode, where positive ions gain electrons

what can be produced at the cathode?

• metals are produced if the metal is less reactive than hydrogen

• hydrogen can be produced if the metal is more reactive than hydrogen

why are inert electrodes used during electrolysis?

so that it doesn’t react with the electrolyte or products

what can be produced at the anode?

• oxygen is produced

• if the solution has halide ions (chloride, bromide, iodide) then the halogen (chlorine, bromine, iodine) is produced

what is cryolite and why is it used?

aluminium oxide which is dissolved in cryolite to lower its melting point to save money on energy costs

explain why the positive electrode must be continually replaced

it wears away as the graphite (carbon) reacts with oxygen to form carbon dioxide

OILRIG

oxidation is loss reduction is gain

half equation for oxidation

element/ ion → ionⁿ⁺ + ne⁻

half equation for reduction

ionⁿ⁺+ ne⁻ → element

half equation for ionisation of water

H₂O_(l) → H⁺_(aq) + OH^-_(aq)

What is meant by a weak acid?

• do not ionise fully in water

• small proportion of acid particles release H+ ions

What is meant by a strong acid?

• ionise completely in water

• all acid particles release H+ ions

all acids form ___ ions in aqueous solutions

H+

all alkali form ___ ions in aqueous solutions

OH-

which indicator can measure pH? what is the positive result for acidic?

• universal indicator

• red/ orange

what does it mean if a solution is pH 7?

it is neutral

what does it mean if a solution is less than pH 7?

it is acidic

what does it mean if a solution is greater than pH 7?

it is alkali

which colours do the following produce in universal indicator;

weak alkalis and strong alkalis

• weak; blue

• strong; purple

which colours do the following produce in universal indicator;

weak acids and strong acids

• weak; yellow

• strong; red/ orange

which colour do neutral solutions produce in universal indicator?

green

equation for neutralisation between an acid and alkali/ base

H+(aq) + OH-(aq) → H₂O(l)

state 3 examples of weak acids

ethanoic, citric and carbonic acid

dilute

a solution with a small amount of solute compared to the solvent

concentrated

a solution with a large amount of solute compared to the solvent