topic 4 chemical changes

what happens during electrolysis

An electric current is passed through an electrolyte which causes the ions to move towards the electrodes where they react and the compound decomposes

what happens to the positive ions during electrolysis?

the positive ions in the electrolyte are attracted to the cathode and gain electrons (they are reduced)

what happens to the negative ions during electrolysis?

the negative ions in the electrolyte will move towards anode and lose electrons (they are oxidised)

what happens when ions gain or lose electrons in electrolysis?

they form the uncharged element and are discharged from the electrolysis

what is the negative electrode called?

cathode

what is the positive electrode called?

anode

what is the product at the negative electrode?

metal

what is the product at the positive electrode?

non-metal

Why can an ionic solid not be electrolysed?

The ions are in fixed positions and can't move

why can an molten ionic compounds be electrolysed?

because the ions can move freely and conduct electricity

what happens to positive metal ions in electrolysis?

they are reduced to the element at the cathode

what happens to negative non-metals in electrolysis?

they are oxidised to the element at the anode

when is electrolysis used to extract metals?

When the metal is more reactive to be reduced with carbon OR if the metal reacts with carbon

what is the product at the positive electrode when breaking down aluminium oxide?

oxygen

what is the product at the negative electrode when breaking down aluminium oxide?

aluminium

after electrolysis of aqueous solutions how can you test the gaseous products to work out what was produced?

-chlorine bleaches damp litmus paper turning it white
-hydrogen makes a squeaky pop with a lighted splint
-oxygen will relight a glowing splint

when you electrolyse aqueous solutions what do you have to factor in?

the ions in the water

What do half equations show?

The reactions at the electrodes

what are positive ions called

cations

what are negative ions called

anions

why are large amount of energy used in the extraction process?

to melt the compounds and to produce and electrical current

how do you carry out the electrolysis of a solution pratical?

-set up the apparatus
-clamp electrolysis cell in position
-switch on the battery
-run for a few minutes to make any necessary observations
-record your results

what observations can be made at the anode?

bubbling, smell produced

what observations can be made at the cathode?

bubbling

what properties of aluminium make it useful?

-resists affects of chemicals
-unreactive
-strong but flexible
-light

What is aluminium extracted from?

aluminium

Why is cryolite used in the extraction of aluminium?

aliminium dissolves in it so it conducts electricity, it also lowers the boiling point to 1000 degrees

what happens at the anode in the extraction of aluminium?

reacts with the oxygen produced to form CO2 then needs replacing

what is brine?

Sodium chloride solution (salt water)

what is produced at the negative electrode in the electrolysis of brine?

hydrogen gas

what is produced at the positive electrode during electrolysis?

chlorine gas

what is an acid + base

salt + water

what do acids + carbonates form

salt + carbon dioxide + water

how do you make copper sulfate

-heat acid until it starts to boil
-add CuO in small amounts while stirring until no more will dissolve
-filter to remove undissolved copper chloride
-heat solution is evaporating basin to evaporate water. heat until crystals start dissolve
-leave to cool and crystalise

What is the reactivity series?

Potassium
Sodium
Lithium
Calcium
Magnesium
aluminium
Carbon
Zinc
Iron
tin
lead
Hydrogen
Copper
silver
gold
platinum

what is a displacement reaction?

A reaction in which a more reactive element takes the place of a less reactive element in a compound

what is the formula for hydrochloric acid?

HCl

what is the formula for nitric acid?

HNO3

what is the formula for sulfuric acid?

H2SO4 (aq)

when an acid reacts with a base what happens?

a base reacts with an acid to form a neutral solution. it neutralises the acid. bases are usually metal oxide or hydroxides.

acid + metal

salt + hydrogen

how do you make a salt?

-using a measuring cylinder measure 20cm3 of acid into the beaker
-stand the beasker on a tripod gauze and warm gently
-add half a spatula of copper oxide powder into the acid and stir using a glass rod
-keep acid warm - not boiling - continue adding copper oxide until no more dissolve
- allow to cool and thenn filter and discard the residue
-pour the filtrate into the evaporating basin. heat solution until volume is halved.