c4 - chemical changes Flashcards
what are unreactive metals known as?
unreactive metals are found in the Earth as the metal itself.
They are known as ‘pure metals’
To extract the metal from the oxide, we need to
use a chemical reaction.
how can we do this?
There are 2 ways:
- Displacement Reactions
- Reduction using carbon
what is meant by a displacement reaction?
A more reactive element will push out (displace) a less reactive element from its compound.
eg
magnesium + iron oxide –> magnesium oxide + iron
Any element higher than iron would be able to displace the oxide
but these elements are really expensive so in practice, we use carbon that is cheaper.
what is extracting metals using carbon?
Carbon is a non-metal that likes to react with oxygen
more than the metals below it in the reactivity series
what is oxidation in terms of oxygen
gain of oxygen
what is reduction in terms of oxygen
loss of electrons
what is oxidation in terms of electrons
(OILRIG)
oxidation is loss of electrons
what is reduction in terms of electrons
(OILRIG)
reduction is gain of electrons
examples of 3 strong acids
-hydrochloric acid (HCl)
-sulfuric acid (H^2SO^4)
-nitric acid (HNO^3)
what are the two ways we measure pH
-pH probe
-universal indictor
what ions do acids form
H+ ions (hydrogen ions)
what ions do acids form
OH- ions (hydroxide ions)
what is the difference between a strong and weak acid
strong acids fully ionise
weak acids partially ionise
metal oxide + acid –> __________
salt + water
metal hydroxide + acid –> _______________
salt + water
metal carbonate + acid –> _______________
salt + water + carbon dioxide
what do these acids form
1) sulfuric acid
2) hydrochloric acid
3) nitric acid
1) sulphate
2) chloride
3) nitrate
what do we use to extract from the reactivity series
potassium
sodium
calcium
magnesium
aluminium
CARBON
zinc
iron
tin
lead
HYDROGEN
copper
silver
gold
platinum
potassium to aluminum:
most reactive metals extracted using electrolysis
carbon to lead :
extracted using reduction with carbon
hydrogen to platinum :
inert = unreactive
making salts practical for
copper sulphate crystals
1) measure 40 cm^3 of sulfuric acid using a measuring cylinder and pour it into a beaker
2) set up the bunsen burner using a heatproof mat, a tripod and a gauze
3) heat the sulfuric acid until warm
4) turn the gas off and using a spatula, add the copper oxide and mix it with a stirrer
5) repeat adding copper oxide until in excess - black powder at the bottom of the beaker so all sulfuric acid has reacted
6) with funnel paper fold twice and place into a funnel with a conical flask under
7) pour the mixture into the funnel paper and with the remaining solution add into a crystallisation dish (evaporating basin)
8) leave overnight for crystallisation to occur for copper sulfate crystals to form.
what is electrolysis?
using electricity to split something up
can solid ionic compounds conduct electricity?
Solid ionic compounds CANNOT conduct electricity
Why?
The ions are locked in place and are NOT FREE TO MOVE
what does the ionic compound need to be in order to carry out electrolysis?
- Dissolved in water
- Molten (melted)
Why?
So the forces of attraction are broken and the IONS ARE FREE TO MOVE so the
ions can now conduct electricity
what is the negative electrode known as?
cathode (covered with electrons)
what is the positive electrode known as?
anode (lack of electrons)
what does molten lead bromide break up into
Pb 2+
2Br-
half equation of Pb2+ and 2Br-
Pb(2+) + 2e(-) –> Pb (reduction)
2Br(-) - 2e(-) –> Br 2 (oxidation)
what is aluminium known as ?
Bauxite
what do we need to add to aluminium to lower the melting point?
cryolite
half equation of Al(3+) and O(2-)
(aluminium oxide)
Al(3+) + 3e(-) –> Al
2O(2-) - 4e(-) –> O2
what are the rules of the CATHODE?
-if the metal is more reactive than hydrogen then HYDROGREN is produced
-If the metal is less reactive then a metal is produced
what are the rules of the ANODE?
-If halide (group 7) is present then the halogen is produced
-If halide is not present then water and oxygen is made
half equation of NaCl ?
NaCl is broken into Na+ and Cl-
H20 is also produced which makes H+ and OH- ions.
Anode: Cl- is produced
half equation: 2Cl(-) - 2e(-) –> Cl2 (oxidation)
Cathode: H+ is produced
half equation: 2H(+) + 2e(-) –> H2
(reduction)
why is the anode replaced regularly?
The oxygen molecules produced at the anode react with
graphite (carbon), forming carbon dioxide gas
why is electrolysis expensive?
- Melting the compounds such as aluminium coxide requires
a great deal of energy - A lot of energy is required to produce electric current
What is meant by an aqueous solution?
Aqueous solutions are dissolved in water
Water splits to form hydrogen ions and hydroxide ions
what does copper sulfate solution produce
(CuSO4)
Because we have dissolved it in water… we
have:
[ Cu(2+) SO4 (2-) ]
H+ ions and OH- ions
from copper sulfate what is produced at the anode and cathode?
anode: oxygen and water
cathode: copper
half equation of CuSO4
Cu (2+) + 2e(-) –> Cu (reduction_
4OH(-) –> O2 + 2H(2)O + 4e(-)
4OH(-) - 4e(-) –> O2 +2H(2)O
